College  of  Pharmaqy 


Shis  Sunk  10  thr  glmprrtiT  of  Ihr 

QIaltfnrma  (Enlbg^  nf 


(Urpartmntt  of  p^armarii  of 
llmtirruttu  nf  (£altf0rnia) 


COLLEGE  OF  PHARMACY 


THE 


California  College  cf  Pharmacy 


GEOLOGICAL 


> 


OBSERVER.*,/ *, 


BY 


SIR  HENRY  T.  DE  LA  BECHE,  C.B.,  P.B.S.,  &c. 


DIBECTOE-GENEEAL  OP  THE  GEOLOGICAI,  SURVEY  OF  THE  UNITED  KINGDOM. 


PHILADELPHIA: 

BLANCHARD    AND    LEA. 

1851. 


v' 


C.   SHERMAN,  PRINTER. 


PREFACE. 


IT  has  been  well  remarked  by  Humboldt,*  that  to  behold  is  not 
necessarily  to  observe,  that  is,  to  compare  and  combine.  The  history 
of  Geology,  like  that  of  all  sciences  depending  for  their  effective 
advance  on  experiment  or  correct  observation,  amply  proves  the  truth 
of  this  statement.  We  are  not  required  to  look  far  back  to  be  fully 
aware  of  the  many  brilliant  hypotheses  which  have  given  way  before 
the  advance  of  correct  research.  It  was  not  that  these  brilliant  hypo- 
theses were  intended  as  substitutes  for  sound  geological  knowledge, 
based  on  correct  data,  or  that  those  who  formed  them  were  not  as 
capable  as  any  who  may  in  after-times  succeed  in  still  farther  syste- 
matically embodying  the  accumulated  data  of  such  times,  but  merely 
that  correct  observations  were  not  then  sufficiently  abundant,  and  that 
powerful,  and,  sometimes,  impatient  minds  often  supplied  their  place 
with  conceptions  more  captivating  than  well  founded.  It  is  obvious 
that  with  a  hundred  well-established  facts  more  can  be  accomplished 
than  with  ten,  the  deductions  from  which,  however  apparently  correct, 
may  even  be  fallacious  as  respects  those  derived  from  the  consideration 
of  the  greater  number.  Let  it  not,  nevertheless,  be  hastily  concluded 
that  the  views  which  have  passed  away  have  not  materially  advanced 
Geology,  as  those  of  a  similar  character  have  aided  the  progress  of  other 
sciences.  Without  them,  though  a  few  may  have  been  impediments  for 
the  time,  many  a  subject  would  have  longer  remained  disregarded  by  its 
zealous  investigator.  Even  the  controversies  which  have  from  time  to 
time  appeared,  many  from  differences  of  opinion  arising  the  more  readily 

*  Kosmos. 


41  ins 


Xll  PREFACE. 

as  the  subject  was  less  perfectly  understood,  gave  a  certain  impulse  to 
progress  which  the  commencement  of  many  inquiries  so  often  demands. 
The  following  work  was  undertaken  in  the  hope  that  the  experience 
of  many  years  might  assist,  and,  perhaps,  abridge  the  labours  of  those 
who  may  be  desirous  of  entering  upon  the  study  of  Geology,  and  espe- 
cially in  the  field.  Its  object  is,  to  afford  a  general  view  of  the  chief 
points  of  that  science,  such  as  existing  observations  would  lead  us  to 
infer  were  established ;  to  show  how^the  correctness  of  such  observations 
may  be  tested ;  and  to  sketch  the  directions  in  which  they  may  appa- 
rently be  extended.  Having  been,  to  a  certain  extent,  founded  upon 
a  little  treatise,  entitled  "How  to  Observe  in  Geology,"  long  since  out 
of  print,  a  somewhat  similar  name  has  been  retained  for  the  present 
volume. 

H.  T.  DE  LA  BECHE. 


CONTENTS. 


PAGE 

Introduction,  .  .'.,..  .  .  .  .  .  .  xxiii 

n. 

Decomposition  of  rocks,              .             .             .             .             .             .             .  .33 

Formation  of  soils,  .             .             .             .             .             .             .             .             .  33 

Decomposition  of  granitic  rocks,             .             .             .             .             .             .  .34 

Decomposition  of  sandstones  and  limestones,          .....  38 

Influence  of  organic  remains  and  structures  on  decomposition,             .             .  .38 

Decomposition  of  rocks  containing  oxides  of  iron,  .....  40 

III. 

Removal  of  the  parts  of  rocks  by  water,  .  .  .  .  .  .42 

Soluble  substances,  .  ......  42 

Carbonate  of  lime — -travertine,  ,  .  .  .  .  .  .43 

Analyses  of  running  water,  .......  44 

Composition  and  specific  gravity  of  sea-water,  .  .  »  .45 

Silica  in  water,        .........  46 

Hot  springs,  geysers,      .........        46 

Springs  on  the  outcrop  of  strata,     .......  47 

Springs  on  faults,  .........        47 

Cause  of  land-slips,  ........  52 

Substances  mechanically  suspended  in  water,  .  .  .  .  .  .54 

Transport  of  detritus  by  rivers,       .......  55 

Deposit  of  detritus  in  valleys,  ......        60 

Action  of  rivers  on  their  beds,         .......  62 

Removal  of  lakes  by  river  action,          .  .  .  .  .  ,  .68 

Formation  and  discharge  of  lakes,  ......  69 

IV. 

Lacustrine  deposits,       .  .  .  .  .  .  .  .  .71 

V. 

Action  of  the  sea  on  coasts,  .......  74 

Difference  of  tidal  and  tideless  seas,     .......  75 

Unequal  abrasion  of  coasts,  .  .  .  .  .  .  .  79 

Shingle  beaches,  .........  82 

Chesil  Bank,  .........  83 

Coast  sand-hills,  ........  86 


XIV  CONTENTS. 

VI. 

PAGE 

Distribution  and  deposit  of  sediment  in  tideless  seas,        ....  89 

Deposits  of  the  Nile,      .........        90 

Of  the  Po  and  Rhone,         ...                         ....  91 

Contemporaneous  deposits  of  gravel,  sand,  and  mud,    .             .             .             .  .92 

Volcanic  ashes  and  lapilli, ........  94 

Deposits  in  the  Black  Sea  and  the  Baltic,          .            .            .            .            .  .97 

Influence  of  ice  in  the  Baltic,         ...                         ...  99 

Gulf  of  Mexico  and  Mississippi,            .            .  .99 

VII. 

Distribution  and  deposit  of  sediment  in  tidal  seas,  .  .  .  101 

Bars  at  river  mouths,     .........      102 

Rise  and  influence  of  the  tides,       .  .  .  .  .  .  .  103 

Deposits  in  estuaries,     .........      108 

Delta  of  the  Ganges,  ........  109 

Of  the  Quorra,   ..........      110 

Deposits  on  the  coast  near  Swansea,  .  .  .  Ill 

Influence  of  waves,       .  .  .  .  .  .  .  .  .112 

Form  of  the  sea-bed  round  the  British  Islands,       .  .  .  .  .  114 

Influence  of  currents,        ..  .  .  .  .  .  .  .116 

Specific  gravity  of  sea- water,          .    •         .  .  .  .  .  .  119 

Distribution  of  sediment  over  the  floor  of  the  ocean,     .  .  .  .  .121 

VIII. 

Chemical  deposits  in  seas,  .             .  .          •  .             .             .             .             .             124 

Deposits  in  the  Caspian  and  inland  seas,  •    . ,           .             .             .                         .      124 

Calcareous  deposits,             .             .  .             .             ..             .             .             128 

Formation  of  oolitic  rocks,          .•'«.'•  .                                       .             .             .128 

Salts  in  sea-water,  .            ...  .                                                                           129 

IX. 

Preservation  of  remains  of  existing  life  in  mineral  matter,  .  •         .            .            .132 

Plants  and  vegetable  matter,           ....  .133 

Bogs,      .  .      133 

Dismal  Swamp,       ......  .135 

Rafts  in  the  Mississippi,             .                          .  .136 

Animal  remains — on  the  land,        .             .             .             .  .             .             .             137 

Vertebrata,        .....  ....      138 

Ossiferous  caverns  and  lake  deposits,          .  .             138 

Insects,  .  .141 

Land  molluscs,        ....  .                         .141 

Effects  of  showers  of  volcanic  ashes,    .            .  ...      142 

Estuary  deposits,     .             .             .             .             .             .  .             .             .             145 

Footprints  on  mud,        .........      147 

Marine  deposits  and  remains,         ....  .            .            149 

Modification  of  conditions  on  coasts  of  America,           .  .            .            .            .150 

Of  the  Pacific  Ocean,          ...  ...             152 

Of  the  Indian  Ocean,    .  .154 

Coasts  of  Africa  and  Europe,          .                                     .  .156 

Arctic  Sea,          .....  ....      156 


CONTENTS. 


XV 


PAGE 

Distribution  of  marine  life, .  .  .  .  .  .  .  .  158 

Modifications  from  temperature  and  pressure,  .  .  .  .  .  .159 

From  light  and  supply  of  air,          .  .  .  .  .  .  .  161 

Researches  of  Trofessor  E.  Forbes  in  the  JEgean  Sea,  ....      162 

Zones  of  depth,        .........  163 

Professor  LOven  on  the  molluscs  of  Norway,   ......      166 

Zones  of  depth  in  the  British  Seas,  ......  168 

Organic  remains  deposited  in  the  deep  ocean,  .  .  .  .  .  .171 

On  coasts,    .  .  .  ,  .  .  .  .  .  .  172 

Coral  reefs  and  islands,  .  .  .  .  .  .  .  .179 

Distribution  of  coral  animals,  .......  179 

Chemical  composition  of  coral, .  .  .  .  .  .  .  .181 

Keeling  Atoll,          .....  ...  182 

Form  of  coral  islands,   .  .  .  .  .  .  .  .  .186 

Barrier  reefs,  .........  189 

Lagoon  islands,  .  .  .  .  .  .  .  .  .190 

Isle  of  Bourbon,      .........  192 

Great  Barrier  Reef  Of  Australia,  .  .  .  .  .  .  .      193 

Coral  reefs  of  the  Red  Sea,  .  .....  198 

Conditions  for  the  occurrence  of  coral  reefs,      ......      198 

Influence  of  volcanic  action  on  coral  reefs,  .....  202 

Composition  of  coral  reef  accumulations,  ......      204 

Influence  of  changes  in  the  level  of  sea  and  land, .  .  .  .  207 

Reefs  near  Bermuda,     .  .  .  .  .  .  .  .  .210 

X. 

Transportal  of  mineral  matter  by  ice,         .  .  .  .  .  .  216 

Height  of  snow-line,       .  .  .  .  .  .  .  .  .217 

Glaciers,      ..........  218 

Cause  of  the  movement  of  glaciers,       .......      222 

Glacier  moraines,    .........  224 

Motion  of  glaciers,         .........      227 

Grooving  of  rocks  by  glaciers,         .  .  .  .  „  .  .  229 

Advance  and  retreat  of  glaciers,  .......      231 

Glaciers  of  the  Himalaya,  .  .  .  .  .  .  .  .  233 

Arctic  glaciers  reaching  the  sea,  .  .  .  .  .  .  .233 

Northern  icebergs  and  their  effects,  .  .  „  .  .  .  237 

Antarctic  glaciers  and  ice  barrier,          .......      239 

Geological  effects  of  Antarctic  icebergs,      ...  .  .  .  .  244 

Glaciers  of  South  Georgia,         ........      246 

Glaciers  of  South  America,  .......  247 

Transportal  of  detritus  by  river  ice,       .......      248 

Geological  effects  of  coast  ice,          .......  251 

Effects  of  grounded  icebergs,     ........      254 

General  geological  effects  of  ice,     .......  255 

Influence  of  a  general  increase  of  cold,  .  .  .  .  .  .257 

Modifications  of  temperature  from  changes  in  the  distribution  of  sea  and  land,    .  257 

Erratic  blocks,   .  .  .  .  .  .  .  .  .  .      260 

Effects  of  gradual  rise  of  the  sea-bottom  strewed  with  ice-transported  detritus,     .  262 

Effects  of  a  supposed  depression  of  the  British  Islands,  .  .  .  .      264 

Increase  of  Alpine  glaciers,  .......  268 

Transportal  of  erratic  blocks  by  glaciers,  .  .  .  .  .  .271 

Former  existence  of  glaciers  in  Britain,       ......  273 

Elevation  of  boulders  by  coast  ice  during  submergence  of  land,  .  .  .275 

Erratic  blocks  of  the  Alps,  .......  276 


XVI  CONTENTS. 

PAGE 

Erratic  blocks  of  Northern  Europe,      .  .  .  .  .  .  278 

Erratic  blocks  of  America, .  .  .  .  .  .  .  .  279 

Mollusc  remains  in  superficial  detritus,  .  .  .  .  .  .282 

Arctic  shells  found  in  British  deposits,        .....  283 

Evidence  of  a  colder  climate  in  Britain,  ......      284 

Extinct  Siberian  elephant,  .........  286 

Changes  of  land  and  sea  in  Northern  Europe,  .  .  .  .  .289 

Extinction  of  the  great  Northern  mammals,  .  .  .  .  .  290 

Range  of  the  Mammoth,  ........     291 

Frozen  soil  of  Siberia,        .  .  .  .  .  .  .  .  293 

XI. 

Ossiferous  caves  and  osseous  breccia,   .  .  .  .  .  .  .294 

Former  connexion  of  Britain  with  the  Continent,  .  .  .  .  .  295 

Mammoth  remains  found  in  British  seas,          .  .  .  .  .  .295 

Kirkdale  Cave,        .........  298 

Mud  in  ossiferous  caves,        •    .  .  .  .  .  .  .  .      300 

General  state  of  these  caverns,        .......  300 

Human  remains  in  Paviland  Cave,       .......      302 

Caves  formed  dens  of  extinct  carnivora,     ......  303 

Human  remains  in  ossiferous  caverns,  .......      304 

Complicated  accumulations  in  bone  caves,  .....  306 

Pebbles  in  ossiferous  caves,       .  .  .  •    .  . .  .  .      308 

Deposits  in  subterranean  river  channels,    ......  309 

Osseous  breccia  in  fissures,        .  .  .  .  .  .  .'.311 

Changes  in  the  entrances  to  caves,  .  ,.  .  .  .  .  313 

Occurrence  of  Mastodon  remains,        .  .  .  .  .  .  .315 

Association  with  those  of  the  Mammoth,   .  .    -'        .  .  .  .  316 

Extinct  mammals  of  Central  France,    .  .  .  .  .  .  .317 

xn. 

Volcanoes  and  their  products,         .  .  .  .  .  .  .  317 

Height  above  the  sea,    .  .  .  .  .  .  .  .  .318 

Craters  of  elevation  and  eruption,  .  .  .  .  .  .  .  318 

Fossiliferous  volcanic  tuff  beds,  .  .  .  .  .  .  .320 

Several  craters  on  one  fissure,         .  .  .  .  .  .  .  322 

Volcanic  vapours  and  gases,     .  .  .  .  .  .  .  .323 

Volcanic  sublimations,         .....*..  324 

Molten  volcanic  products,          .  .  .  .  .  .  .  .325 

Flow  of  lava  streams,         ........  326 

Vesicular  lavas,  .  .  .  .  .  .  .  .  .327 

Volcanic  cones,       .........  330 

Cotopaxi,  ..........      331 

Volcanoes  of  Hawaii,          ........  332 

Effects  of  the  lava  on  trees,       ........      338 

Vesuvius,    ..........  339 

Etna, 340 

Iceland, 341 

Stromboli  in  constant  activity,  .......      342 

Intervals  of  long  quiescence,          .......  343 

Sudden  formation  of  Jorullo,     ........      344 

Sudden  formation  of  Monte  Nuova,  ......  344 

Falling  in  of  the  volcano  Papandayang  in  Java,          .  .  .  345 


CONTENTS.  Xvii 

PAGE 

Subterranean  lakes  with  fish,          .  .  .  .  .  .  346 

Discharge  of  acid  waters,          .  .  .  .  .  .  .  .      346 

Inundations  from  volcanoes,  .  .  .  .  .  .  .  347 

Chemical  nature  of  volcanic  products,  .  .  .  .  .  .348 

Trachyte  and  dolerite,         ........  349 

Composition  of  the  felspathic  minerals,  ......      352 

Composition  of  lava  rocks,  .......  353 

Composition  of  obsidians,          .  .  .  .  .  .  .354 

Composition  of  olivine  and  leucite,  .  .  .  .  .  355 

Diffusion  of  minerals  in  volcanic  rocks,  .  .  .  .  .  .356 

Fusibility  of  minerals  in  volcanic  rocks,     ......  357 

Sinking  of  minerals  in  fused  lava,         .......      358 

Fusion  of  rocks  broken  off  in  volcanic  vents,         .....  359 

Lamination  of  streams  of  lava,  .......      360 

Laminae  of  spherules  in  obsidian,  .  .  .  .  .  .  361 

Composition  of  volcanic  ashes,  .  .  .  .  .  .  .362 

Modified  composition  of  volcanic  ashes,     ......  362 

Volcanic  tuff,      ..........      363 

Composition  of  palagonite  tuff  of  Iceland,  .  .  .  .  .  364 

Modification  of  volcanic  tuffs  by  gases  and  vapours,    .  .  .  .  .365 

Solution  of  palagonite  tuff  in  acids,  .  .  .  .  .  .  366 

Solfataras,  ..........      367 

The  Geysers,  and  their  mode  of  action,  Iceland     .....  368 

Siliceous  deposits  from  the  Geysers,      .......      370 

Sulphurous  waters  of  Iceland,         .  .  .  .  .  .  .  370 

Gypsum  deposits  of  Iceland,     .  .  .  .  .  .  .  .371 

Fusibility  of  volcanic  products,       .......  372 

Fissures  in  volcanoes  filled  by  molten  lava,      ......      373 

Lava  ejected  through  fissures,         .  .  .  .  .  .  .  374 

Direction  of  fissures  in  volcanoes,          .......      376 

Effects  of  sea  on  volcanic  gases,     .  .  .  .  .  .  .  376 

Softening  and  raising  of  tuffs  and  lavas,  .  ...      377 

The  Caldera,  Island  of  Palma,        ....  378 

Sections  of  Etna  and  Vesuvius,  .......      380 

Form  and  structure  of  Etna,  .  .  .  .  .  .  .  381 

Origin  of  the  Val  del  Bove,  Etna,          .  .  .  .  .  .  .381 

Fossiliferous  volcanic  tuff  of  Monte  Somma,  Vesuvius,      ....  382 

Mixed  molten  volcanic  rocks  and  conglomerates,          .  .  .  .  .      383 

Modification  of  submarine  volcanic  deposits,          ,  .  .  .  .  384 

Peak  of  Teneriffe,          .........      384 

Santorin  Group,        .........  385 

Raised  fossiliferous  volcanic  tuff  of  Santorin  Group,     .....      389 

Quiet  deposits  inside  the  Santorin  Group,  .  .  .  .  .  389 

Island  of  St.  Paul,  Indian  Ocean,  .......      390 

Distribution  of  volcanoes  in  the  ocean,       ......  392 

Distribution  of  volcanoes  on  continents,  and  amid  inland  seas,  .  .  .392 

Variable  proximity  of  volcanoes  to  water,  .....  394 

Extinct  volcanoes,          .........      395 

Mineral  and  chemical  composition,  and  structure  of  basalt,  .  .  .  396 

XIII. 

Salses  or  mud  volcanoes,  ........  401 

Nitrogen  evolved  from  mud  volcanoes,  Taman,     .  .  .  .  .  405 

Boracic  acid  of  Tuscany,  ........  406 

2 


XV111  CONTENTS. 

XIV. 

MM 

Earthquakes,  ......  .  406 

Connexion  of  volcanoes  and  earthquakes,         ......      407 

Extent  of  earthquakes,        ........  408 

Movement  of  the  earth-wave  during  earthquakes,       .....      409 

Sea-waves  produced  during  earthquakes,  .  .  .  .  .  410 

Transmission  of  earthquake-waves  complicated  by  different  mineral  structures,         .      4 12 
Unequal  transmission  of  earthquakes,         .  .  .  .  .  .  413 

Locally  extended  range  of  earthquakes,  .  .  .  .  .  .414 

Earthquakes  traversing  mountain  chains,  .  .  .  .  .  415 

Fissures  produced  during  earthquakes,  .  .  .  .  .  .415 

Settlement  of  unconsolidated  beds  adjoining  hard  rocks  during  earthquakes,        .  416 

Breaking  of  great  sea-wave,  of  earthquakes,  on  coasts,  .  .  .  .418 

Effects  of  earthquakes  on  lakes  and  rivers,  .  .  .  .  .  419 

Flame  and  vapours  from  earthquake  fissures,  .  .  .  .  .419 

Sounds  accompanying  earthquakes,  ......  420 

Elevation  and  depression  of  land  during  earthquakes,  .  .  .  .421 

Coast  of  Chili  raised  during  earthquakes,  .  .  .  .  .  423 

Effects  of  earthquakes  in  the  Runn  of  Cutch,  .  .  .  .  .423 

XV. 

Quiet  rise  and  subsidence  of  land,  .  .  .  .  .  .  424 

Rise  and  depression  of  coast  in  the  Bay  of  Naples,     .  .  .  .  .425 

Elevation  and  depression  of  land  from  increase  and  decrease  of  heat,     .  . .  427 

Gradual  rise  of  land  in  Sweden  and  Norway,  .....      428 

Raised  coasts  in  Scandinavia,         .  .  .  .  .  .  429 

Gradual  depression  of  land  in  Greenland,        ......      430 

Movements  of  coasts  in  the  Mediterranean,  .  430 

Unstable  state  of  the  earth's  surface,    .  .  .  .  .  .431 

XVI. 

Sunk  (submarine)  forests  and  raised  beaches,        .....  432 

Sunk  forests  of  Western  Europe,           .......  433 

Sunk  forests  beneath  the  sea  in  roadsteads,             .....  434 

Mode  of  occurrence  of  sunk  forests,     .  .  .  .  .  .  .434 

Localities  of  sunk  forests,                .......  435 

Remains  of  mammals  and  insects  in  sunk  forests  of  Western  England,           .             .  436 

Footprints  of  deer  and  oxen  amid  the  rooted  trees  of  sunk  forests  in  South  Wales,  438 

Sunk  forests  viewed  with  regard  to  the  varied  heights  of  tide  on  tidal  coasts,      .  439 

Raised  beaches  concealed  by  detritus,               ......  440 

Raised  beaches  of  Plymouth,  Falmouth,  and  New  Quay,               .             .             .  441 

Raised  dunes  of  blown  sand,  Perran  Bay,  Cornwall,                ....  445 

Distribution  of  detritus  in  the  English  Channel,  and  in  sea  south  of  Ireland,        .  446 

Care  required  in  tracing  raised  coast-lines,        ...             ...  447 

Raised  coast-lines,  Scandinavia,      .......  448 

XVII. 

Temperature  of  the  earth,        .....  .     449 

Temperature  of  different  depths  in  Siberia,  .  .  .  449 

Temperatures  found  in  Artesian  wells,  ......      450 

Heat  of  waters  rising  through  faults,  and  other  fissures,    .  .  .  .  451 

Variable  temperature  from  unequal  percolation  of  water  through  rocks,          .  .451 

Temperature  of  waters  in  limestone  districts,        .....  454 


CONTENTS.  xix 

XVIII. 

PAGE 

Mode  of  accumulation  of  detrital  and  fossiliferous  rocks,         ....  455 

Detrital  rocks  chiefly  old  sea-bottoms.          ......  456 

Mixture  of  beefs  with  and  without  fossils,         ......  457 

Variable  mode  of  occurrence  of  organic  remains  among  detrital  and  fossiliferous  rocks,  458 
Beaches  on  the  shores  of  land  at  the  time  of  the  Silurian  deposits  and  old  red  sand- 
stones,     ..........  460 

Beaches  of  the  new  red  sandstone  period  in  the  Mendip  Hills,  and  near  Bristol,        .  462 

Beaches  at  the  time  of  the  lias,       .......  464 

Lias  resting  on  disturbed  beds  of  carboniferous  limestone,       ....  466 

Varied  modes  of  occurrence  of  the  lias,     .             .             .             .             .             .  467 

Boring  molluscs  of  the  inferior  oolite  period,    .  .  .  .  .  .468 

Overlap  of  the  inferior  oolite,  Mendip  Hills,          .             .             .             .             .  469 

Lias  conglomerate,  pierced  by  boring  molluscs,             ....  469 

Land  of  the  time  of  the  lias,           .......  470 

Evidence  of  land  from  fresh-water  deposits,     .  .  .  .  .  .471 

Effects  produced  on  coasts,  rivers,  and  lakes,  by  continued  elevation  of  land  above 

sea,                                      472 

Elevation  of  land  over  a  wide  area,     .......  474 

Effects  of  closing  the  Straits  of  Gibraltar,                .....  474 

Unequal  elevation  of  land,        ........  475 

Lakes  on  the  outskirts  of  mountains,           .             .                          .             .             .  476 

Mixture  of  organic  remains  of  different  periods  from  submergence  of  land,                .  478 

Variable  effects  of  submergence  of  present  dry  land,        ....  480 

Evidence  afforded  by  the  coal  measures,           ......  482 

Stigmaria  beds  in  the  coal  measures,          ......  482 

Stems  of  plants  in  their  positions  of  growth  in  the  coal  measures,;      .             .             .  483 

Filling  up  of  hollow  vertical  stems,  and  mixture  of  prostrate  plants  with  them,    .  484 

Growth  of  terrestrial  plants  in  successive  planes  in  the  coal  measures,            .             .  486 

Thickness  of  South  Wales  coal  measures,               .....  488 

False  bedding  in  coal-measure  sandstones,       ......  489 

Surfaces  of  coal-measure  sandstones,          ......  489 

Drifts  of  matted  plants  in  the  coal  measures,    ......  490 

Extent  of  coal  beds,            .             .             .             .             .             .             .             .  491 

Partial  removal  of  coal  beds,    ........  492 

Channels  eroded  in  coal  beds,  Forest  of  Dean,      .             .                          .             .  492 

Lapse  of  time  during  deposit  of  coal  measures,            .....  493 

Pebbles  of  coal  in  coal  accumulations,        ......  494 

Marine  remains  in  part  of  the  coal  measures,                .....  495 

Gradual  subsidence  of  delta  lands,              .             .             .             .             .  496 

Fossil  trees  and  ancient  soils,  Isle  of  Portland,               .....  497 

Conditions  under  which  the  ancient  soils  and  growth  of  plants  were  produced  at 

Portland,              ......  498 

Wealden  deposits,  Southeastern  England,          ....                           .  499 

Raised  sea-bottom  round  British  Islands,    ......  500 

Overlap  of  cretaceous  beds  in  England,            .             .             .     •                     .             .  500 

Cracked  surfaces  of  deposits,          .....  501 

Footprints  of  air-breathing  animals  on  surfaces  of  rocks,         ....  502 

Rain-marks  on  surfaces  of  rocks,    ......  503 

Elevation  or  depression  of  the  bottom  in  the  ocean,     .....  504 

Character  of  the  surfaces  of  rocks,             ......  505 

Friction-marks  on  rock  surfaces,             .......  506 

Ridged  and  furrowed  surfaces  of  rocks,     ......  507 

Effects  of  earthquakes  on  sea-bottoms,               ......  509 

Diagonal  arrangement  of  the  minor  parts  of  beds  among  detrital  rocks,  .             .  510 


XX  CONTENTS. 

PAGE 

Beds  formed  by  unequal  drifts,  .  .  .  .  .  .  .512 

Mode  of  occurrence  of  organic  remains,    .             .             .             .             .             .  512 

Distribution  of  organic  remains,  .  .  .  .  .  .  .517 

Effect  of  the  rise  and  fall  of  land  on  the  distribution  of  organic  remains,              .  520 

Distribution  of  organic  remains  with  respect  to  different  kinds  of  sea-bottoms,            .  522 

Infusorial  remains,               .             .                          .             .             .             .             .  524 

Chemical  composition  of  organic  remains,         .  .  .  .  .  .525 

Caution  as  to  forms  of  life  supposed  characteristic  of  different  geological  times,    .  525 

XIX. 

Igneous  products  of  earlier  date  than  those  of  modern  volcanoes,         .             .             .  526 

Simple  substances  forming  igneous  rocks,  ......  526 

Volcanic  products  amid  the  older  rocks,  .  .  .  .  .  .527 

Fossils  amid  old  igneous  products,               ......  529 

Volcanic  tuff  and  conglomerates  among  the  Silurian  deposits  of  "Wales  and  Ireland,  .  530 
Old  volcanic  products   intermingled  with   the   Devonian   rocks   of  Southwestern 

England,               .........  532 

Igneous  rocks  associated  with  the  carboniferous  limestone  of  Derbyshire,         .             .  534 

Relative  geological  date  of  the  Wicklow  and  Wexford  granites,    .             .             .  536 

Date  of  the  granites  of  Devon  and  Cornwall,    ......  537 

Uncertain  dates  of  some  igneous  dykes,      ......  539 

Granitic  or  porphyry  dykes,  known  as  elvans  in  Cornwall  and  Devon,            .             .  540 

Igneous  rocks  in  the  lower  portion  of  the  new  red  sandstone  series  in  Devonshire,  542 

Dates  of  the  Cornish  and  Devonian  elvans,             .....  542 

Elvans  of  Wicklow  and  Wexford,         .  .          .  1  •*'  .  .  .543 

Chemical  composition  of  igneous  rocks,      ......  544 

Effect  of  silicate  of  lime  in  igneous  rocks,         ......  544 

Mode  of  occurrence  of  granites  in  Southwestern  England  and  Southeastern  Ireland,  546 

Outline  of  the  granite  range  of  Wicklow,    ......  547 

Granite  veins,    ..........  548 

Chemical  composition  of  granitic  rocks,       .             .             .             .             .             .  549 

Schorlaceous  granites  of  Cornwall  and  Devon,              .....  550 

Slight  covering  of  granite  by  the  older  rocks  in  Wicklow,  Wexford,  and  Cornwall,  552 

Serpentine  and  diallage  rock  of  Cornwall,              .....  554 

Serpentine  of  Caernarvonshire,  ...... 

Serpentine  of  Anglesea,       ........  555 

Chemical  composition  of  serpentine,     .... 

Composition  of  serpentine  and  olivine  compared,  ..... 

Composition  of  greenstone  and  syenite,              ......  558 

Resemblances  and  differences  between  the  ordinary  granitic  and  hornblendic  rocks,  558 

Granitic,  felspathic,  hornblendic,  and  serpentinous  rocks  ejected  at  various  times,       .  560 

Relative  fusibility  of  igneous  rocks,              ......  5G2 

Modification  of  the  matter  of  igneous  rocks,      ......  562 

Additional  minerals  entering  into  the  composition  of  ordinary  igneous  rocks,        .  563 

General  character  of  igneous  rocks,       .            .            .            ...            .            .  564 

XX. 

Consolidation  and  adjustment  of  the  component  parts  of  rocks,      .             .  565 

Adjustment  of  the  component  parts  of  calcareous  and  argillaceous  deposits,    .             .  566 

Arrangement  of  similar  matter  in  nodules,              .             .             .  567 
Central  fractures  in  septaria,     ... 

Nodules  of  phosphate  of  lime  in  rocks,       ....  569 

Spheroidal  concretions  in  the  Silurian  rocks,     ....                         .  570 


CONTENTS.  XXI 

PAGE 

Crystals  of  iron  pyrites  in  clay  and  shales,              .             .             .             .             .  571 

Mode  of  occurrence  of  sulphate  of  lime,  .  .  .  .  .  .571 

Modification  in  the  structure  of  rocks  from  exposure  to  changes  of  temperature,  .  572 

Chloride  of  sadium  disseminated  amid  rocks,  ......  574 

Variable  deposits  of  detrital  matter,             .             .             .             .             .             .  575 

Importance  of  silica  and  the  silicates  in  the  consolidation  of  the  detrital  rocks,            .  576 

Alteration  of  rocks,  on  minor  scale,  by  heat,            .             .             .             .             .  577 

Formation  of  crystals  in  altered  rocks,  .......  578 

Crystalline  modification  of  rocks,     .......  578 

Alteration  of  rocks  near  granitic  masses,            ......  579 

Readjustment  of  parts  of  igneous  rocks,       ......  580 

Production  of  certain  minerals  in  altered  rocks,             .             .             .             .             .  580 

Mineral  matter  transmitted  into  altered  rocks,         .             .             .                      •    .  581 

Mica  slate  and  gneiss,    .........  582 

Cleavage  of  rocks,                ........  583 

Cleavage  in  sandstones  and  shales,       .......  584 

Cleavage  in  shales  and  limestones,              .             .             .             .             .             .  585 

Minor  interruptions  to  cleavage  action,               .              .             .             .                           .  585 

Cleavage  on  the  large  scale,             .             .             .             ...             .             .  586 

Range  of  cleavage  through  contorted  rocks,       ......  587 

Double  cleavage,      .             .             .             .             .             .             .             .             .  588 

Relative  dates  of  cleavage,         .             .             .             .             .             .             .             .  588 

Elongation  and  distortion  of  organic  remains  by  cleavage  action,  .             .             .  589 

Different  directions  of  cleavage  in  the  same  or  juxtaposed  districts,      .             .             .  590 

Joints  in  rocks,         .........  592 

Directions  and  range  of  joints,   ........  593 

Joints  in  granite,      .             .             .             .             .             .             .             .             .  594 

Joints  in  sedimentary  rocks,       .  .  .  .  .  .  .  .595 

Joints  among  conglomerates,            .......  596 

Joints  in  limestone,        .........  596 

Movements  of  rocks  after  jointing,               ......  597 

Complication  of  bedding,  jointing,  and  cleavage,           .             .             .             .             .  598 

XXI. 

Bending,  contortion,  and  fracture  of  bedded  rocks,               ....  599 

Earth's  radius  compared  with  mountain  heights,           .....  600 

The  volume  of  the  earth  compared  with  mountain  ranges,             .             .             .  600 

Effects  of  a  gradually  cooling  globe,      .......  602 

Mountain  ranges  viewed  on  the  large  scale,            .             .              .             .             .  603 

Directions  of  mountain  chains,               .......  603 

Conditions  effecting  the  obliteration  or  preservation  of  mountain  chains,                .  6C4 

Lateral  pressure  of  beds  of  rock  amid  mountains,       .                           .              .             .  606 

Bending  and  folding  of  Deposits  in  the  Appalachian  zone,  North  America,           .  609 
Flexures  and  plications  of  rocks  in  the  Alps,  and  district  of  older  deposits  of  the 

Rhine,             .                       •   .             .             .             .             .             .             .             .  610 

Igneous  rocks  amid  contorted  beds,             .             .             .             .             .             .  611 

Contorted  coal  measures  of  South  Wales,          .  .  .  .  .  .612 

Contortion  of  the  component  parts  of  beds,             .             .             .             .              .  612 

Faults, 613 

Production  and  direction  of  fissures  through  rocks,             .             .             .             .  614 

Evidence  of  the  relative  dates  of  fissures,        .  .  .  .  .  .616 

Fallacious  appearance  from  a  single  movement  shifting  various  fissures,               .  618 
Fissures  split  at  their  ends,        .             .             .             .             .             .             .             .621 

Lines  of  least  resistance  to  fissures,             .             .             .             .             .             .  621 

Range  of  mineral  veins  and  common  faults  in  Southwestern  England,             .             .  622 


XXII  CONTENTS. 

PAGE 

Range  of  faults  near  Swansea,        .             .             .             .             .             .             .  625 

Inclination  of  faults,        ....              .                           .                           .  626 

Parts  of  deposits  preserved  by  faults,         .             .             ....  627 

Complicated  faults,        ......  .627 

XXII. 

Filling  of  fissures  and  other  cavities  with  mineral  matter,            .             .             .  628 

Sulphurets  of  lead,  copper,  &c.,  replacing  shells,          .....  629 

Filling  of  minor  fissures,    .             .             .             .             .             .             .             .  630 

Solubility  and  deposit  of  mineral  matter  in  fissures,    .....  630 

Solubility  of  sulphate  of  baryta,     ......  632 

Deposits  from  solutions  in  fissures,        .......  633 

Effects  produced  in  heated  fissures  beneath  seas,                .             .             .             .  634 

Many  similar  substances  found  in  mineral  springs  and  veins,               .             .             .  635 

Frequent  occurrence  of  sulphur,  arsenic,  &c.,  with  certain  metals  in  mineral  veins,  635 
Action  and  reaction  of  substances  upon  each  other  in  fissures  and  cavities,    .             .636 

Character  of  metalliferous  veins  amid  associated  dissimilar  rocks,             .             .  638 

Condition  of  mineral  veins  traversing  elvan  dykes  in  Cornwall,          .             .             .  640 

Influence  of  the  different  rocks  traversed  on  the  mineral  contents  of  fissures,       .  642 
Mode  of  occurrence  of  lead  ores  amid  the  limestones  and  igneous  rocks  of  Derbyshire,  644 

"  Flats"  of  lead  ore  in  limestone  districts,         .                          ....  645 

Metalliferous  deposits  in  the  joints  of  rocks,           .....  646 

Relative  different  dates  of  mineral  veins,          ......  648 

Modification  of  the  contents  of  mineral  veins  in  their  depth  and  range,                .  650 

Modifications  of  the  upper  part  of  mineral  veins  from  atmospheric  influences,           .  652 

Sulphurets  of  lead  and  zinc  converted  into  carbonates  in  mineral  veins,               .  652 

Replacement  of  mineral  matter  of  one  kind  by  another  in  veins,        .             .             .  654 

Coating  of  the  walls  of  fissures  by  layers  of  mineral  matter,         .             .             .  655 
Fissures  coated  by  dissimilar  substances,           .             .             .             .             .             .656 

Several  successive  movements  through  the  same  fissure,   .             .             .             .  657 

Sliding  of  the  sides  of  fissures  on  mineral  matter  accumulated  in  them  at  intervals,  .  660 

Fractures  through  the  mineral  contents  of  fissures,             ....  662 

Modification  of  the  contents  of  fissures  at  the  crossing  of  veins,          .             .             .  663 

Effects  on  the  contents  of  fissures  meeting  or  crossing  at  small  angles,     .             .  663 

XXIII. 

Partial  removal  or  denudation  of  rocks,        -    .             .             .             .             .             .  664 

Great  denudation  arising  from  the  action  of  breakers,        ....  665 

Ancient  exposure  of  the  coasts  of  the  area  of  the  British  Islands  to  the  Atlantic,         .  666 

Care  required  respecting  the  amount  of  denudation  of  overlapping  rocks,            .  666 

Island  masses  of  deposits  left  by  denudation,  .             .             ...             .             .  668 

Districts  of  bent  and  plicated  beds  worn  down  by  denudation,     .             .             .  668 

New  slices  of  land  now  being  cut  away  by  breaker  action,     ....  669 

Amount  of  matter  removed  by  denudation,            .....  670 

Denudation  in  parts  of  England  and  Wales,     ......  671 

Needful  attentions  to  the  greater  geological  problems,       .            .            .  673 

XXIV. 

APPENDIX  : — 

Geological  maps  and  sections,       .......  675 

Additional  notices  of  subjects  mentioned  previously,              .            .            .  681 


INTRODUCTION. 


OBSERVATIONS  have  now  been  sufficiently  extended  and  multiplied  to 
show  that,  during  a  long  lapse  of  time,  the  surface  of  our  planet  has 
been  undergoing  modifications  and  changes.  Of  these  the  most  marked 
have  been  produced  by  the  uprise  of  mineral  matter  in  a  molten  state 
from  beneath  that  surface;  the  wearing  away  and  removal  to  other 
localities  of  this  matter,  either  in  its  first  state,  after  cooling,  or  in  some 
secondary  condition,  by  atmospheric  influences  and  waters  variously  dis- 
tributed for  the  time  being ;  the  preservation  of  the  remains  of  animal 
and  vegetable  life  during  at  least  a  portion  of  this  lapse  of  time  amid 
deposits  accumulated,  for  the  most  part,  in  horizontal  layers  beneath 
waters,  and  by  the  unquiet  state  of  the  earth's  surface  itself,  from  which, 
while  considerable  areas  have  been  at  different  times  raised  slowly  above, 
and  depressed  beneath  the  level  of  the  ocean,  occasionally  whole  masses 
of  mineral  matter  of  various  kinds  have  been  squeezed,  bent,  and  pli- 
cated, sometimes  ridged  up  into  ranges  of  mountains. 

To  enable  the  geologist  systematically  to  proceed  with  his  researches, 
it  became  as  needful  for  him  as  for  other  cultivators  of  science  to  have 
the  power  of  classifying  his  observations.  Of  the  various  classifications 
proposed  or  modified  at  different  times  to  satisfy  the  amount  of  know- 
ledge of  those  times,  it  would  be  out  of  place  here  to  make  mention, 
further  than  to  remark  that  at  present  a  more  mixed  classification  is 
often  employed  than  seems  desirable.  For  example,  it  is  not  unusual 
for  the  term  tertiary  or  tertiaries,  to  be  applied  to  all  accumulations 
posterior  to  the  chalk  of  Western  Europe,  while  the  other  terms  of  secon- 
dary and  primary  or  primitive,  to  which  it  has  reference,  are  scarcely  or 
seldom  now  mentioned.  We  have,  again,  a  mixed  nomenclature  for  the 
groups  of  deposits,  or  the  deposits  themselves,  for  which  it  has  been 
thought  desirable  to  find  distinctive  names.  While  some  groups  are 
referred  to  localities,  such  as  Cambrian,  Silurian,  Jurassic,  and  the 
like ;  others  are  named  after  some  circumstance  supposed  characteristic, 


XXIV  INTRODUCTION. 

such  as  carboniferous,  from  containing  the  great  coal  deposits  of  Europe 
and  North  America ;  or  oolitic,  from  many  of  the  limestones  in  it  being 
oolitic,  that  is,  resembling  the  roe  of  a  fish,  being  composed  of  numerous 
small  rounded  grains,  formed  of  concentrically  arranged  coatings  of  cal- 
careous matter. 

It  has  been  often  considered  that  names  derived  from  localities  where 
certain  deposits  have  been  taken  as  types,  are  preferable  to  those  point- 
ing to  any  mineral  structure,  inasmuch,  as  not  only  can  the  geologist 
readily  make  himself  familiar  with  the  kind  of  accumulations  intended 
to  be  represented  by  the  names,  by  visiting  and  studying  the  localities 
whence  they  are  taken,  but  as  also  particular  mineral  structures  having 
been  repeated  as  often  as  the  conditions  for  them  arose,  they  form  no 
guide  for  determining , the  relative  age  of  rocks,  whatever  may  have  been 
the  impression  when  names  of  that  kind  were  given,  and  geological 
science  less  advanced  than  at  present.  The  two  structural  names  men- 
tioned are  thus  liable  to  objection,  carboniferous  deposits  extending 
from  an  earlier  period  than  that  supposed  to  be  represented  by  the 
term,  and  up  to  the  higher  accumulations  above  the  cretaceous  series 
inclusive,  and  the  oolitic  character  reaching  from  limestones  amid  the 
earlier  fossiliferous  rocks  to  the  present  day.*  The  mixed  character  of 
the  present  geological  nomenclature  arises,  no  doubt,  from  the  manner 
in  which,  from  time  to  time,  various  geologists  have  directed  attention 
to  different  rocks  or  accumulations  of  them,  those  names  having  gene- 
rally remained  which  have  been  found  convenient  and  sufficient,  up  to 
the  present  time,  for  the  purposes  for  which  they  have  been  employed. 

The  igneous  products  being  those  from  which  the  chief  part,  if  not 
the  whole,  of  the  detrital,  and  even  chemical  deposits  have  been  directly 
or  indirectly  derived,  it  would  appear  desirable  to  consider  them  in  the 
first  place.  Whatever  the  views  entertained  of  the  fluid  condition  of 
our  planet,  whence  its  form  has  resulted,  such  fluid  condition  produced 
by  heat  sufficient  to  keep  all  its  component  parts  in  that  state,  the  pre- 
sent condition  of  the  earth's  surface  in  dispersed  localities  shows  an 
abundance  of  points  through  which  igneous  products  are  now  ejected, 
and  the  more  extended  the  observation,  the  more  certain  does  the  in- 
ference appear  correct,  that  the  like  has  happened  from  the  earliest 
times ;  at  least  since  the  seas  were  tenanted  by  life.  It  has  also  been 
ascertained  that  molten  matter  has  risen  from  beneath  in  more  massive 

*  One  of  the  limestones  of  the  lower  Silurian  series  in  North  Wales,  the  Rhiwlas  near 
Bala,  is  oolitic. 


INTRODUCTION.  XXV 

forms,  and  in  a  manner  with  which  we  are  not  familiar,  as  now  occur- 
ring, though  such  molten  masses  may,  indeed,  be  formed  at  depths  in 
the  earth's  crust,  whence  only  future  geological  changes  could  bring 
them  above  the  level  of  the  sea.  At  all  events,  this  massive  form  of 
intrusion  is  found  amid  comparatively  recent  geological  accumulations, 
as  well  as  among  those  of  the  most  ancient  date. 

The  mode  of  occurrence  of  the  igneous  rocks,  which  will  be  found 
treated  of  in  its  place  in  the  following  pages,  would  seem  to  point  to 
their  classification  according  to  their  chemical  and  mineralogical  cha- 
racters, so  that  any  resemblance  or  difference  that  may  exist  between 
them,  may  be  traced  through  the  lapse  of  geological  time,  the  relative 
dates  of  their  appearance  being  obtained  by  means  of  the  accumulations 
with  which  they  may  be  associated,  and  to  which  relative  geological 
dates  can  be  assigned.  Having  entered  upon  these  characters  in  the 
sequel,  the  following  sketch  of  the  more  prominent  of  the  igneous  rocks 
may  here  suffice : — 

G-ranitic  Rocks. — Those  composed  of  a  granular  mixture  of  quartz, 
felspar  (whether  orthoclase,  albite,  or  labradorite),  and  mica,  with, 
occasionally,  the  addition  of  schorl  and  some  other  minerals.  As  the 
aspect  of  these  rocks  varies  considerably  according  to  original  chemical 
composition  or  the  mode  of  cooling,  a  great  variety  of  appearances  are 
assumed,  to  which  names  have  been  assigned.  It  thus  becomes  desirable 
that  these  characters  should  be  given  whenever  it  can  be  accomplished, 
and  that  the  mere  term  granitic  be  accompanied  by  mineralogical  detail, 
and  by  a  statement  of  the  chemical  composition,  so  that  correct  data 
may  be  collected  for  a  proper  appreciation  of  the  real  differences  and 
resemblances  of  the  rocks  commonly  thus  named. 

Felspathic  Rocks. — The  separation  of  these  from  the  foregoing  may 
often  be  regarded  as  somewhat  imaginary,  as  indeed  is  the  case  with 
definite  classifications  of  the  great  bulk  of  the  igneous  rocks,  passing,  as 
they  sometimes  do,  into  each  other  in  masses  of  no  very  extraordinary 
volume.  The  variety  known  as  compact  felspar  is  most  frequently  a  com- 
pound of  the  elements  of  some  felspar,  with  a  surplusage  of  silicic  acid 
beyond  that  required  for  the  silicates  of  that  mineral,  so  that  when  oppor- 
tunities have  occurred  for  crystallization  of  the  parts,  the  result  has  been 
a  compound  of  felspar  and  quartz,  or  a  granitello,  as  it  has  been  sometimes 
termed,  in  that  case  a  modification  of  the  granitic  rocks  when  the  same 


XXVI  INTRODUCTION. 

minerals  may  alone  constitute  a  portion  of  a  general  mass.  The  trachytes 
of  active  volcanoes  and  those  termed  extinct,  and  of  comparatively  recent 
geological  date,  may  represent  the  more  pure  felspathic  rocks,  when  wholly 
formed  of  felspars,  though  it  would  appear  that  similar  rocks  are  also 
found  amid  the  igneous  products  of  very  ancient  geological  periods. 
Felspathic  matter,  that  is,  the  various  component  substances  in  propor- 
tions which  would  form  minerals  of  the  felspar  family  (allowing  for  that 
substitution  of  one  substance  for  another,  termed  isomorphism),  if  crystal- 
lized, should  at  least  constitute  the  great  bulk  of  these  rocks,  whatever 
others  may  be  entangled  among  them. 

Hornblendic  Rocks. — These,  including  among  them  the  rocks  in  which 
augite  is  substituted  for  hornblende,  form  a  somewhat  natural  division, 
so  far  as  the  prevalence  of  these  minerals  may  be  sufficient  to  give  a 
character  to  the  mass  of  an  igneous  rock,  inasmuch  as  silicate  of  lime 
is  a  marked  ingredient,  in  addition  to  the  silicate  of  magnesia,  another 
essential  substance,  and  protoxide  of  iron,  generally  present,  sometimes 
replacing  much  of  the  lime  and  magnesia.  In  this  division,  therefore, 
are  included  the  dolerites  and  basalts  of  active  and  extinct  volcanic 
products,  and  the  greenstones,  generally  of  more  ancient  date.  In 
dolerites,  silicate  of  lime  is  also  present  in  the  labradorite,  when  that 
member  of  the  felspar  family  is  mingled  with  the  augite  of  that  rock. 
Taken  as  a  whole,  the  hornblendic  or  augitic  rocks  are  compounds  of 
those  minerals  and  some  member  of  the  felspar  family,  there  being 
sometimes  an  excess  of  silica  beyond  the  amount  required  for  the 
various  silicates  in  the  hornblende  or  augite,  and  felspar ;  this  excess, 
then,  as  it  were,  thrust  aside  as  quartz. 

Serpentinous  Rocks. — To  a  certain  extent  these  also  appear  a  some- 
what natural  group  of  igneous  products,  especially  when  viewed  with 
reference  to  a  peculiar  aspect  and  the  presence  of  silicate  of  magnesia 
and  combined  water,  as  constituting  the  bulk  of  the  rock.  In  the  sequel, 
we  have  endeavoured  to  show  the  correspondence  between  the  varieties 
of  serpentine,  considered  the  most  pure,  and  olivine,  a  common  mineral 
in  certain  molten  products-  of  active  and  extinct  volcanoes.  The  rocks  of 
this  division  vary,  however,  somewhat  materially  in  their  constituent 
substances,  and  in  the  proportions  of  them.  Taking  bronzite  to  be 
the  mineral  usually  named  diallage,  it  would  appear  little  else  than  the 
silicate  of  magnesia  of  the  matter  of  the  purer  serpentine  mingled  with 
a  minor  proportion  of  protoxide  of  iron,  and  a  little  alumina,  crystal- 
lized, a  small  quantity  of  water  also  forming  a  part  of  it.  The  mineral 


INTRODUCTION.  XXV11 

now  chiefly  named  diallage^  contains  'sufficient  lime  in  addition  to  make 
it  essentially  a  silicate  of  lime  and  magnesia,  with  also  a  marked  quan- 
tity of  oxide  of  iron.  In  the  compound,  sometimes  largely  crystallized, 
termed  diallage  rock  (gabbro\  and  not  unfrequently  associated  with 
serpentine,  the  so-termed  diallage  has  to  be  carefully  examined.  In  all 
these  rocks,  whatever  their  variations,  magnesia  is  a  marked  ingredient. 
Porphyritic  Rocks. — Though,  no  doubt,  various  kinds  of  mineral 
matter  which  have  been  in  a  molten  state  may  be  porphyritic,  that  is, 
have  some  mineral  or  minerals  crystallized  out  and  apart  from  the  mass 
of  the  remainder  of  the  rock,  it  seems  nevertheless  convenient,  for  the 
present,  to  notice  these  rocks  as  a  group.  Even  amid  vitreous  matter, 
from  comparatively  quick  cooling  after  fusion,  definite  chemical  combi- 
nations may  be  crystallized,  and  dispersed  through  such  matter.  This 
can  be  artificially  accomplished  in  our  laboratories,  and  silicate  of  lime 
in  crystals  can  be  obtained  dispersed  through  ordinary  glass.  In  the 
arrangement  of  particles,  beyond  the  vitreous  condition,  forming  the 
compact  and  stony  state,  the  porphyritic  character  is  not  rare  among 
rocks ;  crystals,  such  as  those  of  felspar,  being  dispersed  amid  a  base  of 
compact  mineral  matter.  When  the  latter  is  chiefly  felspathic,  the  rock 
is  usually  known  as  felspar  porphyry.  In  like  manner  crystals  of  other 
minerals  are  also  thus  dispersed  amid  a  similar  base,  such  as  those  of 
quartz  and  mica.  The  base  or  general  mass  of  the  rock  is  occasionally 
granular,  such  as  a  compound  of  felspar  and  hornblende,  constituting 
greenstone,  with  dispersed  crystals  of  felspar  or  hornblende,  such  base 
having  thus  advanced  to  a  state  of  confused  crystallization.  These  are 
usually  termed  greenstone  porphyries.  In  like  manner,  certain  granites 
become  porphyritic,  from  separate  crystals  of  felspar  being  scattered 
among  the  general  compound,  confusedly  crystallized,  and  the  rock  is 
then  called  a  porphyritic  granite.  Even  serpentines  become  in  a  man- 
ner porphyritic  when  crystals  of  bronzite  or  diallage  are  dispersed 
through  a  base  of  that  rock.  The  apparent  conditions  are  that  the 
chemical  composition  and  the  mode  of  cooling  of  the  general  mass  are 
such  that  certain  constituent  substances  can  combine  and  form  separate 
and  definite  crystallized  bodies,  the  remainder  of  the  rock  either  not 
attaining  the  state  when  definite  mineral  compounds  can  be  formed, 
or  only  doing  so  after  the  production  of  the  first-formed  minerals,  and 
then  in  a  confused  manner,  not  interfering  with  the  forms  of  the  crystals 
first  produced. 


XXV111  INTRODUCTION. 

With  regard  to  the  mineral  accumulations  derived  either  directly  or 
indirectly  from  the  igneous  rocks,  and  spread  over  areas  of  varied 
extent  and  form,  by  means  of  water,  there  is  a  large  mass,  more  or  less 
characterized  by  the  presence  among  it  of  the  remains  of  animals  and 
plants  existing  at  different  periods,  and  so  perishing,  that  portions  of 
them,  commonly  only  the  harder  parts,  have  been  entombed  in  the 
mineral  accumulations  of  such  different  times. 

Observation  has  shown  that  these  accumulations  have  succeeded  one 
another,  as  the  various  detrital  deposits  in  lakes  and  seas  now  succeed 
those  which  have  preceded  them,  so  that  when  the  ancient  sea  or  lake 
bottoms,  which,  elevated  into  the  atmosphere,  now  constitute  so  large  a 
portion  of  dry  land,  can  be  studied  in  cliffs  or  other  natural  sections,  or 
by  artificial  cuttings  or  perforations,  their  manner  of  succession  can  be 
ascertained.  The  more  investigations  have  advanced,  the  more  does  it 
appear  that  these  organic-remain  bearing,  or  fossiliferous  rocks,  as  they 
have  been  termed,  have  been  deposited  and  arranged  as  similar  accu- 
mulations now  are  in  rivers,  estuaries,  lakes,  and  seas.  Hence,  the 
geologist,  in  endeavouring  to  ascertain  the  range  of  such  fossiliferous 
deposits  at  any  given  time  upon  the  earth's  surface,  has  to  consider  the 
relative  amount  and  position  of  the  land  and  waters  of  that  time,  with 
all  their  modifying  influences,  as  also  the  various  conditions  under  which 
the  life  of  the  period  may  have  been  distributed,  and  its  remains  en- 
tombed amid  the  detrital  and  chemical  deposits  of  the  day.  In  fact,  he 
has,  from  all  the  evidence  he  can  collect,  to  suppose  himself  studying 
the  state  of  the  earth's  surface,  at  such  given  time,  as  well  with  re- 
spect to  its  physical  condition  as  the  existence  and  distribution  of  life 
upon  it. 

Viewing  the  fossiliferous  rocks  in  this  manner,  it  may  be  that  some 
of  those  divisions  among  them,  which  it  has  been  found  convenient  to 
make  for  their  more  ready  description,  and  the  tracing  of  certain  states 
of  a  sea-bottom  over  minor  areas,  have  been  too  minute,  regarded  as 
divisions  applicable  to  the  surface  of  the  earth  generally,  since  it  is  not 
to  be  supposed  that  particular  mud  or  sand  banks,  however  considerable 
locally,  were  more  likely  to  have  been  formerly  continued,  even  at 
intervals,  over  the  earth's  surface  than  they  now  are.  At  the  same  time 
such  minor  divisions  showing  the  constancy  or  modification  of  conditions, 
as  the  case  may  be,  over  the  minor  areas,  are  important,  inasmuch  as  it 
is  by  a  correct  appreciation  of  this  detail  and  the  careful  consideration 
of  how  much  may  be  regarded  in  that  light  and  how  much  as  more 


INTRODUCTION.  XXIX 

general,  that  we  learn  the  true  value  of  the  latter,  and  the  restrictions 
which  should  be  placed  upon  our  views  derived  from  the  former. 

Assuming  the  general  condition  of  the  earth's  surface  during  the 
accumulation  of  the  varied  deposits  in  which  the  remains  of  animal  and 
vegetable  life  have  been  entombed,  to  have  been  formerly  much  as  at 
present,  regarding  the  subject  on  the  large  scale,  and  without  reference, 
for  the  moment,  to  the  variable  distribution  of  land  and  water,  or  to 
whether  the  heat  in  the  earth  itself  may  or  may  not,  in  remote  times, 
have  had  a  greater  influence  on  the  life  of  those  times  than  at  present, 
the  sea  would  appear  to  have  been  the  chief  receptacle  of  the  various 
mineral  accumulations  of  all  periods,  so  that  classifications  of  the  fossili- 
ferous  rocks,  founded  on  a  succession  of  deposits  in  it,  would  probably 
be  alike  the  most  useful  and  natural.  The  manner  in  which  marine 
invertebrate  animals  now  live,  and  the  mode  in  which  the  remains  of 
similar  animals  occur  amid  the  fossiliferous  rocks,  is  such,  that  this 
division  of  life  seems  now  very  generally  admitted  as  the  most  appro- 
priate on  which  to  base  classifications  founded  on  the  distribution  of 
animals,  the  remains  of  which  are  discovered  entombed  in  rocks.  We 
must  refer  to  succeeding  pages  for  notices  of  the  manner  in  which  the 
remains  of  life  are  now  preserved  in  mineral  deposits,  and  for  certain 
points  connected  with  the  occurrence  of  such  remains  in  the  accumula- 
tions of  various  geological  dates,  which  it  appears  desirable  to  bear  in 
mind  while  studying  the  fossiliferous  rocks.  It  will  be  sufficient  here  to 
mention  that,  after  duly  first  ascertaining  the  actual  relative  superposi- 
tion of  the  various  mineral  accumulations  themselves  for  evidence  of 
their  real  succession,  and  examining  the  remains  of  animal  and  vegetable 
life  which  have  been  found  in  them,  it  has  been  inferred  that  certain  minor 
and  major  divisions  may  be  effected  in  the  general  mass  which  shall  re- 
present the  kinds  of  sea-bottoms  marking  given  and  succeeding  geological 
times.  Without,  in  the  least,  doubting  that  much  modification  may  not  be 
found  needed  in  classifications  founded  upon  the  examinations  of  even 
considerable  areas,  when  an  effective  classification,  representing  the  main 
facts  connected  with  the  accumulation  and  spread  of  fossiliferous  rocks 
over  large  portions  of  the  earth's  surface,  may  be  needed,  it  still  be- 
comes desirable  to  have  that  which  may  satisfy  the  requirements  for  the 
time  being.  The  following  sketch,  therefore,  of  the  general  divisions  at 
present  considered  desirable  for  the  area  of  Western  Europe,  and  sup- 
posed, in  part  at  least,  to  be  found  also  convenient  for  the  mode  of 


XXX 


INTRODUCTION. 


viewing  the  fossiliferous  deposits  in  many  other  parts  of  the  world,  may 
be  useful,  especially  as  respects  the  major  divisions. 


UPPER   STRATIFIED   OR   FOSSILIFEROUS   ROCKS. 

I.  Tertiary,  or  Cainozoic. 
II.  Secondary,  or  Mesozoic. 
III.  Primary,  or  Palaeozoic. 


A.  Upper  Tertiary  - 

B.  Middle  Tertiary 

C.  Lower  Tertiary  - 


A.  Cretaceous  Group 


B.  Marine  equivalents  of 


C.  Jurassic  or  Oolitic  group    - 


I.  TERTIARY,  OR  CAINOZOIC. 

a.  Mineral  accumulations  of  the  present  time. 

b.  Pleistocene. 

c.  Pleiocene. 
a.  Miocene. 

a.  Eocene. 

II.  SECONDARY,  OR  MESOZOIC. 

r  a.  Chalk  of  Maestricht  and  Denmark. 

b.  Ordinary  chalk,  with  and  without  flints. 

c.  Merstham  beds,  or  Upper  Green  Sand. 

d.  Gault. 

e.  Shanklin   Sands,   Vecten,    Neocomian,   or 

Lower  Green  Sand. 

f  Organic  remains  in  these 
a.  Wealden  clay  ftre  Qf  ft  fluyiatile)  lft. 

6.  Hastings  sands  j      CU8trine)     Qr    egtuaiy 
c.  Purbeck  series    ^     character.* 

'  a.  Portland  oolite  or  limestone. f 

c.  Portland  sands. 

d.  Kimmeridge  clay. 

e.  Coral  rag,  and  its  accompanying  grits. 
/.  Oxford  clay,  with  Kelloways  rock. 

g.  Cornbrash. 

h.  Forest  marble,  and  Bath  oolite, 
t.  Fuller's  earth,  clay,  and  limestone. 
k.  Inferior  oolite,  and  its  sands. 
I.  Lias,  upper  and  lower,  with  its  intermediate 
marlstone. 


*  The  recent  researches  of  Professor  Edward  Forbes  among  the  Purbeck  series  have 
fully  illustrated  the  prudence  of  not  trusting  to  fresh-water  molluscs  as  characterizing 
particular  divisions  in  deposits,  at  least  those  ranging  downwards  to  that  part  of  the 
fossiliferous  series,  he  having  ascertained  that  it  required  most  careful  critical  exami- 
nation to  distinguish  the  fresh-water  shells  of  that  series,  as  it  occurs  at  Purbeck,  from 
those  of  certain  existing  fresh-water  molluscs  in  England  and  part  of  Europe. 

|  The  minor  divisions  of  this  group  have  been  given  with  reference  to  those  usually 
employed  in  England,  for  the  sake  of  English  observers.  Many  modifications  have  been 
shown  to  be  effected  in  other  European  countries.  Of  these  divisions  that  of  the  Oxford 
clay  and  lias  would  appear  much  extended. 


INTRODUCTION.  XXXI 


s 


a.  Variegated  marls,  Marnes  Irishes,  Keuper. 
6.  Muschelkalk.f 

D.  Trias  group*  j  c  Red  sandstone)  £res  Bigarre",  Bunter  sand- 

stein. 


III.  PEIMARY,  OR  PALEOZOIC. 

f  a.  Zechstein,   dolomitic  or  magnesian  lime- 
\         stone. 

A.  Permian  group  .  <  6<  Rothe  todte  liegende,  lower  new  red  con- 

C          glomerate  and  sandstones,  Gres  Rouge. 

f  a.    Coal  measures,    Terrain   Houiller,   Stein 

B.  Marine  equivalents  oft       -  •< 

Kohlen,  Geberge. 

a.  Carboniferous    and    mountain    limestone, 

with  its  coal,  sandstone,  and  shale  beds 

C.  Carboniferous  limestone  group  ^         in  some  districts.     Calcaire  carbonifere, 

Bergkalk. 

b.  Carboniferous  slates  and  yellow  sandstone. 

f  a.  Various  modifications  of  the  old  red  sand- 

D.  Devonian  group  < 

(.          stone  series. 

a.  Upper ;  Ludlow  Rocks,  Wenlock  shale  and 
limestone,  Woolhope  Limestone. 

E.  Silurian  group  -        -        -        -      ^  b.  Middle ;    Caradoc   sandstone   and  conglo- 

merate. 

c.  Lower ;  Llandeilo  and  Bala  beds.  v 
a.  Barmouth  sandstones,  Penrhyn  slates,  &c. 

Various  rocks  subjacent  to  the  Silurian 

,         series  in  Wales  and  Ireland,  and  above 

F.  Cambrian  group  < 

the  mica  and  chlorite  slates,  quartz,  and 

other  rocks  of  Anglesea   and  part    of 
C  aernarvonshire. 


*  The  Trias  and  Permian  groups  afford  an  example,  as  regards  the  British  Islands, 
of  a  classification  taken  from  organic  remains  in  preference  to  the  mode  of  occurrence 
of  the  rocks  themselves,  these  groups  here  constituting  parts  of  a  general  series  of 
deposits  with  a  somewhat  marked  general  character,  known  as  the  new  red  sandstone. 
Certain  general  physical  conditions  were  prevalent  during  the  accumulation  of  these 
deposits  in  Great  Britain,  and  certain  portions  of  Western  Europe,  at  the  time  that  a 
modification  in  the  life  of  the  period  was  apparently  effected  in  the  same  area  and  those 
adjacent  to  it  on  the  north  and  east. 

•j-  In  the  collections  lately  brought  to  England  by  Captain  Strachey,  Bengal  Engi- 
neers, after  an  examination  of  the  Himalaya  range,  the  forms  of  certain  organic  remains 
from  the  Thibet  side  of  those  mountains  remind  the  geologist  of  those  found  marking 
the  Muschelkalk  of  Germany ;  an  interesting  circumstance,  considering  the  range  of 
that  rock  in  Europe. 

J  When  the  great  thickness  of  these  deposits  in  Europe  and  America  is  considered,  it 
becomes  very  desirable  to  find  their  marine  equivalents,  inasmuch  as  the  conditions 
under  which  the  great  mass  of  these  coal  measures  have  been  accumulated,  as  has  been 
noticed  in  the  sequel,  could  scarcely  constitute  otherwise  than  minor  parts  of  the  gene- 
ral deposits  of  the  time.  It  is  easy  to  conceive,  as  has  indeed  been  done,  that  the 
marine  equivalents  might  contain  either  the  organic  remains  usually  found  in  the 


XXX11  INTRODUCTION. 

LOWER   STRATIFIED   ROCKS. 

Although  alteration  in  the  mineral  character  of  the  fossiliferous  rocks, 
as  is  noticed  in  the  sequel,  from  the  influence  of  intruded  igneous  matter 
in  a  molten  state,  or  arising  from  other  modifying  causes,  often  produces 
mica  slates,  hornblende  slates,  gneiss,  and  other  forms  of  laminated  and 
stratified  deposits  with  a  peculiar  aspect,  there  appears,  nevertheless, 
evidence  in  Scandinavia  and  the  British  Islands,  and  also  in  other  parts 
of  Europe,  to  show  that  beneath  all  the  fossiliferous  rocks  above  noticed, 
there  are  mica  and  chlorite  slates,  quartz  rocks,  crystalline  limestones, 
gneiss,  hornblende,  and  other  rocks,  of  earlier  production.  These  may 
indeed  be  merely  altered  or  metamorphosed  detrital  and  chemical  de- 
posits of  earlier  times,  and  possibly  organic  remains  may  be  eventually 
discovered  in  them ;  but  until  this  shall  happen  it  seems  desirable  to 
keep  them  asunder,  for  the  convenience  of  showing  previous  accumula- 
tions to  those  noticed  in  the  last  division.* 

It  would  be  out  of  place  to  attempt  extended  descriptions  of  the 
various  rocks  noticed  in  the  above  sketch.  Information  respecting 
them  will  be  obtained  by  reference  to  works  in  which  such  descriptions 
are  inserted,  and  still  better  by  studying  collections,  with  the  aid  of  a 
competent  person,  in  which  their  varied  characteristics,  as  well  mineral 
as  palaeontological  (when  fossiliferous),  may  be  carefully  considered  and 
effectively  displayed.  The  field,  however,  is  the  great  source  of  geo- 
logical knowledge,  however  important  the  cabinet,  in  its  place,  may 
also  be :  it  is  there  that  the  observer  learns  to  appreciate  the  greater 
problems  of  geology,  and  where  he  may  himself  so  materially  assist  in 
obtaining  correct  views  of  the  modifications  which  the  earth's  surface 
has  undergone  in  past  times,  and  of  the  causes  tending  to  obliterate  its 
present  condition. 

deposit  beneath  them  in  parts  of  Western  Europe,  or  those  found  in  the  group  above 
them,  or  a  mixture  of  both.  In  Northern  England  the  alternations  of  conditions  by 
which  Coal  beds  were  included  in  the  carboniferous  limestone,  did  not  interrupt  those 
for  the  existence  of  a  marked  kind  of  marine  animal  life  in  the  same  localities. 

*  Though  a  complicated  district,  and  requiring  much  caution  during  examination, 
the  Island  of  Anglesea,  now  so  readily  accessible,  taken  in  conjunction  with  the  adjoin- 
ing portions  of  Caernarvonshire,  will  afford  the  observer  good  opportunities  for  studying 
some  portion  of  this  division,  the  more  especially  as  the  Cambrian  group  can  be  well 
seen  in  the  vicinity  of  Bangor,  Caernarvonshire.  Hence,  perhaps,  the  term  Mono,  series, 
might  not  be  inapplicable  to  these  lower  stratified  rocks,  viewed  merely  as  a  convenient 
name  for  the  present,  this  series  being  thus  easily  studied  in  connexion  with  the  Cam- 
brian and  Silurian  rocks  of  North  Wales. 


THE 


GEOLOGICAL  OBSEKYEB. 


As  geological  knowledge  advances,  the  more  evident  does  it  become 
that  we  should  first  ascertain  the  various  modifications  and  changes 
which  now  take  place  on  the  surface  of  the  earth,  carefully  considering 
their  causes,  and  then  proceed  to  employ  this  knowledge,  so  far  as  it 
can  be  made  applicable,  in  explanation  of  the  facts  seen  in  connexion 
with  the  geological  accumulations  of  prior  date.  This  done,  we  should 
proceed  to  view  those  not  thus  explained,  with  reference  to  the  con- 
ditions and  arrangements  of  matter  which  the  form  of  our  planet,  the 
known  distribution  of  its  heat,  the  temperature  of  the  surrounding 
space,  and  other  obvious  circumstances,  may  lead  us  to  infer  would  be 
probable  during  the  lapse  of  geological  time. 

I.  Decomposition  of  HocJcs. — The  geological  observer  cannot  long 
have  been  engaged  in  his  investigations  before  he  will  be  struck  with 
the  tendency  of  rocks  to  decompose  by  the  action  of  atmospheric  in- 
fluences upon  them.  He  will  soon  perceive  that  this  decomposition  is 
both  chemical  and  mechanical ;  that  certain  mineral  bodies  more  readily 
give  way  before  these  influences  than  others ;  and  that  from  altered 
conditions,  as  regards  them,  the  same  kinds  of  rock  will  more  easily  de- 
compose in  one  situation  than  in  another. 

It  is  in  consequence  of  this  decomposition  that  we  have  soils  sup- 
porting that  growth  of  vegetation  upon  which  animal  life  depends,  as 
adjusted  upon  our  planet ;  for  soils  are  but  the  decomposed  parts  of 
sea  or  lake  bottoms  and  of  igneous  accumulations,  with  the  remains  of 
the  vegetation  which  has  grown  on  them,  and  of  the  animals  which  have 
lived  upon  the  plants.  From  the  configuration  of  the  surface  the  de- 
composed portions  of  rocks,  forming  soils,  may  not  always  cover  those 
from  whence  they  were  derived,  for  they  may  and  sometimes  have  been 
carried,  mechanically  suspended  in  water,  to  various  distances,  and  there 
deposited,  in  such  a  manner  as  to  be  mingled  with  the  decomposed 
portions  of  other  rocks,  or  wholly  cover  over  the  latter.  Be  this, 

3 


34  DECOMPOSITION    OF    ROCKS. 

however,  as  it  may,  the  decomposed  parts  of  rocks  form  the  base  of 
the  soils,  affording  soluble  mineral  matter  to  the  plants  requiring  it, 
and  presenting  a  physical  structure  capable  of  supporting  their  growth. 

The  decomposition  of  rocks,  in  its  various  stages,  will  require  much 
attention  on  the  part  of  the  observer,  so  that  he  may  properly  classify 
the  facts  coming  within  the  range  of  his  researches.  Among  rocks  of 
igneous  origin,  such  as  granites,  greenstones,  and  the  like,  he  will  find 
that  the  decomposition  of  felspar  is  among  the  chief  causes  of  the 
disintegration  of  the  igneous  masses  of  which  this  mineral  may  form  a 
part.  It  would  be  out  of  place  here  to  enter  upon  the  composition  of 
the  various  minerals  of  the  felspar  family  ;*  it  will  be  sufficient  to  refer 
to  those  portions  of  them  which  are  soluble,  such  as  the  silicates  of 
potash  or  soda,  as  the  case  may  be.  The  particles  once  loosened  by  the 
abstraction  of  the  matter  removed  in  solution,  rains  and  changes  of  tem- 
perature, particularly  in  regions  visited  by  frosts,  act  mechanically,  and 
the  surface  of  the  rock,  under  favourable  conditions,  is  removed.  From 
a  repetition  of  the  same  causes  the  rock  becomes  decomposed  to  various 
depths,  according  to  circumstances.  In  cases  where  the  remaining 
portions  are  either  too  large  or  so  situated  as  not  to  be  readily  carried 
away,  a  coating  of  the  disintegrated  insoluble  part  remains,  and  to  a 
certain  extent  protects  the  solid  rock  beneath  from  that  decomposition 
which  it  would  otherwise  have  suffered. 

In  many  granitic  regions  ample  opportunities  of  observing  the  amount 

Fig.  1. 


of  decomposition  thus  produced  are  afforded;  high  tors  or  bosses  of 
rock  rising  above  portions  in  a  decomposed  state  (fig.  1),  while  hard 
masses,  having  the  fallacious  appearance  of  boulders,  rounded  by  attri- 

*  Seven  analyses  of  common  felspar  by  Klaproth,  Vauquelin,  Bucholz,  Rose,  Ber- 

thier,  and  Beudant  would  give  as  a  mean — 

Silica,  .  .        64-04 

Alumina,      .  .  .  .  .18-94 

Potash,        .  «...        13-66 

Lime,  .....          0-76 

Oxide  of  iron,  .....  0-74 

For  albite,  or  felspar,  into  the  composition  of  which  soda  enters  instead  of  potash, 

four  analyses  by  Tengstrom,  Eggertz,  Rose,  and  Stromeyer  give — 

Silica,  .  .  .  .69-45 

Alumina,      .  .  .  .  .  .19-44 

Soda,  9-95 

Lime,  ...  .  0-22 

Magnesia,    .  .  .          0-13 

Oxides  of  iron  and  manganese,       .  0-27 


DECOMPOSITION    OF    ROCKS.  35 

tion,  are  included  in  the  loose  decomposed  granite,  as  represented  be- 
neath (fig.  2). 

Fig.  2. 


d  d 

This  illustration  is  taken  from  part  of  the  road  between  Okehampton 
and  Moreton  Hampstead,  Devon,  a  represents  the  vegetable  soil ;  b 
decomposed  granite  ;  c  c  solid  rounded  masses  of  undecomposed  granite, 
included  in  the  decomposed  part ;  and  d  d  solid  granite. 

In  such  a  section  as  this,  great  care  should,  however,  be  taken,  so  that 
it  may  be  certain  that  c  c  are  not  transported  boulders  of  granite,  included 
in  smaller  granitic  gravel,  as  sometimes  happens  with  granitic  drift,  near 
the  sources  whence  it  has  been  derived.  Fortunately  in  this  case  the  ob- 
server would  be  assisted  by  the  presence  of  large  crystals  of  felspar  dis- 
seminated through  all  parts  of  the  rock,  both  decomposed  and  undecom- 
posed, and  which  are  beautifully  preserved,  remaining  uninjured  in  their 
forms  and  in  their  relative  positions  throughout  the  decomposed  granite. 

In  granitic  regions,  sections  such  as  that  beneath  (fig.  3),  in  which  a 

Fig.  3. 


represents  the  vegetable  soil,  as  it  is  commonly  termed,  b  the  decom- 
posed, and  c  the  solid  granite,  are  not  unfrequent.  Sections  of  this 
appearance  should,  however,  be  carefully  examined,  and  it  be  clearly 
ascertained  that  the  granitic  particles  at  b  are  of  the  same  kind  and  in 
the  same  general  relative  positions  as  those  at  c,  and  that  there  can  be 
no  chance  of  their  having  been  brought  into  their  present  position  by 
moving  water.  The  quantity  of  transported  granitic  matter  around 
granite  districts,  as  also  among  them,  is  sometimes  so  considerable  that 
a  superficial  deposit  of  granitic  particles,  covering  a  very  different  kind 
of  rock,  may,  without  due  care,  be  mistaken  for  a  mass  of  decomposed 
granite.  In  the  same  way  the  remains  of  the  rock  of  one  part  of  a 
granitic  region  may  be  removed  and  cover  the  rock  of  another  portion. 
Among  those  trappean  rocks  in  which  hornblende*  forms  a  marked 

*  The  analyses  of  hornblende  vary.    The  following  is  that  of  Pargas,  by  Bousdorf, 
and  approaches  the  mean  of  several  analyses  of  hornblende  from  different  places  : — 
Silica,  .  .  .  .  .  .45-69 

Alumina,      .  •         .  .  .  .  .         12-18 

Lime,  ......         13-83 

Magnesia,     ......        18-79 

Protoxide  of  iron,     .....  7-32 

manganese,      ....  0-22 

Fluoric  acid,  .  .  .  -   .          1*50 


36  DECOMPOSITION    OF    ROCKS. 

component  part,  it  sometimes  happens  that  this  mineral  is  found  decom- 
posed, the  rock  presenting  a  ferruginous  aspect,  from  the  iron  in  it 
having  been  converted  into  a  peroxide.  Greenstones,  in  which  the  fel- 
spar and  hornblende  have  both  been  decomposed,  are  in  some  situations 
thickly  coated  with  a  loose  covering.  The  variable  manner  in  which  a 
mass  of  trap  that  has  been  placed  under  equal  atmospheric  conditions 
has  been  unequally  decomposed,  will  often  afford  an  excellent  illustra- 
tion of  the  original  differences  in  the  rock,  arising  not  only  from  a  dif- 
ferent arrangement  of  the  component  parts,  but  also  from  their  varied 
manner  of  aggregation,  in  consequence  of  differences  in  cooling. 

Some  dykes,  as  well  of  granitic  as  of  trappean  rocks,  afford  excellent 
examples  of  the  variable  power  to  resist  the  same  order  of  decomposing 
influences  according,  chiefly,  to  the  differences  arising  from  modifications 
of  cooling.  Some  granitic  dykes,  or  elvam,  as  they  are  termed  in 
Cornwall,  do,  as  in  the  following  section  (fig.  4),  show  an  amount  of 

Fig.  4. 


decomposition  gradually  increasing  towards  the  central  portion.  In  the 
above  a  a,  56,  and  c  represent  the  different  parts  of  a  granitic  dyke,  or 
elvan,  traversing  slate  rocks,  dd.  Assuming  in  this  case  that  the 
elementary  component  parts  of  the  dyke  were  originally  the  same,  and 
that  the  differences  found  have  arisen  from  variable  cooling,  as  it  is  now 
well  understood  has  frequently  been  the  case,  the  decomposition  has 
been  effected  according  to  the  facility  with  which  the  soluble  portions 
could  be  attacked  by  atmospheric  influences  and  be  subsequently  removed. 
The  two  outward  parts  of  the  dyke  (a  a\  are  considered  to  be  composed, 
as  often  happens,  of  a  hard  siliceous  rock,  the  elements  of  the  granitic 
matter  having  taken  that  form  from  comparatively  quick  cooling,  so  that 
this  modification  of  the  matter  of  the  dyke  has  resisted  decomposition 
better  than  the  rest.  At  b  6,  inside  the  hard  rock,  another  modification, 
arising  from  more  slow  cooling,  is  supposed  to  exhibit  a  porphyry,  some 
mineral,  very  frequently  felspar,  crystallizing  out  amid  the  base,  itself 
less  compact  than  the  preceding  variety.  Not  unfrequently  in  such 
cases  the  felspar  is  decomposed,  and  the  insoluble  portions  even  removed 
when  directly  exposed  to  the  atmosphere.  Still  proceeding  inwards, 
the  rock  becomes  more  and  more  granitic,  until,  finally,  the  central  por- 
tions are  well  crystallized,  and  then  exposed  to  the  full  action  of  the 
decomposing  influences. 

We  often  thus  find,  within  a  short  distance,  a  good  example  of  varia- 
ble decomposition  arising   from  differences  in  physical  structure,  the 


DECOMPOSITION    OF    BOOKS. 


3T 


chemical  composition  of  the  mass  remaining  the  same  ;  a  variation,  very 
instructive,  since  it  enables  the  observer  readily  to  appreciate  the  in- 
equalities of  surface  which,  in  many  regions  composed  of  the  same 
kind  of  igneous  rocks,  arise  from  changes  in  physical  structure  alone, 
some  variations  having  better  resisted  decomposition  or  abrasion  than 
others.  At  the  same  time  he  should  carefully  study  the  modifications 
in  hardness,  and  the  capability  of  resisting  decomposition  arising  from 
changes  in  chemical  composition,  such,  for  instance,  as  those  observable 
among  the  granites  which  occasionally  graduate  into  schorl  rock,  in 
Devon  and  Cornwall.* 

Of  the  curious  forms  assumed  by  granitic  rocks  from  variable  resis- 
tances to  decomposition,  those  named  the  Kettle  and  Pans,  at  St. 
Mary's,  Scilly  (fig.  5),  may  be  taken  as  a  good  example.f 

Fig.  5. 


While  rocks  of  a  generally  similar  chemical  composition,  such  as  those 
above  noticed,  are  found  to  decompose  in  a  variable  manner,  according 
to  the  different  aggregation  of  their  component  parts,  it  would  readily 
be  anticipated  that  any  rocks  formed  of  different  materials,  brought  to- 

*  The  following  may  be  taken  as  an  estimated  general  view  of  the  chemical  difference 
between  common  granite,  composed  of  two-fifths  of  quartz,  two-fifths  of  felspar,  and 
one-fifth  of  mica,  and  schorl  reck,  supposed,  for  illustration,  the  proportions  varying 
materially,  to  be  formed  of  equal  parts  of  schorl  and  quartz  :  — 

Silica,        ...... 

Alumina,  ...... 

Potash,      ...... 

Soda,         ...... 

Lime,         ...... 

Magnesia,          ..... 

Oxide  of  iron,    ..... 

Oxide  of  manganese,          .         .         . 

Fluoric  acid,      ..... 

Boracic  acid,      ..... 
f  Though  the  true  origin  of  the  "  Rock  Basins,"  as  they  have  been  termed,  is  in 
general  sufficiently  clear,  it  may  often  have  happened  that,  owing  to  a  convenient  situa- 
tion, the  Druids  may  have  employed  them  for  their  purposes,  either  as  they  naturally 
occurred,  or  artificially  modified. 


Granite. 

Schorl  Rock. 

74-84 

68-01 

12-80 

17-91 

7-48 

0-35 

0-98 

0-37 

0-14 

0-99 

2-22 

1-93 

6-85 

0-12 

0-81 

0-21 

1-79 


38  DECOMPOSITION    OF    ROCKS. 

gether  as  sands  and  gravel,  and  subsequently  consolidated  by  some 
cementing  substance,  would  be  found  to  decompose  irregularly  and 
according  to  the  different  powers  of  their  component  parts  to  resist  the 
chemical  and  mechanical  influences  to  which  they  may  be  exposed.  The 
observer  will  soon  perceive  that,  taken  generally,  the  cementing  matter 
of  sandstones  and  conglomerates  decomposes  first,  liberating  the  grains 
of  sand  and  the  pebbles,  which  have  originally  remained  such  from  their 
hardness,  and  they  are  thus  ready  to  be  again  carried  by  moving  waters 
to  other  situations,  there  to  form  the  parts  of  new  accumulations.  The 
rapidity  of  decomposition  in  such  cases  necessarily  varies  according  to 
the  nature  of  the  cementing  substance.  A  calcareous  cement,  though 
hard,  will  more  readily  give  way  before  the  chemical  influences  acting 
on  limestones  than  ordinary  siliceous  matter,  though  the  latter  may  be 
less  compact ;  while  a  siliceous  cement,  if  porous,  may  be  more  easily 
removable  by  the  combined  action  of  frost  and  thaw. 

The  hardest  limestones,  even  those  termed  marbles  when  crystalline, 
will  be  observed  to  decompose  on  the  surface.  The  action  is  necessarily 
variable,  and  dependent  on  the  different  resisting  powers  of  the  rock, 
on  the  one  hand,  and  the  exposure  to  the  needful  decomposing  influences 
on  the  other.  It  will  soon  appear  that  a  crystalline  vein,  running 
through  an  ordinary  limestone,  stands  out  in  salient  relief,  showing  that 
the  arrangement  of  particles  in  the  crystalline  form,  notwithstanding 
that  the  carbonate  of  lime  is  then  generally  more  pure  than  in  the  body 
of  the  rock,  is  better  able  to  resist  atmospheric  influences  than  in  a 
less  definitely  arranged  position. 

Proceeding  to  further  examination,  we  perceive  that  not  only  the 
crystalline  veins  thus  protrude  upon  the  surface  of  the  limestone  rocks, 
but  that  many  an  organic  remain  does  the  same,  and,  in  some  instances, 
we  only  clearly  distinguish  that  a  limestone  is  fossiliferous  by  this  kind 
of  decomposition,  the  common  internal  fracture  ill  exhibiting  the  fact. 
That  this  harmonizes  with  the  comparatively  undecomposed  condition 
of  the  crystalline  vein  becomes  apparent  when  we  examine  the  structure 
of  these  organic  remains.  The  shells  either  retain  to  great  extent  the 
original  crystalline  or  other  definite  arrangement  of  their  parts,  so  essential 
to  their  well-being  when  the  animals  of  which  they  once  constituted  the 
hard  portions  were  alive,  or  having  been  decomposed  in  the  body  of  the 
rock  during  the  lapse  of  time,  the  empty  spaces  (or  casts,  as  they  are 
commonly  termed)  have  been  filled  with  crystalline  carbonate  of  lime, 
which  has  percolated  in  solution  through  the  pores  of  the  rock  into  the 
cavities.* 

*  It  was  considered  useless  further  here  to  remark  on  the  composition  of  organic 
remains.  It  may,  however,  be  noticed  that  the  bones  and  teeth  of  fish,  reptiles,  birds, 
and  mammalia  have  been  often  secured  from  complete  decomposition  and  removal  by 
the  presence  of  the  phosphate  of  lime  contained  in  them,  and  that  into  the  cavities  left 
after  the  original  decomposition  of  shells  other  less  soluble  substances  than  carbonate 
of  lime  have  been  infiltrated,  such  for  example  as  into  the  cavities  of  the  Gryphcea  in- 


DECOMPOSITION    OF    ROCKS. 


39 


By  this  kind  of  decomposition  we  often  learn  that  many  a  limestone 
is  really  little  else  than  a  mass  of  organic  remains  cemented  by  a  minor 
quantity  of,  chemically  deposited  carbonate  of  lime.  Some  of  our 
hardest  limestones,  those  known  as  carboniferous  or  mountain  limestones, 
afford  excellent  examples  of  this  fact.  The  beds  of  this  rock,  for  hun- 
dreds of  feet  in  depth,  are  sometimes  found  composed  of  little  else  than 
the  disintegrated  joints  of  encrinites,  mingled  with  shells  and  a  few 
corals.* 

By  the  aid  of  decomposition  we  not  only  learn  that  many  limestones 
are  little  else  than  such  accumulations  of  the  harder  parts  of  molluscs 
and  other  creatures,  many  of  which  have  lived  and  died  in  the  places 
where  we  discover  their  remains  ;  but  we  also  find  revealed  the  arrange- 
ments of  the  component  parts  of  rocks,  as  well  igneous  as  accumulated 
by  means  of  water,  which  do  not  otherwise  appear,  arrangements  of 
parts  exceedingly  important  when  we  study  the  original  manner  in  which 
rocks  have  been  accumulated,  or  the  modifications  and  changes  to  which, 
during  the  lapse  of  geological  time,  they  have  been  subjected.  Many  a 
sandstone,  well  weathered,  as  it  is  termed,  will  exhibit,  as  beneath  (fig.  6), 

Fig.  6. 


a  honeycombed  and  irregular  appearance,  arising  from  the  different 
character  of  parts  of  the  cementing  substance,  either  original  or  sub- 
sequent to  the  accumulation  of  the  rock,  as  the  case  may  be,  and  many 
another  structure,  also  of  importance,  such  as  the  concretionary  struc- 
ture of  some  igneous  rocks,  then  alone  becomes  apparent.  We  should, 
for  example,  probably  be  ignorant,  without  weathering,  of  this  arrange- 

curva  and  other  shells,  in  the  lias  of  Glamorganshire,  where  silica  has  replaced  the 
original  matter  of  the  shells. 

*  This  fact  may  be  well  studied,  among  other  localities,  on  the  southern  coast  of 
Pembrokeshire,  where  the  cliffs  afford  excellent  opportunities  of  observing  the  mode  in 
which  the  materials  of  its  carboniferous  limestone  have  been  accumulated. 


40  DECOMPOSITION    OP    ROCKS. 

ment  of  parts  in  the  granitic  or  el  van  dyke,*  a  a,  cutting  through  slates, 
b  by  at  Watergate  Bay,  Cornwall,  and  figured  beneath  (fig.  7). 


The  division  of  rock  masses  by  cleavage  greatly  aids  their  decompo- 
sition, since  it  renders  them  slaty,  when  this  would  not  happen  from 
any  original  accumulation  of  sand  or  mud  in  thin  layers,  one  above  the 
other,  and  the  like  arises  from  those  separations  in  planes,  named  joints, 
further  distant  from  each  other,  and  which  with  the  cleavage  planes 
will  be  further  considered  in  the  sequel.  By  these  means  water  more 
readily  percolates  through  many  rocks  than  it  would  otherwise  do,  and 
thus  a  greater  amount  of  soluble  matter  may  be  attacked  than  would 
otherwise  have  happened  in  the  same  time. 

Many  hard  rocks  break  up  superficially  in  a  manner  showing  little 
symmetry  of  form  in  the  fragments,  so  much  so  that  their  shape  seems 
more  due  to  the  irregular  action  of  the  decomposing  influences,  than  to 
differences  of  resistance  from  original  structure.  A  compact  limestone 
or  hard  sandstone  may  often  be  seen  broken  up  beneath  the  soil,  in  the 
manner  exhibited  in  the  accompanying  section  (fig.  8),  in  which  a  re- 
rig.  8. 


presents  the  vegetable  soil,  c  c  a  hard  limestone  or  sandstone,  and  b  b 
fragments  of  the  same  rock,  largest  towards  c  c,  and  evidently  having 
constituted  portions  of  the  subjacent  highly  inclined  beds,  while  the 
upper  fragments  are  smaller  and  more  confusedly  mixed,  though  still 
angular.  It  sometimes  happens  when  the  rock,  so  broken  up,  is  a 
sandstone,  that  the  chemical  change  of  the  iron  in  the  cementing  matter, 
subsequently  to  the  formation  of  the  fragments,  is  well  seen.  Upon 
breaking  these  fragments,  sections,  as  beneath  (fig.  9),  will,  in  such  cases 

*  This  dyke  is  composed  of  quartz,  felspar,  and  mica,  containing  disseminated  crys- 
tals of  felspar. 


DECOMPOSITION    OF    ROCKS. 


41 


present  themselves.     A  central  portion  will  remain  unchanged,  sur- 
rounded by  irregular  zones  (b  5),  commonly  of  a  brownish  red,  arising 

Fig.  9. 


from  chemical  action  from  the  sides  of  the  fragment,  by  which  the 
protoxide  of  iron  has  been  converted  into  a  peroxide.  Similar  changes 
of  the  protoxide  of  iron  into  the  peroxide,  are  observable  among  the 
argillaceous  limestones,  such  as  the  lias,  and  are  indeed  sufficiently 
common. 

In  some  very  earthy  limestones,  which  may  rather  be  considered  to 
have  been  once  silt,  highly  impregnated  with  calcareous  matter,  the  dis- 
appearance of  the  latter  in  the  higher  parts  of  the  rock,  even  to  many 
feet  in  depth,  has  been  so  complete,  and  the  peroxidation  of  the  iron  so 
extensive,  that  a  rusty-looking,  porous  substance  alone  remains.  Among 
some  of  the  older  accumulations  such  a  rock  may  often  be  seen,  and  be 
found  the  only  means  by  which  beds,  here  and  there  containing  a  larger 
percentage  of  carbonate  of  lime,  can  be  traced  or  connected.  Among 
the  older  rocks  also,  many  a  layer  of  a  rusty  colour  exhibits  a  total 
disappearance  of  the  carbonate  of  lime  of  the  numerous  shells  which 
once  constituted  the  bulk  of  the  layer,  their  casts,  or  the  spaces  which 
they  once  filled,  alone  remaining,  while  the  iron  contained  in  the  mud 
or  silt  which  first  enveloped  them,  has  been  converted  altogether  into  a 
peroxide. 

While  thus  the  iron  contained  in  many  rocks  exhibits  a  gradual 
change  to  a  peroxide,  many  red  marls  and  sandstones  show  an  altera- 
tion from  the  peroxide  of  iron,  giving  a  general  red  tint  to  these  deposits, 
to  a  protoxide.  Beneath  the  vegetation,  and  by  the  sides  of  natural 
joints,  the  red  colour  will  be  seen  converted  into  a  green  or  bluish  green, 
the  change  being  due  to  the  effects  of  decomposing  vegetation,  which 
has  robbed  the  adjacent  peroxide  of  iron  of  a  portion  of  its  oxygen. 
This  is  a  point  of  much  interest  when  we  study  the  cause  of  the  streaks 
of  green  or  bluish  green  amid  the  red  marls  and  sandstones  of  different 
geological  ages,  and  which  have  probably  arisen  from  causes  in  opera- 
tion at  the  period  when  the  whole  has  been  accumulated.  When  we 
examine  into  the  variations  and  modifications  of  colour  arising  from  the 
present  effects  of  decomposing  vegetation,  the  old  changes  have  to  be 


42  REMOVAL    OF    PARTS    OF    ROCKS    BY    WATER. 

carefully  separated  from  the  modern,  since  both  are  sometimes  exhibited 
in  the  same  sections. 

The  observer  must  be  careful,  in  his  estimate  of  the  amount  of  de- 
composition which  rocks  may  sustain  from  atmospheric  influences,  duly 
to  consider  the  power  of  vegetation  to  prevent,  assist,  or  otherwise 
modify  it,  according  to  circumstances.  Vegetation  may  prevent  de- 
composition, by  presenting  a  certain  barrier  to  the  effects  of  sudden 
frosts  and  thaws ;  assist  the  action  of  heavy  rains  by  keeping  the  higher 
parts  of  rocks  more  permanently  wet  than  they  would  otherwise  be  ;  or 
greatly  modify  it  by  the  various  effects  produced  by  the  kind  of  plants 
which  may  cover  the  land  at  given  times ;  for  a  portion  of  country 
covered  by  forest  trees  would  be  differently  circumstanced,  as  regards 
the  probable  decomposition  of  the  rocks  of  which  it  is  formed,  than 
when  the  same  portion  was  either  broken  for  tillage  or  spread  over  with 
pastures.  As  a  whole,  the  study  of  the  decomposition  of  rocks  is  one 
of  much  importance,  since  by  it  we  learn  a  variety  of  facts  connected 
with  the  original  accumulation  of  mineral  masses,  with  which  otherwise 
we  should  be  unacquainted,  and  at  the  same  time  it  often  teaches  us 
properly  to  appreciate  the  changes  and  modifications  which  have  oc- 
curred since  such  original  accumulation.  It  enables  us  to  form  a  correct 
judgment  of  the  amount  of  matter  which  may  thus  be  prepared  for  re- 
moval and  for  accumulation  elsewhere.  We  see  causes  and  effects  that 
have  been  in  operation  whenever  land  arose  from  beneath  water  into 
the  atmosphere,  however  modified  they  may  have  been  by  alterations  of 
conditions,  such  as  those  now  found  between  the  tropics,  and  in  the 
arctic  or  antarctical  regions,  or  which  may  have  taken  place  in  the 
atmosphere  of  our  planet  from  its  earliest  state. 

II.  Removal  of  the  Parts  of  Rocks  by  Water. — As  spring  waters  are 
not  pure  waters,  but  hold  different  substances  in  solution  according  to 
circumstances,  and  as  it  is  evident  that,  at  least,  the  bulk  of  such  waters 
are  only  rains  which  have  percolated  through  rocks,  and  variably  pour 
out  again  according  to  conditions,  the  substances  so  in  solution  must 
have  been  removed  from  the  rocks.  However  small  the  soluble  matter 
found  in  any  single  spring  may  be,  on  the  average,  collectively  its 
amount  is  considerable,  particularly  when  we  regard  the  changes  which 
rocks  must  have  undergone  from  this  cause  alone  during  the  lapse  of 
any  geological  time,  when  conditions  may  have  thus  permitted  the  re- 
moval of  soluble  matter  from  any  given  mass  of  them. 

With  the  removal  of  lime  as  a  carbonate  we  are  commonly  familiar, 
since  by  the  loss  of  the  excess  of  carbonic  acid  required  to  retain  it  in 
solution,  this  substance  is  thrown  down  in  different  forms  varying  from 
a  simple  incrustation  upon  vegetable  matter,  or  upon  stones  or  rocks, 
amid  or  over  which  it  may  flow,  to  hard  and  compact  limestones,  some 
taking  a  crystalline  form  under  favourable  circumstances,  as  is  fre- 


REMOVAL    OF    PARTS    OF    ROCKS    BY    WATER.  43 

quently  so  well  shown  in  the  beautiful  stalactites  and  stalagmites  of 
many  caverns  in  limestone  countries.  It  is  no  uncommon  thing  in  cal- 
careous districts  to  find  the  fragments  of  limestones  which  have  been 
detached  from  faces  of  rock  by  atmospheric  influences,  firmly  cemented 
together,  as  a  breccia,  by  carbonate  of  lime,  left  by  the  waters  which 
have  percolated  through  them. 

In  the  calcareous  countries  of  the  tropics,  where  evaporation  is  more 
rapid  than  in  the  temperate  climates,  the  deposit  of  carbonate  of  lime 
may  often  be  studied  with  much  advantage.  Heavy  rains  falling  amid 
a  mass  of  vegetation,  the  decaying  parts  of  which  furnish  the  needful 
carbonic  acid,  carry  this  with  them  amid  the  beds,  joints,  and  caverns 
of  the  limestones ;  carbonate  of  lime  is  thus  removed,  and  when  the 
waters  again  emerge  charged  with  bicarbonate  of  lime,  and  are  exposed 
to  the  heats  of  a  tropical  sun,  incrustations  are  formed  in  the  shallow 
and  slow-moving  portions  of  the  streams,  and  trees  may  even  become 
imbedded  by  the  shifting  course  of  the  waters,  as  is  well  seen  at  the 
Roaring  River  on  the  north  side  of  Jamaica,  where  waters  containing 
much  bicarbonate  of  lime,  after  leaping  over  a  cliff,  run  roaring  amid  a 
forest,  the  lower  portions  of  the  trees  of  which  they  encase  with  carbo- 
nate of  lime,  and  shift  their  channels  as  new  accumulations  compel  them 
to  follow  a  new  direction. 

In  shallow  sheltered  bays  also  of  tropical  coasts,  to  which  water  con- 
taining calcareous  matter  may  slowly  find  its  way,  the  solution  becoming 
thus  highly  concentrated  by  evaporation  as  it  flows  onward,  opportuni- 
ties are  occasionally  afforded  for  observing  the  formation  of  the  little 
rounded  grains  of  calcareous  matter  in  concentric  coatings,  termed 
oolites,  a  slight  ripple  being  sufficient  to  produce  a  to-and-fro  motion 
on  the  beach  on  which  the  calcareous  matter  is  being  deposited.  Upon 
breaking  these  calcareous  grains,  sometimes  a  fine  particle  of  common 
sand,  or  broken  shell  forms  the  nucleus,  at  others  it  would  appear  that 
a  simple  particle  of  the  calcareous  matter  itself,  before  it  became  at- 
tached to  any  other  solid  substance,  was  sufficient  for  the  purpose. 

Though  many  countries  show  deposits  of  carbonate  of  lime  from  waters 
flowing  over  them,  parts  of  Italy  have  so  long  been  remarked  on  this 
account,  that  the  name  travertino  has  not  unfrequently  been  given  to 
such  accumulations.*  This  deposit  has  also  a  peculiar  interest  in  that 
land,  inasmuch  as  we  there  sometimes  find  early  architectural  works  of 

*  Not  only  have  we  excellent  opportunities  of  there  studying  the  calcareous  deposits 
thrown  down  from  waters  of  ordinary  temperatures,  but  those  also  from  thermal  springs, 
in  which  other  substances  are  mingled  in  a  manner  to  produce  very  interesting  results. 
Of  this  kind  is  the  intermingling  of  silica  with  the  other  deposits  at  the  baths  of  San 
Filippo,  where  the  waters  have  a  temperature  of  122°  Fah1.  (one  spring  being  about  a 
degree  higher),  and  contain  in  solution,  silica,  sulphate  of  lime,  bicarbonate  of  lime, 
and  sulphate  of  magnesia.  The  ground  around  is  composed  of  travertine  deposited  by 
the  springs. 


44  REMOVAL     OF    PARTS    OF    ROCKS    BY    WATER. 

the  ancients,  as  for  example,  the  remains  of  the  temples  at  Paestum, 
constructed  of  travertine,  containing  the  remains  of  the  same  kinds  of 
terrestrial  and  lacustrine  shells  which  now  exist  in  the  vicinity,  and  be- 
come entombed  in  the  travertine  now  forming.  Of  large  accumulations 
of  calcareous  matter  depositing  under  the  atmosphere  and  not  beneath 
bodies  of  water,  the  plains  of  Pamphylia  would  appear  to  afford  a  very 
striking  example.  The  coasts  of  Karamania  have  long  been  known  to 
present  good  instances  of  beaches  consolidated  by  the  percolation  of 
carbonate  of  lime  amid  the  pebbles,  thus  forming  a  conglomerate.  We 
may  thus  obtain  not  only  breccias  and  conglomerates  upon  the  land,  by 
the  evaporation  of  water,  charged  with  bicarbonate  of  lime,  without  the 
aid  of  lakes,  but  also  sheets  of  limestone,  the  overflow  of  rivers  and  the 
shifting  of  their  courses  causing  the  necessary  deposits.  It  would  be 
desirable,  where  fitting  opportunities  for  studying  the  latter  kind  of 
accumulations  may  be  found,  carefully  to  examine  the  differences  be- 
tween them  and  those  deposits  effected  in  tranquil  bodies  of  water,  such 
as  lakes.  We  should  expect,  while  the  gradual  rise  and  overflow  of  the 
rivers  may  here  and  there  bury,  by  means  of  the  calcareous  deposits 
from  them,  the  fluviatile  or  lacustrine  molluscs  living  previously  in  fa- 
vourable situations,  that  there  would  be  much  showing  the  drift  of  ani- 
mal and  vegetable  substances  borne  onwards  to  localities  where  their 
further  progress  was  arrested,  and  where  they  became  entombed  beneath 
the  limestone  afterwards  formed  over  them. 

Although  limestone  may  thus  silently  and  unperceived  be  transported 
from  one  locality  to  another,  since  the  clearest  waters  may  contain  the 
bicarbonate  of  lime  in  abundance,  many  other  substances  are  also,  in  a 
similar  manner,  borne  onwards  in  solution ;  and  it  becomes  desirable,  in 
the  present  state  of  geological  science,  that  the  mass  of  this  matter,  and 
the  proportions  of  the  substances  commonly  composing  it,  should  be 
examined.  Something  is  done  by  every  analysis  made  of  spring  and 
river  waters ;  and  the  desire  to  obtain  good  waters  for  domestic  pur- 
poses, has  lately  led  observers  to  connect  the  rocks  from  which  springs 
issue  and  afford  the  supply  to  rivers  with  the  quality  of  waters ;  but  it 
would  be  well  more  systematically  to  study  the  soluble  matter  conveyed 
away  in  this  manner  by  moving  water.  Much  may  be  accomplished  by 
taking  up  the  water  in  clean  bottles,  well  corking,  sealing,  and  securing 
them  ;  noting  the  state  of  the  springs,  streams,  and  rivers  at  the  time  as 
regards  the  quantity  of  the  water  in  them,  and  by  obtaining  a  section  of 
the  rivers  at  some  convenient  situation,  and  a  proper  insight  into  their 
velocities  at  the  time  of  taking  the  water,  so  that  a  fair  estimate  may 
be  obtained  of  the  amount  of  soluble  matter  transported.  It  should  be 
recollected  that  when  swollen  by  rains,  though  substances  in  solution 
amid  the  rocks  may  be  then  forced  more  abundantly  out  of  some  than 
at  other  times,  the  amount  of  soluble  matter  is  not  increased  in  propor- 


KEMOVAL    OF    PARTS    OF    ROCKS    BY    WATER.  45 

tion  to  the  water,  since  much  rain  or  melted  snow  then  runs  off  the 
ground  without  penetrating  amid  the  rocks.  Common  salt  (chloride  of 
sodium)  will  be  found  more  frequent  than  may  be  usually  supposed  in 
spring  and  river  waters.  When  we  consider  the  number  of  rocks  which, 
from  their  organic  contents,  we  have  reason  to  suppose  were  formed 
beneath  the  sea,  and  which  have  been  deposits  of  mud,  silt,  sand,  or 
gravel,  now  elevated  into  the  atmosphere,  so  that  rain  waters  percolate 
through  them,  we  shall  not  be  surprised  at  the  presence  of  chloride  of 
sodium,  since  it  is  to  be  expected  that  this  and  other  salts  in  solution 
in  sea  waters  would,  formerly  as  now,  be  disseminated  amid  mechanical 
deposits  effected  in  the  sea.* 

*  According  to  the  researches  of  Dr.  Marcet  (Phil.  Trans.,  1819),  500  grains  of  sea 
water,  taken  from  the  middle  of  the  North  Atlantic,  contained — 
Chloride  of  sodium,    .         .         .         .13-4 
Sulphate  of  soda,        .         .         .         .2-33 
Muriate  of  lime,         ....       0-995 
Muriate  of  magnesia,         .        .         .       4-955 

21-680 

The  same  author  obtained  the  following  results  from  experiments  on  the  specific 
gravity  of  waters : — 

Sp.  Gr. 

Arctic  Ocean,        ....         1-02664 
Northern  Hemisphere,  .         .         .         1-02829 

Equator, 1-02777 

Southern  Hemisphere,   .        .         .        1-02882 

Yellow  Sea, 1-02291 

Mediterranean,      ....        1-0293 
Sea  of  Marmora,  ....        1-01915 
Black  Sea,     .         .         .  1-01418 

White  Sea, 1-01901 

Baltic, 1-01523 

Ice-Sea  Water,       ....        1-00057 
Lake  Ourmia         ....         1-16507 
Dr.  Marcet  concluded  from  his  researches — 

1.  That  the  Southern  Ocean  contains  more  salt  than  the  Northern  Ocean,  in  the  ratio 
of  1-02919  to  1-02757. 

2.  That  the  mean  specific  gravity  of  sea  water  near  the  equator  is  1-02777,  interme- 
diate between  that  of  the  Northern  and  Southern  Hemispheres. 

3.  That  there  is  no  notable  difference  of  sea  water  under  different  meridians. 

4.  That  there  is  no  satisfactory  evidence  that  the  sea,  at  great  depths,  is  more  salt 
than  at  the  surface. 

5.  That  the  sea,  in  general,  contains  more  salt  where  it  is  deepest  and  most  remote 
from  land ;  and  that  its  saltness  is  always  diminished  in  the  vicinity  of  large  masses  of 
ice. 

6.  That  small  inland  seas,  though  communicating  with  the  ocean,  are  much  less  salt 
than  the  ocean. 

7.  That  the  Mediterranean  contains  rather  larger  proportions  of  the  salt  than  the 
ocean. 

M.  Lenz,  who  accompanied  Kotzebue's  expedition,  inferred  that — 

1.  That  the  Atlantic  Ocean  is  salter  than  the  South  Sea ;  and  that  the  Indian  Ocean, 


46       REMOVAL  OF  PARTS  OF  ROCKS  BY  WATER. 

Silica  is  well  known  as  in  solution  in  some  waters ;  chiefly,  however, 
found  in  appreciable  quantities  in  those  which  are  thermal.  The  gey- 
sers of  Iceland  have  been  long  celebrated  for  their  abundant  siliceous 
deposits.*  Silica  has  borne  such  a  part  in  the  consolidation  of  rocks, 

being  the  transition  from  one  to  the  other,  is  salter  towards  the  Atlantic,  on  the  west, 
than  towards  the  South  Sea,  on  the  east. 

2.  In  each  of  these  three  great  oceans  there  exists  a  maximum  of  saltness  towards 
the  north,  and  another  towards  the  south ;  the  first  being  further  from  the  equator 
than  the  second.     The  minimum  between  these  two  points  is  a  few  degrees  south  of 
the  equator  in  the  Atlantic,  and  probably  also  in  the  Pacific,  though  M.  Lenz's  obser- 
vations did  not  extend  sufficiently  low  in  the  Pacific. 

3.  In  the  Atlantic,  the  western  portion  is  more  salt  than  the  eastern.     In  the  Pacific, 
the  saltness  does  not  appear  to  alter  with  the  longitude. 

4.  In  proceeding  north  from  the  northern  maximum,  the  specific  gravity  of  the  water 
diminishes  constantly  as  the  latitude  increases. 

5.  From  the  equator  45°  N.,  the  sea,  to  the  depth  of  1000  fathoms,  possesses  the 
same  degree  of  saltness. — Edinburgh  Journal  of  Science,  1832. 

As  we  have  elsewhere  observed  (Geological  Manual,  3d  edition,  p.  5),  the  saltness  of 
the  sea,  particularly  that  of  its  surface,  would  much  depend  on  the  proximity  of  nearly 
permanent  ice,  and  of  large  or  numerous  rivers.  Thus  the  Baltic,  White,  Black,  and 
Yellow  Seas  are  less  salt  than  the  main  ocean,  because  they  are  supplied  with  compa- 
ratively large  quantities  of  fresh  water.  From  the  small  proportion  of  salt  contained 
in  the  Black  Sea  and  Sea  of  Azof,  the  bays  of  the  former  frequently  contain  ice,  and 
the  latter  is  stated  to  be  frozen  over  during  four  months  of  the  year.  The  superior 
saltness  of  the  Mediterranean,  though  an  inland  sea,  is  considered  to  arise  from  the 
evaporation  of  its  surface  being  greater  than  the  fresh  water  with  which  it  is  supplied, 
or,  unless  it  should  be  still  becoming  more  salt,  to  the  differences  in  this  respect  which 
once  existed,  and  which  the  present  supply  of  fresh  water  is  unable  to  change.  Two 
great  currents,  one  from  the  Black  Sea,  the  other  from  the  Atlantic,  flow  into  the 
Mediterranean  in  consequence  of  this  evaporation,  one  fresher,  the  other  salter,  than 
the  body  of  its  waters. 

*  Sir  George  Mackensie  (Travels  in  Iceland]  mentions  that  the  deposits  from  the 
Geysers  extend  to  about  half  a  mile  in  various  directions,  with  a  thickness  of  more  than 
twelve  feet.  The  leaves  of  birch  and  willow  are  fossilized,  every  fibre  being  discernible. 
Grasses,  rushes,  and  peat,  are  in  every  stage  of  petrifaction.  Dr.  Black  found  the 
waters  from  the  Geysers  and  the  hot  springs  of  Reikum  (Iceland)  to  contain  in  a 
gallon — 

Geyser.  Reikum. 

Soda,  .  .  5-56  .  .  3-00 

Alumina,        .  .  2-80  .  .  0-29 

Silica,  .  .  31-50  .  .  21-83 

Chloride  of  sodium,    .  14-42  .  .  16-96 

Sulphate  of  soda,       .  8-57  .  .  7-53 

The  siliceous  deposits  from  hot  springs  (temperature  73°  to  207°  Fah1.)  in  the 
volcanic  districts  of  Fumas,  St.  Michaels,  Azores,  are  important.  Dr.  Webster  (Edin- 
burgh Phil.  Journal,  vol.  vi.)  gives  an  interesting  account  of  them.  The  siliceous 
deposits  are  noticed  as  most  abundant  in  layers  from  a  quarter  to  half  an  inch  in 
thickness,  accumulated  to  the  depth  of  a  foot  and  upwards.  Compact  masses  of 
siliceous  deposits  are  mentioned  as  having  been  broken  up  and  re-cemented  by  silica, 
and  the  compound  is  represented  as  beautiful.  The  height  of  some  of  this  breccia  is 
estimated  at  thirty  feet,  and  the  general  accumulation,  including  a  clay,  also  deposited 
from  the  waters  of  the  hot  springs,  as  considerable,  forming  low  hills. 

Dr.  Turner  (Elements  of  Chemistry)  found  that  the  hots  springs  of  Pinnarkoon  and 


REMOVAL  OF  PARTS  OP  ROCKS  BY  WATER.       47 

that  wherever  opportunities  occur  of  observing  the  effects  arising  from 
the  action  of  the  silica-bearing  waters,  they  should  receive  careful  atten- 
tion. The  manner  in  which  silica  may  be  taken  up  in  its  nascent  state, 
and  in  which  it  is  discovered  in  heated  waters,  are  circumstances  of 
much  importance  when  we  have  to  consider  its  mode  of  occurrence  in 
veins,  or  its  agency  in  agglutinating  the  particles  of  mud,  silt,  and  sands 
in  beds  of  rock.  It  is  now  known  not  only  that  certain  plants  require  this 
substance,  but  that  it  is  essential  to  some  animals  ;  so  that  the  study  of 
the  mode  in  which  silica  may  be  taken  up  in  solution,  distributed,  and 
used,  not  only  by  plants  and  animals,  but  also  for  the  consolidation  and 
filling  up  of  the  fractures  of  rocks,  is  one  of  much  interest. 

Springs  are  presented  to  our  attention  chiefly  under  two  forms.  First, 
from  the  combination  of  porous  and  less  permeable  rocks  in  such  a 
manner  that  the  water  passing  readily  through  the  former  and  with  dif- 
ficulty through  the  latter,  any  sides  of  hills  or  other  exposures,  where  its 
outpouring  is  more  easily  effected  than  in  other  directions,  lines  of  springs 
may  form ;  and,  secondly,  from  out  of  those  breaks  and  dislocations  of 
rocks  which  have  been  termed  faults,  and  which  become  channels  into 
which  waters  are  either  drained  laterally,  or  forced  up  from  beneath. 
Let  the  following  section  (fig.  10)  represent  one  of  a  country  composed 

Fig.  10. 


of  different  rock  deposits,  somewhat  similar  to  those  in  our  oolitic  dis- 
tricts, for  example,  a  a  being  portions  of  a  porous  and  calcareous  rock, 
such  as  some  of  those  oolites  are,  based  upon  a  clay,  bbb,  itself  reposing 
upon  a  sand,  c  c  <?,  chiefly  composed  of  siliceous  grains,, and  this  again 
resting  upon  a  clay,  d. 

We  should  here  have  the  conditions  for  a  marked  example  of  the 
springs  of  the  first  class.  The  rain  falling  upon  a  a  would  percolate 
through  it,  taking  up  calcareous  matter  by  aid  of  carbonic  acid  in  the 
rain  water,  or  obtained  in  its  passage  through  the  vegetable  covering 
and  soil,  and  not  being  able  to  permeate  readily  through  the  subjacent 

Loorgootha  (India),  not  situate  in  a  volcanic  country,  contained  twenty-four  grains  of 

solid  matter  in  a  gallon,  composed  of— 

Silica,         .            .            .            .            .            .  21-5 

Chloride  of  sodium,            ....  19-0 

Sulphate  of  soda,    .            .            .            .            .  19-0 

Carbonate  of  soda,             ....  19-0 

Pure  soda,               .....  5-0 

Moisture,    .            .            .            .            .            .  16-5 

100-0 


48       REMOVAL  OF  PARTS  OF  ROCKS  BY  WATER. 

clay,  b  b  6,  it  would  be  thrown  out  as  spring  water  at  the  junction  of  the 
two  rocks.  This  water  would  probably  contain  much  bicarbonate  of 
lime.  The  subjacent  clay  might  furnish  some  water  in  the  valley  v,  a 
slight  portion  of  the  rains  finding  its  way  amid  the  particles  of  clay, 
already  moist,  so  that  a  minor  surplus  had  to  ooze  out  under  favourable 
conditions.  We  will  suppose  that,  as  often  happens,  the  spring  water 
thus  afforded  would  contain  iron  (from  the  decomposition  of  iron  pyrites), 
and  sulphate  of  lime  (iron  pyrites  and  selenites  being  often  common  in 
such  clays).  Beneath,  in  the  two  hills  to  the  left  of  the  section,  the 
rain  falling  would  not  readily  find  its  way  from  above  to  c  c,  though 
laterally  this  bed  may  be  exposed  to  it,  as  a  part  is  on  the  right  of  our 
figure.  This  bed  has  been  considered  as  principally  composed  of  sili- 
ceous grains,  and  to  be  based  on  a  comparatively  impervious  bed,  d, 
which  may  be  a  clay.  Springs  would  find  their  way  out  of  this  bed  in 
the  valley  v,  and  we  should  expect  that,  though  they  may  contain  cer- 
tain matters  in  solution,  these  would  not  be  the  same,  at  least  not  in 
such  abundance,  as  from  the  beds  a  and  b. 

A  stream,  therefore,  flowing  down  the  valley  v,  would  collect  waters 
differently  charged  with  the  substances  which  rains  on  their  passage 
through  the  rocks  had  brought  out  in  solution ;  and  though  the  waters 
of  such  a  stream  would  present  us  with  a  kind  of  mean  of  all  the  sub- 
stances abstracted  in  solution  from  the  various  rocks,  they  would  not 
show  those  obtained  from  any  kind  of  rock  taken  by  itself,  and  these, 
consequently,  would  have  to  be  studied  where  the  springs  flowed  from 
each  bed.  The  streams,  moreover,  contain  the  top  waters  which,  during 
rains,  flow  over  the  surface,  carrying  off,  independently  of  the  matters 
mechanically  transported,  those  which  can  be  taken  away  in  solution, 
and  which  had  not  formed  component  parts  of  any  of  the  solid  rocks 
passed  near  or  over  in  their  course,  such  matters  being  commonly  de- 
rived immediately  from  animal  and  vegetable  sources. 

The  observer  would  readily  expect  this  simple  mode  of  occurrence  of 
dissimilar  rocks,  furnishing  water  holding  different  substances  in  solution, 
to  be  variously  modified,  so  that  while  studying  the  kind  of  matter  thus 
abstracted  from  rocks,  he  should  so  carefully  direct  his  researches  as  to 
connect  springs  of  this  order  with  the  kind  of  rocks  traversed  by  the 
rain  waters. 

The  joints  and  cleavage  among  certain  rocks  greatly  complicate  the 
subject  in  some  districts,  and  in  others  contorted  and  crumpled  strata 
so  occur,  that  long  troughs  and  irregularly  formed  basins  of  water  are 
held  up  amid  the  beds  and  rocks  pervious  to  water  in  some  localities, 
while  dome-shaped  masses  tend  to  throw  these  reservoirs  off  in  others. 
In  the  cases  of  the  basins  and  troughs,  the  water  remaining  during  the 
drier  times  may  perfect  many  solutions,  which,  when  the  rainy  seasons 
come  to  act,  are  borne  away  in  springs,  at  that  season  only  of  im- 
portance. 


REMOVAL    OF    PARTS     OF    ROCKS     BY    WATER.  49 

Springs  of  the  second  class  of  springs  are  commonly  more  constant 
as  to  the  quantity  and  quality  of  the  waters  they  deliver,  and  in  this 
manner  when  they  traverse  many  dissimilar  beds,  furnishing  the  solu- 
tions of  different  substances,  they  are  like  the  streams  above  noticed, 
as  regards  such  substances.  We  do  not,  therefore,  learn  from  them 
the  kind  of  loss  any  particular  rock  may  sustain  from  this  cause,  though 
they  may  be  useful  in  showing  the  solutions  delivered  from  the  fissures. 
Let  fin  the  accompanying  section  (fig.  11)  be  a  dislocation  traversing 


a     / 

various  dissimilar  beds,  so  that  the  bed  a  is  thrown  down,  as  it  is 
termed,  and  that  we  find  other  and  upper  beds,  g  h  and  z,  occu- 
pying the  same  general  levels,  as  a  b  c  d  and  e,  on  the  other  side  of  the 
fault.  In  such  a  case  the  various  waters  percolating  through  the  latter 
would  find  their  way  into  the  dislocation  with  those  of  g  on  the  opposite 
side,  and  the  solutions  derived  from  all  these  beds  would  be  mingled  in 
the  waters  of  the  fault,  flowing  out  at/  in  greater  or  less  abundance, 
according  to  circumstances.  We  have  here  merely  regarded  the  solu- 
tions derivable  from  the  waters  percolating  through  the  upper  beds ; 
but  as  in  the  greater  proportion  of  faults  we  possess  no  means  of  judg- 
ing of  the  depths  to  which  the  dislocation  may  descend,  we  cannot  form 
a  correct  opinion  of  the  kind  of  rocks  which  may  be  traversed  by  them. 

Thermal  springs,  not  in  volcanic  countries,  have  been  traced  either 
immediately  to  such  dislocations,  or  the  evidence  has  been  such  as  to 
lead  us  to  suppose  that  they  may  be  merely  covered  over  by  beds, 
through  which  a  sufficient  passage  has  been  found  for  the  discharge  of 
the  waters  rising  among  dislocated  rocks  beneath.  The  case  of  the 
Bath  springs  is  not  improbably  one  of  the  latter  kind,  the  heated 
waters  rising  through  some  of  those  dislocations  or  faults  which  traverse 
the  older  rocks  of  the  district  (coal  measures,  carboniferous  limestone, 
and  old  red  sandstone),  covered  over  unconformably  by  the  new  red 
sandstone  series  and  lias  (as  these  beds  are  known  to  do  many  disloca- 
tions of  such  older  rocks  in  that  country),  the  waters  thus  finding  their 
way  through  cracks  or  passages  in  the  superincumbent  beds. 

Connecting  the  heat  of  thermal  fault  waters  with  the  increase  of 
temperature  of  the  crust  of  the  globe  inwards,  as  inferred  from  the  in- 
crease of  heat  as  we  bore  artesian  wells,  or  descend  in  mining  operations, 
the  temperature  of  such  waters  would  always  be  considerable,  were  it 
not  that  such  temperature  may  be  much  modified  by  the  conditions 
under  which  the  waters  are  borne  upwards  and  discharged.  Let  //,  in 
fig.  12,  represent  a  fault  traversing  various  rocks  to  a  depth  at  which 

4 


50 


REMOVAL  OF  PARTS  OF  ROCKS  BY  WATER. 


the  water  in  it  obtains  a  temperature  of  212°  Fahrenheit.  These  waters 
could  only  be  discharged  at  that  temperature,  if  the  rate  of  out- 
Fig.  12.  flow  were  so  considerable,  and  the 
volume  of  water  so  large,  as  to  be  un- 
influenced by  the  cooling  conditions 
which  would  exist  in  the  rocks  through 
which  they  had  to  pass.  Towards  the 
surface,  these  rocks  would  take  the 
temperature  of  the  part  of  the  world 
in  which  they  may  be  situate,  variable 
near  such  surface,  but  at  a  certain 
depth,  according  to  latitude  and  local 
conditions  influencing  surface  tempera- 
ture, assuming  a  constant  temperature 
unaltered  by  the  climatal  changes 
or  modifications  above.  Between  this 
fixed  situation,  which  in  fig.  12  we  will 
for  illustration  assume  to  be  at  a,  and 
that  beneath,  where  a  very  high  tem- 
perature may  exist,  such  as  212°  Fah- 
renheit, the  boiling  point  of  water 
under  a  pressure  of  atmosphere  equal 
to  about  thirty  inches  of  mercury  on 
the  surface  of  the  earth,  the  water 
in  the  cleft  or  fault,  would  be  at  intermediate  temperatures.  Some 
waters,  supposing  a  ready  discharge  of  them  to  exist  upwards,  might 
have  a  tendency  to  percolate  through  the  adjacent  rocks,  and  enter  the 
main  fissure  at  depths  not  far  beneath  that  of  the  lowest  constant  tem- 
perature, thus  assisting  to  cool  the  upflowing  waters,  independently  of 
the  decrease  of  temperature  effected  by  that  of  the  rocks  themselves. 
No  doubt,  under  the  conditions  supposed,  the  sides  of  the  fissure  would 
be  heated  at  given  depths  beyond  that  temperature  which,  if  the  heated 
waters  did  not  rise  through  them,  they  would  possess,  but  the  discharge 
of  waters,  as  a  whole  constant,  and  other  conditions  the  same,  there 
would  be  a  final  adjustment  of  the  order  supposed.  This  would  be  a 
state  of  things  conducive  to  the  entrance  of  many  substances  in  solu- 
tion into  the  main  fissure,  which  might  not  be  introduced  into  spring 
waters,  either  at  all  or  so  readily  and  abundantly  in  the  first  class  of 
springs.  The  greater  heat  as  the  rocks  increase  in  depth,  and  the  per- 
meation of  waters  through  them,  at  high  temperatures,  we  should  ex- 
pect would  be  favourable  to  the  removal  of  silica,  often  perhaps,  only 
to  short  distances,  one  kind  of  rock  being  modified  by  its  gain  in  this 
manner,  and  another  by  its  loss.  Any  thrown  out  in  solution  would  be 
so  much  removed  from  them,  to  be  employed  elsewhere  in  the  modifica- 


REMOVAL  OF  PARTS  OF  ROCKS  BY  WATER.       51 

tions  now  effecting  on  the  surface,  always  assuming,  for  illustration,  that 
the  rocks  traversed  by  the  fissures  furnished  the  matters  held  in  solu- 
tion by  the  waters  flowing  upwards  through  them.  A  supposition  which 
will  require  to  be  modified  if  we  consider  that  some  substances  or  por- 
tions of  them  may  be  borne  up  into  the  cracks  which  had  not  previ- 
ously formed  parts  of  solid  rocks.  Under  any  view,  the  solutions  con- 
tained in  these  fault  waters,  are  conveyed  away  from  the  mouths  of  the 
fissures,  and  so  much  of  them  as  have  been  added  to  waters  percolating 
downwards  from  the  atmosphere,  or  in  any  manner  through  or  from  the 
adjacent  rocks,  has  caused  a  loss  to  such  rocks,*  and  afforded  matter, 
capable  of  ready  transport,  to  be  employed,  as  circumstances  may  per- 
mit, elsewhere  in  the  formation  of  solid  matter,  or  as  an  addition  to 
solutions  in  the  waters  of  lakes  and  seas. 

Deep  mines  afford  opportunities  for  observing  the  rate  at  which  rain 
waters  may  percolate  through  the  body  or  fissures  of  rocks  downwards, 
and  analyses  of  these  waters  so  obtained,  give  the  substances  they 
have,  during  the  time  of  their  passage,  taken  up  in  solution.  In 
mineral  veins,  the  waters  which  would  remain  in  them,  or  flow  out  as 
surplus,  being  in  some  mines  pumped  out  to  depths  of  .even  1800 
or  2000  feet,  we  no  doubt  have  surface  waters  descending  further 
than  they  would  otherwise  do  in  the  same  time,  the  check  to  their 
progress,  interposed  by  the  water  disseminated  amid  the  adjoining 
rocks,  or  in  the  fissure,  being  thus  removed,  but  at  the  same  time 
the  evidence  as  to  the  power  of  the  surface  waters  to  descend  in  the 
time  that  may  be  observed,  and  as  to  the  kind  of  solutions  effected 
by  them  in  that  time,  is  valuable. 

Great  care  is  required  to  give  due  importance  to  local  conditions 
in  such  investigations,  such  as  the  comparative  readiness  with  which 
the  waters  may  be  conducted  downwards  by  means  of  an  unworked 
continuation  of  the  mineral  veins — having  easy  water  communications 
with  the  workings  in  the  mines,  the  absence  or  relative  abundance  of 
great  joints  or  other  fissures  in  the  adjoining  rocks,  the  chance  of  any 
rivulet  or  stream  passing  over,  when  swollen  by  rains,  fissures  or  cracks 
communicating  with  the  main  vein,  and  the  like. 

In  some  coal  districts,  the  beds  of  under-clay  (as  those  are  often 
termed  which  are  found  supporting  or  intermingled  with  the  coal  beds) 
are  usually  so  impervious  to  water,  that  where  faults  or  fractures  of  beds 
are  rare,  the  collieries  are  little  troubled  with  water.  This  impervious 
character,  employing  the  term  in  a  general  manner,  is  well  marked  in 
coal  measure  districts  where,  as  in  parts  of  South  Wales  and  Monmouth- 

*  Dr.  Daubeny  points  to  the  very  common  presence  of  nitrogen  in  thermal  waters  as 
a  proof  that  the  water  in  them  has  been  originally  derived  from  the  surface  of  the 
earth,  that  it  there  contained  atmospheric  air,  and  that,  descending,  this  air  was  de- 
prived of  its  oxygen  by  some  process  of  combustion. 


52  KEMOVAL    OF    PARTS    OF    ROCKS    BY    WATER. 

shire,  the  beds  having  a  slight  inclination,  and  being  cut  through  by 
mountain  valleys,  springs  of  the  class  first  noticed  are  thrown  out  in 
lines,  marking  those  of  the  coal  beds,  the  waters  percolating  through 
which  are  stopped  downwards  by  the  under-clays.  A  system  of  de- 
posits in  which  'these  beds  and  others  of  tough  shale  occur,  would  pre- 
sent difficulties  to  the  ready  percolation  of  the  water  downwards.  At 
the  same  time,  slight  observation  will  soon  show,  that  though  water  may 
not  find  its  way  in  a  sufficiently  rapid  manner  in  some  collieries  to  be 
important,  it  is  still  most  frequently  there  disseminated  among  the  par- 
ticles and  joints  of  the  rocks.  Indeed,  the  manner  in  which  water  is 
disseminated  among  rocks  is  deserving  of  all  attention,  particularly 
when  we  regard  it  as  a  means  by  which  change  and  modification  of 
chemical  composition  may  be  effected.* 

The  springs  of  the  first  class  noticed  as  outflowing  on  the  sides  of 
hills  and  mountains,  and  on  sea  cliffs,  are  frequently  productive  of  land- 
slips, as  they  are  often  termed,  the  percolation  of  water  in  particular 
planes  or  directions  so  softening,  or  chemically  removing  the  rocks, 
that  a  superincumbent  weight  not  being  held  laterally  by  sufficient  co- 
hesion of  tjie  mass,  is  launched  into  the  valleys  or  seawards  as  the  case 
may  be,  thus  producing  a  degradation  of  the  land,  throwing  it  into  con- 
ditions fitted  for  more  ready  removal  by  rivers  and  the  sea.  Small 
landslips  are  very  common,  and  are  well  seen  in  our  oolitic  districts, 
where  the  intermingled  clays  slipping  into  the  valleys  bring  down  the 
more  consolidated  superincumbent  beds  with  them.  In  the  coal  district 
of  South  Wales  good  examples  of  a  larger  kind  are  to  be  found,  and  in 
many  mountainous  regions  they  are  sufficiently  common. 

The  slide  or  fall  of  the  Rossberg  or  Ruffiberg  on  the  2d  September, 
1806,  afforded  a  memorable  instance  of  the  destruction  produced  by  the 
percolation  of  water  through  bedded  rocks  in  such  a  manner  that,  the 
needful  cohesion  of  parts  being  destroyed,  a  great  mass  slid  over  an 
inclined  plane  of  subjacent  rocks.  The  following  section  (fig.  13)  will 

Fig.  13. 


serve  to  illustrate  this  fall,  and  some  others  of  the  like  kind.     If  in  the 
mountain,  a,  water  percolate  through  the  porous  strata  b  to  the  clay 

*  The  simple  experiment  of  accurately  weighing  a  piece  of  rock  immediately  after  it 
is  struck  off  in  a  metal  mine  or  colliery,  drying  it  thoroughly  in  a  sand-bath,  and  then 
reweighing  it,  will  often  show  more  moisture  to  have  been  removed  than  might  have 
been  expected,  the  result  being  necessarily  very  variable  from  differences  in  the  poro- 
sity of  the  substance. 


REMOVAL  OF  PARTS  OF  ROCKS  BY  WATER.       53 

bed  c  c,  the  surface  of  the  latter  would  become  slippery,  and  the  cohe- 
sion being  insufficient  to  counteract  the  action  of  gravity,  and  no  proper 
support  be  found  in  the  valley,  the  mass  would  be  launched  in  the  valley 
d.  In  the  case  of  the  Rossberg  (a  mountain  5196  feet  above  the  sea)  the 
upper  beds  were  composed  of  conglomerates  resting  upon  matter,  which 
being  partially  removed  by  the  percolation  of  water,  and  the  beds  at  a 
high  angle  (about  45°)  a  launch  of  the  upper  beds  took  place,  and  a 
beautiful  valley  was  covered  with  rocks  and  mud.* 

The  under  cliffs  between  Lyme  Regis  and  Axmouth,  as  well  as  those 
on  the  back  of  the  Isle  of  Wight,  illustrate  the  destruction  of  cliffs  by 
means  of  springs.  The  following  section  (fig.  14)  will  show  the  condi- 
tions under  which  the  under-cliffs  are  produced  at  Pinhay,  near  Lyme 

Fig.  14. 


Regis,  a  is  gravel ;  5,  chalk ;  c,  upper  green  sand,  porous  substances 
through  which  the  rain  waters  percolate  to  the  clay  bed  d,  composed  of 
the  lower  part  of  the  green  sand  beds  c,  and  the  upper  part  of  the  lias 
bed  e,  the  upper  green  sands  having  overlapped  the  intermediate  rocks 
observable  in  the  southeast  of  England,  and  here  resting  upon  the  lias. 
The  water  being  thus  arrested  in  its  progress  downwards,  escapes  where 
it  finds  the  least  resistance ;  in  this  case  towards  the  face  of  a  cliff,  ori- 
ginally formed  by  the  action  of  the  sea  on  the  coast.  The  clay  is  gra- 
dually removed ;  the  superincumbent  green  sand,  chalk,  and  gravel  lose 
their  support,  give  way,  and  fall  towards  the  sea.'  The  lias  e  is  not 
removed  by  the  action  of  the  coast-breakers  so  fast  at  the  cliffy,  as  the 
rocks  above  are  by  the  effect  of  the  land  springs,  therefore  the  upper 
cliff  retreats,  leaving  a  mass  of  fragments  confusedly  intermingled  at  /, 
which  has  a  constant  tendency  to  move  seawards,  both  from  the  destruc- 
tion of  the  lias  cliff  </,  by  the  breakers,  and  from  the  water  percolating 
through  the  mass  and  loosening  its  base,  so  that  it  gradually  moves  to- 
wards the  shore.  The  chalk  and  green  sand  fragments  are  often  suffi- 
ciently large  and  hard  to  afford,  by  their  overfall,  protection  to  the  lias 
cliff,  and  thus  a  very  confused  but  instructive  coast  section  is  exposed 
to  the  observer. 

The  rain  waters  not  absorbed  by  the  rocks,  act  mechanically  on  the 

*  The  villages  of  Goldau  and  Busingen,  the  hamlet  of  Huelloch,  a  large  part  of  the 
village  of  Lowertz,  the  farms  of  Unter-  and  Ober-Rothen,  and  many  scattered  houses 
in  the  valley,  were  overwhelmed  by  the  ruin.  Goldau  was  crushed  by  masses  of  rocks, 
and  Lowertz  invaded  by  a  stream  of  mud.  The  lives  lost  were  estimated  at  from  800 
to  900. 


54  REMOVAL    OF    PARTS    OF     ROCKS    BY    WATER. 

surface  of  the  land,  removing  to  lower  levels  such  decomposed  portions 
of  the  rocks  as  their  volume  and  velocity  can  transport.  The  mixed 
effects  of  decomposition  from  atmospheric  causes,  and  of  soaking  of  the 
surface  on  hillsides,  are  often  well  shown  in  slate  countries,  a  certain 
depth  beneath  the  soil  exhibiting  the  turning  over  of  the  edges  of  the 
slates  towards  the  valleys ; — as  it  were  the  tendency  of  the  moistened 
matter  of  the  surface  to  slide  by  its  gravity  to  the  lower  ground. 

The  accompanying  figure  will  illustrate  this  fact,  one  of  much  impor- 
tance to  the  observer,  for  without  attention  to  it  he  might  commit  grave 
errors  as  to  the  true  dip  of  strata,  when  only  a  slight  depth  of  section 

Fig.  15. 


may  be  exposed  on  a  hillside.  In  the  above  figure  the  real  dip  of  beds 
is  represented  as  the  very  reverse  of  that  which  might  be  inferred  from 
a  hasty  glance  at  the  surface.  Although  it  may  be  supposed  that  the 
difference  between  this  sliding  down  of  the  surface  towards  the  lower 
grounds  and  the  true  dip  was  always  so  apparent  as  not  to  be  mistaken, 
the  depth  to  which  this  action  has  occasionally  extended  is  sufficient  to 
justify  caution  in  many  districts. 

Upon  a  hillside  and  among  the  rills,  hollows,  and  little  plains  which 
may  sometimes  be  there  found,  an  observer  may  often  have  good  oppor- 
tunities of  studying  the  power  of  water  mechanically  to  transport  the 
decomposed  portions  of  rock  brought  within  its  influence.  He  will  soon 
perceive,  that  not  only  according  to  the  specific  gravity,  but  to  the  form 
also  of  these  portions,  is  their  removal  effected,  and  that  the  manner  of 
removal  is  of  two  kinds.  In  one  case  they  are  bodily  carried  in  mecha- 
nical suspension  in  the  water,  while  in  the  other  they  are  swept  onwards 
by  its  friction  on  the  bottom.  Small  hollows  will  occasionally  show  the 
mode  in  which  the  matter  so  mechanically  suspended  or  pushed  onwards 
is  brought  to  rest,  and  well  illustrates  the  manner  in  which  accumula- 
tions on  the  great  scale  may  be  and  are  effected. 

If  we  suppose  the  observer  placed  in  a  granitic  district  where  there 
is  much  decomposition  of  the  felspar,  such,  for  example,  as  much  of 
that  near  St.  Austle,  in  Cornwall,  he  will  soon  find  that  while  the  fine 
decomposed  remains  of  the  felspar  readily  mingle  with  the  waters  which 
a  heavy  fall  of  rain  may  produce,  the  particles  of  quartz  and  mica  are 
more  commonly  swept  along  the  bottom,  except  where,  from  the  slopes 
being  considerable,  the  water  may  have  sufficient  rapidity  to  gather 


TRANSPORT    OF    DETRITUS    BY    RIVERS.  55 

them  up  in  mechanical  suspension.  While  the  volume  of  the  particles 
of  quartz  may  be  larger,  they  are  often  more  round,  so  that  they  are 
commonly  more  readily  pushed  along  the  bottom  than  the  grains  of 
mica,  not  only  flatter,  but  possessing  greater  specific  gravity.*  The 
milky-looking  water  containing  the  decomposed  felspar  is  borne  on- 
wards, slight  deposits  taking  place  where  an  expansion  of  the  bed  of 
the  rill  or  rivulet  may  permit  comparatively  still  water,  until  sufficient 
quiet  is  found  for  the  general  deposit,  while  the  quartz  or  mica  are 
strewed  in  little  ridges,  or  thrust  into  holes,  remaining  there  if  the 
force  of  the  stream  will  permit. 

Much  information  may  be  derived  as  to  the  manner  in  which  detritus 
is  pushed  forwards  by  rivers  into  bodies  of  still,  or  comparatively  still, 
water,  by  observing  sand  brought  down  by  a  rivulet  into  a  small  pool 
of  stagnant  water,  where  the  sand  ceases  to  be  forced  forwards,  and 
consequently  accumulates.  It  will  be  seen  that  little  delta-form  heaps  of 
sand  accumulate  where  the  rivulet  enters  the  pool,  on  the  fan-shaped 
tops  of  which  the  channels,  over  which  the  moving  water  pushes  the 
grains  of  sand,  are  continually  shifting.  Let  a  in  the  following  sketch 
(fig.  16)  represent  a  pool  of  still  water,  into  which  a  rivulet  b  pushes 

r.16. 


forward  sand,  then  such  sand  will  be  found  to  accumulate  at  c,  falling 
down  into  the  pool  #,  in  such  a  manner  that  a  truncated  heap  of  sand 
is  produced,  which  increases  superficially,  as  shown  by  the  concentric 
lines  at  c.  If  now,  attention  be  directed  to  the  manner  in  which  the 
grains  of  sand  have  been  accumulated  vertically,  it  will  be  found  that 
they  have  been  arranged  as  in  the  annexed  section  (fig.  17),  in  which  a 

Fig.  17. 


represents  the  surface  of  the  pool,  d  its  bottom,  b  the  slope  of  the 
rivulet  pushing  forward  the  grains  of  sand,  and  c  successive  coats  of 
sand  formed  by  the  grains  falling  over  into  still  water,  such  grains 
supporting  themselves  in  the  same  manner  as  in  any  rubbish  heap,  from 
the  top  of  which  rubbish  is  continually  thrown  over.  By  diverting  from 
their  courses  the  small  streams  of  water  which  run  down  sandy  sea 
beaches  on  many  coasts,  very  valuable  information  may  be  obtained  as 
to  the  manner  in  which  grains  of  sand  are  forced  forward,  and  arranged 

*  The  specific  gravity  of  quartz  is  about  2-63,  while  that  of  common  mica  is  2-94. 


56         TRANSPORT  OF  DETRITUS  BY  RIVERS. 

by  the  pushing  action  of  running  water.  When  brought  into  the  deeper 
pools  among  the  sands,  the  deltas  produced  are  extremely  instructive, 
and  in  such  cases  the  angle  formed  by  the  layers  or  coatings  above  each 
other,  as  the  sands  accumulate,  is  commonly  found  to  be  about  28°  or  30°. 

Having  examined  the  mode  in  which  decomposed  portions  of  rocks, 
as  well  as  those  worn  off  by  the  friction  of  the  streams,  can  be  trans- 
ported by  moving  water  on  the  small  scale,  an  observer  will  more  readily 
appreciate  the  transport  and  deposit  of  detritus  on  the  great  scale  in 
the  course  of  rivers,  with  or  without  the  intervention  of  lakes,  as  the 
case  may  be,  and  its  removal  towards  lower  levels  and  the  sea.  The 
manner  in  which  it  is  either  taken  up  in  mechanical  suspension,  or 
merely  shoved  along  the  bottoms  of  rivers,  is  precisely  the  same  in 
principle  as  in  the  little  rivulets,  though  the  effects,  from  their  greater 
magnitude,  are  more  striking  in  the  one  case  than  in  the  other.  Larger 
masses  may  be  shoved  forwards,  because  the  volume  of  water  may  be 
larger,  sufficient  to  move  those  onwards,  the  resistance  of  which  the 
minor  streams  could  not  overpower,  yet  the  cause  of  their  removal  is  of 
the  same  kind.* 

The  observer  will  soon  perceive,  that  while  at  one  time  detritus  only 
of  a  given  magnitude,  form,  or  specific  gravity,  can  be  either  pushed 

*  The  following  list  of  the  specific  gravities  of  some  rocks  which  we  have  elsewhere 
given  (Researches  in  Theoretical  Geology]  may  be  useful  in  showing  their  power  of  removal, 

in  fragments  or  pebbles,  by  running  water,  all  other  conditions  as  to  velocity  and  volume 
of  the  water,  and  volume  and  form  of  the  fragments  or  pebbles,  being  the  same. 

Calcaire  grossier  (Paris)         -        -  2-62  Devonian  sandstone,  calcareous  (II- 

Chalk  (Sussex)        -        -        -        -  2-49        fracombe) 2-77 

Upper  green  sand  (Wilts)        -        -  2-57  Silurian  sandstone  (Snowdon)  -         •    2-76 

Lower  green  sand  (Wilts)        -        -  2-61  Argillaceous  slate  (Devon)       -         -2-77 

Portland  oolite  (Portland)       -        -  2-55  Carrara  marble       -                          -    2-70 

Forest  marble  (Pickwall)        -        -  2-72  Mica  slate  (Scotland)      -        -        -    2-69 

Bath  oolite  (Bath)  -  247  Gneiss  (Freyburg)  -                               2-72 

Stonesfield  slate  (near  Stow-on-the-  Domite  (Puys  de  Dome)  -        -        -    2-37 

Wold) 2-66  Trachyte  (Auvergne)       -        -        -    242 

Lias  Limestone  (Lyme  Regis)  -        -  2-64  Basalt  (Scotland)    -        ...    2-78 

Red  marl  of  the  new  red  sandstone  Basalt  (Auvergne)  -  2-88 

(Devon)        ...                 .  2-61  Basalt  (Giant's  Causeway)      -        -    2-91 

Muschelkalk,   fossiliferous    (Gottin-  Greenstones,  various  (different  coun- 

gen) 2-62  tries)  ....         2-69  to  2-95 

Coal  sandstone,  Pennant  (Bristol)   -  2-60  Sienite  (Dresden)    -        -        -        -    2-74 

Coal  shale  with  impressions  of  ferns  Porphyry  (Saxony)  -                       2-62 

(Newcastle)          -        ...  2-59  Serpentine  (Lizard,  Cornwall)          -    2-58 
Millstone  grit  (Bristol)    -        -        -  2-58  Diallage  rock  (Lizard,  Cornwall)      -    3-03 
Carboniferous  limestone  (Bristol)     -  2-75  Hypersthene  rock  (Cock's  Tor,  Dart- 
Carboniferous  limestone  (Belgium)  -  2-72        moor) 2-88 

Old  red  sandstone,  micaceous  (Here-  Sienitic  granite  (Vosges)          -        -    2-85 

fordshire) 2-69  Granite,  gray  (Brittany)          -        -    2-74 

Old  red  sandstone  (Worcestershire)  2-65  Granite  (Normandy)        -        -        -    2-66 

Silurian  sandstone  (Hartz)       -        -  2-64  Granite,  mica,  scarce  (Scotland)      -     2-62 

Devonian  sandstone  (Ilfracombe)     -  2-69  Granite  (Heytor,  Devon)          -        -    2-66 


* 

TRANSPORT  OF  DETRITUS  BY  RIVERS.         57 

onwards  by,  or  be  mechanically  suspended  in,  the  rivers,  at  another  the 
detritus,  previously  at  rest,  is  readily  borne  onwards,  and  effects  pro- 
duced which,  without  the  needful  evidence,  he  would  scarcely  have  con- 
sidered probable  from  examining  those  produced  during  the  ordinary 
condition  of  the  same  river.  From  the  details  given  of  the  effects  of 
great  floods,  as,  for  example,  that  of  the  Moray,  much  valuable  insight 
may  often  be  obtained  as  to  the  effects  which,  during  a  long  lapse  of 
time,  may  be  produced  along  the  line  of  a  river  course  by  repeated 
action  of  this  kind. 

The  minor  floods,  commonly  known  as  freshets,  more  or  less  common 
in  all  rivers,  are  geologically  important,  not  only  as  respects  the  greater 
movement  outwards  of  detrital  matter  at  such  times  by  the  mechanical 
action  of  the  water,  but  also  as  they  often  surprise  terrestrial  animals 
in  low  localities,  and  transport  them  with  plants  to  still  lower  situations, 
or  into  the  sea,  in  the  latter  case  covering  up  these  as  well  as  estuary 
and  marine  animals  in  a  common  deposit  of  mud  and  silt. 

In  some  countries  the  freshets,  or  rises  of  river,  are  periodical,  pro- 
duced from  periodical  causes  inland,  as,  for  example,  that  of  the  Nile, 
and  deposits  are  then  effected  which  do  not  receive  additions  until  the 
annual  time  of  rise  again  comes  round.  From  this  state  of  things  to 
frequent  alternations  of  floods  and  low  states  of  rivers,  there  is  every 
modification,  so  that  the  results  of  the  deposits  may  be  expected  to  be 
as  modified  as  the  causes  of  their  production.* 

When  it  is  intended  to  ascertain  the  volume  of  water  descending  a 
river  at  a  given  time,  and  the  amount  of  matter  which  may  be  then  held 
in  mechanical  suspension  by  it,  in  order,  by  a  fair  average,  to  estimate 
the  volume  of  water,  and  the  amount  of  matter  in  mechanical  suspen- 
sion, borne  seaward  or  into  lakes  during  a  year,  or  any  amount  of  time 
thought  desirable,  much  care  is  required  so  that  the  estimate  may 
approximate  toward  the  truth. 

The  section  of  a  river  presents  us  with  waters  moving  with  different 
velocities,  and  consequent  transporting  powers ;  and  where  the  greatest 
weight  of  water  occurs  with  equal  velocities,  the  greatest  pushing  or 

*  As  we  have  elsewhere  observed  (Geological  Manual,  3d  edition),  there  are  few 
rivers  more  instructive  than  the  Mississippi,  man  as  yet  not  having  effected  many 
important  changes  on  its  banks,  and  we  contemplate  great  natural  operations,  such  as 
cannot  be  so  well  observed  in  those  which  have  been  more  or  less  under  his  dominion 
for  a  series  of  ages.  Its  course  is  so  long,  and  through  such  various  climates,  that  the 
freshets  produced  in  one  tributary  are  over  before  they  commence  in  another ;  and 
hence  arise  those  frequent  deposits  of  detritus  at  the  mouths  of  the  tributaries.  These 
latter  have  their  waters  ponded  back,  and,  to  a  certain  distance,  stagnant,  by  the  rush 
of  the  floods  in  the  great  river  across  their  embouchures,  and  in  consequence  a  deposit 
is  effected,  which  remains  until  a  subsequent  flood  in  the  tributary  removes  it.  (Hall's 
Travels  in  North  America.)  Captain  Hall  states  that  when  the  Ohio  is  in  flood  it  stag- 
nates the  waters  of  the  Mississippi  for  many  leagues,  and  that  when  the  Mississippi  is 
in  flood,  it  dams  up  the  waters  of  the  Ohio  for  seventy  miles. 


58 


TRANSPORT    OF    DETRITUS    BY    RIVERS. 


forcing  onwards  of  the  bottom.     If  in  the  accompanying  section  (fig.  18), 
g  f  g  represent  that  of  a  river  course  ;  the  greatest  velocity  of  the  water 


d    c 


Fig.  18. 


y 

p   p    p     f     p    p    p 

would  be  at  a,  and  this  will  decrease  towards  the  sides  and  bottom, 
where  the  friction  would  be  greatest,  as  may  be  represented  by  the 
layers  of  water  65,  c  c,  dd. 

Let  the  fig.  19  represent  a  longitudinal  section  of  the  layers  of  water 
corresponding  with  those  in  the  cross  section  (fig.  18).     Assuming  that 


Fig.  19. 


the  motion  of  the  particles  of  water  in  the  layer  a  is  sufficient  to  keep 
some  of  the  matter  mechanically  suspended,  and  some  not  quite  so  sus- 
pended, the  latter  will  sink  by  the  action  of  gravity ;  not,  however,  at 
once  falling  to  the  bottom,  but  entering  the  second  supposed  layer  of 
water,  5,  where  the  velocity  being  less,  it  descends  in  less  time  through 
it,  and  so  on  through  the  other  layers  c  and  d,  describing  a  curve  i  n. 
As  regards  the  amount  of  mechanically  suspended  detritus  in  such  a 
section,  we  should  anticipate  that  it  would  be  very  unequally  dispersed. 
As  far  as  respected  the  movement  of  its  particles  the  water  in  the  layer 
a  would  be  capable  of  keeping  detritus  of  any  volume,  form,  and  density 
in  mechanical  suspension  which  the  river  could  so -carry,  while  the  lower 
layers  would  receive,  and,  during  its  descent,  carry  forward  all  the 
detritus  falling  down,  from  the  conditions  being  unfavourable  to  its 
further  suspension  in  the  upper  layers  of  water. 

The  section,  fig.  19,  is  assumed  to  be  one  taken  through  the  centre  of 
the  stream ;  if  to  this  we  add  other  longitudinal  sections  taken  through 
the  lines,  pppppp,  fig»  18,  we  should  have  two  series,  one  on  each  side 
of  the  central  section,  the  terms  of  which  could  rarely  agree,  either  in 
respect  to  the  velocities  of  the  water,  the  power  of  transport,  or  in  the 
amount  of  detritus  contained  in  them.  So  far,  therefore,  from  it  being 
easy  to  estimate  the  amount  of  detritus  borne  down  in  mechanical  sus- 
pension, or  forced  along  its  bottom  by  friction  by  a  river,  it  is  a  subject 
requiring  very  great  caution  and  skill,  even  to  obtain  an  approximate 
rough  estimate  of  the  fact. 

When  the  water  has  been  obtained  from  which  it  is  intended  to  sepa- 


TRANSPORT    OP    DETRITUS    BY    RIVERS. 


59 


rate  the  matter  borne  down  by  rivers,  and  by  a  sufficient  number  of 
trials  in  different  parts  of  the  river,  to  estimate  the  amount  of  such 
matter  passing  a  given  locality,  it  is  needful  not  to  evaporate  the  water, 
as  has  often  been  done,  for  by  this  proceeding  the  matter  in  solution  is 
obtained  as  well  as  that  in  mechanical  suspension.  A  measured  volume 
of  water  should  be  passed  through  a  filter,  and  the  weight  of  the  matter 
that  may  be  thus  collected  carefully  ascertained. 

Fully  to  appreciate  the  distance  to  which  the  various  kinds  of  detritus 
may  be  borne  by  moving  water  until  they  be  deposited,  attention  should 
be  directed  to  the  quantity  and  kind  which  can  merely  be  pushed  for- 
ward by  a  given  velocity  of  such  water,  acting  by  friction  on  the  bottom 
or  sides  against  which  it  may  pass,  and  to  the  quantity  and  kind  the 
same  velocity  may  keep  mechanically  suspended  at  the  same  time. 

As  rivers  are  enabled  to  transport  in  mechanical  suspension,  or  sweep 
forward  detritus  on  the  bottom,  according,  in  a  great  measure,  to  their 
velocities,  and  as  the  latter,  other  things  being  equal,  increase  with  the 
slope  of  the  river  channels,  duly  to  estimate  the  power  of  a  river  to 
carry  forwards  to  the  sea  or  lakes  the  detritus  thrown  into  the  higher 
grounds,  all  the  changes  of  slopes  should  be  properly  appreciated. 
Thus,  if  a  b  (fig.  20)  represent  the  slope  of  a  river  in  one  place,  and  b  c 

Fig.  20. 


the  slope  of  the  same  river  in  another,  and  the  amount  of  water  be 
neither  increased  nor  diminished  by  tributary  streams  or  diverging 
branches,  the  river  will  have  greater  velocity  at  a  b  than  at  b  <?,  and 
consequently  smaller  pebbles  and  finer  sand  can  remain  at  the  bottom 
at  b  c  than  at  a  b. 

The  checks  which  a  river  may  sustain  in  its  course,  such  as  lakes, 
patches  of  level  land,  and  the' like,  should  be  duly  noted.  Without  this 
precaution  it  might  be,  and  indeed  has  been,  inferred  that  all  the  pebbles 
found  far  down  a  river  course  had  been  there  swept  by  the  river  in  its 
present  state.  While  this  is  often  true,  care  should  be  taken  to  ascer- 
tain that  the  needful  conditions  present  themselves.  Frequently,  when 
a  river  takes  its  rise  among  high  mountains,  its  onward  course  is,  though 
often  rapid,  interrupted  by  tracts  of  level  country,  or  even  lakes,  where 
the  pebbles  and  heavier  detritus  are  arrested ;  and  yet  pebbles  derived 
from  the  rocks  of  the  high  mountains  may  be  abundantly  found  in  the 
river-bed  further  down  than  these  obstacles,  such  pebbles  having  been 
brought  to  the  channel  in  which  the  river  now  takes  its  course  by  pre- 


60 


TRANSPORT  OF  DETRITUS  BY  RIVERS. 


vious  geological  conditions  of  the  area.  Thus,  Alpine  pebbles  in  some 
of  the  river  courses  of  northern  Italy,  could  not  have  been  borne  from 
the  Alps  into  the  plains  of  Lombardy  by  existing  rivers,  since  the  Lago 
Maggiore,  the  Lago  di  Como,  and  others,  necessarily  stop  the  progress 
of  the  pebbles  borne  from  the  high  Alps  by  the  torrents  which  now  feed 
these  lakes. 

By  attending  to  the  kinds  of  rock  traversing  a  valley,  we  have  often 
good  opportunities  afforded  of  studying  the  manner  in  which  detritus, 
derived  from  them,  may  become  mingled  by  the  action  of  the  river 
waters.  Care  must,  however,  be  taken  to  avoid  considering  as  such 
those  pebbles  which  may  have  formed  by  the  action  of  breakers  while 
the  land  may  have  been  emerging  from  the  sea,  and  which  may  have 
been  at  that  time  gathered  into  the  lower  parts  of  the  valleys,  or  have 
subsequently  been  brought  into  them  from  the  sides  of  hills  or  mountains 
by  the  long-continued  action  of  rains  and  minor  streams  of  water.  Let 
the  annexed  plan  (fig.  21)  a  b  represent  the  course  of  a  river  through  a 


district  composed  of  marked  but  different  rocks,  c  <?,  d  d,  and  e  e,  into 
a  low  country,  where  its  movement  becomes  sluggish,  and  let  the  fall 
of  the  river-bed  be  such  as  to  give  sufficient ,  velocity  to  a  needful  body 
of  water  to  push  or  sweep  forward  pebbles  of  the  size  of  an  egg,  where 
the  full  force  of  the  water  can  be  directed  upon  them.  The  river  being 
capable  of  forcing  forward  on  the  bottom  pebbles  of  this  size,  those  of 
minor  size,  other  things  being  equal,  would  be  driven  onwards,  and 
there  would  finally  be  a  size,  weight,  and  form  of  detritus  held  up  in 
mechanical  suspension  by  the  movement  of  the  water. 

Under  such  conditions  there  would  necessarily  be  a  deposit  of  the 
detritus,  pushed  forward  by  the  water,  wherever  sufficient  obstacles 
produced  a  less  velocity  in  the  river ;  and,  as  the  river  varied  in  this 
power  according  to  the  quantity  of  water  in  it,  the  accumulations  thus 
formed  would  possess  an  irregular  character,  somewhat  as  in  the  annexed 
section,  one  through  several  minor  deposits,  depending  upon  small  shifts 
in  the  direction  and  force  of  the  propelling  current. 

As  the  river  in  the  plan  (fig.  21)  is  supposed  capable  of  shoving 
pebbles  onwards  to  the  commencement  of  the  low  ground//,  irregular 
accumulations  of  pebbles  would  be  expected  at  Z,  where  the  force  of  the 
river  can  no  longer  drive  them  forwards.  It  would  not,  however,  be 


TRANSPORT     OF    DETRITUS    BY    RIVERS.  61 

anticipated  that  the  finer  silt  or  mud  could  be  there  accumulated,  except 
in  very  minor  quantities  in  still  places ;  since  the  power  to  keep  such 

Fig.  22. 


detrital  matter  mechanically  suspended  would  be  gradually  lost  by  the 
river.  Indeed  the  time  required  for  its  settlement,  particularly  of  the 
finer  parts,  might  be  such  that  the  whole  body  of  water  could  continue 
to  move  through  the  lowlands  in  a  turbid  and  discoloured  condition, 
slowly  parting  with  the  detrital  matter  disseminated  through  it. 

It  would  be  expected  that,  under  the  conditions  noticed,  accumula- 
tions would  take  place  along  the  line  of  the  river  course ;  and  that, 
unless  these  deposits  were  cut  up  by  floods  and  so  carried  further  on- 
wards, the  river-bed  would  be  raised.  The  power  of  a  river  to  keep  its 
channel  clear,  and  even  to  work  it  deeper,  is  commonly  obvious  where 
the  river  runs  with  rapidity ;  •  but  it  is  not  always  so  obvious,  without 
careful  investigation,  that  its  bed  has  been  raised,  more  particularly  by 
the  pebbles  and  sands  shoved  forward  at  the  bottom. 

In  many  plains  modified  by  rivers  the  shoving  forward  of  detritus  is 
shown  by  the  mode  of  its  accumulation,  mingled  often,  however,  with 
other  accumulations  so  thin  and  wide  spread  as  obviously  to  have  been 
deposited  from  mechanical  suspension,  so  that  both  modes  have  contrib- 
uted to  the  formation  of  these  plains.  Although  we  might  feel  certain 
that  the  beds  of  rivers  must  shift  in  great  plains  as  these  beds  get  raised, 
the  waters  taking  the  course  of  the  lower  surface,  when  such  are  pre- 
sented, yet  it  is  interesting  to  observe  in  some  countries, — in  Italy  for 
example, — where  artificial  embankments  have  been  formed  to  keep  the 
rivers  flowing  through  fertile  plains  in  their  channels,  that  the  beds  of 
rivers  get  thus  above  the  plains ;  and  that  roads  rise  up  these  banks  on 
either  side.  In  the  little  plain  of  Nice,  the  river  ridges  from  this  course 
are  striking,  a  loose  conglomerate  behind  furnishing  an  abundance  of 
pebbles  to  the  river  bed.  The  following  section  (fig.  23)  will  serve  to 


illustrate  this  fact,  a  b  being  the  level  of  the  country,  in  cultivation  for 
many  centuries,  upon  which  the  artificial  banks  have  been  gradually 
raised  to  c  d,  to  protect  the  cultivated  lands  from  invasion  by  the  detri- 
tus forced  forward  by  the  river  e.  In  consequence,  the  detritus  which 
would  have  escaped  upon  the  plain  has  been  raised  from /to  e,  notwith- 
standing the  somewhat  general  plan  of  throwing  the  detritus  thus  accu- 
mulated over  the  sides  upon  the  protecting  banks  c  and  d,  thus  artifi- 


62  ACTION    OF    RIVERS    ON    THEIR    BEDS. 

cially  deepening  the  channel  when  the  waters  in  the  river  may  be  suffi- 
ciently low  for  the  purpose.  The  Po  presents  on  the  larger  scale  a  well- 
known  example  of  the  rise  of  its  bed,  so  that  it  is  higher  than  the  houses 
in  Ferrara,  and  the  like  may  always  be  expected  under  similar  conditions. 
A  river  may  so  raise  its  bed  as  for  some  time  not  to  find  a  new  main 
channel  amid  the  adjoining  plain,  its  turbid  waters  when  in  flood  escap- 
ing over  the  banks  without  actually  causing  a  breach,  as  is  shown  in  the 
annexed  section  (fig  24),  where  b  represents  a  river  which  has  so  raised 


Fig.  24. 
b 


its  bed  that  there  are  tracts  of  country  on  either  side  at  a  slightly  lower 
level.  In  floods  such  a  river,  spreading  over  the  adjacent  land,  would 
leave  all  the  detritus  mechanically  suspended  in  its  waters,  a  a,  upon 
the  ground  beneath  up  to  the  rising  grounds  d  d,  as  did  not  retire  with 
the  water  until  its  level  was  that  of  the  banks  of  the  river,  with  the  ad- 
dition of  such  sedimentary  matter  as  may  have  been  deposited  from  the 
top  waters,  before  they  so  retired  into  the  river  channel.  The  more 
common  action  of  a  flood  is  represented  in  the  section  beneath  [fig.  25), 


where  a  river  (b)  not  raising  its  bed  (the  flood  waters  merely  removing 
mud  from  the  bottom,  the  only  sediment  there  collected),  the  overflow 
of  turbid  water  (a  a)  returns  to  the  river  bed,  depositing  only  such  mat- 
ter in  mechanical  suspension  as  the  time  of  repose  may  have  permitted. 
In  these  ways  much  sedimentary  matter  is  distributed  over  plains  during 
floods. 

The  matter  pushed  forward  by  rivers,  or  held  in  mechanical  suspen- 
sion in  their  waters,  has  hitherto  been  regarded  only  with  reference  to 
the  removal  of  that  arising  from  the  decomposition  of  rocks  by  atmo- 
spheric influences.  We  have  now  to  consider  the  erosion  of  clays,  sands, 
and  gravels,  and  of  hard  rocks  by  means  of  the  rivers  themselves. 

In  many  a  river  course  it  may  readily  be  observed,  that  incoherent 
sands  and  gravels  are  cut  into  by  the  mere  friction  of  the  water,  even 
when  clear.  That  such  a  moving  body  should  so  act  would  be  expected, 
and  no  doubt  we  should  also  anticipate  that  amid  incoherent,  or  easily- 
removed  substances,  any  modification  in  the  course  of  a  river  would 
speedily  produce  change  in  other  parts ;  but  it  is,  nevertheless,  extremely 
interesting  to  experiment  on  the  course  of  streamlets  passing  among 
sands  ;  as,  for  instance,  on  some  extended  shores  at  low  tides,  and  trace 
the  effects  of  even  slight  alterations  in  the  stream  courses.  The  cutting 


ACTION    OF    RIVERS    ON    THEIR    BEDS.  63 

into  one  bank  throws  the  water  upon  another,  not  previously  worn  away, 
and  the  whole  bed  of  the  stream  gets  modified.  Such  experiments  tend 
to  make  us  more  readily  appreciate  also  those  modifications  of  rivers, 
from  the  actual  cutting  powers  of  their  waters,  which  are  seen  on  the 
great  scale  in  some  parts  of  the  world.  They  also  show  the  distance  to 
which  the  fall  of  a  cliff,  the  filling  up  of  a  cavity,  by  which,  as  forming 
a  lake,  the  force  of  a  flood  may  have  been  previously  stayed  in  its  full 
course,  and  other  obvious  circumstances  have  produced  modification  and 
change. 

There  are  few  persons  who  have  not  noticed  the  manner  in  which 
rivers  are  disposed  to  take  serpentine  courses  in  level  countries,  a  fact 
as  easily  observed  amid  the  meadows  of  the  flat  portions  of  many  valleys, 
of  very  limited  dimensions,  as  among  the  vast  bends  of  the  Mississippi, 
or  any  other  of  the  great  rivers  flowing  under  similar  conditions.  The 
rivers,  by  their  friction,  cut  into  the  ground  presented  to  their  course, 
and  by  working  away  the  earth,  clay,  sands,  or  gravel,  of  bend  against 
bend,  modify  their  channels.  The  waters  necessarily  cut  away  such 
banks  at  the  bottom  of  each  bend.  Hence,  if  two  bends  be  opposite  to 
each  other,  as  those  of  the  river  in  the  annexed  sketch  (fig.  26),  are  at 

Fig.  26. 


a,  5,  and  £,  they  will  tend,  by  continued  erosion,  to  approximate  to  each 
other,  and  finally  to  meet,  so  that  eventually  the  river  course  becomes 
shortened  by  the  amount  of  the  bends  previously  passed  over. 

Although  some  effects  must  follow  the  action  of  clear  water  upon 
bodies,  the  parts  of  which  have  not  sufficient  cohesion  to  resist  removal, 
it  is  by  the  assistance  of  matter  either  mechanically  suspended  in,  or 
forced  onward  by  the  water,  that  rivers  most  readily  cut  into  their 
channels  and  erode  their  banks.  By  this  assistance  they  wear  even  into 
hard  rocks,  removing  the  obstacles  impeding  their  courses,  and  which 
prevent  the  formation  of  a  convenient  general  slope.  As  among  the 
simplest  forms  in  which  water  acts  by  aid  of  mineral  matter  upon  rocks,  we 
may  take  the  vertical  holes  drilled  in  even  some  of  the  hardest  by  means 
of  pebbles  so  situated,  that  a  rotatory  action  is  given  them,  each  in  one 
place,  by  moving  water.  These  are  well  known  in  many  situations, 
where  bars-  of  rock  stretch  across  river  beds,  and  falls  of  water  are  thus 
produced.  A  pebble  borne  down  by  floods  gets  so  established  in  an 
eddy  that  it  remains  there,  and  by  constant  friction,  works  a  vertical 
hole  downwards,  sometimes  to  the  depth  of  several  feet.  In  some 
situations,  where  the  obstacle  has  been  much  lowered  by  the  erosive 
action  of  a  stream,  sections  of  the  annexed  kind  may  be  seen.  In  rare 


64  ACTION    OF    RIVERS    ON    THEIR    BEDS. 

instances  the  pebble,  as  at  a  (fig.  27),  may  still  be  seen,  the  section 
having  been  such  as  not  to  have  allowed  it  to  fall  out.     Hard  trap-rocks 

Pig.  27. 


are  sometimes  thus  drilled,  one  pebble  or  several  having  been  kept 
grinding  downwards.  In  some  situations  this  drilling  into"*bars  of  rocks 
must  have  tended  considerably  to  their  ultimate  removal. 

It  is  however  when  a  river  is  in  flood,  large  pebbles  grinding  and 
driving  against  rocks  which  may  be  exposed  to  the  fury  of  the  torrent, 
and  minor  detritus,  either  hurried  onwards  on  the  bottom,  or  in  mechan- 
ical suspension,  grating  against  and  rasping,  as  it  were,  such  obstacles, 
that  the  erosive  power  is  most  effective.  Huge  blocks  are  forced  on- 
wards, leaving  the  furrows  which  have  marked  their  course  to  attest 
that  course  in  some  situations,  while  the  slower  and  finer  friction  of 
small  pebbles  and  sand  produces  a  smooth  surface  in  others. 

When  endeavouring  to  ascertain  the  abrasion  which  may  be  due  to 
rivers,  the  amount  of  decomposition  which  any  rocks  in  their  course 
may  have  suffered,  prior  to  the  supposed  abrading  action,  should  be 
carefully  estimated,  so  that  too  much  importance  should  not  be  given 
to  such  action.  It  being  known  that  the  decomposition  of  many  rocks 
is  greatly  assisted  by  such  rocks  being  kept  alternately  in  a  wet  and 
dry  condition,  the  observer  should  notice  if  the  water  in  any  river  course 
he  may  study,  rises  and  falls,  and  in  a  manner  sufficient  to  have  an 
appreciable  influence  on  the  rocks  washed  by  it. 

Much  care  is  required  when  we  seek  to  refer  the  formation  of  a  ravine 
through  which  a  river  may  find  its  way  to  the  cutting  power  of  the  river 
itself.  There  is  no  want  of  evidence  that  even  minor  streams,  more 
particularly  when  swollen  by  rains,  cut  channels  for  themselves  in 
various  directions.  In  many  a  mountain  region  this  is  a  fact  of  common 
occurrence.  A  little  study  will  show  the  observer  that  some  ravines 
are  cut  back  very  readily  when,  as  beneath  (fig.  28),  beds,  horizontal, 
or  not  far  removed  from  that  position,  and  composed  of  comparatively 
hard  rocks,  such  as  sandstones,  are  based  upon  softer  substances,  such 
as  clays  or  shales.  From  the  combined  action  of  atmospheric  influences, 
and  that  of  the  falling  water,  with  sometimes  also  the  aid  of  water  per- 
colating between  the  hard  and  soft  rocks,  the  lower  beds  give  way,  and 
being  composed  of  easily  comminuted  substances,  are  soon  removed  in 


ACTION    OF    RIVERS    ON    THEIR    BEDS. 


65 


mechanical  suspension  by  the  torrent,  while  the  hard  rocks,  losing  their 
support,  are  precipitated  to  the  base  of  the  fall.  This  mode  of  cutting 
back  a  channel,  with  vertical  or  nearly  vertical  walls,  in  the  first  in- 
stance, however  they  may  be  afterwards  modified  by  subsequent  falls, 


Fig.  28. 


or  erosion  by  tidal  streams,  may  be  as  well  seen  in  hundreds  of  little 
brooks,  where  the  needful  conditions  of  hard  and  soft  and  nearly  hori- 
zontal strata  are  to  be  found,  as  in  the  valley  of  the  Niagara,  where 
the  production  of  a  ravine  of  this  kind  is  exhibited  on  so  large  a  scale. 
If  a  barrier,  such  as  a  lava  current,  be  suddenly  thrown  across  a 
valley,  the  waters  behind  it,  upwards,  are  necessarily  sustained  to  the 
height  of  the  lowest  part  of  the  new  obstacle  opposed  to  their  further 
progress  downwards.  Let  a  section  be  presented  to  the  attention  of  an 
observer,  such  as  that  beneath  (fig.  29),  where  a  lava  current,  a,  crosses 

Fig.  29. 


a  pre-existing  valley  in  granite,  5,  #,  and  c  is  a  ravine,  with  d  e  a  river 
running  through  it.  He  should  see  if  the  stream  of  lava,  #,  has  been 
actually  cut  through,  or  if  it  has  never  completely  filled  the  valley,  so 
that  a  space  may  have  been  left  between  the  high  part  of  the  lava,  e, 
and  the  bank  of  granite,  d,  through  which  the  waters  readily  found 
their  way,  the  modifying  action  of  the  atmosphere  and  the  river  giving 
the  fallacious  appearance  of  a  ravine  wholly  cut  by  the  latter. 

The  observer  will  have  carefully  to  distinguish  between  ravines  which 
the  rivers   may  have  cut,  and  those  which  are  mere  cracks  or  rents 

5 


66  ACTION    OF    RIVERS    ON    THEIR    BEDS. 

through  which  the  drainage  waters  of  any  district  may  happen  to  find 
their  way.  Therefore  he  must  carefully  search  for  evidence  sufficient 
to  prove  that  the  ravine  may  belong  to  either  the  one  or  the  other  of 
these  classes.  Let  A  and  B  (fig.  30),  represent  sections  of  two  ravines. 

Fig.  30. 


In  general  appearance  they  might  correspond ;  and  even  supposing  a 
crack  or  rent,  it  may  have  been  such  as  so  slightly  to  move  the  opposite 
masses  of  rock  as  to  be  inappreciable.  The  observer  should  endeavour 
to  trace  some  bed  of  rock,  such  as  #,  unbroken  from  one  side  to  the 
other,  across  the  course  of  the  river.  Should  he  discover  such  a  bed 
thus  fairly  connecting  the  sides  of  the  ravine  together  (no  twist  in  the 
crack  or  rent  presenting  a  fallacious  appearance  of  an  unbroken  bed), 
the  ravine  may  still  not  be  due  to  the  cutting  action  of  the  river  itself, 
for  it  may  have  been  a  channel  of  communication  from  one  body  of 
water  to  another  at  a  time  when  the  land  may  have  been  sufficiently 
submerged  for  the  purpose.  Hence  fair  evidence  would  still  be  required 
to  show  that  the  river  really  cut  the  channel. 

If  the  observer  should  be  unable  to  trace  the  rocks  unbroken  across 
the  ravine,  the  evidence  would  remain  uncertain,  for  under  the  supposi- 
tion that  the  sides  so  correspond  as  to  render  a  dislocation  doubtful, 
blocks  of  rock,  pebbles,  and  sand,  may  as  well  cover  a  crack,  such  as  c 
in  B,  as  a  continuous  mass  of  rock.  Should,  'however,  the  beds  on 
either  side  of  the  ravine,  if  prolonged,  not  meet,  that  is,  if,  as  in  the 
following  section  (fig.  31),  a  horizontal  and  marked  bed,  a,  be  higher 

Fig.  31. 


on  one  side  than  on  the  other,  he  will  gee  that  the  line  of  ravine  corre- 
sponds with  a  lino  of  dislocation  where  this  want  of  correspondence  of 
sides  is  apparent,  and  by  further  search  he  should  ascertain  if  this  dis- 
location can  be  traced  in  the  same  line.  Should  this  be  so,  it  still 
re-mains  to  be  ascertained  if  the  river  has  really  done  more  than  modify 


ACTION    OF    RIVERS    ON    THEIR    BEDS. 


67 


the  effects  of  an  action,  along  the  line  of  dislocation,  by  which  the 
ravine  may  have  been  originally  worked  out.  If,  instead  of  horizontal, 
we  find  vertical  beds  of  rock,  as  in  the  annexed  map-sketch  (fig.  32),  in 


2  i 


which  a  b  represents  the  course  of  a  river  through  a  ravine,  and  that  a 
marked  series  of  beds,  1,  2,  3,  and  4,  do  not  correspond  if  prolonged 
across  the  river,  then  also  it  would  be  evident  that  the  latter  flowed  in 
a  line  of  dislocation. 

Should  the  rise  of  the  river-bed  be  such  that  a  series  of  falls  be  found 
at  the  higher  part  of  the  ravine,  so  that  eventually  the  level  of  the 
river-bed  be  equal  to  the  higher  parts  of  the  ravine,  it  will  be  evident 
that  no  strait  with  water,  in  the  manner  of  a  sea-channel,  was  the  cause 
of  the  ravine,  since,  by  submerging  the  land,  the  ravine  would  merely 
form  an  arm  of  the  sea,  and  be  liable  to  be  filled  up  by  the  detritus 
borne  by  the  river  from  higher  levels  into  it. 

Upon  tracing  up  lines  of  valley  for  the  purpose  of  studying  any 
modifications  they  may  have  sustained  from  the  action  of  rivers  and 
other  running  waters  upon  them,  it  will  often  be  seen,  particularly  in 
mountainous  regions,  that  level  spaces  present  themselves,  having  the 
appearance  of  lake  bottoms,  the  river  meandering  through  these  plains, 
and  not  unfrequently  finding  its  way  to  lower  levels  through  gorges  or 
ravines  of  various  magnitudes.  It  is  generally  supposed  that  by  lower- 
ing the  level  of  the  lake  outlet,  the  barrier  ponding  back  the  water  has 
been  removed  sufficiently  for  its  passage  under  ordinary  circumstances 
onwards,  it  being  merely  during  very  heavy  floods,  that  any  water  is 
spread  over  these  plains.  On  the  small,  as  well  as  on  the  large  scale, 
this  explanation  would  often  appear  probable.  If,  as  in  the  following 
section  (fig.  33),  supposed  to  represent  three  lakes,  a,  5,  and  <?,  on  the 


line  of  a  mountain  valley,  the  erosive  action  of  the  river  would  lower 
the  barriers  d,  e,  and  /,  the  cavities  a,  5,  and  <?,  would  cease  to  be  filled 
by  water,  and  we  should  have  plains  in  their  stead,  the  old  bottoms  of 


68  REMOVAL    OF    LAKES    BY    RIVERS. 

the  lakes,  with  the  river  meandering  through  them,  and  rushing  through 
gorges  or  ravines  at  d,  e,  and  /. 

With  respect  to  the  effects  produced  by  the  cutting  back  of  ravines 
to  such  bodies  of  water,  once  supposed  capable  of  causing  overwhelm- 
ing floods,  at  lower  levels,  it  should  be  observed  that  the  depth  of 
water  at  lake  outlets  is  generally  inconsiderable,  so  that  the  letting 
out  and  lowering  of  the  lake  waters  would  be  gradual.  To  illustrate 
this,  let  the  subjoined  section  (fig.  34)  represent  the  case  of  a  river  cut- 
ting back  its  channel,  in  the  manner  of  the  Niagara  (assuming  that 
conditions  were  favourable  for  so  doing),  towards  Lake  Erie,  so  that  the 
latter  became  drained  by  the  operation.  Let  h  e  represent  the  slope, 
exaggerated,  of  the  lake  bed  from  A,  where  the  surplus  waters  are  de- 
livered over  the  barrier  ground,  and  /'  o  the  level  of  the  river  below  the 
falls  cutting  back  the  channel.  Supposing  //'  to  represent  the  place  of 
the  falls,  at  any  given  time,  it  is  clear,  the  same  course  continuing,  that 

Fig.  34. 


o       f  g'  h'  h'  k1  m'  n' 

they  may  be  further  cut  back  to  g  g'  and  even  to  h  A',  without  dimi- 
nishing the  quantity  of  water  in  the  lake.  Once,  however,  at  h  h\ 
every  succeeding  cutting  will  occasion  more  water  to  pass  over  them, 
by  draining  the  waters  of  the  lake  to  the  level  of  jthe  top  of  the  new 
falls,  so  that  when  these  have  retreated  to  i  i',  the  surface  of  the  lake 
will  sink  to  i  c,  and  the  mass  of  water,  over  the  whole  lake,  and  above 
the  new  level,  will  have  passed  over  the  falls  in  addition  to  the  ordinary 
drainage  discharge.  This  addition  would  add  to  the  velocity  and  cut- 
ting power  of  the  falls,  which  would  be  expected,  all  other  conditions 
being  the  same,  to  retreat  more  rapidly  to  k  k',  reducing  the  general 
level  of  the  lake  to  k  d  in  less  time  than  it  reduced  it  from  a  b  to  i  c. 
In  like  manner,  the  level  of  the  lake  would  be  reduced  to  n  e,  which  we 
may  assume,  for  illustration,  as  its  greatest  depth ;  but  every  succeeding 
retreat  of  the  falls  lowering  the  general  level  so  that  the  lake  presented 
a  minor  area,  the  lake  waters  discharged  would  gradually  become  less, 
until,  finally,  nothing  more  than  the  river  would  meander  through  the 
drained  bottom  of  the  lake.  In  considering  the  mode  in  which  a  lake 
may  be  drained  by  the  cutting  back  of  the  outlet  river  channel,  it  should 
not  be  forgotten  tliat,  when  large,  the  average  loss  from  evaporation 
becomes  less  as  the  surface  is  diminished,  so  that  the  supply  by  the  tri- 
butary rivers  and  streams  is  not  much  diminished  by  this  cause,  and 
more  water  finds  its  way  through  the  outlet  to  the  lower  levels. 

In  volcanic  regions  we  may  expect  a  modification  in  the  drainage  of 
valleys  by  the  flow  of  lava  currents  across  them,  and  lakes  may  be 


FORMATION    AND    DISCHARGE    OF    LAKES.  69 

.formed  in  Alpine  regions  by  the  fall  of  masses  of  mountain  into  narrow 
valleys.  From  the  former  cause  many  permanent  alterations  in  the 
drainage  may  be  effected,  the  dammed-up  waters  finding  a  new  outlet, 
more  particularly  amid  accumulations  of  ashes  and  cinders.  In  the 
case  of  a  lava  current  traversing  a  valley,  the  deepest  part  of  a  lake 
thus  formed  might  be  at  the  lower  part,  as  in  the  annexed  section  (fig. 


35),  where  the  previous  slope  of  a  river-bed  has  been  interrupted  by  the 
flow  of  a  lava  current  b  across  a  valley,  so  that  the  river  waters  are 
ponded  back,  and  form  a  lake  at  a.  Supposing  that  a  lava  current 
fairly  stopped  the  river  course,  even  rising  somewhat  on  the  opposite 
side  of  such  a  valley,  and  thus  preventing  the  conditions  noticed  above 
(p.  65),  such  a  barrier  might  long  remain,  the  stoppage  of  the  river 
waters  preventing  any  kind  of  detritus,  which  previously  had  been 
forced  onwards  along  the  bottom,  from  further  progress,  at  the  same 
time  causing  -much  of  the  mechanically  suspended  matter  to  fall.  Both 
conditions  would  be  favourable  to  the  filling  up  of  the  lake,  such  de- 
posits again  to  be  cut  through,  should  the  barrier  of  the  lava  current 
be  eventually  removed.  And  it  is  to  be  observed  that  the  cutting  away 
of  the  barrier  would  be  more  easily  effected  when  the  lake  was  filled  up, 
and  gravel  and  sand  could  be  brought  to  scour  and  wear  away  the  chan- 
nel of  the  rapids  or  water-falls  from  b  to  c. 

When  mountain  masses  have  fallen  across  narrow  valleys,  as  they  are 
known  to  have  done,  and  have  ponded  back  the  waters,  it  may  readily 
happen  that  debacles  may  be  formed,  producing  very  great  effects  at 
lower  levels,  and  causing  the  removal  of  masses  of  rock  under  such 
conditions,  which  the  ordinary  condition  of  the  waters  in  the  valley,  with 
every  regard  to  floods,  would  appear  to  render  improbable.  The  observer 
may  learn  to  appreciate  the  effects  of  such  falls  by  throwing  a  dam 
of  loose  sand  and  gravel  across  any  small  stream,  so  that  the  waters 
be  ponded  back.  At  first  the  removal  of  the  barrier  will  be  slight,  but 
after  a  time  the  waters  rush  out,  sweeping  a  part  of  the  dam  before 
them,  and  removing,  in  their  course  downwards,  stones  and  blocks,  which 
their  vegetable  coatings  show  have  for  years  well  resisted  all  ordinary 
floods. 

Sometimes  also  in  mountain  regions,  a  cross  valley  may,  from  a 
thunderstorm  falling  upon  the  area  which  it  drains,  thrust  forward  such 


70  FORMATION    AND    DISCHARGE    OF    LAKES. 

a  mass  of  rubbish  across  a  main  channel  as  to  pond  back  its  waters,. 
which  finally  clearing  away  the  barrier  thus  formed,  rush  suddenly 
onwards  to  lower  levels.  At  other  times  the  effects  of  a  tributary, 
delivering  itself  at  right  angles,  or  nearly  so,  to  the  main  river,  are 
more  gradual ;  and  in  parts  of  a  chief  valley,  where  the  fall  of  the 
latter  is  not  so  considerable  as  to  produce  a  rapid  current,  more  per- 
manent changes  are  produced.  The  annexed  sketch  represents  one 

Fig.  36. 


m 


of  those  cases,  not  uncommon  in  some  regions,  where  a  tributary 
comes  through  a  lateral  gorge,  high  above  the  main  valley,  thrust- 
ing forward  the  detritus  borne  along  it,  so  as  to  form  a  sort  of  half 
cone.  The  increase  of  such  a  mass  will  modify  the  line  of  the  main 
river,  if  the  latter  be  unable  to  remove  the  detritus  thus  borne  across 
its  course.  In  favourable  situations,  such  as  in  some  parts  of  the 
Alps,  cottages  and  cultivation  will  be  seen  on  those  parts  of  the 
mound  where  the  more  or  less  divided  streams  of  the  tributary  do 
not  rush  furiously  onwards  to  lower  levels. 

Among  the  causes  of  debacle  and  change  in  drainage  depressions, 
we  should  not  omit  the  consideration  of  glaciers  falling  across  val- 
leys from  adjacent  heights,  since  the  great  debacle  down  the  valley 
of  the  Rhone  in  1818,  is  still  fresh  in  the  memory  of  many  who  wit- 
nessed its  transporting  power,  and  who  would  scarcely  otherwise  have 
been  disposed  to  credit  the  effects  produced.  After  successive  falls 
from  the  glacier  of  Getroz,  during  several  years,  into  a  narrow  part  of 
the  Val  de  Bagnes,  in  the  Vallais,  the  accumulation  finally  became  such 
that  the  waters  of  the  Dranse,  which  previously  found  their  way  amid  the 
fallen  blocks  of  ice,  were  ponded  back.  A  lake  was  thus  formed  about 
half  a  league  in  length,  and  it  was  estimated  to  contain  800,000,000 
cubic  feet  of  water.  By  driving  a  gallery  at  a  lower  level  in  the 
icy  barrier,  this  quantity  was  supposed  to  be  reduced  to  530,000,000 
cubic  feet,  a  mass  of  water  which,  effecting  a  passage  between  the  ice 
and  the  rock  on  one  side,  was  let  off  in  about  half  an  hour  down  the 


LACUSTRINE    DEPOSITS.  71 

Val  de  Bagnes  into  the  valley  of  the  Rhone,  and  thus  into  the,  lake  of 
Geneva,  where,  fortunately,  by  the  spread  of  the  waters,  their  destruc- 
tive force  was  lost.  Huge  blocks  of  rock  were  moved  by  this  debacle, 
and  a  great  mass  of  matter  swept  away  to  lower  levels. 

Lacustrine  Deposits. — Mention  has  been  already  made  of  the  deposits 
effected  in  the  still  portions  of  stream  courses,  and  of  the  inclined  angle 
which  the  layers  of  sand  and  gravel  take,  after  being  forced  along  the 
bottom  of  the  stream-bed,  and  thrown  over  little  delta  protrusions  into 
the  pools  of  water.  The  mode  of  detrital  deposit  to  be  observed  in  the 
lakes  is  the  same  as  in  the  little  pools,  the  difference  is  chiefly  in  the 
magnitude  of  the  accumulations.  The  little  pools  differ  principally  from 
lakes  from  being  liable  to  be  swept  by  floods,  and  the  deposited  detritus 
to  be  thus  once  more  lifted  and  borne  onwards,  which  does  not  happen 
in  lakes  of  fair  magnitude.  Moreover,  discoloured  flood  waters  spread 
over  the  pools,  and  not  over  pieces  of  water  deserving  the  name  of  lakes. 
Lakes  necessarily  vary  much  as  to  the  repose  of  their  waters  according 
to  their  depths.  In  the  deeper  parts  of  such  a  body  of  fresh  water  as 
that  of  the  lake  of  Geneva,*  there  is  no  cause  for  movement  from  altered 
temperature  of  the  water,  for  experiments  would  appear  to  show  that 
this  temperature  always  remains  the  same  at  the  great  depths,  that  of 
the  greatest  density  of  fresh  water  being  found  at  all  seasons  of  the 
year.  In  such  situations  also  the  waves  raised  by  the  winds  on  the 
surface  are  not  felt,  and  whatever  chemical  or  mechanical  accumulations 
there  take  place  would  remain  undisturbed,  so  long  as  the  present  con- 
ditions are  continued. 

In  the  shallow  parts  of  the  same  lake,  and  necessarily  also  in  shallow 
lakes  generally,  the  waves  (sooner  raised  in  fresh-water  lakes  than  in 
the  sea  by  the  same  force  of  wind,  because  the  fluid  put  into  motion  is 
of  less  density)  stir  up  the  finer  mud  and  silt,  while  the  breakers  act 
upon  the  shore,  and  for  the  time  keep  heavier  matter  in  motion  and 
mechanical  suspension.  As,  therefore,  the  deep  cavities  holding  lakes 
become  filled  up,  there  may  be  an  irregularity  in  part  of  the  accumula- 
tions in  the  higher  portions  not  observable  beneath. 

If  attention  be  directed  to  the  mode  in  which  detrital  matter  is 
protruded  into  great  lakes,  such  as  those  of  North  America,  Switzer- 
land, or  Northern  Italy,  it  will  rarely  happen  that  the  contributing 
streams  or  rivers  are  not  found  to  pour  in  detritus  of  various  kinds  and 
in  different  ways.  Let  us  consider  that  the  accompanying  plan  (fig.  37) 
represents  that  of  a  lake  divided  into  two  unequal  portions,  and  that  it 

*  In  a  series  of  soundings  of  the  lake  of  Geneva,  made  in  1819,  and  chiefly  under- 
taken for  the  purpose  of  seeing  how  far  the  temperature  of  the  water  in  it  corresponded 
with  that  assigned  to  the  greatest  density  of  fresh  water,  an  account  of  which  was  pub- 
lished, with  a  chart,  in  the  "  Bibliotheque  Universelle,"  for  1819,  we  found  the  greatest 
depth  of  the  lake  to  be  164  fathoms,  or  984  feet,  opposite  Evian. 


72  LACUSTRINE    DEPOSITS. 

is  supplied  with  water,  in  addition  to  the  rain  which  may  fall  upon  it,  by 
the  rivers  c,  d,  and  e ;  that  c  is  a  chief  river,  draining  a  large  district,  and 


d  and  e  two  torrents,  descending  occasionally  from  adjacent  mountain 
heights  with  great  force,  while,  at  other  times,  they  contain  little  water. 
Let  us  further  suppose  that  the  waters  of  the  river  c  are  generally 
turbid,  like  those  of  the  glacier  rivers  of  the  Alps,  and  that  they  vary 
in  quantity  at  different  times,  so  that  the  river  both  forces  forward  and 
holds  mechanically  in  suspension  variable  amounts  of  matter.  From 
such  conditions  as  these  we  may  assume  that,  though  variable,  the  accu- 
mulations, brought  down  into  the  lake  by  the  river  c,  would  still  be 
more  uniformly  spread  than  those  resulting  from  the  sudden  rushes  of 
water  down  the  torrents  e  and  d,  the  stones  or  pebbles,  borne  forwards 
by  the  latter,  being  larger  than  the  detritus  forced  onwards  by  the  main 
feeding  river  c. 

In  order  to  appreciate  the  difference  of  accumulation  arising  from 
these  conditions,  it  may  be  desirable  to  assume  that  the  depth  of  the 
lake  is  uniform,  or  nearly  so,  throughout,  though  of  course  the  original 
form  of  the  lake  basin  would  influence  the  products.  The  river  c  would 
accumulate  the  detritus  it  can  force  along  its  channel,  in  the  manner 
previously  noticed,  while  at  the  same  time  it  would  discharge  a  body  of 
turbid  water  into  the  still  waters  of  the  lake.  The  force  of  the  former 
is  checked  by  the  latter ;  and  the  turbid  water,  being  heavier  than  that 
of  fresh-water  lakes,  would  sink  in  clouds  toward  the  bottom,  as  may  be 
seen  where  the  Rhone  enters  the  lake  of  Geneva,  and  in  various  other 
similar  situations.  The  velocity  with  which  the  turbid  water  would  enter 
the  lake  would  carry  it  to  various  proportionate  distances,  until  its  mo- 
tion became  finally  checked.  It  is,  however,  interesting  to  observe  that, 
from  the  difference  in  specific  gravities,  when  turbid  waters  fall  to  the 
bottom,  these  steal  quietly  upon  that  bottom  for  considerable  distances, 
it  being  long  before  they  part  with  the  fine  matter  which  they  hold  in 
mechanical  suspension.  The  fine  matter  brought  down  by  the  Rhone 
is  found  in  mud  beneath  the  still  deep  waters  of  the  lake  of  Geneva, 
many  miles  beyond  the  discharge  of  the  turbid  waters  of  the  river  into 
that  lake.* 

*  If  a  long  trough  be  filled  with  clean  water,  and  turbid  water  be  very  quietly 
poured  into  it  at  one  end,  the  mode  in  which  the  latter  finds  its  way  beneath  the  former 
will  at  once  be 


LACUSTRINE    DEPOSITS.  73 

Assuming  the  depth  of  the  lake  to  have  been  such  that  turbid  could 
so  creep  beneath  the  clear  waters  as  to  form  a  deposit  of  mud  or  clay, 
we  should  have  the  bottom  of  the  minor  division  of  the  lake  coated  with 
this  finely  comminuted  matter,  while  a  delta-like  protrusion  of  the  sand 
and  pebbles  was  formed  over  it.  Supposing  the  commencement  of  such 
accumulations  to  be  in  a  rock  cavity,  the  basin  of  the  lake,  we  should 
expect  them  to  take  somewhat  of  the  form  seen  in  the  following  section 
(fig.  38),  where  a  represents  the  first  gravel  and  sand  deposits,  forced 
over  at  c,  b  mud,  gradually  accumulated  over  the  rock  basin,  d  the  ad- 


vance  of  the  delta  over  the  mud,  and  g  the  surface  of  the  lake  beyond 
the  delta.  Under  such  conditions  we  should  have  irregular  beds  of  sand 
and  gravel,  with  occasional  patches  of  clay,  the  result  of  deposits  in 
local  stagnant  places,  based  upon  a-  clay  which  here  and  there,  in  its 
upper  portion,  might  contain  sand  or  sandy  clay,  the  effects  of  floods 
carrying  such  matter  in  mechanical  suspension  beyond  the  delta  into 
deeper  water,  and  there  depositing  it  upon  the  mud. 

Still  referring  to  the  plan,  fig.  37,  we  should  expect  the  accumulations 
at  the  junction  of  the  torrents,  d  and  e,  with  the  lake,  to  be  much  modi- 
fied in  character.  To  render  the  case  more  illustrative,  we  may  consider 
that,  from  the  nature  of  the  rocks  traversed  by  the  respective  torrents, 
little  else  than  fragments  of  hard  substances  are  shoved  forward  by  d, 
while  much  earthy  matter  and  soft  rocks,  easily  comminuted  by  friction, 
are  mingled  with  the  harder  fragments  thrust  into  the  lake  by  e.  If  a 
small  amount  of  earthy  matter  be  carried  forward  by  d,  the  accumulation 
where  the  torrent  enters  the  lake  would  form  little  else  than  a  protruding 
mass  of  fragments,  composed  of  beds  different  in  position,  but  dipping 
at  angles  varying  probably  from  20°  to  30°  around  the  general  curve 
of  the  protrusion ;  while  such  finely  comminuted  matter  as  was  held  in 
mechanical  suspension  would  descend  to  the  bottom,  and  steal  along 
beneath,  as  previously  mentioned,  adding  to  the  mud  derived  from  the 
chief  stream  c.  The  accumulations  formed  at  b  by  the  torrent  c,  would 
be  of  a  mixed  character  between  those  produced  by  c  and  d.  These 
causes  continuing,  the  lake  would  be  eventually  filled  up  by  clays,  saiyls, 
and  gravels  brought  into  it  by  the  rivers  and  torrents,  the  surface  waves 
acting  upon  much  of  the  higher  accumulations  as  the  general  depth 
decreased.  Finally,  the  out-falling  river/,  clear  as  that  of  the  Rhone, 
where  it  quits  the  lake  of  Geneva,  while  the  lake  lasted,  would  be  joined 
to  the  river  c ;  d,  and  e,  as  two  tributary  streams  adding  their  waters 
to  it,  and  the  whole  would  traverses  plain,  much  as  represented  beneath 


74  ACTION    OF    SEA    ON    COASTS. 

(fig.  39),  muddy  sediment  being  added  to  the  surface  of  the  plain  from 
time  to  time  by  floods,  and  the  torrents  still  thrusting  forward  fragments 
of  rock  and  pebbles  where  they  joined  it. 


Great  modifications  of  the  mechanical  accumulations  here  noticed 
will  readily  present  themselves  to  the  attention  of  an  observer ;  and,  if 
he  will  combine  some  of  them  with  the  chemical  deposits  previously 
noticed,  and  add  the  harder  parts  of  the  animals  which  have  either  lived 
in,  or  been  drifted  into,  the  lakes,  as  also  the  leaves  of  trees  and  other 
plants,  and  the  branches  and  trunks  of  trees  which  may  eventually  fall 
to  the  bottom  after  having  been  borne  onwards,  sometimes  quietly,  at 
others  confusedly  and  rapidly,  he  may  better  appreciate  the  still  greater 
modifications  to  which  lacustrine  accumulations  may  be  subject. 

Action  of  the  Sea  on  Coasts. — Before  we  consider4  the  accumulations 
effected  in  the  sea,  it  is  desirable  to  call  attention  to  the  action  of  the 
sea  on  coasts,  since  that  action  often  contributes,  in  no  small  degree,  to 
the  matter  of  which  these  deposits  are  formed. 

The  sound  produced  by  the  grating  and  grinding  of  the  pebbles  of  a 
shingle  beach,  even  when  the  breakers  on  shore  are  comparatively  unim- 
portant, can  scarcely  have  escaped  the  attention  of  those  who  have  even 
for  a  short  time  visited  coasts  where  such  beaches,  and  they  are  com- 
mon, are  to  be  found.  It  will  soon  be  apparent,  that  this  friction,  if 
continued  for  ages,  must  not  only  wear  down  the  pebbles  to  sand,  but 
grind  away  and  smooth  off  even  the  hard  rocks  exposed  to  such  power- 
ful action.  It  is,  however,  when  the  observer  sees  the  huge  masses  of 
rock  moved  by  the  breakers  arising  from  a  heavy  gale  of  wind,  blowing 
on  shore  from  over  a  wide  spread  of  open  sea,  or  from  the  long  lines  of 
wave  known  as  a  ground  swell,  that  he  not  only  learns  to  value  the 
force  of  the  water  taken  by  itself,  thus  projected  against  a  coast,  but 
also  the  additional  power  it  derives  to  abrade  the  cliffs  which  may  be 
opposed  to  the  breakers  from  the  size  and  abundance  of  the  shingles 
they  can  then  hold  in  mechanical  suspension. 

i  ii-rly  to  appreciate  the  power  of  breakers,  a  geologist  should  be 
present  on  an  exposed  ocean  coast,  such  as  that  of  Western  Ireland,  the 
Land's  End  (Cornwall),  or  among  the  Western  Islands  of  Scotland,  du- 
ring ;i  heavy  and  long-continued  gale  of  wind  from  the  westward,  and 
mark  the  effects  of  the  great  Atlantic  waves  as  they  break  and  crash 


ACTION    OF    SEA    ON  .COASTS.  75 

upon  the  shore.  He  will  generally  find  in  such  situations  that,  though 
the  rocks  are  scooped  and  hollowed  into  the  most  fantastic  forms,  they 
are  still  hard  rocks ;  for  no  others  could  long  resist  the  breakers,  which, 
with  little  intermission,  act  upon  them.  Not  only  blocks  of  rock  rest- 
ing on  the  shore  are  driven  forward  by  the  repeated  blows  of  such  break- 
ers (and  it  should  be  recollected  that  the  mere  tonnage  of  water  in  a 
heavy  breaker  is  not  inconsiderable),  but  those  also  firmly  bolted  down 
on  piers  are  often  thrown  off  and  driven  aside  in  far  more  sheltered 
situations.  The  history  of  many  a  pier  harbour  is  that  of  the  destruc- 
tive power  of  breakers,  and  those  who  have  witnessed  a  breach  made  in 
such  a  harbour  during  a  heavy  gale  of  wind,  are  not  likely  to  remain 
unimpressed  with  the  importance  of  breakers  in  the  removal  of  land.* 

Slight  attention  to  the  manner  in  which  waves  break  on  a  coast  will 
soon  show  that  upon  the  prevalent  winds  and  the  proportion  of  those 
which  force  the  greatest  waves,  or  seas,  as  they  are  generally  termed, 
on  shore,  will  depend,  other  things  being  equal,  the  greatest  amount  of 
destructive  action.  Thus,  on  a  coast  on  which  western  winds  prevail, 
and  there  is  sufficient  extent  of  open  sea  before  it,  we  should  expect  to 
discover  the  greatest  loss  of  land,  the  force  of  the  breakers  being  there 
the  greatest  and  most  incessant.  As  a  whole,  the  coasts  of  the  British 
Islands  are  exposed  to  the  heaviest  and  most  incessant  breakers  from 
winds  ranging  from  the  N.W.  to  the  S.W. ;  and  but  slight  acquaintance 
with  our  coasts  will  soon  satisfy  the  geologist,  that,  if  the  other  coasts 
of  our  islands  were  exposed  to  an  equal  amount  of  abrading  force,  a 
large  portion  of  them  would  soon  be  cut  away  at  a  far  more  rapid  rate 
than  at  present. 

Taking  an  equal  amount  of  prevalent  winds  and  of  open  sea  over 
which  they  may  range,  it  will  soon  be  observable  that  the  abrasion  of 
rocks,  of  equal  hardness  and  similar  position,  is  modified  according  as 
the  adjoining  seas  are  tidal  or  tideless.  In  the  latter  case,  though  no 
doubt  the  pressure  of  the  wind  upon  water  raises  it  to  levels  above  those 
which  it  commonly  occupies,  the  difference  is  not  so  considerable  as  to 
bring  any  large  faces  of  cliff"  exposed  to  the  action  of  the  breakers.  A 
beach,  moreover,  piled  in  front  of  a  cliff  is,  in  such  seas,  as  rarely  passed 
and  the  cliff  attacked.  In  tidal  seas,  on  the  contrary,  many  feet  are 
vertically  exposed  to  the  fury  of  the  breakers  as  the  tide  rises  and  falls ; 

*  During  a  heavy  gale  in  November,  1824,  and  also  in  another  at  the  commencement 
of  1829,  blocks  of  limestone  and  granite,  from  two  to  five  tons  in  weight,  were  washed 
about  at  the  breakwater,  Plymouth,  like  pebbles.  About  300  tons  of  such  blocks  were 
borne  a  distance  of  200  feet,  and  up  the  inclined  plane  of  the  breakwater.  They  were 
thrown  over  it,  and  scattered  in  various  directions.  In  one  place  a  block  of  limestone, 
seven  tons  in  weight,  was  washed  a  distance  of  150  feet.  We  have  seen  blocks  of  two 
or  three  tons,  torn  away  with  a  single  blow  of  a  breaker  and  hurled  over  into  a  har- 
bour, and  one  of  one  and  a  half  or  two  tons,  strongly  trenailed  down  upon  a  jetty,  torn 
away  and  tossed  upwards  by  the  force  of  another. 


76  ACTION  OF  SEA  ON  COASTS. 

and  beaches  piled  up  in  moderate  weather  are,  in  fitting  situations,  re- 
moved by  the  return  action  of  the  breakers,  so  that  the  cliffs  are  again 
open  to  abrasion.  Moreover,  the  rocks  are  exposed  to  greater  decom- 
position from  being  alternately  wet  and  dry,  a  consideration  of  some 
importance  in  many  climates,  particularly  in  those  where  the  tempera- 
ture falls  below  the  freezing  point  of  water  during  certain  seasons  of  the 
year.  It  should  not,  nevertheless,  be  forgotten,  that  coasts,  where 
breakers  reach  the  cliffs  at  high  water,  are  frequently  protected  by 
beaches  at  low  water  ;  and  that,  therefore,  they  are  removed  from  the 
abrading  power  of  the  waves  during  all  the  time  that  they  fall  on  the 
protecting  beaches, — a  time  which  changes  with  the  varying  state  of  the 
tides  and  of  the  weather  generally. 

Attention  will  not  long  have  been  given  to  the  abrading  action  of 
breakers  on  coasts  before  it  will  be  seen  that  there  are  many  circum- 
stance.s  modifying  the  effects  which  would  be  otherwise  produced.  It 
will  be  observed  that  the  wearing  away  of  coasts  is,  among  the  softer 
rocks  more'  especially,  often  much  accelerated  by  land  springs  which,  as 
it  were,  shove  portions  of  the  cliffs  into  the  power  of  the  breakers  by  so 
moistening  particular  beds  or  portions  of  them,  that  much  of  the  cliff 
loses  its  cohesion,  and  is  launched  seaward.  The  loss  thus  sustained  in 
some  coasts  is  very  considerable. 

So  far  from  being  thus  brought  by,  so  to  speak,  inland  influences 
within  the  reach  of  the  sea,  in  other  situations  we  find  the  higher  parts 
of  cliffs  protruding  over  the  sea  beneath,  as  in  the  annexed  sketch  (fig.  40,) 

Fig.  40. 

^ 


when  we  suppose  the  parts  of  the  rock  to  be  so  coherent  that  the  break- 
ers have  been  enabled  to  excavate  the  lower  part  of  the  cliff  in  the  man- 
ner here  represented.  The  same  action  continuing,  a  time  must  come 
when  the  weight  of  the  overhanging  portion  will  outbalance  the  cohesion 
of  the  rock,  and  this  mass  will  fall.  Breakwater,  as  it  then  becomes  to 
a  part  of  the  cliff,  much  will  depend  as  to  the  length  of  time  it  may  so 
act,  according  to  the  manner  in  which  it  has  fallen,  particularly  if  stra- 
tiiird.  If  composed  of  beds  of  rock,  and  the  slope  of  these  beds  face  the 


ACTION    OF    SEA    ON    COASTS. 


77 


sea,  as  in  the  following  sketch  (fig.  41),  the  breakers  will  have  less  power 
to  act  upon  them,  than  if  the  edges  of  the  strata  were  presented  to  the 

Fig.  41. 


sea,-  as  represented  beneath  (fig.  42),  in  which  position  they  offer  the 
least  resistance  to  the  destructive  action  of  the  sea. 


It  will  be  sometimes  found,  that  a  hard  rock  constitutes  the  high  part 
of  a  cliff,  while  the  lower  portion  is  composed  of  a  softer  substance,  such 
as  a  clay  or  marl,  and  that  masses  of  the  harder  rock  falling  from  above 
afford  protection,  for  a  time,  to  the  lower  part  of  the  cliff.  Thus,  let  a,  in 
the  annexed  section  (fig.  43),  represent  the  upper  portion  of  a  cliff  formed 
of  hard  beds  of  rock,  such  as  sandstone,  while  b  is  a  marl  or  clay,  then  the 

Fig.  43. 


action  of  the  sea,  cZ,  upon  the  cliff  would  undermine  it,  and  cause  the 
fall  of  masses  of  the  hard  rock,  <?,  which,  accumulating  at  its  base,  would 


78 


ACTION    OP    SEA    ON    COASTS. 


tend  to  protect  it,  according  to  the  quantity  of  fallen  rock,  the  size  of 
the  masses,  and  their  hardness.  It  will  be  found  that  cliffs,  composed 
as  a  whole  of  somewhat  soft  rocks,  and  clays,  marls,  or  slightly  indu- 
rated sandstones,  are  protected  at  their  bases  by  an  accumulation  of  in- 
durated portions  of  these  rocks.  Thus  let  the  accompanying  section 


Fig.  44. 


(fig.  44)  represent  a  clay  in  which  there  are  nodules  of  argillaceous  lime- 
stones, as  a  a  (and  those  of  septaria  in  clays  are  often  large),  which 
when  washed  out  by  removal  of  the  clay,  accumulate  on  the  beach  b. 
These  then  tend  to  protect  the  base  of  the  cliff  from  the  destructive  ac- 
tion of  the  breakers,  c.  The  study  of  any  extended  line  of  coast,  com- 
posed of  horizontal  or  slightly  inclined  beds  of  rocks  of  unequal  hard- 
ness, will  present  abundant  examples  of  the  modified  protection  afforded 
to  the  base  of  cliffs  from  the  accumulation  of  masses  derived  from  them. 
Striking  examples  are  often  to  be  found  on  our  shores  of  the  wearing 
away  of  the  land  by  the  action  of  the  breakers,  so  that  rocks  stand  out 
in  the  sea  detached  from  the  main  body  of  the  land,  but  which  once 
evidently  formed  part  of  it.  Perhaps  the  accompanying  sketch  (fig.  45) 
of  the  cliffs  near  Bedruthan,  Cornwall,  may  afford  an  idea  of  the  manner 

Fig.  45. 


in  which  some  of  our  coasts  are  thus  cast  back  by  breakers.     The  islets 
here  represented  have  been  formed  by  such  an  abrasion  of  the  rocks  to 


ACTION    OF    SEA    ON    COASTS.  79 

the  present  cliffs  of  the  main  land,  that  portions,  somewhat  harder,  and 
better  resisting  the  action  of  the  breakers  than  the  rest,  have  remained. 
The  breakers  not  unfrequently  work  round  portions  of  the  cliffs,  forming  a 
cave  through  a  projecting  point  or  headland.  This,  from  the  continuance 
of  the  same  destructive  action,  become  gradually  enlarged,  the  roof, 
from  the  want  of  support,  falls,  and  the  point  becomes  an  island,  round 
which  the  breakers  work  their  way,  gradually  increasing  the  distance 
between  it  and  the  main  land.  Beneath  #,  in  the  sketch,  a  point  will  be 
seen  to  be  now  separating  from  the  main  land,  and  forming  into  an 
island. 

As  might  be  expected,  amid  the  wearing  away  of  coasts  by  breakers, 
innumerable  instances  present  themselves  of  unequal  action  on  the  harder 
and  softer  substances,  according  to  their  exposure  to  the  destructive 
power  employed  upon  them,  so  that  long  channels  and  creeks,  and  coves 
of  every  variety  of  form,  are  worked  away  in  some  situations,  while  hard 
rocks  protrude  in  others.  Coves  afford  shelter  to  the  fisherman,  from 
being  hollowed  out  in  some  localities,  while  the  hard  ledges  act  as  natu- 
ral piers  in  others.  The  annexed  sketch  (fig.  46)  of  Polventon  Cove, 
on  the  east  of  Trevose  Head,  Cornwall,  may  be  taken  as  a  fair  illustra- 
tion of  a  harbour  scooped  out  by  the  action  of  the  breakers,  which  have 
so  worn  away  the  slate  a,  from  a  line  of  hard  greenstone,  5,  that  the 
latter  forms  a  natural  pier,  named  the  Merope  Rocks,  affording  shelter 
from  the  northwest  winds,  which,  when  strong,  are  much  to  be  dreaded 
on  this  coast.* 

Tig.  46. 


It  is  not  often,  however  we  should  expect  that  it  must  sometimes 
occur,  that  a  mere  trace  of  beds,  superincumbent  upon  dissimilar  rocks, 
can  be  found  on  coasts,  showing  how  such  may  be  entirely  removed  from 
the  subjacent  rocks  by  the  action  of  the  breakers.  In  this  respect,  the 
annexed  sketch  (fig.  47)  may  be  useful.  It  represents  a  small  patch,  a, 
of  a  conglomerate  of  the  New  Red  Sandstone  series,  named  the  Thurle- 
stone  Rock  (in  Bigbury  Bay,  South  Devon),  reposing,  with  a  moderate 

*  Polventon  Cove  was  at  one  time  well  known  as  a  smuggling  station,  and  is  now 
often  visited  by  vessels  waiting  for  the  tide  into  Padstow  Harbour,  a  few  miles  distant. 


80 


ACTION    OF    SEA    ON    COASTS. 


dip  seaward,  unconforinably  upon  the  edges  of  Devonian  slates,  b.     Here 
the  breakers  have  almost  entirely  removed  the  red  conglomerate  which 


Fig.  47. 


was  deposited  upon  the  slates,  and,  no  doubt,  once  covered  them  far 
more  extensively  than  is  now  observable. 

In  estimating  the  abrading  power  of  breakers  on  an  extensive  line  of 
coast,  it  is  desirable  not  only  to  direct  attention  to  the  relative  hardness 
of  the  rocks  of  which  it  is  composed,  but  also  to  the  position  of  the  beds 
(if  the  rocks  be  stratified),  and  the  planes  of  slaty  cleavage  and  of  joints. 
It  will  soon  be  apparent  that  among  stratified  rocks,  lines  of  coast,  under 
otherwise  equal  circumstances,  depend  on  the  direction  and  dip  of  the 
beds.  Their  position  relatively  to  the  force  of  the  breakers  is  necessa- 
rily important ;  for  if  a  series  of  beds,  such  as  those  in  the  accompa- 
nying sketch  (fig.  48),  dip  seaward,  the  action  of  breakers  falling  on 

Fig.  48. 


them  in  the  manner  represented  would  be  comparatively  trifling,  since 
the  return  of  one  breaker  down  the  seaward  slope  of  the  beds,  diminishes 
the  force  of  the  next  falling  upon  it,  and  the  power  of  the  remainder, 
rushing  up  the  slope,  is  gradually  expended,  and  meets  with  no  direct 
obstacle  upon  which  it  can  destructively  act.  The  positions  in  wlm-h 
the  edges  of  the  beds  of  any  given  rock  are  exposed  to  the  action  of  the 
sea,  are  those  where  the  abrading  power  of  the  breakers  is  most  suc- 
cessfully exerted.  Let  us  suppose  that  the  annexed  plan  (fig.  49),  re- 
presents a  line  of  coast  exposed  to  the  north  and  west,  and  that  the 
abrading  action  of  the  breakers  is  equal  from  both  points ;  then  the 


ACTION    OF    SEA    ON    COASTS.  81 

effects  produced  will  depend  upon  the  resisting  powers  of  the  rocks  them- 
selves. Taking  the  country  to  be  composed  of  beds  of  slates  and  sand- 
stones, having  a  strike  or  direction  from  east  to  west,  and  a  dip  of  about 

Fig.  49. 


45°  to  the  north ;  then,  supposing  no  cleavage  planes,  and  the  slates  to 
be  parallel  with  the  sandstone  beds,  the  resisting  powers  of  the  rocks 
would  be  greatest  on  the  northern  coast,  since  the  beds  would  there  all 
slope  seaward,  while  the  same  rocks  would  be  liable  to  much  abrasion 
on  the  west,  the  edges  of  the  beds  being  exposed  in  that  direction.  Nu- 
merous indentations  would  be  the  result,  similar  to  those  represented  in 
the  plan,  the  softest  beds  being  worn  into  the  deepest  coves,  and  the 
harder  constituting  the  most  prominent  headlands. 

In  all  investigations  as  to  the  loss  of  land  from  the  action  of  the  sea 
upon  it,  dependence  can  rarely  be  placed  on  old  maps  of  coasts,  which 
are  for  most  part  very  inaccurate ;  indeed,  there  would  be  no  difficulty 
in  producing  those  which  would,  when  compared  with  a  good  modern 
survey,  apparently  show  an  increase  of  half  or  three-quarters  of  a  mile 
on  a  cliff  coast,  where,  in  fact,  there  had  been  considerable  loss. 

We  have  seen  that  cliffs  become  abraded  by  the  action  of  the  breakers, 
sometimes  alone,  at  others  combined  with  that  of  the  atmosphere  and  of 
land-springs.  The  mineral  matter  so  brought  within  the  influence  of 
the  sea  has  to  be  removed,  and  observation  soon  shows,  that  while  one 
part  of  it  is  caught  up  in  mechanical  suspension,  and  is  then  liable  to 
be  carried  away  by  the  movements  of  tides  or  currents,  another  portion 
remains  and  is  exposed  to  the  grinding  action  of  the  breakers  on  the 
coast.  This  latter  portion  necessarily  varies  in  size,  from  the  block,  which 
can  only  be  shaken  by  the  blows  of  heavy  breakers  discharged  upon  it,  act- 
ing with  their  greatest  power,  to  the  small  pebble  temporarily  caught  up 
in  mechanical  suspension,  even  by  minor  breakers,  but  which  again  sinks 
to  the  bottom  when  not  exposed  to  their  influence. 

It  will  be  observed,  respecting  shingle  beaches,  that  during  a  heavy 
on-shore  gale,  every  breaker  is  more  or  less  charged  with  the  materials 
composing  the  beach,  and  that  the  shingles  are  forced  forward  as  far  as 
the  broken  wave  can  reach,  their  shock  against  the  beach  driving  others 
before  them,  not  held  in  temporary  mechanical  suspension.  Shingles 
are  thus  projected  on  the  land  beyond  the  reach  of  the  retiring  waves, 
and  there  accumulate  in  long  ridges  parallel  to  the  coast,  especially 


82  ACTION  OF  SEA  ON  COASTS. 

where  the  land  is  low  behind  the  shingle  beach.  Heavy  on-shore  gales 
and  high  tides  combined  necessarily  produce  the  greatest  accumulation 
of  shingle  in  such  localities,  and  although  occasionally  a  breach  may  now 
and  then  be  formed  at  such  times,  it  becomes  speedily  filled  up  by  the 
piling  action  of  the  breakers. 

Attention  to  a  shingle  beach  will  soon  show,  notwithstanding  the 
minor  removal  of  portions  from  one  place  to  another,  backwards  and 
forwards,  and  the  modifications  arising  from  the  obliteration  of  the  little 
lines  of  beach,  not  unfrequently  produced  during  moderate  weather,  that 
as  a  whole  it  travels  in  the  direction  of  the  prevalent  breakers  until  ar- 
rested against  some  projecting  portion  of  the  coast.  This  must  happen, 
if  any  force  act  upon  the  shingles  more  in  one  direction  than  another, 
since  they  would  be  compelled  to  travel  in  conformity  with  it ;  and  ob- 
servation proves  that  such  is  the  fact,  for  not  only  do  we  find  pebbles  of 
known  rocks  thus  moved  from  the  particular  portion  of  cliff  whence  they 
have  been  derived,  but  also,  though  breakers  appear  to  adjust  themselves 
to  the  tortuous  character  or  outline  of  a  coast,  that  there  is  always  a 
slight  oblique  action  in  consequence  of  the  main  direction  of  the  wind 
at  the  time. 

One  of  the  simplest  forms  in  which  the  shingles  of  a  beach  are  seen 
to  have  travelled  is  where,  as  in  the  annexed  plan  (fig.  50),  we  find  a 

Fig.  50. 


spit  of  shingle  beach,  d,  composed  of  pebbles  evidently  derived  from  a 
coast,  5,  stretching  in  the  direction  whence  the  prevalent  winds  blow, 
the  shingle  beach  being  unable  to  cross  over  to  the  opposite  coast  (a)  in 
consequence  of  the  flow  and  ebb  of  the  tide  in  and  out  of  an  estuary 
(e,  c\  into  which  a  river  (/)  discharges  itself  at  the  higher  end.  In 
such  cases,  and  they  are  to  be  seen  in  many  situations,  the  rush  of  water 
is  able  to  keep  the  channel  open  between  the  spit  of  beach  d  and  the 
coast,  not  in  the  direction  of  prevalent  winds,  the  ebb  tide,  especially 
when  the  river  is  in  flood,  effectually  keeping  clear  the  passage,  and 
throwing  off  the  shingle,  which  strives  to  cross  over  and  block  up  the 
estuary. 

There  are  good  examples  on  the  coast  of  Devonshire,  at  Teignmouth 
and  Exmouth,  of  tongues  of  beach  thus  formed,  but  trending  in  different 


ACTION  OF  SEA  ON  COASTS.  83 

directions,  exposure  to  the  prevalent  breakers  being  clearly  seen  to  be 
the  cause  of  the  opposite  directions  taken  by  the  beaches.  At  Teign- 
mouth,  a  small  portion  only  of  the  beach  is  derived  from  the  rocks  on 
the  southward,  and  the  river  mouth  is  protected  from  the  southerly  and 
southwest  winds,  but  exposed  to  the  eastward  and  northeast.  Hence, 
the  beach  is  driven  to  the  southward,  and  the  river  keeps  its  channel 
open  by  escaping  against  the  hard  cliffs  of  the  Ness  Point.  The  reverse 
of  this  action  is  observed  at  Exmouth. 

We  have  various  examples  on  our  coasts  (the  Looe  Pool,  near  Hel- 
stone,  Cornwall,  and  Slapton  Pool,  in  Start's  Bay,  Devon,  are  illustrative 
instances),  where  the  river  waters  being  insufficient  to  contend  with  the 
beach-piling  action  of  the  breakers,  the  outlet  for  the  fresh  waters  is 
completely  crossed  by  beaches,  and  lakes  are  formed  behind  them,  the 
surplus  waters  percolating  through  the  shingles.  From  this  state  of 
things  to  the  escape  of  a  river,  by  passing  close  to  a  hard  cliff,  there  is 
every  modification.  In  many  localities  exposed  to  open  sea,  the  minor 
streams  will  be  found  dammed  up  by,  or  cutting  through  beaches,  accord- 
ing to  the  state  of  the  weather.  A  heavy  on-shore  gale  throws  up  a  bar 
of  beach,  which  a  flood  from  the  land  removes,  and  so  the  conditions  alter- 
nate, with  every  kind  of  modification.  The  following  (fig.  51)  is  a  sec- 
Fig.  51. 


tion  through  the  beach  and  lake  at  Slapton  Sands,  Start  Bay,  a  being 
the  sea,  which  throws  up  the  beach  5 ;  c,  the  fresh-water  lake  behind 
the  beach ;  d,  the  weathered  and  decomposed  portion  of  the  slate  rocks, 
e.  This  section  is  interesting  also  from  showing  that,  at  the  present  re- 
lative levels  of  sea  and  land  in  that  locality,  the  sea  has  not  acted  on 
the  hill  d  e,  since  the  loose  incoherent  substance  of  d  would  have  been 
readily  removed  by  the  breakers. 

The  Chesil  Bank,  on  the  coast  of  Dorsetshire,  affords  a  good  example 
of  the  driving  forwards  of  shingle  in  a  particular  direction  by  breakers, 
produced  by  the  action  of  prevalent  winds.  It  is  about  16  miles  long, 
connecting  the  island  of  Portland  with  the  main  land,  and  for  about 
eight  miles  from  that  island,  is  backed  by  a  narrow  belt  of  tidal  water, 
known  as  the  Fleet.  From  its  position,  the  heavy  swells  and  seas  from 
the  Atlantic  often  break  furiously  on  this  bank,  which  protects  land 
that  would  otherwise  soon  be  removed  by  them.  The  following  (fig.  52) 

Fig.  52. 


84 


ACTION    OF    SEA    ON    COASTS. 


is  a  section  across  the  Chesil  Bank,  a  being  the  bank ;  5,  the  water 
termed  the  Fleet ;  <?,  small  cliffs  formed  by  the  waves  of  the  Fleet,  and 
by  falls  from  the  effects  of  land-springs  ;  d,  various  rocks  of  the  oolite 
group,  protected  from  removal  by  the  Chesil  Bank,  and  e,  the  sea,  open 
to  the  Atlantic.  In  this  case,  also,  we  seem  to  have  an  example  of  the 
Atlantic  breakers  not  having  reached  the  land  behind,  since  the  relative 
levels  of  the  sea  and  land  were  such  as  we  now  find  them.  A  gradual 
sinking  of  the  coast  would  appear  to  afford  an  explanation  of  the  phe- 
nomena observed,  and  is  a  supposition  harmonizing  with  the  facts  pre- 
viously noticed  at  Slapton  Sands. 

The  general  travelling  of  shingles  on  a  coast,  much  modified  by  con- 
ditions, may  be  illustrated  by  the  following  plan  (fig.  53),  in  which  G, 


Fig.  53. 


C,  B,  A,  and  F,  represent  a  line  of  coast  exposed  to  the  prevalent 
winds  W,  W.  The  lines  of  waves  are  shown  by  dotted  lines,  made  to 
curve  inwards  behind  protecting  headlands.  In  consequence  of  the 
configuration  of  the  coast,  and  its  chief  exposure  to  the  action  of 
breakers,  the  shingle  would  tend  to  travel  from  A  to  F  on  the  one  side, 
and  from  A  to  G  on  the  other.  There  would  be  little  impediment  to 
their  course  along  the  line  A  F,  until  the  river  on  the  right  presented 
itself,  where  K  represents  the  cliff  of  hard  rock,  and  F,  the  tongue  of 
drifted  beach,  arising  from  the  conditions  previously  noticed  (p.  82). 
Between  A  and  G  the  effects  would  be  different,  particularly  if  it  be 
assumed  that  the  point  of  land  B  projects  into  deep  water.  Consider- 
ing the  river  at  D  as  small,  the  beach  would  traverse  its  mouth,  and  be 
only  removed  during  heavy  floods,  so  that  the  mass  of  shingle  would 
tend  to  travel  towards  the  point  B,  and  there  descend  and  accumulate 


ACTION  OF  SEA  ON  COASTS.  85 

in  deep  water.  Supposing  C  another  point  of  land  jutting  into  deep 
water,  it  would  only  bar  the  progress  of  the  shingle  travelling  from  M 
to  it,  a  beach  closing  the  entrance  of  the  estuary  at  E,  assumed  to  be 
shallow,  and  under  the  conditions  previously  mentioned  as  existing  at 
the  Looe  Pool  and  Slapton,  the  back  waters  being  unable  to  force  out- 
wards the  beach  accumulated  by  the  breakers. 

At  L  (fig.  53),  we  have  shown  a  marsh  accumulation  behind  the  pro- 
tecting influence  of  the  shingle  beach  F,  this  accumulation  being  a 
deposit  from  the  checked  waters  of  the  river,  by  the  action  of  the  flood- 
tide,  when  rains  had  caused  detritus  to  be  borne  down  in  mechanical 
suspension  by  the  river.  The  annexed  plan  (fig.  54)  may  aid  in  show- 
Fig.  54. 


ing  the  modification  often  observable  where  the  tongue  of  beach  is  com- 
posed of  sand,  backed  by  sand-hills ;  a  represents  a  tract  of  low  level 
land,  which  may  either  have  been  formed  by  the  filling  up  of  an  estuary 
under  existing  conditions,  or  be  the  bottom  of  an  estuary  of  a  previous 
time,  now  raised  ;  5,  6,  a  sandy  beach  and  sand-hills,  protecting  the  low 
land  from  the  ravages  of  the  sea ;  e,  e,  a  river  which  makes  good  its 
course  to  the  sea,  by  keeping  close  to  the  hard  cliff  c.  We  have  assumed 
that  a  small  stream,  such  as/,  occurs,  so  that  it  does  not  find  its  way  to 
the  main  stream,  but  loses  itself  in  pools  amid  the  sand-hills,  the  mud 
from  it  tending  to  consolidate  and  cement  the  blown  sands,  binding  them 
together,  and  hence  supporting  a  vegetation  which  would  not  otherwise 
have  found  the  conditions  for  its  growth. 

In  these  situations  there  is  often  a  severe  struggle  between  the  action 
of  the  sea  (swept  by  prevalent  winds,  w,  w,  piling  sand  upon  the  beach, 
5,  5),  assisted  by  that  of  the  wind  on  the  sand  hills,  and  the  waters  of 
the  river.  The  effect  of  such  a  little  stream  as  /  is  not  unfrequently  to 
give  much  firmness  to  the  end  of  the  beach  and  sand-hills  towards  g, 
while  the  sand  blown  over  towards  the  main  river  is  caught  up  by  it, 
and  again  carried  out  to  sea,  particularly  during  floods. 

Let  us  now  consider  sandy  beaches  and  sand-hills,  bordering  coasts 
generally.  The  sand  on  sea-shores  is  derived  from  the  rivers  bearing 


86  COAST    SAND-HILLS. 

it  down  in  mechanical  suspension,  or  forcing  it  forward  on  the  bottom 
to  the  sea ;  from  the  wearing  away  of  cliffs  of  sand  and  sandstone  by 
breakers,  or  from  the  attrition  of  the  pebbles  or  shingles  on  beaches, 
so  that  finally  they  become  mere  sand.  To  these  causes  must,  in  cer- 
tain localities,  be  added  the  trituration  of  shells  and  corals,  ejected 
from  the  sea,  and  piled  up  as  beaches,  in  some  places  by  themselves,  at 
others  variously  mingled  with  ordinary  sand. 

Regarding  the  common  occurrence  of  sea-shore  sand  of  a  certain 
average  degree  of  fineness,  it  should  be  observed,  that  as  detritus  ap- 
proaches that  size  it  becomes  more  and  more  difficult  to  reduce  it  fur- 
ther, since  it  is  then  more  and  more  easily  caught  up  in  mechanical 
suspension  by  breakers,  and  therefore  grain  cannot  so  readily  be  ground 
against  grain.  Once  removable  in  mechanical  suspension  by  the  ordi- 
nary action  of  the  waves  and  currents,  the  finer  sedimentary  matter  is 
borne  to  situations  where  it  can  be  deposited,  in  consequence  of  the 
needful  tranquillity  of  the  water,  a  tranquillity  either  arising  from 
depth,  or  shelter  from  waves  and  currents  capable  of  disturbing  the 
deposit. 

The  accumulation  of  sand-hills  can  as  readily  be  studied  on  various 
portions  of  our  own  coasts,  as  in  those  parts  of  the  world  where  the 
shores  present  little  else  than  sandy  dunes  for  hundreds  of  miles.  A 
low  line  of  coast  with  a  shallow  sea  outside,  and  presenting  a  fair  expo- 
sure to  breakers,  is  usually  sufficient  for  their  production.  The  greater 
amount  of  shore  dry  at  low  water  in  tidal  seas,  and  the  greater  the 
exposure  to  prevalent  winds,  the  larger  is  commonly  the  accumulation 
of  the  sand-hills,  other  conditions  being  equal.  The  cause  is  sufficiently 
obvious.  A  large  tract  of  sand,  exposed  between  high  and  low  water- 
mark, and  under  the  influence  of  a  strong  on-shore  wind,  is  soon  par- 
tially dried  on  its  surface,  and  the  dried  sand  is  swept  inland  beyond 
the  reach  of  the  breakers  of  the  rising  tide,  which  could  have  again 
caught  up  this  sand  in  mechanical  suspension,  and  have  distributed  it. 

It  is  desirable  that  the  observer  should  select  some  day,  when  a 
strong  on-shore  wind  blows  over  a  tract  of  sand,  and  the  drier  the  state 
of  the  atmosphere  the  better,  to  see  the  manner  in  which  the  grains  of 
sand  are  transported  inland,  and  to  mark  the  various  modifications  of 
surface  which  arise  from  the  deposit  of  the  sand  among  the  sea-weeds  or 
pebbles,  should  any  occur.  He  will  find  that,  while  some  grains  of  sand 
may  be  held  in  mechanical  suspension  by  the  wind,  at  a  height  of  an 
inch  or  so  from  the  sandy  surface  beneath,  the  friction  of  the  air  on  the 
latter  produces  such  retardation  of  the  wind  current,  that  similar  grains 
of  sand  are  merely  swept  along  the  bottom.  In  such  respects  this  per- 
fectly accords  with  the  movements  of  detritus  in  river  channels,  and 
above  noticed.  The  difference  is  merely  that  the  transporting  power  is 
air  in  the  one  case,  and  water  in  the  other.  Indeed,  this  action  is  so 


COAST    SAND-HILLS.  87 

completely  of  the  same  kind,  that  the  furrows  and  ridges  produced  by 
the  friction  of  water  currents  over  arenaceous  accumulations,  may  be 
advantageously  studied  where  wind  currents  drive  over  sand. 

To  observe  the  manner  in  which  the  sands  furrow  and  ridge,  and 
move  onwards,  a  time  should  be  chosen  when  the  wind  is  not  sufficiently 
powerful  to  hold  the  sand  in  mechanical  suspension,  but  merely  to  drive 
or  push  it  onwards.  The  ridging,  as  shown  in  the  annexed  section 
(fig.  55),  is  accomplished  by  the  driving  of  the  grains  with  sufficient 

Fig.  55. 


force  by  the  wind  acting  in  the  direction  w,  w,  merely  to  carry  onwards 
those  on  the  surface,  the  retardation  of  which  by  friction  on  those  be- 
neath so  acts  thart;  the  grains  at  b1  are  driven  on  to  the  ridge  a\  and  by 
accumulation  (the  power  of  the  wind  being  sufficient  to  cut  down  the 
ridges  to  a  kind  of  general  level  or  curve,  as  the  case  may  happen  to 
be),  fall  over  into  the  furrow  52,  and  so  on  with  the  ridges  a2  and  a3.  As 
the  friction  is  continued,  the  crests  of  the  ridges  advance,  and  their 
places  are  occupied  by  furrows,  to  be  replaced  by  ridges.  When  the 
velocity  of  the  wind  is  favourable  for  researches  of  this  kind,  an  observer 
will  best  see  the  advance  of  the  ridges,  by  placing  himself  amid  the 
moving  surface,  and  directing  his  attention  to  the  ridges  nearest  him, 
at  the  same  time  making  due  allowance  for  the  obstacles  presented  by 
his  feet,  which  will  produce  modifying  influences,  readily  appreciated. 

Arrived  at  the  margin  of  the  shore  line,  the  sands  pushed  forward  in 
the  manner  noticed,  or  caught  up  in  mechanical  suspension,  when  the 
winds  are  sufficiently  powerful,  accumulate,  forming  ranges  of  sand  hills, 
in  some  countries  characteristic  of  long  lines  of  coast.  By  their  accu- 
mulation and  tendency  to  move  inland,  in  the  direction  of  the  prevalent 
and  more  powerful  winds,  they  produce  changes  upon  the  adjoining  low 
lands,  and  even  upon  considerable  slopes  of  adjoining  hills.  The  sands 
accumulated  in  the  Bay  of  Biscay,  may  be  considered  as  affording  an 
illustrative  instance  of  this  encroachment  on  the  land,  and  the  modifi- 
cations thence  produced,  inasmuch  as  great  changes  are  known  to  have 
been  there  effected  during  the  historical  period. 

The  advance  of  these  dunes  is  described  as  irresistible,  and  at  a  rate 
of  60  and  72  feet  per  annum.  They  force  before  them  lakes  of  fresh 
water,  formed  by  the  rains,  which  cannot  find  a  passage  into  the  sea  in 
the  shape  of  streams.  Forests,  cultivated  lands,  and  houses  disappear 
beneath  them.  Many  villages  noticed  in  the  middle  ages  have  been 
covered,  and  a  few  years  since  it  was  stated,  that  in  the  department  of 
the  Landes  alone,  ten  villages  were  threatened  with  destruction.  "  One 


88  COAST    SAND-HILLS. 

of  these  villages,  named  Mimisan,  has  been,"  said  Cuvier,  "  striving  for 
20  years  against  them ;  and  one  sand-hill,  more  than  60  feet  high,  may 
be  said  to  be  seen  advancing.  In  1802,  the  lakes  invaded  five  fine  farms 
belonging  to  St.  Julien ;  they  have  since  covered  a  Roman  causeway, 
which  led  from  Bordeaux  to  Bayonne,  and  which  was  seen  about  40 
years  since,  when  the  waters  were  low.  The  Adour,  which  was  once 
known  to  flow  by  Vieux  Bouoaut,  and  to  fall  into  the  sea  at  Cape 
Breton,  is  now  turned  aside  more  than  a  thousand  toises."* 

There  are  few  extended  lines  of  coasts  which  will  not  aiford  opportu- 
nities for  the  observation  of  sand-hills,  and  their  mode  of  accumulation 
and  change,  for  strong  winds  acting  upon  even  a  comparatively  exposed 
surface,  soon  produce  a  marked  alteration  of  their  form.  Successive 
accumulations,  shown  by  the  remains  of  surface  vegetation  grown  during 
times  where  it  could  partially  establish  itself,  are  cut  away  and  heaped 
up  into  other  hillocks,  new  matter  derived  from  the  sea  being  added  to 
the  general  mass.  At  times,  the  action  of  a  strong  offshore  wind  forces 
sand  back  to  the  sea,  acting  not  only  on  the  sand-hills  over  which  it 
blows,  but  also  on  the  dry  surface  of  the  sands  bared  between  high  and 
low  tide,  or  still  more  easily  acted  upon  when  left  dry  for  a  longer  time, 
between  the  highest  lines  of  neap  and  spring  tides. 

As  the  sand  commonly  found  in  sand-hills  is  not  usually  borne  high 
in  mechanical  suspension  by  the  winds,  such  districts  will  not  long  have 
engaged  the  attention  of  an  observer,  before  he  will  notice  the  power  of 
running  water,  even  of  small  streams,  if  their  courses  be  unobstructed 
and  fairly  rapid,  to  prevent  the  extension  of  blown  sands.  The  sand 
drifted,  falling  into  the  streams,  is  borne  onwards  by  these  waters,  and 
is  thus  prevented  from  traversing  them.f  Sand-drifts  are  sometimes 
also  found  stopped  by  the  flow  of  tidal  waters  in  and  out  of  lagoons. 
Of  this  kind,  the  accumulation  of  sand  at  the  northern  side  of  a  spit  of 
land,  terminated  by  sand-hills,  near  Tramore,  on  the  eastern  coast  of 
Ireland,  may  be  considered  as  a  good  example. 

As  having  a  geological  bearing,  the  observer  would  do  well  to  direct 
his  attention  to  the  manner  in  which  the  remains  of  vegetable  and 
animal  life,  both  terrestrial  and  marine,  become  mingled  in  sand-hills. 
Portions  of  seaweeds  will  frequently  be  found  blown,  when  dry,  amid 
the  terrestrial  vegetation  of  the  sand-hills ;  and  the  shells  of  the  helices, 
which  are  often  found  in  multitudes  in  such  situations,  get  mingled  with 
marine  shells,  or  their  fragments. 

In  some  situations,  the  sand-hills  are  largely  composed  of  comminuted 

*  Cuvier,  Dis.  xur  les  Revolutions  du  Globe.  A  thousand  toises  is  about  G400  English 
feet,  or  somewhat  less  than  a  mile  and  one  quarter. 

f  Good  examples  of  this  fact  may  be  observed  on  the  coast  of  Cornwall.  The  Terran 
Sands  are  thus  bounded  for  nearly  two  miles  between  Treamble  and  Holy  Well  Bay. 
Much  land  is  stated  to  have  been  covered  by  drifts  from  the  Perran  Sands,  in  consequence 
of  a  small  stream  having  been  covered  by  mining  operations  near  Gear. 


SEDIMENT    IN    TIDELESS    SEAS.  89 

shells,  ground  to  that  state  by  the  breakers ;  and  in  such  cases,  consoli- 
dation of  parts  of  them  may  be  observable,  having  the  hardness  of  many 
sandstones.  The  carbonate  of  lime  of  the  shells  becomes  acted  upon  by 
the  carbonic  acid  in  the  rain  waters,  with  additions  from  decomposing 
vegetation,  when  plants  have  established  themselves  on  the  surface  of 
the  sand,  and  a  final  deposit  of  the  carbonate  of  lime,  thus  held  in  solu- 
tion, agglutinates  the  grains  of  sand  together.  Indurated  sands  of  this 
kind  are  sufficiently  hard,  occasionally,  to  be  employed  for  building 
purposes.* 

Distribution  and  Deposit  of  Sedimentary  Matter  in  Tideless  Seas. — 
As  tideless  seas  might  be  considered  as  mere  salt-water  lakes,  the  dis- 
tribution and  deposit  of  detritus  in  them  would,  as  a  whole,  resemble 
that  of  fresh-water  lakes,  particularly  of  those  attaining  the  magnitude 
of  the  great  North  American  lakes,  but  for  the  difference  in  the  relative 
specific  gravities  of  their  waters.  Slight  attention  on  the  part  of  an 
observer  to  the  overflow  of  rivers  swollen  by  rains,  and  charged  with 
mechanically  suspended  matter,  into  the  sea,  will  show  him  that  the 
discoloured  waters  of  the  rivers,  instead  of  falling  beneath  the  waters 
into  which  they  flow,  as  is  seen  at  the  higher  part  of  the  lake  of  Geneva, 
and  numerous  other  lakes,  proceed  seawards  on  the  surface  of  the  sea 
waters,  and  often  to  considerable  distances.  The  cause  is  simply  that, 
though  discoloured  by  the  detrital  matter  held  in  mechanical  suspen- 
sion, these  river  waters  are  still  specifically  lighter  than  the  sea  waters 
into  which  they  flow,  until,  by  being  finally  checked,  and  by  mingling 
with  the  sea  waters,  the  fine  matter  falls  from  its  mechanical  suspension 
to  the  bottom  beneath. 

The  distances  to  which  the  river  waters  sometimes  flow  seaward, 
transporting  fine  detrital  matter,  parting  with  it  gradually,  must,  when 
the  great  rivers  of  the  world  become  full  and  turbid,  be  often  very  con- 
siderable. Colonel  Sabine  has  stated,  that  at  three  hundred  miles  dis- 
tant from  the  mouth  of  the  Amazons,  discoloured  water,  supposed  to 
come  from  that  river,  was  found,  with  a  specific  gravity  of  1'0204,  float- 
ing above  the  sea  water,  of  which  the  specific  gravity  was  1-0262,  the 
depth  of  the  lighter  water  being  estimated  at  126  feet.  It  would  be  well 
that  observers  should  direct  their  attention  to  such  facts,  for  their  accu- 
mulation would  tend  much  to  show  us  the  extent  to  which  fine  sedimen- 
tary matter  may  be  thus  borne  beyond  the  action  of  tides  and  coast 

*  The  consolidated  calcareous  sand  of  New  Quay,  Cornwall,  has  been  long  used  as  a 
building  stone ;  not  only  is  the  neighbouring  church  of  Crantoch  built  of  this  modern 
sandstone,  but  very  ancient  stone  coffins  have  also  been  discovered,  composed  of  the 
same  consolidated  sand,  in  the  adjoining  churchyard.  The  grains  are  so  firmly  ce- 
mented in  this  New  Quay  sandstone,  that  where  it  graduates  into  a  kind  of  conglome- 
rate, pebbles  of  quartz  and  hard  sandstone  are  generally  broken  through  by  a  blow  on 
the  compound  rocks. 


90  DISTRIBUTION    AND    DEPOSIT    OF 

currents.*  As  much  matter  may  be  thus  distributed  in  chemical  solu- 
tion, valuable  information  might  also  be  collected  as  to  •  the  kind  and 
quantity  of  substances  so  held  in  solution. 

From  the  varied  depths  near  its  shores,  the  Mediterranean  affords  us 
a  good  example  of  the  deposits  effected  in  seas  which  are  commonly 
termed  tideless.  The  great  rivers  which  discharge  themselves  into  it, 
such  as  the  Nile,  Po,  and  Rhone,  now  transport  little  sedimentary  mat- 
ter that  is  not  finely  comminuted,  and  of  easy  mechanical  suspension. 
The  Nile,  which  has  been  estimated  to  deliver  a  body  of  water  annually 
into  the  Mediterranean  about  250  times  that  which  flows  out  of  the 
Thames,  beginning  to  rise  in  June,  attaining  its  maximum  height  in 
August,  and  then  falling  until  the  next  May,  must  thrust  forward,  from 
its  periodical  rise  and  fall,  fine  sedimentary  matter  with  great  regularity, 
tending  thus  to  produce  consecutive  layers  or  beds  of  mud  and  clay  of 
considerable  uniform  thickness  and  character,  in  those  situations  where 
modifying  conditions  do  not  interfere.  Part  of  the  fine  matter  brought 
down  from  the  interior  in  mechanical  suspension  is  deposited  on  the 
lower  grounds  traversed  by  the  Nile ;  and  it  has  been  calculated  that 
the  surface  of  Upper  Egypt  has,  in  this  manner,  been  raised  more  than 
six  feet  since  the  commencement  of  the  Christian  era.  The  fine  matter 
not  so  deposited,  passing  with  the  river  waters  seaward,  is  necessarily 
borne  furthest  outwards  when  the  greatest  force  of  the  river  water  pre- 
vails, namely,  in  August  of  each  year. 

The  matter  thus  borne  seaward  may  be  kept  more  or  less  time  me- 
chanically suspended,  according  to  the  agitation  of  the  surface  by  winds, 
but,  as  a  whole,  there  must  be  an  average  area  over  which  it  is  thrown 
down  ;  the  greatest  distance  of  the  deposit  from  the  mouths  of  the  Nile 
being  attained  in  August,  though  the  greatest  thickness  of  a  year's  de- 
posit will  be  nearer  the  land.  As  the  river  mouths  advance,  these 
sheets  of  fine  sediment  would  be  expected  to  extend  further  seaward, 
overlapping  each  other. 

Where  the  surface  of  the  sea  cuts-  the  slightly  inclined  plane  of  sedi- 
mentary matter,  partly  in  the  sea,  and  partly  on  the  land,  the  breakers 
separate  the  finer  from  the  coarser  substances,  keeping  the  former  easily 
in  mechanical  suspension,  and  removing  them  from  the  shore  outwards. 
The  result  is,  an  arenaceous  boundary,  with  banks  so  formed,  as  to 
include  lagoons,  such  as  are  seen  in  the  accompanying  sketch  of  the 
delta  of  the  Nile  (fig.  56),  at  Lakes  Mareotis,  Bourlos,  and  Menzaleh. 

*  Very  little  practice  would  enable  those  who  may  have  opportunities  of  making 
such  observations  to  ascertain  the  amount  of  matter  mechanically  suspended  in  waters 
of  this  kind.  If  the  scales  be  not  very  delicate,  by  pouring  a  large  volume  of  the  water 
through  a  filter,  previously  weighed,  such  an  approximation  to  the  truth  may  be  ob- 
tained as  to  be  useful.  As  previously  observed  (p.  59),  mere  evaporation  of  the  water 
would  give  not  only  the  matter  in  mechanical  suspension,  but  that  also  in  chemical 
solution. 


SEDIMENT    IN    TIDELESS    SEAS.  91 

These  lakes  gradually  fill  up,  the  shore  advances,  and  so,  even  sup- 
posing the  same  relative  level  of  sea  and  land  not  to  be  altered  through 
a  long  succession  of  ages,  the  bed  of  the  Mediterranean  becomes  more 
shallow  in  that  region,  and  a  mass  of  matter,  such,  for  the  most  part, 
as  would  eventually  form  clay,  is  accumulated ;  the  upper  portion  sandy, 
from  the  action  of  the  breakers  upon  the  level  of  the  sea,  and  from  the 
sifting  action,  so  to  speak,  of  the  waves  further  seaward,  at  depths 
where  that  influence  could  be  felt. 

Fig.  56. 


From  the  periodical  character  of  the  rise  of  water  in  the  Nile,  the 
equivalent  periodical  deposits  might  even  be  marked  by  bands  or  layers 
extending  to  distances  bearing  a  relation  to  the  amount  of  transporting 
power  of  the  river  waters,  so  that  coarser  particles  could  be  carried  fur- 
ther and  over  more  extended  areas  at  one  time  than  at  another.  The 
general  deposit,  however,  gradually  advancing  seaward,  successive  annual 
accumulations  would,  as  a  whole,  overlap  each  other. 

When  we  regard  the  Po  and  Rhone,  we  have  not  the  same  very 
marked  periodical  rise  of  their  waters ;  though  no  doubt,  taken  as  a 
whole,  there  may  annually  be  times  when  more  matter  is  borne  outward 
than  at  others.  With  the  exception  of  the  regularity  of  effects  likely 
to  be  produced  by  the  rise  and  fall  of  their  waters,  the  accumulations 
formed  by  deposits  from  the  detrital  matter  borne  seaward  by  the  Po 
and  Rhone  would,  however,  be  similar  to  those  of  the  Nile  ;*  the  same 

*  As  respects  the  Po,  M.  Prony  considered  himself  authorized  to  conclude,  from  the 
examination  of  a  large  amount  of  evidence,  "First,  that  at  some  ancient  period,  the 
precise  date  of  which  cannot  now  be  ascertained,  the  waves  of  the  Adriatic  washed  the 
shores  of  Adria.  Secondly,  that  in  the  twelfth  century,  before  a  passage  had  been 
opened  for  the  Po  at  Ficarrolo,  on  its  left  or  northern  bank,  the  shore  had  already 


92  DISTRIBUTION    AND    DEPOSIT    OF 

discharge  of  fresh  waters  holding  matter  in  mechanical  suspension  over 
the  surface  of  the  sea,  the  same  sifting  of  the  detritus  so  borne  sea- 
ward, where  the  action  of  the  waves  can  reach  it,  and  the  same  general 
order  of  accumulations.*  As  the  general  mass  of  matter  advanced, 
there  would  be  mud  or  clay  formed  at  the  greatest  distance  from  the 
land,  over  which  the  sands,  separated  from  the  finer  or  mud-forming 
particles  in  the  shallow  water  and  along  shore,  would  gradually  be 
spread,  mingled  here  and  there  with  a  patch  of  clay,  or  silt  clay,  depo- 
sited in  the  lagoons,  behind  lines  of  beach  thrown  up  by  the  breakers. 

These  rivers  are  merely  mentioned  as  marked  examples.  An  inspec- 
tion of  a  good  chart  of  the  Mediterranean  will  show  that  there  are 
many  others,  the  floods  in  which  only  bear  mud  and  sands  into  it,  the 
heavier  detritus  not  reaching  the  shore,  the  fall  of  the  river  beds,  and 
the  force  of  their  waters,  being  insufficient.  In  all  such  cases,  the  ac- 
cumulations would  be  mud  or  clay  for  a  base,  with  an  arenaceous  top, 
so  far  as  the  causes  we  have  noticed  could  prevail.  It  will  be  obvious, 
that  clay  may  be  accumulating  in  the  depths  seaward,  while  sands  are 
advancing  from  the  shore  towards  them,  so  that  if,  at  any  future  geolo- 
gical period,  the  whole  became  uplifted  above  the  level  of  the  sea,  we 
might  have  a  sheet  of  arenaceous  matter  covering  another  of  clay,  the 
parts  of  each,  though  continuous,  formed  at  different  times,  and  portions 
of  the  clay  equivalent  to  parts  of  the  sand.  There  would  be  zones,  so 
to  speak,  of  arenaceous  matter  corresponding  with  the  advance  of  the 
coast,  and  not  separated  from  the  common  sheet  of  that  of  which  it 
forms  a  part,  being  formed  at  the  same  time  with  a  layer  of  clay,  which 
a  prolongation  of  the  sandy  coating  would  cover  at  a  subsequent  period. 

The  same  sea  fortunately  furnishes  numerous  examples  of  short  rivers, 
with  rapid  falls  of  their  beds,  and  occasional  abundant  supplies  of  water, 
thrusting  pebbles  into  it.  The  effects  produced  are  the  same  as  when 
torrents  discharge  themselves  into  lakes,  with  the  difference  that  the 
muddy  part  of  waters  flow  over  the  surface  of  the  sea,  the  sand  separa- 
ting from  it.  According  to  the  depth  of  water,  and  this  is  some- 
times considerable,  is  the  sand  accumulated ;  if  fairly  deep,  the  sand 
falls  not  far  distant  from  the  coast,  while  the  pebbles  accumulate  on  the 

been  removed  to  the  distance  of  9000  or  10,000  metres  (5J  to  6  miles)  from  Adria. 
Thirdly,  that  the  extremities  of  the  promontories  formed  by  the  two  principal  branches 
of  the  Po,  before  the  excavation  of  the  Taglio  di  Porto  Viro,  had  extended  by  the 
year  1600,  or  in  400  years,  to  a  medium  distance  of  18,600  metres  (about  1H  miles) 
beyond  Adria;  giving  from  the  year  1200  an  average  yearly  increase  of  the  alluvial 
land  of  25  metres  (82  feet).  Fourthly,  that  the  extreme  point  of  the  present  single  pro- 
montory, formed  by  the  alluvions  of  the  existing  branches,  is  advanced  to  between 
32,000  to  33,000  metres  (about  19J  to  20J  miles)  beyond  Adria;  whence  the  average 
yearly  progress  is  about  70  metres  (229£  feet)  during  the  last  200  years,  being  a 
greatly  more  rapid  proportion  than  in  former  times." — Cuvier,  Dis  sur  les  Kev.  du  Globe. 
*  It  should  be  remarked  that  there  are  also  calcareous  accumulations  at  the  mouth 
of  the  Rhone. 


SEDIMENT    IN    TIDELESS    SEAS.  93 

shore,  and  the  embouchure  of  the  river  is  extended.  Though  the  gene- 
ral bed  of  shingles  (the  upper  part  acted  upon  by  the  breakers,  as  upon 
airy  other  shingle  beach)  would  advance  as  a  whole,  with  an  even  upper 
surface,  the  accumulation  of  gravel  or  shingles  would  be  formed  by  many 
irregular  protrusions  produced  by  changes  in  the  direction  of  the  river's 
mouth.  The  depth  being  favourable,  we  should  expect,  under  such  con- 
ditions, an  accumulation  of  the  following  kind  (fig.  57),  a  a  being  a  sec- 
Fig.  57. 


tion  of  the  land,  formed  of  beds  of  rock  (represented  as  dipping  inland, 
merely  to  separate  them  clearly  from  the  other  deposits),  b  the  bed  of 
the  river,  bearing  down  pebbles,  sand,  and  mud  into  the  sea,  the  level  of 
which  is  shown  by  the  horizontal  line  e  ;  d  exhibits  the  first  accumula- 
tion of  pebbles  thrown  over  the  steep  shore,  the  pebbles  falling  to  the 
bottom,  and  the  sand  only  being  deposited  in  a  regular  layer,  more  out- 
wards ;  c  the  continuation  of  the  sandy  layer  seaward  ;  ff  the  mud  de- 
posited beyond  the  sand,  and  continued  also  ;  g  the  extension  of  the 
pebbles  over  the  sand,  at  some  given  time.  In  such  an  accumulation 
we  should  expect,  after  both  sand  and  gravel  had  overspread  the  clay,  a 
lower  deposit  of  clay,  above  this  another  of  sand,  and  over  the  sand, 
gravel ;  parts  of  the  gravel,  sand,  and  clay,  notwithstanding  the  exten- 
sion of  each  layer  continuously  in  the  manner  stated,  being  equivalent 
to  each  other  in  age,  for  the  reasons  before  assigned. 

Where  depths  were  less  considerable,  we  should  expect  an  intermix- 
ture of  the  gravel  and  sand  in  a  more  regular  manner,  and  with  an  ar- 
rangement depending  on  the  action  of  the  breakers  upon  them  ;  this 
action  tending  to  pile  back  the  shingles,  as  a  whole,  while  it  permitted 
the  sandy  sediment  to  be  caught  up  in  mechanical  suspension,  and  thus 
it  might  be  carried  outwards  by  the  river  waters,  in  places  where  the 
stream  of  these  waters  could  be  felt.  As  previously  observed,  the  finer 
and  mechanically  suspended  particles  would  be  borne  over  the  surface  of 
the  sea,  according  to  the  volume  and  velocity  of  the  outpouring  river 
waters,  eventually  forming  a  layer  of  mud  or  clay  where  deposited.  It 
will  be  obvious,  that  as  the  volume  and  velocity  of  the  river  waters 
varied,  so  would  be  their  power  to  carry  outwards,  beyond  the  influence 
of  the  breakers,  mechanically  suspended  matter  of  different  volume  and 
weight,  and  hence  that,  within  a  certain  range,  there  might  be  mixed 
layers  of  sand,  silt,  or  mud,  according  to  circumstances. 

Not  only  do  the  rivers  thus  contribute  matter,  borne  down  by  them 
to  the  shores,  to  be  there  arranged  by  the  breakers,  or  thrust  out  into 
the  sea  and  deposited  in  it,  but  every  river  also  bears  down  some  matter 


94  DISTRIBUTION    AND    DEPOSIT    OF 

in  chemical  solution,  to  be  added  to  the  solutions  present  in  the  seas.  In 
tideless  seas,  each  river  sends  down  its  solutions  into  water  which  may, 
to  a  great  extent  be  considered  stagnant,  so  that  at  the  embouchures  of 
the  rivers  the  substances  so  borne  down  prevail  within  distances  to  which 
the  river  waters  may  act.  In  many  localities  around  the  Mediterranean, 
the  river  waters  transport  large  quantities  of  bicarbonate  of  lime  in 
solution.  While  we  may  consider  that  much  of  this  substance  is  con- 
sumed by  fish,  crustaceans,  and  molluscs,  for  their  harder  parts,  there 
is  probably  a  large  surplus  which  eventually  takes  the  form  of  calcareous 
accumulations  beneath  the  sea.  The  rivers  which  transport  bicarbonate 
of  lime  abundantly  would,  when  in  flood,  probably  also  carry  forward 
sedimentary  matter,  so  that  at  the  mouths  of  such  rivers  we  might  have 
alternate  times,  variable  probably  in  duration,  when  the  rivers  were  clear 
and  carried  forward,  as  compared  with  the  volume  of  water,  a  large  pro- 
portion of  bicarbonate  of  lime,  and  when  this  substance  bore  a  far  less 
proportion  to  the  volume  of  water,  while  fine  detritus  was  abundant. 
Under  such  conditions  we  should  have  alternately  layers  of  mud  and  cal- 
careous matter,  or  mud  more  calcareous  at  one  time  than  at  another,  so 
that  eventually  the  calcareous  matter  might  tend  to  separate  into  no- 
dules, and  in  lines  corresponding  to  the  times  when  it  was  most  abun- 
dantly thrown  out  of  the  rivers.  In  like  manner  we  might  have  sulphate 
of  lime,  commonly  enough  in  solution  in  some  rivers,  mingled  with  the 
mud,  and  eventually  crystallizing  out  as  selenite,  a  mineral  so  frequently 
discovered  in  various  clay  beds.  Many  other  combinations  of  different 
substances,  some  in  solution,  others  mechanically  suspended,  and  borne 
down  by  the  same  rivers,  will  readily  present  themselves  to  the  mind  of 
the  observer,  and  suggest  attention  to  the  conditions  under  which  both 
are  carried  out  into  tideless  seas. 

When  considering  deposits  in  tideless  seas,  we  must  not  forget  those 
resulting  from  the  fall  of  ashes  and  lapilli,  thrown  out  from  volcanoes. 
The  Mediterranean  may  fortunately  be  considered  with  reference  to  this 
kind  of  accumulation  also,  as  there  are  volcanoes  in  action  in  it,  and  on 
its  shores.  The  great  eruption  in  79,  which  not  only  overwhelmed  Her- 
culaneum  with  lava,  but  showered  ashes  in  such  profusion  upon  Pompeii 
as  to  bury  that  town,  could  not  fail  to  have  thrown  a  large  amount  of 
ashes  and  lapilli  into  the  sea;  and  considering  the  distances  to  which 
ashes  are  known  to  have  travelled  from  volcanic  vents,  the  ashes  at  least 
may  have  been  widely  spread.  It  will  be  obvious  that  whatever  kinds 
of  sedimentary  accumulations  they  subsided  upon  through  the  sea,  the 
ashes  would  mingle  with  them,  coating  over  such  deposits  where  tran- 
quillity reigned,  either  from  the  depth  of  water  or  other  causes,  with  a 
layer  of  ash.  Where  the  action  of  waves  on  the  bottom,  or  of  breakers 
on  the  coasts,  could  be  felt,  in  whatever  tranquil  state  the  ashes  may 
have  fallen  originally  to  the  bottom,  they  would  be  mixed  up  with  the 


SEDIMENT    IN    TIDELESS    SEAS.  95 

mud,  sand,  or  pebbles,  as  the  case  might  be,  when  thus  acted  upon,  so 
that  the  particles  of  the  ash  would  be  disseminated  among  them.  All 
rivers  upon  which  the  ashes  fell  would  probably  bear  much  of  them  out- 
wards in  mechanical  suspension,  for  the  fine  matter  which  can  be  up- 
borne and  be  carried  by  the  winds  to  great  distances  would  not  readily 
subside  through  the  river  waters. 

Under  this  view,  the  deeper  parts  of  the  Mediterranean,  and  especially 
those  to  which  other  sedimentary  matter  could  not  be  carried  by  the 
movement  of  sea  currents,  or  the  drift  of  river  waters  outwards,  would 
be  those  where  the  layers  of  ash  would  be  most  unmixed  with  other  mat- 
ter, excepting  as  regards  the  deposit  of  any  substances  from  chemical 
solution  in  the  sea,  and  to  which  its  great  tranquillity  may  be  favourable. 
We  do  not  know  the  depths  at  which  calcareous  accumulations  may  now 
be  forming  in  the  Mediterranean,  but  whether  in  shallow  or  deep  situa- 
tions, any  ashes  falling  upon  them  would  either  accumulate  in  layers,  or 
be  mingled  up  with  limestone,  according  to  the  rapidity  with  which  the 
one  may  subside,  or  the  calcareous  matter  be  deposited. 

Not  only  are  there  volcanoes  on  the  borders  of  this  sea,  of  the  magni- 
tude of  Etna  and  Vesuvius,  throwing  out  ashes  and  lapilli,  but  we  have 
had  evidence  in  our  times,  so  lately  as  1831,  of  the  uprise  of  a  volcano 
through  the  sea,*  between  Pantellaria  and  the  coast  of  Sicily,  and  from 
deep  water. f  Columns  of  black  matter  are  described  as  being  thrown 
out  of  the  crater,  to  the  height  of  three  or  four  thousand  feet,  spread- 
ing out  widely  even  to  windward.  The  upper  part,  above  the  sea  at 
least,  seemed  to  have  been  solely  composed  of  ashes,  cinders,  and  frag- 
ments of  stone,  commonly  small.  Among  these,  fragments  of  limestone 
and  dolomite,  with  one  several  pounds  in  weight,  of  sandstone,  were  ob- 
served, appearing  to  show  that  the  volcanic  forces  had  broken  them  off 
beds  of  these  kinds  of  rock,  when  the  igneous  matter  had  been  propelled 
through  them. 

An  island  so  constituted,  could  not  long  resist  the  destructive  action 
of  the  breakers,  and  thus,  as  soon  as  the  supply  of  ashes,  cinders,  and 
fragments  of  rock  ceased,  it  was  cut  away  by  them,  and  reduced  to  a 
shoal.  During  the  time  that  this  volcanic  mass  was  accumulating,  a 
large  amount  of  ashes  and  cinders  must  have  been  mingled  with  the 
adjacent  sea  before  it  reached  its  surface,  and  no  slight  amount  would 

*  To  the  island  thus  formed  the  various  names  of  Sciacca,  Julia,  Hotham,  Graham, 
and  Corrao  were  given.  Dr.  Davy,  who  visited  this  volcanic  island  on  the  5th  August, 
1831,  has  given  a  detailed  account  of  it  in  the  Phil.  Trans,  for  1832.  M.  C.  Prevost 
was  charged  by  the  Academy  of  Sciences  of  Paris  to  visit  and  report  upon  it.  He 
reached  the  island  on  the  28th  September  of  the  same  year.  It  was  then  about  2300 
feet  in  circumference,  with  two  elevations,  from  100  to  200  feet  high,  on  different  sides 
of  the  crater,  the  latter  filled  with  boiling  water. 

f  Captain  Smyth  proved  (Phil.  Trans.  1832)  that  the  volcano  did  not  rise  from  the 
Adventure  Bank,  as  was  first  supposed,  but  to  the  westward  of  it,  and  from  deep  water. 


96  DISTRIBUTION    AND    DEPOSIT    OF 

be  distributed  around,  when  ashes  and  cinders  could  be  vomited  into  the 
air.  Add  to  this  the  quantity  caught  up  in  mechanical  suspension  by 
the  breakers,  and  there  would  be  no  small  amount  to  be  accumulated 
over  any  deposits  forming,  or  formed  on  the  bottom  around  this  locality, 
and  out  of  the  reach  of  any  lava  currents  which  might  have  flowed 
beneath  the  level  of  the  sea.  The  breakers,  while  they  removed  the 
lighter  substances,  would,  as  it  were,  so  sift  the  whole  that  the  heavier 
fragments  would  gradually  subside  to  lower  levels,  and  eventually  be- 
neath the  action  of  seas  breaking  above,  or  simply  moving  the  bottom 
during  very  heavy  weather.  Finally,  there  would  be  a  collection  of 
fragments,  cemented  by  ash  and  cinders,  in  which  there  would  not  only 
be  pieces  of  igneous  rocks,  but  of  limestone,  dolomite,  and  sandstone 
also,  for  we  are  not  to  suppose  that  the  pieces  found  accidentally  on  the 
surface  were  those  alone  thrown  out  of  the  crater. 

Thus,  then,  in  the  Mediterranean  a  very  complicated  series  of  con- 
temporaneous accumulations  is  now  in  progress,  its  uneven  bottom* 
being  variably  covered,  according  to  conditions,  by  the  matter  brought 
into  it  either  in  solution  or  mechanical  suspension  by  rivers ;  eroded 
from  its  shores  by  the  action  of  the  breakers,  or  ejected  by  volcanoes,  the 
whole,  excepting  lava  currents  or  large  sudden  accumulations  of  ashes 
and  cinders,  more  or  less  mingled  with  the  remains  of  organic  life,  these 
remains  themselves  sometimes  sufficient  to  form  long-continued  layers 
or  beds. 

Though,  for  convenience,  the  Mediterranean  has  been  treated  as  a 
tideless  sea  and  without  motion,  this  is  not  strictly  correct,  inasmuch  as 
small  tides  are  felt  in  it,  and  currents  are  found.  Indeed,  as  respects 
the  latter,  when  powerful  winds  by  their  friction  force  the  surface 
waters  in  some  given  direction  for  the  time,  well  seen  when  driven 
against  any  part  of  the  boundary  coasts,f  the  movement  is  then  suf- 
ficient to  carry  any  substances  mechanically  suspended,  to  distances 

*  In  considering  the  deposits  now  taking  place  in  this  sea,  we  should  bear  in  mind 
that  it  is  divided  into  two  chief  basins  (see  Captain  Smyth's  charts)  by  a  winding  shoal, 
the  Skerki,  connecting  Sicily  with  the  coast  of  Africa.  The  run  of  soundings  upon  this 
shoal,  proceeding  from  the  African  to  the  Sicilian  coast,  gives  34,  48,  60,  38,  74,  20,  70, 
62,  91,  16,  16,  32,  7,  32,  48,  34,  64,  70,  72,  38,65,  and  13  fathoms,  whence  its  inequali- 
ties may  be  seen.  There  are  soundings  in  140,  157,  and  260  fathoms  on  either  side, 
and  places  where  bottom  has  not  been  reached  with  190  and  230  fathoms  of  line. 

f  An  observer  may  often  have  opportunities  in  the  ports  of  the  Mediterranean  of 
seeing  the  rise  or  depression,  as  the  case  may  be,  of  the  sea,  according  as  the  winds  at 
the  time  may  be  blowing  with  strength  off  or  on  shore.  Canals  frequently  afford  good 
opportunities  of  observing  this  kind  of  action  of  wind  on  water ;  for  the  canal  levels, 
in  still  weather,  being  accurately  known,  it  becomes  easy  to  see  how  much  these  waters 
are  raised  or  depressed  as  the  winds  may  press  them  in  one  direction  or  another.  Mr. 
Smeaton  found  that  in  a  canal,  four  miles  in  length,  the  water  was  kept  up  four  inches 
higher  at  one  end  than  at  the  other,  by  the  action  of  the  wind  along  the  canal.  The 
Caspian  Sea  is  several  feet  higher,  at  either  end,  according  as  a  strong  northerly  or 
southerly  wind  may  prevail. 


SEDIMENT    IN    TIDELESS    SEAS.  97 

proportionate  to  the  power  and  continuance  of  the  winds.  When  these 
waters  again  come  to  a  state  of  repose,  the  return  action  will  be  similar. 
There  are  also  currents  in  the  Mediterranean,  such  as  that  out  of  the 
Black  Sea  into  it  through  the  Sea  of  Marmora,  and  the  current  at  the 
Straits  of  Gibraltar,  which  sets  in  from  the  Atlantic,*  the  latter  modi- 
fied, however,  by  the  tides  as  respects  the  African  and  European  shores 
of  the  Straits. f  The  current  from  the  Atlantic  is  described  as  setting 
eastward  into  the  Mediterranean  at  the  rate  of  about  11  miles  in  24 
hours,  passing  along  the  African  shore,  and  being  felt  at  Tripoli  and 
the  island  of  Galitta.J  An  eastern  current  flows  between  Egypt  and 
Candia,  and  at  Alexandria.  Arrived  at  the  coast  of  Syria  it  turns 
northwards,  and  then  advances  between  Cyprus  and  the  coast  of  Kara- 
mania.  Such  currents  would  necessarily  aid  in  transporting  matter 
both  in  solution  and  mechanical  suspension,  the  last-mentioned  current 
especially  acting  on  that  brought  down  by  the  Nile. 

From  the  lower  specific  gravity  of  the  water  in  the  Black  Sea  (p.  45), 
the  fine  detritus,  borne  into  it  by  the  waters  of  the  Don,  Dnieper,  Dnie- 
ster, and  Danube,  would  be  carried  less  distances,  comparatively,  over 
the  saline  waters  than  those  of  the  Nile,  Po,  and  Rhone  over  the  Me- 
diterranean, while  from  the  same  cause,  supposing  an  equal  force  of  wind 
to  act  upon  both  seas,  any  continued  suspension  of  that  matter  which 
might  be  due  to  the  agitation  of  waves,  would  be  greater  in  the  Black 
Sea  than  in  the  Mediterranean,  the  waters  of  the  former  offering  less 
resistance  to  the  wind  from  their  inferior  specific  gravity.  §  In  the 
Baltic  the  specific  gravity  is  still  less  (p.  45),  and  therefore  the  deposit 
of  detritus  borne  down  the  rivers  discharging  themselves  into  it,  would 

*  Both  these  currents  have  been  attributed  to  the  evaporation  of  the  surface  waters 
of  the  Mediterranean,  that  sea  not  receiving  a  sufficient  equivalent  from  the  discharge 
of  rivers  into  it,  or  the  fall  of  rain  upon  it,  so  that  the  Black  Sea  furnishes  waters  on 
the  one  side  and  the  Atlantic  on  the  other,  in  order  to  keep  it  at  the  height  required. 

f  "On  the  European  side,  west  of  the  island  of  Tarifa,  it  is  high  water  at  llh,  but 
the  stream  without  continues  to  run  2h.  On  the  opposite  shore  of  Africa,  it  is  high 
water  at  10h,  and  the  stream  without  continues  to  run  until  lh ;  after  which  periods  it 
changes  neither  side,  and  runs  eastward  with  the  general  current.  Near  the  shore  are 
many  changes,  counter  currents,  and  whirlpools,  caused  by  and  varying  with  the  winds. 
Near  Malaga  the  stream  runs  along  shore  about  eight  hours  each  way.  The  flood  sets 
to  the  westward." — Purdy,  Atlantic  Memoir.  The  tide  rises  three  feet  at  Malaga. 

J  An  under  and  counter  current  has  been  considered  to  set  westward,  but  of  late  this 
has  been  doubted.  However  this  may  be,  Admiral  Beaufort  has  shown,  while  noting 
the  current  which  flows  westward  from  Syria  to  the  Archipelago,  that  "counter  currents 
or  those  which  return  beneath  the  surface  of  the  water,  are  also  very  remarkable.  In 
some  parts  of  the  Archipelago  they  are  sometimes  so  strong  as  to  prevent  the  steering 
of  the  ship;  and  in  one  instance,  on  sinking  the  lead,  when  the  sea  was  calm  and  clear, 
with  shreds  of  bunting  of  various  colours  attached  at  every  yard  of  the  line,  they 
pointed  in  different  directions  all  around  the  compass." — Beaufort's  Karamania. 

$  From  the  relative  small  amount  of  salt  contained  in  the  Black  Sea  waters,  the 
shallower  parts  are  sometimes  frozen.  The  Sea  of  Azof,  into  which  the  Don  discharges 
itself,  is  represented  to  be  frozen  over  during  three  or  four  months  of  the  year. 

7 


98  DISTRIBUTION    AND    DEPOSIT    OF 

still  further  approximate  towards  that  observable  in  fresh-water  lakes. 
Like  most  lakes,  also,  the  Black  and  Baltic  seas  have  outflowing  cur- 
rents,* so  that  the  evaporation  on  their  surface  is  not  equal  to  the  fresh 
water  discharged  into  them.f 

Supposing  no  counter  and  constant  currents  bringing  in  salt  water 
from  the  Mediterranean  to  the  Black  Sea,  and  from  the  German  Ocean 
to  the  Baltic,  and  that  the  discharged  waters  from  both  seas,  carry  off 
the  average  saline  waters  of  each,  these  seas  would  gradually  become 
less  saline  in  proportion  to  the  different  amount  of  salts  in  solution  car- 
ried out  to  the  adjoining  seas,  and  those  brought  in  by  the  rivers  dis- 
charged into  them.J  Upon  this  view,  therefore,  both  the  Baltic  and 
Black  Seas  may  at  previous  periods  have  been  more  saline  than  at 
present.  Considering,  as  geological  evidence  would  lead  us  to  infer, 
that  the  area  now  covered  by  the  Caspian  and  that  occupied  by  the 
Black  Sea,  were  once  beneath  a  common  sea,  changes  in  geological  time 
having  separated  them  as  now  found :  in  the  Caspian  we  should  have 
evaporation  sufficient  to  overpower  the  influence  of  the  fresh  water 
poured  in  by  the  Volga,  Ural,  and  the  minor  rivers,  while  in  the  Black 
Sea  the  supply  of  fresh  water  is  beyond  the  evaporation.  Hence  the 
Caspian  remains  a  salt  lake,  while  the  Black  Sea  may  be  gradually  be- 
coming more  and  more  a  fresh-water  lake,  the  Caspian  not  only  retain- 
ing its  original  saline  contents,  but  becoming  more  saline  if  either  the 
salts  brought  down  by  the  rivers  are  beyond  any  deposit  which  may  dis- 
pose of  them,  or  the  evaporation  be  greater  than  the  supply  of  water 
from  the  Volga,  Ural,  or  laik,  and  minor  streams.§  Upon  such  an  hy- 
pothesis, though  at  first  the  deposits  in  each  would  be  under  the  same 
conditions,  these  would  gradually  change  as  regards  effects  arising  from 

*  The  velocity  of  the  current,  in  the  narrowest  part  of  the  Sound  (Baltic),  is 
about  three  miles  per  hour ;  but  the  ordinary  general  rate,  in  fine  weather,  is  about  a 
mile  and  a  half  or  two  miles.  The  current  flowing  from  the  Black  Sea  runs  commonly, 
in  the  Thracian  Bosphorus,  from  three  to  five  miles  per  hour,  according  to  the  direction 
and  force  of  the  winds. 

f  Strong  opposing  winds  force  back  the  current  out  of  the  Baltic,  and,  if  sufficiently 
long  continued,  will  raise  the  level  of  that  sea. 

J  In  equal  weights  (3  Ibs.)  of  water  taken  from  the  East  Friesland  coast,  and  from 
Rostock  in  the  Baltic,  the  following  proportional  differences  in  saline  contents  were 
found : — 

German  Ocean.  Baltic. 

Chloride  of  sodium,         .        .        .       522  263 

Muriate  of  magnesia,     .        .        .       198-5  111 

Sulphate  of  lime,  ....        23  12 

Sulphate  of  soda,  ....  1-3  1 

Residue, 1-5  1 

\  There  is  considered  to  be  good  evidence  of  the  Caspian  having  stood  at  higher 
levels  than  at  present,  those  more  corresponding  with  the  actual  level  of  the  Black  Sea, 
beneath  which  the  surface  of  the  Caspian  is  now  81-4  feet. 


SEDIMENT    IN    THE    GULF    OF    MEXICO.  99 

the  increasing  difference  in  the  specific  gravities  of  the  respective 
waters.* 

Although  ice  may  form  in  the  shallow  bays  of  the  Black  Sea,  and 
the  branch  known  as  the  Sea  of  Azof  be  often  frozen  over  in  the  winter 
months,  so  that  ice,  floating  away  from  the  coasts,  may  be  the  means 
of  conveying  fragments  of  rock  and  pebbles  into  situations  to  which  they 
would  not  be  otherwise  transported,  the  ice  in  the  Baltic,  from  the 
geographical  position  of  that  sea,  is  a  means  of  adding  to  deposits  in  it 
of  a  more  important  kind.  According  to  particularly  severe  seasons, 
are  the  more  marked  instances  of  extensive  sheets  of  ice  over  parts  of 
this  sea,  and  cases  are  recorded  where  great  distances  could  be,  and 
were,  traversed  by  travellers  under  extraordinary  conditions.  Large 
areas  are  commonly  frozen  for  nearly  three  months  in  the  year,  the  ice 
on  the  south  commonly  breaking  up  in  April,  while  in  the  gulfs  of 
Bothnia  and  Finland  it  may  continue  until  the  middle  of  May.  Though 
the  Baltic  may  be,  as  regards  the  ordinary  acceptation  of  the  term, 
tideless,  it  is  nevertheless  liable  to  those  local  changes  of  level  which 
are  due  to  the  pressure  of  powerful  winds  blowing  for  a  time  from  par- 
ticular points,  and  it  is  described  as  often  vexed  by  such  winds.  Ice, 
therefore,  around  the  shores  of  its  numerous  islets  and  uneven  coasts, 
may  often  be  broken  up,  particularly  towards  the  warmer  weather,  with 
shingles  from  the  shore,  and  fallen  fragments  from  the  cliffs  in  and 
upon  it,  and  be  transported  seaward,  the  shingles  and  pieces  of  rock 
being  there  deposited,  and  thus  adding  gravels  and  distributed  angular 
fragments  to  and  among  the  more  common  accumulations  formed  in  this 
sea,  the  depth  of  which  varies  from  shallows,  backed  by  marshes,  to  two 
localities  on  the  southeast  where  the  line  gives  respectively  110  and 
115  fathoms.f 

The  Gulf  of  Mexico,  its  waters  forced  up  by  the  pressure  acting  from 
the  Atlantic,  through  the  Caribbean  Sea,  may,  for  geological  purposes, 
be  considered  as  a  tideless  sea,  with,  among  others,  a  great  river,  the 
Mississippi,  delivering  matter  in  solution  and  mechanically  suspended 
into  it.  The  great  movement  of  water  coming  round  the  Cape  of  Good 
Hope  from  the  Indian  Ocean,  and  considered  as  a  constant  current 
produced  by  the  trade  winds,  assisted  by  the  motion  of  the  earth,  sets 
from  the  Ethiopic  Sea,  united  with  an  equatorial  current  of  the 
Atlantic,  across  that  ocean,  against  the  West  Indian  Islands.  This 
pressure  forces  a  constant  stream  of  water  into  the  Mexican  Gulf,  by 
the  western  side  of  the  Yucatan  Channel,  with  commonly  a  reflow  close 

*  A  peculiar  bitter  taste  observable  in  the  Caspian  waters  is  attributed  to  the  presence 
of  naphtha,  which  abounds  in  some  localities  on  its  shores.  The  basin  of  the  Caspian 
appears  of  very  unequal  depth,  this  varying  from  the  steep  coast  extending  from  the 
Balkan  Bay  to  that  of  Mertroi'  Kultyuk— off  which  a  line  of  450  fathoms  Joes  not  reach 
the  bottom  in  some  places — to  long-continued,  very  shallow  shores  in  others. 

f  The  general  depth  has  been  estimated  at  GO  fathoms. 


100 


DISTRIBUTION    AND    DEPOSIT    OF 


to  Cape  Antonio,  at  the  west  extremity  of  Cuba.     Thus  pressed  up, 
the  waters  escape  between  Cuba  and  the  Florida  reefs  in  the  current 


Fig.  59. 


SEDIMENT  IN  TIDAL  SEAS.  101 

known  as  the  Gulf  Stream  ;*  so  that  the  waters  in  the  Gulf  of  Mexico 
form  a  kind  of  comparatively  tideless  sea,  in  which  deposits  are  effected 
much  as  in  the  Mediterranean.  Though  other  rivers  throw  detritus 
into  this  area,  collectively  of  much  importance,  the  Mississippi  is  that, 
by  its  additions  to  the  land,  and  by  the  discharge  of  matter  mechanically 
suspended  in  its  waters,  which  is  the  most  important.  On  the  opposite 
page  is  a  plan  (fig.  59)  of  the  very  characteristic  advance  of  deposits 
from  this  river  into  the  waters  of  the  gulf. 

The  manner  in  which  the  main  channel  is  bounded  by  lines  of  bank, 
rising  above  the  sea,  towards  its  final  outlet,  well  marks  the  retardation 
produced  by  the  friction  of  the  banks  as  they  arise.  The  various  lakes, 
with  the  cross  channels,  are  also  highly  illustrative  of  this  order  of 
accumulation. 

As  might  be  anticipated,  when  the  fall  of  the  Mississippi,  during  its 
greatest  floods,  is  estimated  at  only  one  inch  and  a  half  in  a  mile 
between  New  Orleans  and  the  sea,  a  distance  of  about  100  miles ; 
while,  when  its  waters  are  low,  the  fall  is  scarcely  perceptible  for  the 
same  distance ;  little  mineral  matter  can  be  carried  seaward,  in  mecha- 
nical suspension,  beyond  that  which,  when  deposited,  would  form  mud 
or  clay.  This  great  river,  therefore,  now  throws  little  other  mineral 
matter  into  the  Gulf  of  Mexico  than  the  component  parts  of  mud  and 
clay,  that  which  rises  by  accumulation  above  the  surface  of  the  sea 
being  liable  to  be  sifted  by  the  shore  waves,  the  finest  being,  to  a 
certain  extent,  separated  at  the  sea  level.  A  vast  mass  of  this  fine 
sediment  must  have  been  thrown  down,  and  is  now  accumulating  in  the 
Mexican  Sea  ;  the  chief  addition  to  this  mass  of  mud  or  clay,  indepen- 
dently of  the  hard  remains  of  fish,  crustaceans,  and  molluscs,  being 
wood,  the  transport  of  which  down  the  Mississippi  and  its  tributaries  is 
most  abundant.  Not  only  is  this  wood  arrested  in  its  progress  in 
various  places,  or  entangled  among  the  channels  of  the  delta,  but  much 
of  it  passes  out  seaward.  Millions  of  logs  and  trunks  of  trees  are 
transported  several  miles  outwards  during  floods,  so  that  it  becomes 
difficult  to  navigate  among  them.f  . 

Distribution  and  Deposit  of  Sedimentary  Matter  in  Tidal  Seas. — 
Upon  the  coasts  of  the  continents  and  of  islands  amid  the  ocean  waters, 
not  only  is  there  a  rise  and  fall  of  the  sea-level  twice  in  each  day,  but  the 
river  waters  discharged  into  the  ocean  are,  for  the  most  part,  ponded 
back  by  each  rise  of  the  tide,  to  be  let  loose  at  its  fall  with  so  much  of 

*  The  breadth,  length,  and  velocity  of  this  long-celebrated  current  would  appear  to 
vary.  Winds  often  affect  it,  diminishing  its  breadth  and  augmenting  its  velocity,  or 
augmenting  its  breadth  and  diminishing  its  velocity.  In  mid-channel,  on  the  meridian 
of  the  Havanna,  under  ordinary  circumstances,  it  has  a  velocity  of  about  two  miles 
and  a  half  per  hour.  Off  the  most  southern  parts  of  Florida,  and  at  about  one-third 
over  from  the.  Florida  reefs,  it  runs  at  the  rate  of  about  four  miles  per  hour. 

f  Captain  Basil  Hall,  Travels  in  North  America,  vol.  iii. 


102  DISTRIBUTION    AND    DEPOSIT    OF 

the  sea  water  as  had  been  forced  up  the  river  channels  during  the  flood 
tide.  Here  we  have  a  very  material  modification  of  the  discharge  of 
matter,  either  in  solution  or  mechanically  suspended  in  the  rivers,  as 
compared  with  its  delivery  into  tideless  seas  by  the  same  means. 
According  to  the  varied  character  of  the  rivers  where  they  discharge 
themselves  into  tidal  seas ;  as  regards  the  greater  or  less  amount  of 
water  in  them  at  different  times  ;  the  kind  of  coast  at  their  embouchures  ; 
depth  of  water,  exposure  to  prevalent  winds,  and  other  conditions ;  so, 
no  doubt,  is  the  delivery  of  these  waters  modified ;  but  in  all  they  are 
exposed  to  checks  from  the  rise  of  tide  at  their  mouths.  The  opposition 
of  the  sea  to  the  rivers  at  the  height  of  the  tide  necessarily  varies  with 
the  change  from  neap  to  spring  tides ;  the  amount  of  check  which  the 
sea  gives  to  the  outflow  of  the  fresh  water,  thus  alternating,  on  the 
minor  scale ;  though,  as  a  whole,  a  very  constant  effect  is  produced,  the 
greatest  resistance  being  offered  at  the  heights  of  equinoctial  spring 
tides. 

From  the  check  thus  given  to  the  discharge  of  waters  containing 
matter  in  mechanical  suspension,  or  pushed  forward  by  rivers  in  their 
channels,  there  is  a  tendency  to  form  accumulations  across  the  course 
of  rivers,  commonly  known  as  bars.  These,  the  observer  will  find  to 
occur  variably,  ^accor  ding  as  the  real  mouth  of  the  river  maybe  high  up 
a  deep  branch  of  the  sea  (or,  in  other  words,  where  the  sea  level  may 
cut  high  up  a  valley  or  depression,  which  thus  becomes  partly  sub-aerial, 
partly  sub-marine),  or  be  situated  on  the  general  unbroken  line  of  a 
coast,  even,  perhaps,  protruding  beyond  it,  into  shallow  water.  He 
will  soon  perceive  that,  according  to  such  conditions,  the  breakers  be- 
come important  aids  in  the  accumulation  of  bars ;  having  little  influence 
high  up  an  arm  of  the  sea,  particularly  where  the  channel  is  narrow, 
but  assisting  most  materially  in  their  formation  when  aoiing  upon  an 
exposed  coast,  more  especially  if  the  mouths  of  the  rivers  be  open  to 
strong  and  prevalent  winds.  This  combination  of  checks  given  to 
waters  pushing  forward  and  carrying  detrital  matter  in  mechanical  sus- 
pension, and  of  breakers  striving  to  thrust  back  again  that  matter  which 
may  escape  seaward,  produces  bars  at  the  mouths  of  many  rivers,  alike 
important  as  regards  the  subject  under  consideration,  and  the  intercourse 
of  nations. 

The  effects  of  tidal  action  in,  for  the  time,  arresting  the  outflow  of 
rivers,  will  much  depend  upon  the  heights  which  the  tides,  on  the  ave- 
rage, attain ;  and  an  observer  will  readily  perceive  that,  according  to 
the  obstacles  opposed  to  the  tidal  wave,  and  the  form  of  the  shores 
against  which  it  moves,  will  be  the  change  of  sea  level  between  high  and 
low  -water.  In  the  open  ocean,  where  the  tidal  wave  meets  with,  com- 
paratively, little  opposition,  we  find  the  difference  of  the  sea  level  at 
high  and  low  water  far  less  than  among  funnel-shaped  channels,  and 


SEDIMENT    IN    TIDAL    SEAS.  103 

other  favourable  combinations  of  coast.  Thus,  while  among  the  small 
detached  islands  of  the  Pacific  Ocean  the,  tides  rise  and  fall  about  2  feet, 
and  in  the  Atlantic  from  3  feet  at  St.  Helena,  and  4  to  6  feet  at  the 
Cape  de  Verde  Islands,  to  8  or  9  feet  at  Madeira,  the  equinoctial  spring- 
tides in  the  Bay  of  Fundy  rise  from  60  to  70  feet.* 

An  observer  need  not  travel  from  the  shores  of  the  British  Islands  to 
study  the  dependence  of  the  rise  and  fall  of  tide  upon  local  conditions : 
many  situations  will  afford  him  the  requisite  opportunities.  The  Bristol 
Channel,  since  it  fairly  faces  the  tidal  wave  coming  from  the  Atlantic, 
may  be  taken  as  a  good  example  of  a  considerable  rise  of  tide  produced 
by  the  narrowing  of  an  arm  of  the  sea.  Though  strictly  not  an  un- 
modified ocean  tide,  since  the  wave  has  to  pass  over  nearly  300  miles  of 
soundings,  within  the  edge  of  the  100  fathoms  line,  before  it  strikes  the 
Land's  End,  the  change  from  the  rise  of  18  or  20  feet  at  St.  Ives, 
Cornwall,  to  that  of  46  to  50  feet  at  King  Road  (Bristol)  and  Chepstow, 
is  striking ;  more  particularly  as  the  tides  of  30  feet  at  Lundy  Island, 
and  36  feet  at  Minehead,  show  this  rise  to  be  gradual.  From  the  in- 
creasing elevation  of  channel,  and  friction,  beyond  Chepstow  and  King 
Road,  and  the  withdrawing  of  the  tidal  pressure  from  behind  when  the 
ebb  begins  seaward,  the  height  of  tide  soon  decreases  up  the  Severn. 
The  tidal  waters,  however,  so  suddenly  check  the  discharge  of  the  river 
waters,  that  the  latter  are  as  suddenly  forced  back,  the  flood-tide  rush- 
ing forwards  in  a  great  wave,  commonly  termed  the  lore,  and  causing 
an  instant  rise  of  several  feet  in  the  lower  part  of  the  river,  gradually 
fining  off  to  the  termination  of  all  tidal  action  in  the  Severn,  f 

The  following  plan  (fig.  60)  will  illustrate  the  example  here  given. 
At  a  the  tidal  wave  begins  to  be  higher  than  in  the  open  sea.  At  b  its 
elevation  is  increased  from  the  decrease  of  the  depth  and  breadth  of 
the  channel ;  and  at  c,  from  similar  causes,  the  height  of  tide  is  still 
greater.  We  may  assume,  for  illustration,  that  at  d  the  tidal  wave  be- 

*  A  glance  at  the  map/wrill  show  how  favourably  this  bay  is  situated  for  receiving 
a  body  of  flood  tide  driven  up  between  Cape  Cod  (Massachusetts),  and  Cape  Sable 
(Nova  Scotia),  and  forced  onwards  into  Chignecto  and  Mines  Bay.  Though  there  is  a 
very  considerable  bay  between  Gaspe"  Bay  (Canada)  and  the  North  Point  (Breton  Island), 
on  the  north  of  the  narrow  isthmus  separating  Nova  Scotia  from  New  Brunswick, 
neither  its  form,  nor  the  set  of  tide  into  it,  causes  a  rise  of  water  beyond  about  eight 
feet.  There  is,  therefore,  from  local  causes,  a  difference  of  high  water,  on  either  side  of 
this  narrow  isthmus,  of  about  fifty  or  sixty  feet. 

f  The  same  sudden  rush  of  the  flood,  overpowering  the  ebb  in  tidal  rivers,  is  observed 
in  many  other  localities.  The  bore-wave  up  the  Ganges  is  described  as  so  rapid,  that  it 
scarcely  takes  four  hours  passing  up  a  distance  of  nearly  seventy  miles,  sometimes 
causing  an  instantaneous  rise  of  five  feet  of  tide  at  Calcutta,  and  the  boats  on  the  shore 
on  which  it  breaks  taking  to  the  middle  of  the  river  for  safety  on  its  approach.  A  con- 
siderable bore-wave  is  stated  to  be  observed  at  the  mouth  of  the  Maranon,  or  Amazons, 
during  the  equinoxes.  The  chief  wave  is  from  twelve  to  fifteen  feet  high,  followed  by 
three  or  four  others.  Its  advance  is  very  rapid,  and  its  course  is  stated  to  be  heard  at 
the  distance  of  two  leagues. 


104  DISTRIBUTION    AND    DEPOSIT    OF 

comes  most  elevated,  and  that  afterwards,  towards  e,  from  the  absence 
of  propelling  power  behind,  from  the  actual  fall  of  water  on  the  ebb 
towards  <?,  5,  and  a,  and  from  the  general  rise  of  the  channel,  the  tidal 


wave  becomes  less  and  less  felt,  until  at  /,  its  effect  entirely  ceases. 
The  lore  will  depend  upon  local  causes ;  but  under  the  conditions  no- 
ticed, the  sudden  check  of  the  outflowing  river,  and  corresponding 
sudden  rise  from  the  inflowing  flood  tide,  are  not  unfrequent,  though 
the  bore  may  not  always  be  sufficiently  important  to  arrest  attention. 

The  English  Channel  affords  us  another  good  example  of  a  conside- 
rable rise  of  tide  produced  by  local  obstacles,  and  the  more  instructive, 
as  this  rise  does  not  extend  across  to  the  opposite  coast,  as  is  the  case 
in  the  Bristol  Channel.  On  the  French  side,  the  land  of  the  Cotentin, 
terminating  with  Cape  La  Hogue,  and  the  islands  of  Alderney,  Guern- 
sey, and  Jersey,  with  the  multitude  of  isles,  islets,  and  rocks,  in  the 
Bay  of  St.  Malo,  oppose  a  direct  obstacle  to  the  progress  of  the  tidal 
wave  coming  from  the  Atlantic,  while  the  English  coast  presents  no 
such  obstacle.  In  consequence,  the  sea  level  at  high  water  is  raised 
higher  on  the  one  side  than  on  the  other ;  and  while  the  tides  only  rise 
13  feet  at  Lyme  Regis,  7  feet  in  Portland  Road,  15  feet  at  Cowes,  and 
18  feet  at  Beachy  Head,  the  difference  of  high  and  low  water  is  45  feet 
between  Jersey  and  St.  Malo,  and  35  feet  at  Guernsey. 

Not  only  are  there  these  differences  in  the  rise  of  tide  from  local 
causes,  but  the  relative  direction  of  the  flood  and  ebb,  with  their  conse- 
quent currents,  also  vary  materially  in  some  situations.  Thus,  at  the 
Land's  End  the  flood  tide  runs  9  hours  to  the  north,  and  the  ebb  3  hours 
to  the  south ;  and  numerous  other  modifications  of  the  same  kind,  where 
the  times  of  flood  and  ebb  are  different,  are  to  be  found  on  the  coasts  of 
the  British  Islands. 

As  regards  the  distribution  of  detritus  by  tidal  streams,  the  direction 
of  the  latter  will  not  only  be  found  to  change  considerably  during  the 
progress  of  the  flood  or  ebb,  as  the  case  may  be,  off  many  parts  of  coasts, 
but  the  ebb  very  frequently  commences  on  shore,  while  a  flood  tide  is 
continued  in  the  offing.* 

*  It  has  been  held  that  "the  length  of  time  between  the  changes  of  tide  on  shore 


SEDIMENT  IN  TIDAL  SEAS.  105 

As  so  much,  not  due  to  the  friction  of  tidal  streams  on  coasts  has 
been  attributed  to  it,  instead  of  to  the  action  of  breakers — a  destructive 
action  more  particularly  felt  when  strong  on-shore  winds  and  high  tides 
are  combined — it  would  be  well  for  an  observer  to  study  the  velocity 
and  transporting  power  of  tidal  waters  on  the  sea-shore.  Those  who 
dwell  on,  or  visit,  the  coasts  of  the  British  Islands,  where,  fortunately, 
so  many  modifications  in  tidal  streams  may  be  more  or  less  easily  stu- 
died, will  soon  learn  properly  to  estimate  the  value  of  tidal  friction  on 
land. 

With  respect  to  the  tides  around  the  British  Islands,  those  flowing 
amid  the  Orkney  and  Shetland  Islands,  and  through  the  Pentland  Frith, 
between  the  mainland  of  Scotland  and  the  former,  would  appear  to  be 
among  the  strongest.  They  vary  considerably  in  force,  according  as 
they  are  neap  or  spring  tides.  While  in  Stronsa  Frith  and  North  Ro- 
naldsha  Frith  the  former  only  run  at  the  rate  of  1J  mile  in  the  hour, 
the  latter  make  a  stream  of  5  miles  an  hour.  In  the  Pentland  Frith, 
the  spring  tides  are  stated  to  have  a  velocity  of  9  nautic  miles  an  hour, 
while  at  neap  tides  they  do  not  exceed  3  miles.* 

Round  the  more  prominent  headlands,  the  tides,  as  we  might  expect, 
run  with  greater  velocity  than  in  the  bays  on  each  side  of  which  they 
project,  or  in  the  offing  outside.  The  tidal  wave  striking  the  headlands, 
and  rising  locally  from  this  opposition,  escapes  round  to  the  next  bay, 
thus  causing  an  accelerated  stream  of  tide  for  a  short  distance.  The 
friction  of  the  water  on  the  land  is,  however,  commonly  sufficient  very 
materially  to  diminish  the  strength  of  the  stream  in  immediate  contact 
with  it ;  so  that,  in  calm  weather,  when  the  force  of  the  tide  is  neither 
impeded  nor  accelerated  by  the  force  of  opposing  or  favouring  winds, 
chaff  or  other  light  bodies  thrown  into  the  sea  will  be  seen  to  pass  in  a 
comparatively  slow  course  along  shore,  while  a  strong  stream  of  tide  is 
running  outside. 

How  little  friction  takes  place  in  such  situations  may  often  be  well 
seen  by  the  presence  of  a  coating  of  barnacles,  or  of  sea-weeds,  even 
upon  steep  headlands,  though  exposed  to  the  action  of  breakers,  these 
being,  off  such  deep-water  headlands,  commonly  unaided  in  their  action 
by  sand  or  gravel  in  mechanical  suspension.  It  is  desirable  that  the 
observer  should  carefully  watch  the  shores  of  any  district  he  may  be 
examining,  with  respect  to  tidal  friction,  during  calm  weather,  and  from 

and  the  stream  in  the  offing  is  in  proportion  to  the  strength  of  the  current  and  the  dis- 
tance from  land ;  that  is,  the  stronger  the  current,  and  the  greater  distance  that  current 
is  from  the  land,  the  longer  it  will  run  after  the  change  on  the  shore." — Purdy,  Atlantic 
Memoir.  182y. 

*  The  flood  tide  there  comes  from  the  northwest,  and  is  not  of  unusual  strength  until 
it  meets  with  the  obstacles  of  these  islands  and  the  mainland.  The  change  of  tide 
sooner  on  shore  than  at  a  distance  from  it,  varies  according  to  situation,  amounting  in 
some  places  to  two  or  three  hours. 


106 


DISTRIBUTION    AND    DEPOSIT    OF 


neap  to  spring  tides.  Except  in  the  most  exposed  situations,  he  may 
perceive  how  rarely  even  grains  of  sand,  much  less  small  loose  shingle, 
can  be  moved  by  any  stream  of  tide  in  contact  with  the  coast. 

The  retarding  effect  of  friction  on  the  headlands  is  often  well  exhi- 
bited near  the  strong  streams  of  tide  off  them,  known  as  races,  so  dan- 
gerous, frequently,  when  opposed  to  powerful  winds.  Though  the  tides 
run  in  such  situations  with  the  greatest  force  of  the  locality,  and  the 
waters  are  thrown  about  in  various  directions,  it  often  happens  that, 
between  the  race  and  the  headland,  there  is  more  quiet  water,  sufficiently 
broad  for  the  passage  of  a  boat  in  moderate  weather. 

Tidal  waters  rush  with  great  force  through  channels  formed  between 
the  horns  of  great  bays  and  islands  at  a  short  distance  from  them  ;  such 
is  the  case  with  the  horns  of  Cardigan  Bay  and  of  St.  Bride's  Bay  on 
the  south  of  it,  as  shown  in  the  following  plan  (fig.  61),  where  a  repre- 

Fig.  61. 


sents  Cardigan  Bay,  and  b  St.  Bride's  Bay.  Foul  rocky  ground  extends 
from  the  Smalls  Light  /,  to  Skomer  Island,  c ;  between  which  and  the 
mainland  there  is  an  exceedingly  strong  tide  sweeping  close  to  the  cliffs. 
Supposing  this  to  be  a  flood  tide,  its  force  is  diminished  and  almost  lost 
in  St.  Bride's  Bay,  b.  This  bay  receives  the  flood-tide,  not  only  through 


SEDIMENT    IN    TIDAL    SEAS.  107 

this  channel,  but  also  directly  from  the  Atlantic ;  its  flow  over  the  foul 
ground  between  the  Smalls  Light  and  Grasholm,  and  thence  to  Skomer, 
being  marked  by  broken  water.  Part  of  the  tide  driven  into  St.  Bride's 
Bay  escapes  with  much  force  between  the  mainland  and  Ramsay  Island, 
and  round  the  latter  and  the  rocks  and  islets  known  as  the  Bishop  and 
his  Clerks,  d,  into  Cardigan  Bay.  The  latter  also  receives  an  abundant 
supply  of  the  tidal  wave  direct  from  the  Atlantic ;  and  the  flood  passes 
with  great  strength  between  its  northern  horn  and  Bardsey  Island,  e. 

In  the  three  chief  channels  noticed,  no  doubt  little  comparatively  fine 
sedimentary  matter  could  rest  in  the  run  of  such  tides,  and  any  that 
might  be  thrown  down  by  the  eddies  of  one  tide  would  probably  be  re- 
moved by  the  reverse  action  of  the  other ;  but  these  effects  would  be 
very  local.  That  hard  rocks  readily  resist  such  friction  is  well  shown 
in  the  localities  mentioned,  barnacles  and  sea-weeds  being  commonly 
discovered  on  the  sides  of  the  channels  at  low  water. 

It  will  be  at  once  perceived  that  the  flood  tide  passing  up  rivers  would 
act  very  differently,  according  as  the  channels  were  continued  deep  out- 
wards, or  crossed  by  bars  accumulated  at  their  mouths.  In  the  former 
case,  the  sea  waters  being  specifically  heavier  than  the  river  waters,  as 
it  were,  wedge  up  the  latter,  discharging  outwards,  until  the  levels  have 
been  so  changed  that  the  whole  body  of  tidal  water  is  driven  inland, 
forcing  and  ponding  back  the  fresh  water.*  In  the  more  favourable 
situations  of  this  kind,  therefore,  where  great  floods  are  running  down 
a  river,  the  heavier  waters  of  the  first  of  the  flood  tide  may  be  passing 
up  the  river  while  the  lighter  waters  above  are  running  outwards.  In 
bar  rivers  the  sea  waters  pour  over  the  bars,  and,  if  the  channels  be 
afterwards  shallow,  drive  the  river  waters  at  once  before  them,  while,  if 
behind  the  bar  there  be  water  of  much  greater  depth,  as  sometimes 
happens,  the  heavier  sea  waters  first  flow  into  the  basin  and  raise  the 
waters  in  it,  so  that  when  sufficiently  elevated  with  the  increasing  tide, 
the  whole  passes  up  the  river  with  the  flood  tide,  forcing  back  the  fresh 
water. 

Between  the  action  of  the  tide  in  such  rivers  as  the  St.  Lawrence,  f 
with  its  open  estuary  or  arm  of  the  sea,  and  the  Ganges  and  Quorra, 

*  The  passage  of  the  river  waters  outwards  during  freshets,  from  heavy  rains  in  the 
interior,  while  the  flood  tide  waters  are  flowing  beneath  in  a  contrary  direction,  may 
occasionally  be  seen  well  shown  when  large  vessels  are  at  anchor  in  an  estuary,  as, 
for  instance,  in  the  Hamoaze,  Plymouth,  and  they  ride  with  their  heads  to  the  flood  tide, 
being  sufficiently  deep  in  the  water  to  be  influenced  by  it,  while  small  boats,  secured 
alongside,  ride  with  their  heads  in  the  contrary  direction,  the  outflow  of  the  higher  and 
fresh  water  alone  acting  upon  them. 

•j-  The  St.  Lawrence  affords  a  good  example  of  the  greater  velocity  of  an  ebb  over  a 
flood  tide  in  an  estuary.  Where  the  ebb  from  the  Saguenay  unites  with  that  of  the 
St.  Lawrence,  it  passes  outwards  with  considerable  strength,  and  is  stated  to  run  seven 
nautical  miles  per  hour  between  Apple  and  Basque  Isles.  While  the  ebb  is  thus  strong, 
the  stream  of  flood  tide  is  scarcely  perceptible. 


108  DISTRIBUTION    AND    DEPOSIT    OF 

the  deltas  of  which  protrude  into  the  ocean,  the  one  in  the  Bengal  Sea 
and  the  other  in  the  Gulf  of  Guinea,  every  modification  will  be  found 
in  the  tidal  rivers  of  the  world.  While  checked  by  the  flood  tide,  the 
waters  of  estuaries  will  deposit  the  matter  they  may  hold  in  mechanical 
suspension  as  the  time  will  permit,  and  according  as  the  estuary  waters 
may  or  may  not  be  agitated  by  the  friction  of  the  winds. 

Slight  observation  is  sufficient  to  show  that  highly-discoloured  water 
is  commonly  found  in  estuaries,  and  that  this  is  borne  upwards  and 
downwards  by  the  tides,  escaping  seawards  during  the  ebb  in  some  es- 
tuaries in  one  direction,  while  the  rivers  add  detrital  matter  to  these 
bodies  of  water  in  others.  In  estuaries  like  the  Severn,  at  the  head  of 
the  Bristol  Channel,  the  muddy  water  is  carried  backwards  and  forwards 
with  such  rapidity  that  it  is  only  in  the  sheltered  nooks  and  situations 
that  it  can  find  rest  ^  sufficient  to  deposit  the  fine  sediment,  including 
among  them  the  shores  where  retardation  by  friction  also  produces,  a 
sufficient  state  of  repose  during  the  tides.* 

Many  minor  estuaries  round  the  coasts  of  the  British  Islands  show  the 
filling  up  not  only  of  the  sheltered  places  on  their  sides,  but  also  of  their 
upper  parts,  where  detrital  matter  is  gradually  accumulated.  If  the 
course  of  the  river  has  not  been  long  through  a  level  country,  the  deposits 
at  the  heads  of  estuaries  may  even  be  gravelly,  while  mud  only  is  accu- 
mulated in  the  sheltered  localities.  If  the  annexed  plan  (fig.  62)  repre- 

Fig.  62. 


sent  one  of  these  estuaries,  then  it  will  usually  be  observed  that  the  ac- 
cumulation at  the  head  c  is  more  gravelly  or  sandy,  particularly  in  its 
lowest  parts,  than  in  the  sheltered  situations,  a  and  b.  At  c  we  have 
not  only  the  heavier  matter  thrown  down  by  the  check  of  the  tide  there 
felt,  but  also  all  the  detritus  which  can  be  pushed  along  the  bottom  by  the 
river  d,  during  the  ebb  of  the  tidal  waters  introduced,  and  during  the 
common  discharge  of  the  river  water  when  the  tide  has  fallen,  a  com- 
bined time  in  some  localities  equal  to  nine  and  ten  hours  in  each  twelve. 

*  The  difference  of  the  friction  on  the  sides  of  these  estuaries,  where  mud  is  depo- 
sited, and  more  outwards  in  the  stream  of  tide,  is  commonly  well  shown  by  the  sandy 
bottom  under  the  latter,  the  friction  of  the  water  being  too  great  to  permit  finer  sedi- 
ment to  remain  in  such  situations. 


SEDIMENT    IN    TIDAL    SEAS. 


109 


At  a  and  fr  the  fine  sediment  is  commonly  accumulated  to  the  level  of 
the  highest  ordinary  spring  tides. 

In  estuaries  of  this  class  we  should  anticipate  that  there  would  be 
much  gain  of  land  where  the  discharging  rivers  entered  them,  and,  ac- 
cordingly, in  such  situations  we  often  find  extensive  marshes  and  flats, 
which  would  justify  this  expectation,  even  if  historical  evidence  could 
not  be  adduced.  Of  such  evidence,  however,  there  is  commonly  no  want, 
and  the  heads  of  many  estuaries  around  the  British  Islands,  and  along 
the  ocean  coasts  of  Europe,  are  known  to  have  become  more  shallow 
and  even  to  have  moved  further  outwards,  dry  land  supplying  the  place 
of  marshes  and  mud  banks,  within  historical  times.* 

The  mouth  of  the  Ganges,  extending  across  a  distance  of  about  two 
hundred  miles  (fig.  63),  furnishes  us  with  the  discharge  of  detrital  mat- 
Fig.  63. 


ter  into  a  tidal  sea  of  a  different  character.  Here  the  abundance  of  the 
outflowing  waters,  particularly  during  floods,  is  sufficient  to  carry  out 
a  delta,  more  resembling  those  observed  in  tideless  seas.  In  times  long 
since  passed,  the  Ganges  may  have  discharged  itself  into  an  estuary,  as 
far  northerly  as  the  commencement  of  its  delta,  now  more  than  two 
hundred  miles  from  the  sea,  and  into  the  same  estuary  the  Brahmaputra 
may  have  delivered  its  waters,  these  two  great  drains  of  land  extending 
to  the  Himalaya  Mountains  having  gradually  filled  up  such  an  estuary, 
by  depositing  the  matter  transported  mechanically  in,  or  swept  onwards 
by  them.  Coarse  gravel  is  not  forced  forward  by  the  Ganges  within 
four  hundred  miles  of  its  mouth,  so  that  the  sedimentary  matter  dis- 
charged into  the  sea  is  of  a  finer  character.  To  this  discharge,  both  by 
friction  on  the  bottom  and  in  mechanical  suspension,  checks  are  offered 

*  These  changes  produced,  independently  of  sea  banks  raised  to  keep  out  the  tides. 


110  DISTRIBUTION    AND    DEPOSIT    OF 

by  the  tides  ;  but  the  body  of  fresh  water  is  so  considerable,  as  compared 
with  such  checks,  that  the  sedimentary  deposits  rapidly  gain  upon  the 
sea,  notwithstanding  that  the  general  depth  beyond  the  mouths  of  the 
Ganges  is  by  no  means  inconsiderable.  Innumerable  changes  in  the 
direction  of  the  various  streams  into  which  the  delta  is  divided  are  pro- 
duced inland.*  The  course  of  this  river  is  described  as  affording  good 
examples,  on  the  great  scale,  of  the  alterations  of  channel,  from  the  ac- 
cumulation of  banks  upon  small  obstacles,  to  be  equally  well  studied, 
as  regards  general  principles,  in  hundreds  of  little  streams.  Thus  a  tree 
arrested  in  its  course  will  produce  an  accumulation,  gradually  rising  into 
an  island,  to  be  again  swept  away  by  another  change  of  channel. 

The  great  body  of  fresh  water  discharged  by  the  Ganges  in  floods 
seems,  to  a  great  extent,  to  overpower  the  influence  of  the  tidal  wave, 
so  that  detrital  matter  then  becomes  accumulated  more  in  the  manner  of 
the  Nile,  Rhone,  Volga,  and  other  great  rivers,  discharging  themselves 
into  tideless  seas.f  At  the  junction  of  the  Ganges  and  Brahmaputra, 
below  Luckipoor,  there  is  a  large  gulf  in  which  the  water  is  scarcely 
brackish,  and  during  the  rainy  season  the  sea  is  stated  to  be  overflowed 
by  fresh  water  for  many  leagues  outwards. 

In  the  Quorra  we  have  an  example  of  a  similar  kind,  and  a  vast  body 
of  fresh  water  thrusts  out  a  delta  into  the  ocean.  The  great  stream  of 
water  is  checked,  not  overcome,  in  mid  channel,  though  felt  between  30 
and  40  miles  up  the  river.  In  this  river,  and  in  many  other  tropical 
rivers,  mangrove-trees  add  materially  to  the  power  of  forming  new  land.  J 
Wherever  sufficient  shelter  can  be  obtained,  they  establish  themselves 
in  abundance  ;  their  stilt-like  roots  entangling  any  floating  substances 
washed  near  them ;  producing  a  repose  fit  for  the  deposit  of  the  finest 
sediment,  and  affording  shelter  to  an  abundance  of  reptiles,  fish,  crusta- 
ceans, and  molluscs,  which  seek  and  enjoy  the  protection  they  afford. 

*  Major  Rennel  states  that  during  the  eleven  years  he  remained  in  India,  the  head  of 
the  Jellinghy  river  was  gradually  removed  three-quarters  of  a  mile  further  down.  He 
observes  also,  that  "  there  are  not  wanting  instances  of  a  total  change  of  course  in  some 
of  the  Bengal  rivers.  The  Cosa  (equal  to  the  Rhine)  once  ran  by  Purneah  and  joined 
the  Ganges  opposite  Rajenal.  Its  junction  is  now  nearly  forty-five  miles  further  up. 
Gour,  the  ancient  capital  of  Bengal,  once  stood  on  the  Ganges." — Phil.  Trans.  1781. 

f  The  amount  of  detrital  matter  borne  outwards  by  the  Ganges  has  been  estimated  at 
about  2J  per  cent.,  and  the  average  discharge  of  water  at  500,000  cubic  feet  per  second. 
— (Gleanings  of  Science,  vol.  iii.  Calcutta,  1831.)  If  we  take  the  quantity  at  2  per  cent., 
and  consider  the  transported  matter  to  give  15  cubic  feet  to  the  ton,  we  should  obtain 
57,600,000  tons  per  day,  equal  to  a  mass  of  ordinary  granite,  having  a  base  of  1,000,000 
square  feet,  rising  to  the  height  of  864  feet. 

J  Alluvial  land, is  described  as  forming  into  flat  islands,  covered  by  mangrove-trees 
and  papyrus.  These  are  sometimes  so  acted  upon  by  floods  as  to  be  partially  or  wholly 
swept  into  the  ocean.  Professor  Smith  noticed  a  floating  mass,  probably  washed  out 
of  the  Congo,  about  120  feet  long,  consisting  of  reeds  resembling  the  Donax  and  a  spe- 
cies of  Agrostis,  among  which  branches  of  Jnstida  were  still  growing,  further  north  off 
the  coast  of  Africa. — Tuckfy's  Expedition  to  the  Zaire,  or  Congo. 


SEDIMENT    IN    TIDAL    SEAS.  Ill 

When  we  regard  the  sea-shores  of  the  world  exposed  to  tides,  we  see 
a  great  destructive  power  in  the  breakers,  as  a  whole  in  ceaseless  action, 
grinding  back  and  levelling  off  the  land,  and  throwing  a  mass  of  matter 
into  the  tides  sweeping  round  such  shores,  which  mass,  added  to  that 
thrust  out  of  the  rivers,  has  to  be  distributed  by  the  streams  of  tide  and 
such  ocean  currents  as  can  receive  any  portion  of  it.  Great  rivers,  as 
we  have  seen,  may  transport  matter  in  mechanical  suspension  far  out- 
wards, particularly  when  swollen  by  floods,  and  thus  place  it  within  the 
distributing  influence  of  the  ocean  currents.  Through  these  it  may  take 
a  long  time  to  descend  into  the  quiet  depths  where  it  can  find  a  rest  that 
will  continue  undisturbed  until,  perhaps,  after  a  long  lapse  of  geological 
time,  this  deposit  may  be  upraised,  and  again  placed  within  the  destruc- 
tive influences  of  the  atmosphere  and  surface  waters. 

When  detrital  matter  is  thrown  into  the  tides,  it  is  borne  to  and  fro  by 
them,  according  to  their  flow  and  ebb,  and  the  observer  will  have  abun- 
dant opportunities  of  seeing  on  the  coasts  of  the  British  Islands,  and  on 
the  ocean  shores  of  Europe,  that  the  river  waters  when  swollen  by  rains, 
bear  outwards  with  the  ebb,  and  in  the  direction  that  it  takes  along 
shore,  much  mechanically  suspended  detritus,  which  does  not  again  enter 
the  rivers  unless  under  very  favourable  circumstances.  As  a  whole, 
much  fine  detritus,  thus  derived,  is  carried  coastwise  by  the  ebb,  and 
accumulations  are  formed  of  it,  if  there  be  sufficient  continued  repose  in 
that  direction.  So  that  should  a  sheltering  headland  run  out,  and  a 
bay  be  formed  between  it  and  the  embouchure  of  the  river,  there  is  a 
tendency  to  deposit  the  finer  sediment  in  the  locality  so  sheltered.  We 
may  take  the  coast  of  Swansea  as  affording  an  easily  observed  instance 
of  the  separation  so  effected. 

Two  rivers,  a  and  b  (fig.  64),  the  Towey  and  the  Nedd  (Neath),  when 

Fig.  64. 


in  flood,  bring  down  much  sedimentary  matter,  the  finer  parts  of  which 
are  carried  by  the  ebb  tide  (£,  £,  t)  towards  the  bay  formed  between 
Swansea  (<?)  and  the  Mumbles  (d).  Here  finding  the  necessary  repose, 


112  DISTRIBUTION    AND    DEPOSIT    OF 

the  prevalent  winds  (w)  blowing  from  the  west  and  southwest,  a  part  is 
deposited  and  mud  is  accumulated,  the  remainder  of  the  detrital-bearing 
waters,  escaping  round  the  Mumble  Rocks  (e)  into  the  general  ebb  tide 
passing  westwards  down  the  Bristol  Channel.  While  this  happens  with 
the  finer  sediment,  the  arenaceous  part  of  the  detritus  thrust  out  of  the 
river  is  more  quickly  thrown  down,  and  a  large  part  of  it  becomes  acted 
upon  by  the  breakers,  raised  by  the  prevalent  winds,  and  is  forced  partly 
into  mechanical  suspension  during  heavy  gales,  and  then  borne  in  the 
flood  tides,  and  partly  brushed  onwards  by  the  waves,  breaking  upon 
much  flat  ground  exposed  at  low  water,  towards  the  coast  to  the  east- 
ward (/,/).  Here  the  conditions  for  the  accumulation  of  sand-hills  ob- 
tain, and  the  overplus  of  arenaceous  sediment,  borne  outwards  by  the 
Towey  and  Nedd,  and  not  retained  by  the  sea,  is  blown  by  the  winds 
upon  the  dry  land.  In  this  locality,  therefore,  the  river-borne  detritus, 
thrown  into  the  tides,  becomes  in  a  great  measure  separated,  mud  being 
chiefly  accumulated  in  one  direction,  sand  in  another,  a  surplus  of  the 
latter  being  restored  to  the  land. 

Though  there  is  a  tendency  to  accumulate  the  finer  river-borne  de- 
tritus in  the  direction  of  the  ebb  tides,  this  is  often  met  by  conditions  so 
unfavourable  to  such  a  deposit  that  the  finer  matter  does  not  there  come 
to  rest,  but  is  gradually  transported  outwards  to  sea,  and  may  thus  be 
brought  by  tidal  streams  -even  within  the  influence  of  ocean  currents. 
On  a  shallow  coast  the  breakers  alone,  when  they  can  act  equally  in  the 
direction  of  the  ebb  and  of  the  flood  tide,  prevent  the  accumulation  of  the 
finer  sediment  which,  in  consequence,  can  only  find  rest  by  being  carried 
outwards  into  water  of  the  needful  depth  and  tranquillity. 

The  abrasion  of  coasts  by  breakers  being  the  same,  whether  the  tide 
be  setting  intone  direction  or  another,  as  flood  or  ebb,  the  finer  matter  is 
carried  in  mechanical  suspension  equally  by  the  stream  of  either  along 
the  coasts,  finding  rest  in  the  situations  where  conditions  are  favourable, 
even  entering  estuaries  by  the  flood  tide,  when  such  estuaries  occur  in  the 
line  of  its  course,  the  indraught,  on  the  flood,  carrying  it  in  with  the  tide. 
As  we  have  seen  (p.  81),  the  heavier  parts,  such  as  shingles  and  small 
pebbles,  are  distributed  along  shore,  and  the  arenaceous  portions,  some- 
times on  the  coast,  sometimes  more  seaward,  according  to  circumstances. 

The  agitation  of  the  sea  is  felt  at  different  depths  in  proportion  to  the 
magnitude  of  the  waves  raised  by  the  friction  of  the  wind.  During 
heavy  gales  of  wind,  the  depth  at  which  this  agitation  has  been  observed, 
sufficient,  as  it  were,  to  shake  up  fine  sediment  enough  to  discolour  the 
water,  is  about  90  feet.*  The  disturbing  effects  of  waves  in  minor  depths 
is  often  well  shown  on  shallow  sandy  coasts  by  the  throwing  on  shore  of 

*  The  depth  at  which  the  disturbing  action  of  a  sea-wave  can  be  felt  has  been  esti- 
mated even  so  high  as  500  feet  on  the  Banks  of  Newfoundland. — Emy.  Mouvement  des 
Ondes,  1831,  p.  11. 


SEDIMENT     IN    TIDAL    SEAS.  113 

many  molluscs  in  a  living  state,  known  to  inhabit  the  sands  at  moderate 
depths.  By  the  agitation  of  the  sea  their  sandy  covering  is  removed, 
and  they  are  swept  onward  beyond  their  powers  to  retain  their  position 
at  the  bottom,  and  thus  become  finally  thrown  out  upon  the  coast. 

Besides  the  waves  seen  to  arise  on  the  spot  from  the  action  of  the 
winds,  the  great  undulations  which  are  known  as  swells  and  rollers  (so 
common  on  ocean  shores,  and  due  to  the  friction  of  winds  out  at  sea 
which  do  not  reach  the  land)  disturb  the  sea  bottom  to  a  considerable 
extent,  so  that,  both  heavy  seas  and  swells  combined,  the  finer  sediment 
becomes  removed  from  all  but  favourable  situations  outwards,  and  the 
sands  are  distributed  off  the  coasts,  outside  the  accumulations  fringing 
them,  and  due  to  the  action  of  the  breakers. 

The  flow  and  ebb  of  the  tides  produce  a  motion  tending  to  smooth  out 
and  flatten  the  accumulation  of  detrital  matter  deposited  on  the  sea 
bottom  within  their  influence.  The  smoothing  action  no  doubt  varies 
with  the  strength  of  the  tides,  as  these  may  be  springs  or  neaps,  so  that 
matter  can  be  brought  to  rest  during  the  latter,  which  becomes  removed 
by  the  superior  velocity  and  volume  of  water  of  the  former ;  but,  as  a 
whole,  there  arises  an  adjustment,  producing  a  sea  bottom  of  a  marked 
character.  The  friction  of  the  tidal  wave  on  the  bottom  forms  ridges 
and  furrows  of  the  same  kind  with  those  previously  noticed  as  produced 
by  the  winds  on  loose  sand  (p.  87).  Where  clear  waters  prevail,  and  the 
ridges  and  furrows  are  formed  by  this  kind  of  friction  alone,  the  resem- 
blance is  very  striking,  allowance  being  made  for  the  relative  weight  of 
the  particles  of  sand  in  the  air  and  in  the  water.  Where  waves  act  on 
the  bottom,  it  would  be  expected  that  such  ridges  and  furrows  would  be 
modified  by  the  to-and-fro  action  set  up,  although  the  on-shore  might  be 
greater  than  that  of  the  counter  movement,  in  proportion  as  the  wave 
takes  the  onward  force  of  a  breaker,  the  higher  part  acquiring  gradually 
a  greater  forward  motion  as  the  water  becomes  shallower,  and  the  fric- 
tion on  the  bottom  becomes  increased. 

Almost  every  extensive  sandy  flat  left  by  the  tide,  and  of  such  the 
coasts  of  the  British  islands  afford  abundant  examples,  shows  the  effects 
of  friction  on  the  sand.  An  observer  should  well  study  the  various  mo- 
difications to  be  seen  in  such  situations,  for,  among  arenaceous  accumu- 
lations of  all  geological  ages,  the  effects  of  friction  on  sand  and  silt,  by 
water  in  motion,  is  often  very  evident.  In  many  situations  peculiar  ar- 
rangements of  the  surface  sand  will  be  observed  to  have  arisen  from  the 
draining  off  of  the  tidal  water,  which  has  quitted  a  large  tract  of  sand 
suddenly.  We  have  thus  friction  from  the  rise  and  fall  of  tidal  waters 
on  coasts,  from  the  to-and-fro  action  of  waves  produced  by  winds  (where 
the  depths  are  favourable),  and  from  streams  of  tide,  variable  in  strength, 
usually  acting  in  two  directions,  and  often  in  more,  from  local  causes. 

From  friction  of  all  kinds  much  sedimentary  matter  is  so  shoved  and 

8 


114 


DISTRIBUTION    AND     DEPOSIT     OF 


pushed  along  the  bottom  in  various  directions,  that  from  this  cause  alone 
a  great  flattening  of  the  surface  would  be  effected.  If  to  this  we  add 
the  deposit  of  matter  borne  in  mechanical  suspension,  and  derived  either 
from  rivers  or  the  action  of  breakers,  we  should  expect  a  distribution  of 
detritus  which  if  raised  above  the  level  of  the  sea,  would  offer  the  ap- 
pearance of  a  great  plain.  The  accompanying  map  (fig.  65)  will  show 
the  extent  of  area  around  the  British  islands  within  a  line  of  depth  equal 
to  100  fathoms  (600  feet),  and  which,  if  raised  above  the  level  of  the 
sea,  would  present  to  the  eye  little  else  than  a  vast  plain.  To  form  this 
great  tract  of  smoothed  ground,  no  doubt  the  levelling  action  of  breakers, 
cutting  back  the  coasts,  must  be  duly  regarded ;  so  that  to  this  action, 
to  that  of  the  seas  rolling  in  various  directions,  according  to  the  winds, 

Fig.  65. 


and  .stirring  up  the  bottom  in  sufficiently  shallow  plaers,  and  to  the  distri- 
buting power  of  streams  of  tide,  is  mainly  due  the  present  surface  of  this 


SEDIMENT    IN    TIDAL    SEAS.  115 

area,*  the  extent  of  which  may  be  estimated  by  the  annexed  figure  (fig. 
66),  representing  1000  square  miles,  on  the  same  scale  as  the  map  (fig. 
65). 

Fig.  66. 

a 

It  is  worthy  of  remark,  that  if,  instead  of  the  line  of  100  fathoms 
beneath  the  sea,  that  of  200  fathoms  had  been  selected,  the  second  line 
would  not  have  extended  far  beyond  the  first,  the  slope  increasing  far 
more  rapidly  outside  the  100  fathom  line  than  within  it,  so  that,  after 
preserving  a  very  gentle  slope,  as  a  whole,  outwards  for  the  great  area 
represented  above  (fig.  65,)  the  bottom  of  the  sea  descends  much  more 
suddenly  beyond  it  towards  the  Atlantic. f 

Slight  attention  on  the  coasts  will  show  an  observer  that  the  water 
moving  past  them  in  a  stream  from  tidal  action  travels  backwards  and 
forwards  a  somewhat  limited  distance,  so  that  any  detritus  held  by  it 
in  mechanical  suspension,  and  eventually  thrown  down  from  such  sus- 
pension, could  only  be  deposited  within  a  limited  area,  when  no  dis- 
turbing causes  interfered.  The  water  of  a  tidal  stream,  passing  a  coast 
at  the  average  rate  of  three  miles  per  hour,  will  only  travel  18  miles, 
regarding  the  subject  generally,  before  it  is  swept  back  again  over 
the  same  ground  for  the  like  distance.  The  pressure  of  high  winds, 
both  on  and  off  a  coast,  particularly  if  they  be  long  continued,  forces 
water  against  or  away  from  the  land,  and  so  with  any  other  direction 
a  surplus  of  the  ordinary  body  of  water  may  take  from  the  friction 
of  the  wind.  Hence  the  mere  backward  and  forward  motion  of  the 
same  body  of  water  is  somewhat  modified,  as  also  by  the  great  addi- 
tions made  to  the  usual  volume  of  tidal  water  by  the  discharge  of 
great  floods  from  rivers,  striving  to  force  their  way  over  coast  streams 
of  tide. 

Making,  however,  all  reasonable  allowance  for  these  modifying  in- 
fluences, there  remains  enough  of  continued  local  action  to  procure 
local  accumulations  of  detritus,  more  diversified  in  character  near  the 
coasts  than  at  a  distance  from  them,  on  account  of  the  increased 
velocity  of  tides  immediately  off  chief  headlands,  and  their  dimi- 

*  Always  bearing  in  mind  that  there  is  a  base  beneath  of  tertiary  and  other  rocks, 
over  which  the  sands  and  mud  are  at  present  strewed,  and  which  may  here  and  there 
be  still  uncovered.  In  many  situations,  a  minor  area,  planed  down  by  the  action  of  the 
breakers,  may  yet  be  kept  clean  from  deposits  by  local  causes.  We  may  probably  re- 
gard the  whole  area  as  the  result  of  the  cutting  back  of  coasts  by  breakers,  and  of  de- 
posits from  the  causes  pointed  out,  continued  through  a  long  lapse  of  geological  time, 
movements  of  land  as  regards  its  relative  level  with  the  sea,  and  on  the  large  scale, 
having  contributed  to  its  present  condition. 

f  Here  and  there  are  minor  depressions  in  this  area,  and  among  them  the  trough- 
like  cavities  in  the  North  Seas,  known  as  the  Silver  Pits.  The  bottom  around  the  chief 
pits  is  described  as  rising  gradually  to  it,  when  suddenly  the  interior  sides  descend  from 
a  few  to  40  or  50  fathoms,  forming  steep  interior  escarpments. 


116  DISTRIBUTION    AND    DEPOSIT    OF 

nished  strength  of  stream  in  sheltered  bays,  not  forgetting  estuaries, 
with  and  without  bars  of  different  kinds. 

The  observer  has  now  to  consider  the  distribution  of  fine  matter 
in  mechanical  suspension  by  means  of  ocean  currents.  Some  of  these 
are  known  to  be  very  constant  in  their  courses,  others  periodical,  and 
many  temporary.  We  have  seen  that  the  pressure  of  strong  and  long- 
continued  winds  forces  up  water  by  their  friction  on  its  surface  in  tide- 
less  seas,  and  consequently  would  expect  that  in  the  open  ocean  similar 
winds  would  force  water  before  them,  though  the  absence  of  land  would 
produce  a  modification  in  the  result.  When  the  area  so  acted  upon  was 
bounded  by  a  single  range  of  coast,  the  modification  would  be  less ; 
and  when  two  lines  of  coast  presented  themselves,  between  which  the 
water  could  be  forced,  and  lateral  fall  prevented,  there  would  be  an 
approximation  to  the  effects  observable  at  the  north  and  south  extremi- 
ties of  the  Caspian,  or  on  the  east  and  west  shores  of  the  Black  seas, 
where  the  waters  are  pressed  forward  by  the  needful  winds. 

Independently  of  the  pressure  on  the  surface  of  the  sea  by  winds, 
either  constant  or  nearly  so,  periodical  or  temporary,  it  has  been  sup- 
posed that  the  motion  of  the  earth  gives  a  certain  movement  to  the 
waters  of  the  ocean  from  east  to  west,  thus  increasing  the  power  of 
some  currents,  due  to  the  surface  action  of  winds,  and  interfering  with  the 
movement  of  others.  To  the  motion  of  water  from  this  cause,  the  con- 
tinent of  America,  with  South  Georgia,  South  Orkney,  South  Shetland, 
and  the  icy  regions  extending  to  Victoria  Land,  would  interpose  be- 
tween the  Atlantic  and  the  Pacific,  and  the  continent  of  Asia,  with  the 
Philippines,  Borneo,  the  Moluccas,  New  Guinea,  and  Australia,  would 
oppose  the  westward  movement  of  the  Pacific,  not  forgetting  New  Zea- 
land, and  the  multitude  of  islands  and  islets  of  Polynesia  in  that  ocean. 

The  more  open  space  for  this  supposed  movement  would  be  from  the 
Indian  and  Southern  Oceans  into  the  Atlantic,  the  coast  of  Africa  not 
offering  it  opposition  beyond  the  latitude  of  35°  south.  A  constant 
current  does  run  out  of  the  Indian  into  the  Atlantic  Ocean,  flowing  up 
the  west  coast  of  Africa,  to  the  equatorial  regions,  whence  it  strikes 
over  to  America,  ponding  up  the  water  in  the  Gulf  of  Mexico.  It  has 
been  inferred  that  this  current  is  partly  due  to  the  motion  of  the  earth, 
and  partly  to  prevalent  winds,  those  known  as  the  Trade  Winds  espe- 
cially driving  the  waters  in  the  same  direction. 

The  current  into  the  Atlantic  sweeps  round  the  southern  extremity  of 
Africa  by  the  Agulhas  or  Lagullas  Bank,  the  soundings  on  which  give 
mud  to  the  westward  of  Cape  Agulhas,  and  sand,  containing  numerous 
small  shells,  to  the  eastward.  It  might  hence  be  assumed  that  this 
current  acted  upon  the  bank  at  a  depth  of  360  or  420  feet,  sweeping 
off  the  finer  sediment  from  the  side  exposed  to  its  force,  and  parting 
with  it  in  the  more  still  water  behind  it.  A  mass  of  water  is  inferred 


SEDIMENT    IN    TIDAL    SEAS.  117 

to  run  up  the  west  coast  of  Africa,  from  the  Cape  of  Good  Hope  (be- 
tween the  coast  and  the  waters  of  the  adjacent  ocean)  60  miles  wide, 
1200  feet  deep,  and  of  the  mean  temperature  of  the  ocean,  at  an  ave- 
rage rate  of  one  mile  per  hour.*  There  are  counter  currents,  f  and  the 
main  current  is  considered  to  extend,  as  regards  surface,  to  a  compara- 
tively moderate  distance  from  the  land.  As  a  whole,  this  current  re- 
minds us  of  a  body  of  water  in  movement  westward,  acquiring  additional 
velocity  against  the  southern  extremity  of  Africa,  as  any  minor  mass  of 
water  in  movement  would  against  a  common  projecting  cape  or  head- 
land. We  may  regard  another  great  Atlantic  current,  the  Gulf 
Stream,  as  consequent  on  this  main  current,  after  it  has  traversed  the 
Atlantic  to  the  West  Indies.  Escaping  from  the  Gulf  of  Mexico,  as 
previously  noticed  (p.  99),  the  Gulf  Stream  waters  flow  northerly,  a 
part  passing  off  to  the  eastward,  after  passing  the  Straits  of  Florida, 
probably  to  equalize  the  general  levels  in  that  direction.  As  to  the 
extent  and  velocity  of  the  Gulf  Stream,  the  contradictory  evidence  is 
sufficient  to  show  that  both  are  occasionally  much  modified.  The  winds, 
by  their  friction,  necessarily  affect  the  course  of  the  stream,  according 
to  their  duration,  strength,  and  direction.  In  mid-channel,  in  the  meri- 
dian of  Havanna,  the  velocity  is  estimated  at  2J  miles  per  hour.;  off 
the  most  southern  parts  of  Florida,  and  about  one-third  over  from  the 
Florida  Reefs,  at  4  miles  an  hour.  The  stream  is  considered  to  range, 
in  the  meridian  of  57°  W.  to  42°  45'  N.  in  summer,  and  to  42°  N.  in 
winter.  A  reflow,  or  counter  current,  sets  down  by  the  Florida  Reefs 
or  Keys  to  the  S.W.  and  W.J 

Other  currents  are  known  in  the  Atlantic,  such  as  that  coming  out 
of  Baffin's  Bay,  through  Davis's  Strait, §  considered  to  join  the  Gulf 
Stream,  the  united  body  of  water  crossing  over  to  the  coasts  of  Europe 
and  Africa.  A  southerly  flow  of  water  takes  place  from  the  coast  of 
Portugal  towards  the  Canary  Islands,  modified  by  the  indraught  of  sea 
into  the  Mediterranean.  Beyond  these  islands  a  S.W.  current  is 
noticed  as  probably  due  to  the  influence  of  the  N.E.  trade  wind. 

*  Sir  James  Ross.     Voyage  in  the  Southern  and  Antarctic  Regions,  vol.  i.  p.  35. 

f  Close  to  the  shore  there  is  an  eastern  current.  The  survey  of  the  coast  of  Africa, 
to  the  east  of  the  Cape  of  Good  Hope,  was  made  by  Captain  Owen,  with  the  assistance 
of  this  current,  against  the  force  of  the  trade  wind.  Captain  Horsburgh  mentions 
having  been  carried  by  the  eastern  current,  on  the  south  of  the  main  western  current, 
at  the  rate  of  20  to  30  miles  in  the  24  hours,  and,  in  two  instances,  at  the  rate  of  60 
miles  in  the  same  time. 

J  Many  small  vessels  are  stated  to  make  their  passage  from  the  northward  by  the  aid 
of  this  counter  current. 

§  This  current,  commonly  known  as  the  Greenland  Current,  sets  southerly  down  the 
coast  of  America  to  Newfoundland,  bringing  down  large  icebergs  beyond  the  Great 
Bank.  The  velocity  was  found,  by  Captains  Ross  and  Parry,  to  be  3  to  4  miles  per 
hour  in  Davis's  Strait.  Off  the  coast  of  Newfoundland,  it  sometimes  flows  at  the  rate 
of  2  miles  an  hour ;  but  much  modified  by  winds. 


118  DISTRIBUTION    AND    DEPOSIT    OF 

Constant  currents  are  also  mentioned  in  the  Pacific.  Currents  are 
described  as  setting  off  the  Galapagos  to  the  N.N.W.,  and  at  Juan 
Fernandez,  and  300  leagues  to  the  westward  of  it  to  the  W.S.W.  (16 
miles  per  day).  Great  quantities  of  wood  are  drifted  from  the  con- 
tinent of  America  to  Easter  Island  by  a  stream  of  water  passing  in 
that  direction.  Between  the  Sandwich  Islands  and  the  Marquesas, 
currents  have  been  found  flowing  westward  at  the  rate  of  30  miles  per 
day.  Among  the  Philippine  Islands  a  current  comes  from  the  north- 
east, and  runs  with  considerable  force  among  the  passages  dividing 
them  from  each  other.  Various  other  currents  in  the  Pacific  have  been 
noticed.  There  are  two,  however,  deserving  of  attention,  inasmuch  as 
one,  flowing  northerly  through  Behring's  Straits,  is  thought  to  proceed 
eastward  along  the  north  coast  of  America,*  and  the  other  passes  round 
Cape  Horn  to  the  eastward  for  the  greater  part  of  the  year.f 

In  the  China  and  India  seas  we  find  good  examples  of  periodical 
currents.  The  water  moves  from  the  ocean  into  the  Red  Sea,  from 
October  to  May,  and  out  of  that  sea  from  May  to  October.!  In  the 
Gulf  of  Manar,  between  Ceylon  and  Cape  Cormorin,  the  current  flows 
northward  from  May  to  October,  setting  the  remaining  six  months  to 
the  S.W.  and  S.S.W.  In  the  S.W.  monsoon,  the  current  between  the 
coast  of  Malabar  and  the  Lakdivas  sets  to  the  S.S.E.  with  a  velocity 
varying  from  20  to  26  miles  in  the  24  hours.  The  currents  in  the  China 
Seas,  at  a  distance  from  shore,  commonly  flow,  more  or  less,  towards 
the  N.E.  from  the  middle  of  May  to  the  middle  of  August,  taking  a 
contrary  direction  from  the  middle  of  October  to  March  or  April.  Their 
strength  is  most  felt,  as  might  be  anticipated,  among  the  islands  and 
shoals. § 

With  respect  to  temporary  currents,  they  are  found  to  be  innumera- 

*  Kotzebue  describes  this  current  as  setting  through  Behring's  Straits  with  a  velocity 
of  3  miles  an  hour,  to  the  N.E. 

f  This  current  has  been  doubted ;  but  as  there  is  a  prevalence  of  strong  westerly 
winds  round  Cape  Horn  during  the  greater  part  of  the  year,  the  statement  that  there 
is  such  a  current  may  be  considered  probable.  A  bottle,  thrown  overboard  by  Sir 
James  Ross,  near  Cape  Horn,  was  afterwards  found  near  Port  Philip,  Australia,  having 
passed  eastward  about  9000  miles  in  3£  years.  Allowing  1000  miles  for  detours,  this 
would  be  a  rate  of  about  eight  miles  per  day.  It  was  Sir  James  Ross's  practice,  upon 
throwing  bottles  overboard,  to  load  all  but  that  intended  for  the  surface,  so  that  they 
took  different  depths.  As  sand  was  not  stated  to  be  found  in  this  bottle,  it  was  inferred 
that  it  was  a  surface  bottle  ;  hence  the  winds  alone  had  much  influence  on  its  course. 

J  A  current  commonly  flows  from  the  Persian  Gulf  towards  the  ocean,  during  the 
whole  time  that  the  water  runs  into  the  Red  Sea,  and  flows  into  the  Gulf  from  May  to 
October. 

\  The  strongest  currents  in  these  seas  are  experienced  along  the  coast  of  Cambodia, 
during  the  end  of  November.  They  run  with  a  velocity  of  60  to  70  miles  to  the  south- 
ward, in  the  24  hours,  between  Avarilla  and  Poolo  Cecir  da  Terra.  Some  parts  of  the 
stream  setting  into  the  Straits  of  Malacca,  causes  the  tide  to  run  nine  hours  one  way 
and  three  hours  the  other. 


SEDIMENT    IN    TIDAL    SEAS.  119 

Lie ;  severe  gales  of  wind,  of  long  duration,  readily  forcing  the  surface 
water  before  them.  Among  channels  and  along  coasts  these  are  chiefly 
felt,  the  two  boundary  shores  or  the  single  coast  opposing  the  further 
rise  of  water,  and  throwing  them  off  in  the  manner  of  tidal  waves. 

While  considering  the  movement  of  the  ocean  waters,  the  observer 
should  not  neglect  any  change  in  their  position  which  may  be  due  to 
their  relative  specific  gravities.  Experiments  upon  fresh  water  in  lakes 
long  since  showed  that  a  body  of  the  heaviest  water,  that  approaching 
towards  a  temperature  of  about  39-5°  or  40°,  remained  at  the  bottom 
undisturbed,*  except  by  the  influx  of  river  waters,  charged  with  detritus, 
which  forced  their  way,  spreading  mud  beneath  them  (p.  72).  The 
researches  of  Sir  James  Boss  in  the  Southern  Seas  have  shown  that  in 
a  similar  manner  water  of  a  certain  temperature,  namely,  of  about 
39*5°  Fahr.,  remains  at  the  bottom,  either  colder  or  warmer  water,  as 
the  case  may  be,  floating  above  it.  From  many  observations  made,  it 
was  inferred  that  a  belt  of  this  water,  of  a  given  temperature,  rose  to 
the  surface  in  southern  latitudes,  of  which  the  mean  is  estimated  at 
about  56°  26',  the  whole  body  of  ocean  water  in  that  circle  being  of 
this  uniform  temperature  from  the  surface  to  the  bottom,  while  on  the 
north,  towards  the  tropics  and  equator,  water  of  a  higher  temperature 
floated  above  it,  and  on  the  south,  that  of  a  lower  temperature.f  Thus, 
considering  the  like  belt  of  uniform  temperature  to  appear  in  such  parts 
of  the  northern  hemisphere  as  is  covered  by  the  ocean,J  there  would  be 

*  In  1819  and  1820,  the  author  made  experiments  on  the  Lakes  of  Geneva,  Neuchatel, 
Thun,  and  Zug,  with  a  view  of  investigating  this  subject.  An  account  of  these  experi- 
ments was  published  in  the  "  Bibliotheque  Universelle,"  for  1819  and  1820.  It  was 
found  that,  in  the  Lake  of  Geneva,  the  water  in  September  and  October,  1819,  had  a 
temperature  of  64°  to  67°  Fahr.,  from  the  surface  to  the  depth  of  1  or  5  fathoms,  and 
that  there  was  a  general  diminution  of  temperature  downwards  to  40  fathoms.  From 
40  to  90  fathoms,  the  temperature  was  always  44°,  with  one  exception,  when  it  was  45° 
at  40  fathoms.  From  90  fathoms  to  the  greatest  depths,  which  amounted  to  164  fathoms, 
between  Evian  and  Ouchy,  the  temperature  was  invariably  43-5°.  After  the  severe 
winter  of  1819-20,  the  same  temperature  continued  beneath.  Experiments  on  the 
Lakes  of  Neuchatel,  Thun,  and  Zug,  alike  pointed  to  water  of  a  temperature  approach- 
ing to  the  greatest  density  of  water,  between  39°  and  40°,  being  at  the  bottom. 

f  The  following  were  the  observations  on  which  Sir  James  Ross  founded  his  view  of 
the  position  of  this  circle,  the  water  being  ascertained  in  the  localities  noticed  to  have 
the  same  temperature  from  the  surface  downwards  : — 

Latitude.  Longitude. 

57°  52'  S.  170°  30'  E. 

55  09  132  20 

55  18  149  20  W. 

58  36  104  40 

54  41  55    12 

55  48  54    40 

Voyage  to  Southern  and  Antarctic  Regions,  vol.  ii. 

J  Allowing  the  same  causes  in  operation  in  the  northern  hemisphere,  we  should  ex- 
pect similar  effects,  however  modified  by  local  circumstances.  Scoresby  obtained,  in 
lat.  79°  4'  N.,  long.  5°  4'  E.,  36°  at  400  fathoms,  the  temperature  increasing  from  29° 
at  the  surface.  Another  observation  by  the  same  author,  in  lat.  79°  4'  N.,  gave  37°  at 


120  DISTRIBUTION    AND    DEPOSIT    OF 

three  great  thermic  basins,  two  towards  each  pole  of  the  earth,  and  a 
middle  trough  or  belt,  through  the  central  part  of  which  the  equator 
would  pass.  Sir  James  Ross  points  out  that  in  lat.  45°  S.,  the  tempe- 
rature of  39 '5°  has  descended  to  600  fathoms,  increasing  in  depth  in 
the  equatorial  and  tropical  regions  to  about  1200  fathoms,  the  tempera- 
ture of  the  surface  in  the  latter  being  about  78°.*  On  the  south  of  the 
belt  of  uniform  temperature,  the  line  of  39-5°  is  considered  to  descend 
to  750  fathoms  in  lat.  70°,  the  surface  being  there  at  30°  Fahr. 

To  estimate  a  movement  which  might  be  produced  by  the  settlement 
of  any  water  of  the  density  of  39-5°,  striving  to  occupy  an  equal  depth 
beneath  those  of  inferior  weight,  either  of  greater  or  less  temperature, 
as  the  case  might  be,  to  the  north  and  south  of  these  belts  of  uniform 
temperature,  supposing  that  some  approximation  to  such  a  belt  was  to 
be  found  in  the  northern  hemisphere,  we  should  compare  the  distance 
from  these  belts  with  the  depths  at  which  given  temperatures  have  been 
observed.  This  done,  we  obtain  for  the  slope  on  either  side  of  the 
southern  belt  (assuming  a  plane  for  more  ready  illustration)  of  about  1 
in  1723  to  the  1200  fathoms  of  39-5°  beneath  the  equator,  and  of  about 
1  in  1136  to  the  same  temperature  beneath  750  fathoms  in  70°  south 
latitude.  So  small  an  angle,  with  a  change  of  temperature  so  gradual, 
could  scarcely  produce  a  lateral  movement  in  the  mass  of  ocean  waters 
of  geological  importance,  f 

730  fathoms,  the  surface  being  29°.  Again,  in  lat.  78°  2'  N.,  and  long.  0°  10'  W.,  he 
found  38°  at  761  fathoms,  the  surface  being  32°. 

*  With  regard  to  observations  in  the  tropics,  Colonel  Sabine  found,  in  lat.  20°  30'  N., 
and  long.  83°  30'  W.,  a  temperature  of  45-5°  at  1000  fathoms,  the  surface  water  being 
at  83°.  Captain  Wauchope  obtained,  in  lat.  10°  N.,  and  long.  25°  W.,  61°  at  966 
fathoms,  the  surface  water  being  at  80° ;  and  he  also  found  in  lat.  3°  20'  S.,  and  long. 
7°  39'  E.,  a  temperature  of  42°  at  1300  fathoms,  the  surface  water  being  at  73°. 

f  It  should  be  remarked  that  the  temperature  of  39-5°,  found  by  Sir  James  Ross  in 
situations  leading  to  the  inference  that  such  a  temperature  is  that  of  the  greatest 
density  of  sea  water,  containing  the  ordinary  amount  and  kinds  of  salts  in  solution, 
does  not  well  accord  with  the  experiments  in  the  laboratory.  According  to  Dr.  Marcet, 
those  made  by  him  show  that  the  maximum  density  of  sea  water  is  not  at  40°  Fabr. 
In  four  experiments,  Dr.  Marcet  cooled  sea  water  down  to  between  18°  and  19°,  and 
found  that  it  decreased  in  bulk  till  it  reached  22°,  after  which  it  expanded  a  little,  and 
continued  to  do  so  until  the  water  was  reduced  to  19°  and  18°,  when  it  suddenly  ex- 
panded and  became  ice  at  28°.  According  to  M.  Erman,  also,  salt  water  of  the  specific 
gravity  of  1-027  diminishes  in  volume  down  to  25°,  not  reaching  its  maximum  density 
until  congelation. 

These  results  would  seem  to  point  either  to  some  modifying  influence  acting  upon 
the  waters  of  the  ocean,  to  faujts  in  the  instruments,  to  the  mode  of  employing  them, 
or  to  sources  of  error  in  the  laboratory  experiments  not  suspected.  At  considerable 
depths,  the  heavy  pressure  upon  the  bulbs  of  the  thermometers,  if  used  naked,  might 
be  supposed  to  produce  an  error  as  to  the  mass  of  water  of  uniform  temperature  from 
the  surface  downwards.  If  pressure,  however,  upon  the  bulb,  caused  a  higher  appa- 
rent rise  in  the  thermometers,  this  should  vary  with  such  pressure ;  but  the  results  do 
not  bear  out  this  view,  unless  it  be  assumed  that  the  gradual  increase  of  pressure 
exactly  counterbalanced  a  decrease  of  temperature.  It  is  worthy  of  remark,  that  the 


SEDIMENT  IN  TIDAL  SEAS.  121 

The  agency  of  ocean  currents  in  the  transport  of  matter  mechanically 
suspended  in  their  waters,  and  derived  from  the  decomposition  or 
abrasion  of  land,  will  necessarily  depend  upon  local  conditions.  Here 
and  there  streams  of  tide  may  deliver  such  matter  to  them,  to  be  borne 
in  the  direction  in  which  they  may  move,  and  great  rivers,  such  as  the 
Yang-tse-kiang,  the  Ganges,  the  Indus,  the  Quorra,  and  the  Amazons, 
may  thrust  out  bodies  of  water,  flowing  beyond  the  return  of  the  tidal 
streams  of  coasts,  and  carrying  detritus  to  ocean  currents,  through 
which  it  would  have  gradually  to  descend.  It  might  thus  be  transported 
long  distances,  particularly  if  the  depths  it  might  have  to  descend, 
before  stagnation  of  the  lower  waters  would  prevent  any  than  a  vertical 
fall  of  the  matter,  were  considerable.*  Looking,  however,  at  maps  of 

temperature  of  39-5°  is  about  that  assigned,  from  experiments,  to  pure  water,  and  that 
saline  solutions  are  known  to  become  more  dense  at  less  temperatures.  It  may  be  here 
observed  that  the  water  beneath  90  fathoms  in  the  Lake  of  Geneva  was  found,  both 
after  a  warm  summer  and  a  severe  winter,  to  remain  as  43-5°,  not  39-5°  or  40°,  as 
experiments  in  the  laboratory  would  lead  us  to  expect.  From  observations  on  the 
temperature  of  the  western  Mediterranean  waters,  at  various  depths,  it  is  inferred 
that  all  beneath  200  fathoms  remains  at  a  constant  temperature  of  about  55°.  (D'Ur- 
ville,  Bui.  de  la  Soc.  de  Geographic,  t.  xvii.  p.  82.) 

If  we  take  39-5°  for  the  temperature  of  the  greatest  density  of  sea  water,  we  shall 
have  to  consider  that  the  salts  in  solution  produce  no  influence  upon  such  density,  the 
water  alone  having  to  be  regarded.  It  would  be  very  desirable  that  experiments  re- 
specting the  density  of  sea  water  at  different  temperatures  should  be  repeated  in  the 
laboratory,  and  that  observations  should  be  made  at  different  seasons  upon  the  tempe- 
rature of  deep  fresh-water  lakes,  in  order  to  see  if  we  are  in  any  way  to  regard  the 
temperature  obtained  in  the  sea  of  39-5°,  so  well  observed  by  Sir  James  Ross,  as  a 
result  to  which  some  modifying  influence  may  be  attributed. 

*  Some  very  interesting  observations  respecting  the  surface  density  of  the  sea  off  the 
coast  of  British  Guiana  were  made  by  Dr.  Davy  (Jameson's  "  Edinburgh  Journal,"  vol. 
xliv.,  p.  43,  1848).  He  found  that  where  the  Demerara  River  meets  the  sea,  near 
Georgetown,  the  density  of  the  water  was  1-0036,  and  subsequently  as  follows: — 

1.  11  miles  offshore  —  1-0210 

2.  19  "  —  1-0236 

3.  27  "  =    -0250 

4.  35  "  =     -0236 

5.  43  "  =    -0250 

6.  51  «  =    -0258 

7.  80  "  =  1-0266 

The  specific  gravities  of  Nos.  4  and  5  were  considered  to  have  been  influenced  by  heavy 
showers  of  rain  which  fell  while  the  steamer  on  which  Dr.  Davy  was  on  board  passed. 
This  modification  in  the  density  of  the  surface  waters,  by  tropical  rains,  is  well  shown 
by  the  observations  of  the  same  author,  off  Antigua  and  Barbadoes.  Towards  the  end 
of  a  very  dry  season,  the  specific  gravity  of  the  surface  water,  off  the  former,  was 
found  to  be  1-0273,  while,  after  three  months  of  heavy  rains,  off  Barbadoes,  the  specific 
gravity  was  reduced  to  2-0260.  The  positions  of  these  two  islands  give  such  observa- 
tions considerable  value.  With  respect  to  the  matter  mechanically  held  in  suspension 
in  the  waters  off  British  Guiana,  Dr.  Davy  states  that,  for  many  miles  near  the  land,  it 
was  sufficient  to  give  a  light-brown  tint  to  the  sea,  like  the  Thames  at  London  Bridge. 
It  was  only  at  about  the  distance  of  80  miles  from  shore  that  the  waters  presented  the 
blue  colour  of  the  ocean. 


122  DISTRIBUTION    AND    DEPOSIT    OF 

the  world,  and  studying  the  charts  upon  which  information  respecting 
ocean  currents,  tidal  streams,  and  the  various  kinds  of  bottom  found  by 
sounding,  are  laid  down,  or  consulting  the  works  in  which  similar 
information  is  recorded,  the  great  floor  of  the  ocean  would  appear  to  be 
little  covered  by  the  deposit  of  matter  from  mechanical  suspension 
borne  over  it  by  currents,  and  derived  from  continents  and  the  great 
islands.  The  matter  obtained  from  the  land  seems  chiefly  to  be  thrown 
down  as  a  fringe  of  various  shapes  and  composition,  skirting  the  shores  ; 
sometimes,  from  local  conditions,  extending  to  far  greater  distances 
than  at  others. 

Although  the  great  floor  of  the  ocean  may  not  be  very  materially 
covered  by  deposits  from  ocean  currents,  conveying  detritus  from  the 
great  continents,  Australia,  and  the  larger  islands  of  the  world,  the 
oceanic  islands  may  collectively  furnish  matter  of  importance.  The 
observer  will  find  that  many  of  these  islands  rise  from  comparatively 
considerable  depths,  so  that  detrital  matter  derived  from  them  by  the 
action  of  breakers  (and  they  are  very  commonly  exposed  to  a  nearly 
constant  abrasion  by  the  surf),  moved  by  the  tidal  wave  sweeping  by 
the  islands,  and  thence  delivered  into  any  ocean  currents  passing  near, 
may  be  carried  by  the  latter  to  considerable  distances.  These  oceanic 
islands  are  found  to  be  chiefly  of  two  kinds,  the  one  of  igneous,  the 
other  of  animal  origin.  With  respect  to  the  former,  we  have  not  only 
to  consider  the  detritus  they  may  now  furnish  by  the  action  of  breakers 
upon  them,  but  also  the  transportable  matter  which  may  have  been 
ejected  from  the  igneous  vents  while  they  rose,  by  the  accumulation  of 
molten  rock,  cinders,  and  ashes. 

Instead  of  simply  accumulating  around  the  igneous  vent,  as  would 
happen,  with  certain  modifications  from  the  distribution  of  wind-borne 
ashes  and  small  local  movements  of  water  in  tideless  seas,  not  only 
might  there  be  a  to-and-fro  distribution  of  the  volcanic  matter  carried 
various  distances  in  mechanical  suspension  from  the  tidal  wave  acting 
against  the  new  obstacle  to  its  movement,  but  the  finer  matter  could 
also  be  borne  away  by  any  ocean  current  passing  near,  and  thus  such 
substances  be  carried  far  onward  in  the  direction  of  its  course.  As 
soon  as  any  igneous  matter  is  raised  above  the  sea  level,  so  soon  is  it 
attached  by  the  breakers,  and  only  in  proportion  to  its  solidity  and 
mass  can  the  portion  above  water,  and  partly  removed  from  the 
destructive  action  of  the  surf,  remain  to  be  more  slowly  wasted  by  the 
combined  influences  of  the  atmosphere  and  of  the  sea,  and  to  be  clothed 
with  vegetation,  if  within  climates  fitted  for  its  growth.  Many  an 
inland  in  the  ocean  can  be  regarded  as  little  else  than  tlu»  higher  part 
or  parts  of  a  volcano,  or  some  more  extended  system  of  volcanic  vents, 
rising  above  its  level,  the  mass  and  kind  of  matter  ejected  being  sufficient 
to  keep  it  there.  As  might  be  expected  in  a  great  volcanic  region  like 


SEDIMENT  IN  TIDAL  SEAS. 


123 


that  of  Iceland,  igneous  vents  have  opened  in  the  sea  near  its  shores, 
as  well  as  upon  the  dry  land.  A  volcanic  eruption  is  recorded  as 
having  taken  place  in  1783,  about  30  miles  from  Cape  Reikianes,  and 
another  off  the  same  island  about  1830.*  In  1811,  a  volcanic  eruption 
was  effected  through  the  sea  off  St.  Michaels,  Azores,  and  eventually, 
after  the  ejection  of  much  matter,  columns  of  black  cinders  being  thrown 
to  the  height  of  700  and  800  feet,  an  island  was  formed,  about  300  feet 
high,  and  about  one  mile  in  circumference. 

Fortunately  the  formation  of  this  island  was  observed  and  recorded. 
It  was  first  discovered  rising  above  the  sea  on  the  13th  June,  1811,  and 
on  the  17th  was  observed  by  Captain  Tillard,  commanding  the  "  Sabrina" 
frigate,  from  the  nearest  cliff  of  St.  Michaels.  The  volcanic  bursts 
were  described  as  resembling  a  mixed  discharge  of  cannon  and  musketry, 
and  were  accompanied  by  a  great  abundance  of  lightning.  The  follow- 
ing (fig.  67)  was  a  sketch  made  at  the  time,  and  will  well  illustrate 

Fig.  67. 


the  manner  in  which  ashes  and  lapilli  may  be  thrown  into  any  ocean 
current  or  tidal  stream  passing  along,  to  be  borne  away  by  it. 

This  island,  to  which  the  name  of  Captain  Tillard's  frigate  was  as- 
signed, subsequently  disappeared,  but  whether  simply  by  the  action  of 

*  In  1783,  the  eruptions  of  several  islands  were  observed  as  if  raised  from  beneath, 
and,  during  some  months,  vast  quantities  of  pumice  and  light  slags  were  washed  on 
shore.  "In  the  beginning  of  June,  earthquakes  shook  the  whole  of  Iceland;  the 
flames  in  the  sea  disappeared,  and  a  dreadful  eruption  commenced  from  the  Shaptav 
Yokul,  which  is  nearly  200  miles  distant  from  the  spot  where  the  marine  eruption  took 
place." — (Sir  George  Mackenzie's  Travels  in  Iceland.) 


124  CHEMICAL    DEPOSITS    IN    SEAS. 

the  breakers  alone,  or  from  the  subsidence  of  the  main  mass  beneath,  or 
from  both  causes,  accounts  do  not  enable  us  to  judge.* 

No  doubt  very  many  of  the  supposed  banks  in  the  ocean  upon  which 
the  surf  is  stated  to  have  been  seen  breaking,  and  never  afterwards  found, 
may  be  very  imaginary,  but  it  is  still  possible,  that  here  and  there  state- 
ments of  this  kind  may  be  founded  upon  something  more  positive,  and 
that,  making  all  allowance  for  incorrect  views  as  to  the  latitude  and 
longitude  of  the  supposed  banks,  some  due  to  the  upraising  of  volcanic 
cinders  and  ashes  have  been  observed,  these  finally  so  cut  away,  that 
the  sea  no  longer  broke  over  them.  However  this  may  be,  we  can 
scarcely  suppose  that  over  the  floor  of  the  ocean  all  the  eruptions  from 
every  volcanic  vent  upon  it  have  reached  above  the  surface  of  the  water 
and  remained  there  as  islands,  or  that  some,  which  have  accumulated 
matter  to  depths  not  far  beneath  the  surface  waters,  may  not  occasion- 
ally so  vomit  forth  cinders  and  ashes,  that  these  substances  remain  for  a 
time  above  water  until  removed  by  the  influence  of  breakers. 

Chemical  Deposits  in  Seas. — We  have  previously  adverted  to  the  mixed 
deposits  of  calcareous  and  sedimentary  matter  in  tideless,  or  nearly  tide- 
less  seas,  from  which  alternate  layers  of  argillaceous  limestones  and 
clays,  or  lines  of  argillaceous  limestone  nodules  in  the  latter  might  re- 
sult. According  to  the  specific  gravities  of  the  waters  of  such  seas, 
arising  from  the  different  amount  of  matter  in  solution  in  them,  will,  as 
we  have  seen,  depend  the  distances  over  which  river  waters  can  flow 
outwards,  supposing  such  rivers,  for  illustration,  to  be  equal  in  volume 
and  velocity,  and  as  respects  the  amount  of  matter  in  solution  or  me- 
chanically suspended.  In  this  respect,  the  Caspian,  the  Black,  and  the 
Baltic  seas  would  all  differ,  the  latter  most  approaching  in  the  character 
of  its  waters  to  a  fresh-water  lake.  Comparatively,  these  bodies  of  water 
would  appear  to  afford  greater  tranquillity  than  tidal  seas  for  the  pro- 
duction of  chemical  deposits,  always  allowing  for  the  depths  to  which 
their  waters  may  be  disturbed  by  surface  causes,  such  as  winds  and 
changes  in  atmospheric  temperature. 

In  tideless  seas,  such  as  the  Caspian,  where  the  substances  brought 
down  in  solution  by  the  rivers  accumulate  in  comparatively  still  water, 
we  should  expect  deposits  which  could  not  be  effected  with  equal  facility 
in  the  ocean,  even  in  those  parts  which  adjoin  coasts.  In  the  one  case, 
evaporation  keeps  down  the  body  of  the  water,  probably  even  diminishing 

*  This  is  not  the  only  instance  of  a  volcanic  eruption  forming  a  temporary  island 
above  the  sea-level  among  the  Western  Islands.  It  is  recorded  in  the  MS.  Journals  of 
the  Royal  Society  (a  collection  containing  a  mass  of  curious  information  respecting  the 
progress  of  science  after  the  foundation  of  the  Royal  Society),  that  Sir  II.  Sheres  in- 
formed a  meeting,  of  January  7th,  1690-91,  "That  his  father,  passing  by  the  Western 
Islands,  went  on  shore  on  an  island  that  had  been  newly  thrown  up  by  a  volcano,  but 
that  in  a  month  or  less  it  dissolved,  and  sunk  into  the  sea,  and  is  now  no  more  to  be 
found." 


CHEMICAL    DEPOSITS     IN    SEAS.  125 

its  volume  during  a  long  lapse  of  time ;  while,  in  the  other,  these  solu- 
tions enter  the  great  mass  of  ocean  waters,  and  become  so  lost  in  it,  that 
certain  of  them  may  only,  under  very  favourable  conditions,  be  able  to 
accumulate  as  a  coating  or  bed  upon  any  previously  formed  portion  of 
the  ocean  floor.  The  way  in  which  the  tidal  wave  thrusts  back  river 
waters  twice  in  each  day  (taking  the  subject  in  its  generality),  mingling 
the  common  sea  waters  with  those  of  rivers,  up  the  estuaries,  is  alone  a 
marked  difference  from  the  outpouring  of  the  rivers,  with  their  contained 
solutions  unmixed  until  the  river  waters  flow  over  the  sea.  Instead  of 
comparative  quiet  along  shore,  except  where  disturbed  by  the  action  of 
surface  waves,  the  whole  body  of  water  along  tidal  coasts  is  kept  in 
motion,  moving  alternately  one  way  or  the  reverse,  and  not  unfrequently 
in  various  directions,  in  consequence  of  the  modification  of  the  bottom, 
and  the  mode  in  which  the  tidal  wave  may  strike  variously  formed  or 
combined  masses  of  dry  land. 

We  have  above  called  attention  to  the  differences  in  tideless  or  nearly 
tideless  seas,  arising  from  differences  between  the  evaporation  of  their 
surfaces,  and  their  average  supply  of  water  from  rivers  or  rains.  Not 
only  should  we  thence  expect  the  modification  of  sedimentary  deposits 
previously  mentioned,  but  modifications  also  in  the  chemical  coatings. 
An  isolated  area,  like  the  Caspian,  if  the  evaporation  of  its  waters  be 
greater  than  its  supply,  may,  during  such  decrease,  present  us  with  con- 
ditions favourable  to  a  deposit  of  some  of  its  salts,  while  the  main  mass 
of  the  waters  may  yet  be  well  able  to  hold  such  salts  in  solution.  Any 
shallow  parts  adjoining  the  shores  becoming  isolated,  and  therefore  cut 
off  from  the  river  supplies  afforded  to  the  main  body,  may  readily  be 
deprived  of  all  their  water  by  evaporation,  and  a  sheet  of  saline  matter 
be  the  result.  Indeed,  in  this  manner,  any  substances  in  solution  would 
become  deposited,  and  how  far  they  might  remain  exposed  without  being 
removed  by  atmospheric  influences,  would  depend  upon  the  climate  of 
the  locality.  That  any  such  beds,  the  result,  of  the  evaporation  sup- 
posed, may  be  covered  by  ordinary  sedimentary  deposits,  due  to  geolo- 
gical changes  of  the  locality,  will  be  obvious. 

Around  such  bodies  of  water  as  the  Caspian,  the  observer  possesses 
good  opportunities  for  studying  subjects  of  this  kind,  which  are  of  con- 
siderable interest  geologically,  when  we  consider  the  mode  of  occurrence 
of  gypsum  and  rock-salt  in  many  situations,  the  not  unfrequent  con- 
nexion of  these  substances,  and  the  kinds  of  sedimentary  matter  with 
which  they  are  often  associated.  It  may  be  also  deserving  of  attention 
to  consider  in  such  parts  of  the  world  the  probable  annual  evaporation 
of  the  surface  of  seas  like  the  Caspian,  and  the  annual  supply  of  waters 
from  rivers  and  rain.* 

*  It  is  interesting  to  consider,  in  any  given  land  where  such  bodies  of  water  may  be 
found,  even  though  of  much  less  size,  and  where  it  seems  certain,  from  geological  evi- 


126  CHEMICAL    DEPOSITS    IN    SEAS. 

It  may  have  happened  that,  from  geological  changes,  such  as  might 
readily  convert  the  Persian  Gulf  into  an  isolated  sea,  by  raising  the 
bottom  between  Cape  Mussendom  and  the  opposite  coasts  at  Grou  and 
Sereek,  or  the  Red  Sea,  into  another,  by  raising  the  bottom  at  Bab-el 
Mandeb,  these  masses  of  water  no  longer  communicated  with  the  main 
ocean.  Looking  at  the  climatal  conditions,  and  the  absence  of  any  great 
drainage  from  adjoining  land  flowing  into  it,  the  Red  Sea  would  lose  its 
waters  from  evaporation,  while  with  respect  to  those  of  the  Persian  Gulf, 
it  would  depend  upon  the  difference  between  the  evaporation  and  supply 
of  water  chiefly  obtained  from  the  Euphrates,  Tigris,  and  their  tributa- 
ries. From  existing  information,  we  should  anticipate  that  this  supply 
would  not  equal  the  evaporation,  so  that  both  bodies  of  water  might  be- 
come Caspians. 

It  would  be  well  if  observers,  when  among  such  parts  of  the  world, 
would  gather  information  sufficient  to  show  us  the  probable  results  of 
such  alteration  of  conditions,  especially  as  respects  the  deposits  of  sub- 
stances now  in  solution  in  these  seas,  and  their  intermixture  with  common 
detrital  matter.  Observations  directed  to  such  points  can  scarcely  fail 
to  be  valuable  with  respect  to  geological  theory.  Under  the  supposition 
of  the  conversion  of  the  Red  Sea  into  a  Caspian,  not  only  might  there 
be  a  mixture,  under  favourable  conditions,  of  chemical  deposits  and  de- 
trital accumulations,  but  coral  banks  and  reefs  would  be  also  included 
in  them. 

By  a  glance  at  a  map  of  Asia,  it  will  be  seen  that  a  very  large  area, 
extending  along  70  degrees  of  longitude  from  the  Black  Sea  into  China, 
with  a  varied  breadth  of  15  to  20  degrees  of  latitude,  does  not  drain 
directly  or  indirectly  into  the  ocean.  There  is  reason  to  believe  that  it 
is  a  mass  of  land  which,  from  geological  changes,  has  been  cut  off  from 
such  drainage,  the  Caspian,  the  Sea  of  Aral,  with  numerous  smaller 
bodies  of  water,  now  receiving  such  drainage  waters  as  evaporation  from 

dence,  that  the  present  area  occupied  by  such  waters  is  less  than  formerly,  how  far  the 
climatal  conditions  may  so  influence  the  evaporation  and  supply  of  water  that  a  kind  of 
balance  is  established.  We  may,  for  illustration,  suppose  that,  in  the  first  place,  the 
climatal  conditions  are  such,  after  the  separation  of  a  mass  of  sea  waters  from  con- 
nexion with  the  ocean,  that  a  considerable  diminution  of  the  volume  of  the  separated 
water,  and  consequently,  in  all  probability,  of  the  area  occupied  by  it,  takes  place. 
Then  will  arise  the  local  conditions,  whether  this  diminution  continues  or  whether  any 
balance  of  evaporation  and  supply  becomes  established.  Evaporation,  all  other  things 
being  equal,  will  depend  upon  the  area  exposed.  If  large  rivers,  such  as  the  Volga,  for 
example,  entering  the  Caspian,  bring  much  sediment  into  the  sea  or  lake,  they  tend  to 
make  it  shallow,  and  also,  by  their  deltas,  to  diminish  the  area,  so  that  the  conditions, 
as  to  general  area,  depth,  and  consequent  volume  of  the  water,  alter.  This  alone  might 
destroy  any  balanced  conditions.  There  are  other  circumstances,  such  as  the  supply 
of  water  from  other  sources  than  the  evaporation  of  the  lake  itself,  it  being  borne  by 
prevalent  winds  from  the  ocean,  which  have  to  be  taken  into  account,  and  will  readily 
present  themselves.  The  whole  subject  is  one  of  much  interest  with  respect  to  its  geo- 
logical bearings. 


CHEMICAL    DEPOSITS    IN    SEAS.  127 

the  surface  of  this  great  area  will  permit,  when  gathered  together  in 
different  positions.  The  evaporation  may  completely  overpower  the 
supply  of  water  in  certain  parts  of  such  an  area,  the  salts  in  solution  in 
the  pre-existing  waters  forming  sheets  of  matter  corresponding  with  the 
minor  areas  or  lakes  when  such  solutions  became  saturated  with  common 
salt  or  any  other  substances,  as  the  case  might  be,  the  least  soluble  sub- 
stances being  the  first  thrown  down.  In  a  dry  climate,  such  portion  of 
the  common  detritus,  as  did  not  become  consolidated,  would  be  readily 
swept  about  by  the  winds,  forming  deserts,  such  as  we  find  in  the  region 
noticed,  the  great  Chinese  desert  of  Kobi,  or  Shamo,  being  the  largest  of 
them.  In  all  such  lands  the  explorer  will  not  lose  his  time  by  carefully 
examining  the  shores  of  these  various  inland  seas  and  lakes,  observing 
the  physical  conditions  which  may  produce  the  isolation  of  shallow  parts. 
It  would  be  well  also  to  study  deposits  of  saline  matter  with  reference 
to  their  origin  from  conditions,  which  may  have  readily  obtained,  in  con- 
sequence of  geological  changes,  by  the  separation  of  shallow  water  in- 
dentations fringing  the  ocean,  particularly  in  warm  and  dry  climates,* 
as  well  as  by  the  partial  or  total  evaporation  of  salt  lakes. 

Amid  the  great  flats  which  here  and  there  occur  on  the  shores  of 
tidal  seas,  and  which  may  become  dry  at  certain  times,  so  that  patches 
of  sea-water  irregularly  scattered  over  them  may  be  evaporated,  leaving 
the  salt,  we  have  no  doubt  conditions,  particularly  in  dry  and  warm 
climates,  for  the  accumulation  of  thin  sheets  of  salt,  or  other  substances 
in  solution,  which,  under  favourable  circumstances,  might  be  covered 
up,  and  to  a  certain  extent,  be  preserved  by  detrital  mud ;  but  these 
deposits  would  scarcely  have  the  importance  of  those  previously  noticed. 
At  the  same  time,  such  situations  should  be  examined  with  reference  to 
the  chemical  accumulations  which  may  be  thus  intermingled  with  de- 
trital matter. 

With  respect  to  deposits  from  chemical  solution,  the  calcareous  may 
be  considered  as  the  most  important  geologically.  We  have  previously 
adverted  to  their  production  in  the  air,  and  in  fresh-water  lakes.  The 
cases  of  consolidated  beaches  on  some  coasts,  like  those  noticed  in  Asia 

*  In  all  cases,  where  practicable,  it  is  desirable  to  obtain  information  as  to  the 
matters  in  solution  in  the  various  inland  seas  and  lakes.  They  are  known  to  differ  in 
this  respect,  as  might  be  anticipated.  Thus,  according  to  M.  Eichwald,  the  waters  of 
the  Caspian  contain  much  sulphate  of  magnesia,  in  addition  to  the  other  salts  held  in 
solution.  Those  who  are  possessed  of  sufficient  chemical  knowledge,  if  they  have  with 
them  any  of  the  little  portable  chests  of  the  needful  substances  and  apparatus,  will  have 
a  local  means  of  a  qualitative  analysis.  It  would  be  well  if  they  could  perform  a 
quantitative  one  on  the  spot,  seeing  the  difficulty  of  conveying  bottles  of  water,  to  be 
kept,  perhaps,  a  long  time,  and  amid  high  temperatures.  When  the  observer  may  not 
be  a  chemist,  he  may  still  assist,  under  favourable  conditions  as  to  transport,  by  ob- 
taining the  waters  and  putting  a  sufficient  quantity  into  a  clean  bottle,  immediately 
sealing  it  up  carefully  and  tight,  and  forwarding  it,  as  soon  as  circumstances  may  per- 
mit, to  some  experienced  chemist  for  examination. 


128  CHEMICAL    DEPOSITS    IN    SEAS. 

Minor,  may  be  regarded  as  in  a  great  measure  due  to  the  evaporation 
of  the  water  containing  the  bicarbonate  of  lime  in  solution,  as  it  perco- 
lates through  these  beaches.  In  the  same  manner,  we  seem  to  obtain 
their  consolidation  in  some  places  by  the  oxides  of  iron  and  manganese, 
and  by  other  substances.  Respecting  the  actual  formation  of  beds  of 
limestone  in  the  deeper  sea  by  chemical  deposit  alone,  though  we  feel 
assured  that  it  is  effected,  the  exact  manner  is  scarcely  yet  well  deter- 
mined. The  rivers  flowing  into  both  tideless  and  tidal  seas  alike  trans- 
port calcareous  matter  in  solution  into  them,  though  very  variably ;  in 
scarcely  appreciable  proportions  in  some,  abundantly  in  others.  So  long 
as  the  carbonic  acid  needful  for  the  solution  of  the  carbonate  of  lime 
remains,  the  latter  will  continue  in  the  waters,  but  should  it  be  with- 
drawn, either  by  evaporation  of  the  sea  waters  in  shallow  places,  or  by 
separation  in  any  other  way,  the  carbonate  of  lime,  if  the  lime  be  not 
taken  up  in  any  other  combination,  will  be  deposited. 

With  regard  to  shallow  situations  in  tidal  seas,  particularly  in  warm 
climates,  and  where  pools  of  water  are  left  for  sufficient  time  at  neap 
tides,  we  should  expect  an  evaporation  of  the  water,  at  least  in  part, 
and  a  loss  of  the  carbonic  acid,  enabling  any  carbonate  of  lime  present 
to  be  held  in  solution,  so  that  there  was  a  consequent  deposit  of  calca- 
reous matter.  This  may  be  well  seen  where  waters  highly  charged  with 
bicarbonate  of  lime  flow  slowly  into  some  nook  or  bay,  on  tropical  coasts, 
and  even  in  localities  where  the  rise  and  fall  of  tide  is  small,  as,  for  in- 
stance, around  Jamaica.  It  is  in  such  situations,  under  favourable  con- 
ditions, that  the  little  grains  termed  oolites,  formed  of  concentric  coat- 
ings of  calcareous  matter,  may  be  sometimes  observed  to  form.  A  slight 
to-and-fro  motion,  produced  by  gentle  ripples  of  water,  may  occasionally 
be  seen  to  keep  the  carbonate  of  lime  depositing  in  movement  and  di- 
vided into  minute  portions,  so  that  instead  of  a  continuous  coating  of 
calcareous  matter  upon  any  solid  substances  beneath,  a  multitude  of 
these  little  grains  is  produced.  As  might  readily  be  anticipated,  a 
small  fragment  of  shell  and  even  a  minute  crystal  of  carbonate  of  lime 
is  sufficient  to  form  a  nucleus  for  the  concentric  coatings  of  these  oolitic 
grains.  An  observer  would  do  well,  when  an  opportunity  of  this  kind 
may  present  itself,  to  watch  the  mode  in  which  the  grains  may  be  me- 
chanically accumulated,  like  any  other  grains  of  matter  by  the  wash  of 
the  sea,  or  the  drift  caused  by  minor  tidal  streams,  as  he  will  thereby 
be  the  better  enabled  to  judge  of  the  differences  or  resemblances  he  may 
find  between  the  accumulations  and  the  beds  formed  of  oolitic  grains  in 
the  calcareous  deposits  of  various  geological  ages. 

While  the  mode  in  which  calcareous  matter  may  be  deposited  on  the 
shores  of  seas  may  thus  be  advantageously  studied,  that  in  which  it  is 
effected  in  deep  water  must  necessarily  be  matter  of  inference.  By  the 
means  previously  noticed,  a  large  collective  amount  of  carbonate  of 


CHEMICAL    DEPOSITS    IN    SEAS.  129 

lime,  held  in  solution  by  the  needful  addition  of  carbonic  acid,  is  dis- 
charged by  rivers  into  the  sea ;  more,  no  doubt,  in  some  localities  than 
in  others,  but  still,  as  a  whole,  somewhat  widely.  Although  we  might 
expect  solutions  of  a  great  variety  of  substances  in  the  sea,  the  drainage 
of  the  land  supplying  them  constantly,  our  knowledge  on  this  subject 
would  be  more  advanced  than  it  is  at  present,  if  waters  were  more  col- 
lected in  different  parts  of  the  world,  and  off  a  variety  of  coasts,  than 
they  have  been. 

According  to  Professor  Forchhammer,  the  greatest  amount  of  saline 
matter  in  the  Atlantic  Ocean  is  found  in  the  tropics  far  from  land,  in 
such  places  the  sea-water  containing  3*66  parts  of  saline  matter  in 
100.  He  states,  that  the  quantity  diminishes  in  approaching  the  coasts, 
on  account  of  the  rivers  pouring  their  waters  into  the  sea,  and  that  it 
also  diminishes  on  the  most  western  part  of  the  Gulf  Stream,  where  the 
proportion  is  3 '59  per  cent.  Prof.  Forchhammer  proceeds  to  observe, 
that  by  the  evaporation  of  the  Gulf  Stream  waters,  the  quantity  of 
saline  matter  increases  towards  the  east,  and  reaches  3-65  per  cent.,  in 
N.  lat.  39°  39'  and  W.  long.  55°  16'.  Thence  it  decreases  slowly  to- 
wards the  N.E. ;  and  at  a  distance  of  60  to  80  miles  from  the  western 
shores  of  England,  the  Atlantic  contains  3*57  per  cent,  of  solid  sub- 
stances in  solution.  The  same  proportion  of  salts  is  found  all  over  the 
northeastern  part  of  the  Atlantic,  as  far  north  as  Iceland,  at  distances 
from  the  land  not  affected  by  the  outflow  of  rivers.* 

With  respect  to  the  chemical  character  of  the  saline  substances  in  the 
waters  of  the  Atlantic,  it  would  appear  that  they  do  not  differ  so  much 
as  might  be  supposed.  At  the  same  time,  Professor  Forchhammer 's 
researches  lead  him  to  consider  that  lime  is  rather  rare  around  the  West 
India  Islands,  where  myriads  of  polyps  employ  it  for  their  solid  coral 
structures ;  the  proportion  of  lime  to  chlorine  being  there  as  247  to 
10,000,  while  the  same  substance  is  more  common  in  the  Kattegat, 
where  part  of  the  lime  brought  by  numerous  rivers  into  the  Baltic  is 
carried  to  the  ocean.  In  the  Kattegat  the  proportion  of  lime  to  chlo- 
rine is  as  371  to  10,000.  In  the  Atlantic  Ocean  17  analyses  gave  297 
to  10,000 ;  and  between  Faroe  and  Greenland  18  analyses  afforded  300 
to  10,000.  f 

*  It  will  be  obvious  that  in  all  researches  as  to  the  amount  of  the  saline  contents  of 
the  ocean,  the  depth  from  which  waters  for  examination  may  be  taken  must  be  regarded. 
The  tendency  for  river  and  rain  waters  to  flow  over,  or  keep  above  the  mass  of  sea 
water,  is  well  known,  a  very  gradual  mingling  of  these  waters  being  effected.  While 
so  above  the  general  saline  solutions,  such  fresh  waters  would  be  those  to  evaporate. 
Waters  taken  from  different  depths  are  desirable,  more  particularly  when  we  endeavour 
to  ascertain  the  vertical  as  well  as  the  horizontal  modifications  which  may  exist  in  the 
saline  contents  of  sea  waters. 

f  Forchhammer.    Memoirs  of  the  British  Association  for  the  Advancement  of  Science, 
vol.  xv.  p.  90. 


130  CHEMICAL    DEPOSITS    IN    SEAS. 

Researches  of  this  kind,  limited  as  they  are  at  present,  are  still  suf- 
ficient to  point  out  the  modifying  influences  of  proximity  to  land,  of  the 
heat  of  the  tropics,  of  the  melting  of  ice  in  the  polar  regions,  and  of 
oceanic  currents  flowing  from  one  region,  where  certain  conditions 
prevail,  to  another  where  these  may  be  modified. 

As  geologists,  we  have  to  inquire  if  the  salts  in  solution,  and  derived 
by  means  of  rivers  from  the  land,  are  thrown  down  on  the  sea-floor, 
either  within  a  moderate  distance  from  the  land,  or  further  removed 
in  deeper  oceanic  waters.  If  we  take  the  calcareous  matter,  we  find 
that  it  can  be  transported,  by  means  of  rivers  flowing  outwards,  for 
various  distances  over  the  heavier  sea  waters,  to  be  still  further  carried 
outwards  and  into  greater  depths  of  water,  probably,  if  an  ocean  current 
seizes  on  the  river  waters  thus  situated.  No  small  aid  would  be  afforded 
if,  when  fitting  opportunities  presented  themselves,  waters  from  the 
streams  which  might  thus  be  traversed  were  carefully  examined  with 
reference  to-their  chemical  character.  In  warm  climates  there  might 
be  much  evaporation  from  the  upper  part  of  river  waters  thus  slowly 
passing  along  the  surface  of  the  seas,  productive  of  results,  as  regards 
matter  in  solution,  of  appreciable  value. 

When  we  consult  analyses  of  sea  waters,  to  ascertain  the  condition  in 
which  lime  may  be  present  in  them,  we  find  enough  to  show  that  much 
is  to  be  learnt  by  experiments  made  with  the  aid  which  the  present 
methods  of  analysis  can  afford.  We  can  readily  understand  that  while 
lime  may  be  pouring  into  some  parts  of  the  ocean,  as  a  carbonate  kept 
in  solution  by  the  proper  amount  of  carbonic  acid,  it  might  be  converted 
into  solid  matter  by  animal  life  in  another,  in  regions  where  a  balance 
of  supply  is  not  kept  up,  so  that  eventually  very  unequal  quantities  arc 
distributed  in  solution.  But  it  would  be  well  to  ascertain  such  facts 
carefully,  and  especially  with  reference  to  the  combination  in  which  the 
lime  may  be  found  in  the  different  regions  of  the  ocean.* 

With  respect  to  the  deposit  of  carbonate  of  lime  from  sea  waters,  Dr. 
Lyon  Playfair  suggests  that,  as  river  waters  generally  contain  in  solu- 

*  We  are  indebted  to  Schweiger  for  a  very  careful  analysis  of  the  waters  of  the  Eng- 
lish Channel.  No  doubt  it  is  only  good  for  the  locality,  one  not  favourable  for  a  know- 
ledge of  the  composition  of  oceanic  waters,  being  too  much  shut  in  by  land,  from  which 
river  waters,  differently  charged  with  saline  matter,  are  discharged.  His  analysis  is 
as  follows: — 

Water, 964-74372 

Chloride  of  Sodium,    .     .       27-05948 
"  Potassium,    .        0-76552 
"         "  Magnesium,  .         3-66658 
Bromide  of  Magnesium,  .         0-2929 
Sulphate  of  Magnesia,     .        2-29578 
"  Lime,  .     .     .         l-40i;.;-j 
Carbonate  of  Lime,     .     .        0-03301 
With,  in  addition  to  these  constituents,  distinct  traces  of  iodine  and  ammonia. 


CHEMICAL    DEPOSITS    IN    SEAS.  131 

tion  a  small  quantity  of  silicate  of  potash,  the  carbonic  acid,  dissolved 
in  sea  water,  enabling  the  carbonate  of  lime  to  be  therein  held  in  solu- 
tion, would  act  on  this  silicate,  decomposing  it,  and  forming  a  carbonate 
of  potash.  The  solvent  being  thus  removed  from  the  carbonate  of  lime, 
the  latter  would  be  precipitated,  and  a  new  portion  would  be  formed 
from  the  double  decomposition  of  the  newly-formed  carbonate  of  potash 
on  the  sulphate  of  lime  and  chloride  of  calcium  when  present.  He 
suggests  that  this  process  of  decomposition  may  account  for  the  silica  so 
frequently  found  in  limestones.  It  is,  however,  to  the  action  of  vegeta- 
tion on  sea  waters  that  Dr.  Lyon  Playfair  attributes  a  more  general 
deposit  of  any  carbonate  of  lime  from  them.  He  remarks,  that  marine, 
like  terrestrial  plants,  constantly  require  and  take  away  carbonic  acid 
from  the  waters  around  them,  so  that  the  quantity  necessary  to  keep  any 
carbonate  of  lime  in  solution,  and  which  may  find  its  way  into  the  sea 
waters,  being  removed,  the  carbonate  of  lime  is  thrown  down. 

Independently  of  the  soluble  matter  thrown  into  the  sea  by  rivers 
returning  to  it  frequently  that  which  in  anterior  geological  times  was 
accumulated. in  it,  we  have  to  reflect  that  the  volcanic  action  which  we 
know  has  been  set  up  upon  the  ocean-floor,  sometimes  throwing  up 
matter  above  the  surface  of  the  sea,  forming  islands,  must  as  a  whole 
have  caused  no  small  amount  of  soluble  matter  to  be  vomited  forth. 
Looking  at  the  gases  evolved  and  substances  sublimed  from  sub-aerial 
volcanoes,  we  should  expect  many  combinations  to  be  formed  and  decom- 
positions to  arise.  Seeing  also  the  soundings  around  certain  oceanic 
and  volcanic  islands,  no  slight  pressure  would  have  been  exerted  upon 
the  earlier  volcanic  action  beneath  the  seas, — a  modifying  influence  alone 
of  no  slight  importance.  Surrounded  by  seas  of  inferior  temperature, 
closing  in  upon  the  volcanic  vent  as  the  heated  waters  rose  upwards, 
there  would  be  a  tendency  to  have  certain  substances,  only  soluble  at  a 
high  temperature,  thrown  down  where  the  cooling  influences  could  be 
felt ;  as  also,  when  these  substances  may  be  borne  upwards  by  the 
heated  waters,  to  have  them  distributed  by  any  oceanic  currents  acting 
over  the  locality,  supposing  that  the  heated  waters  either  rose  to,  or 
were  produced  at  distances  beneath  the  surface  of  the  sea  where  these 
currents  could  be  felt.  "Without  entering  further  upon  this  subject,  we 
would  merely  desire  to  point  out  that,  in  volcanic  regions,  the  sea  may 
not  only  receive  saline  solutions  marked  by  the  presence  of  certain 
substances  not  so  commonly  thrown  into  it  by  rivers  elsewhere,  but  that 
also  submarine  volcanic  action  may  be  effective  in  producing  chemical 
deposits,  either  directly  or  indirectly,  which  under  ordinary  conditions, 
would  either  not  be  formed,  or  not  so  abundantly.* 

*  It  would  be  very  desirable  to  ascertain  points  of  this  kind,  so  far  as  examining  the 
sea  waters  around  volcanic  regions  may  enable  the  observer  to  do  so ;  and  more 
especially  when,  by  any  fortunate  chance,  opportunities  may  be  afforded  after  any 
submarine  volcanic  action  may  be  evident  or  supposed. 


132  PRESERVATION    OF    ORGANIC    REMAINS 

With  regard  to  the  mode  in  which  chemical  deposits  may  be  accumu- 
lated, it  is  very  needful  to  consider  that  horizontality  is  not  essential  to 
them.  They  may  be  formed  at  considerable  angles,  against  any  pre- 
viously existing  surface  offering  the  needful  conditions.  Numerous 
deposits  from  solutions  are  effected  as  well  on  the  sides  as  on  the  bot- 
toms of  vessels  containing  them.*  Hence  we  may  have  deposits  on  the 
large  scale,  giving  rise  to  deceptive  appearances.  Let  a,  for  example,  in 
the  annexed  section  (fig.  68)  be  the  surface  of  a  fluid,  such  as  the  sea, 
from  which  the  beds,  &,  have  been  deposited  from  chemical  solution 
(limestones,  for  instance,)  upon  the  pre-existing  surface,  c  d,  of  a  strati- 
fied work,  c  c,  and  it  might,  if  only  a  portion  of  such  a  section  was 

Fig.  68. 


subsequently  exposed,  be  concluded  that  there  had  been  movements  of 
the  land,  tilting  up  these  beds,  when  in  reality  there  may  have  been 
perfect  repose,  as  regards  their  position,  since  the  time  of  their  deposit. 
Even  when,  as  a  whole,  somewhat  horizontal  accumulations  of  this  kind 
might  be  expected,  they  are  often  found  to  have  moulded  themselves 
upon  the  irregularities  of  ground  upon  which  they  were  thrown  down. 

The  manner  in  which  the  remains  of  existing  life  may  be  accumulated 
or  entombed  in  mineral  matter. — This  is  a  subject  of  much  importance 
to  the  geologist  desirous  of  reasoning  correctly  upon  the  mode  in  which 
the  fossiliferous  rocks  may  have  been  accumulated.  The  habits  of 
plants  and  animals  engage  the  attention  of  the  naturalist,  and  by  his 
aid  most  important  benefits  are  conferred  upon  the  geologist,  who  is 
thus  enabled  to  infer  how  plants  or  animals,  found  existing  under 
certain  conditions,  may  contribute  by  their  remains  to  the  mass  of 
mineral  accumulations  now  taking  place,  occasionally  even  forming 
thick  beds,  spread  over  considerable  areas,  without  the  admixture  of 
mud,  and  sometimes  of  any  sediment  derived  from  the  decomposition  or 
mechanical  destruction  of  previously  existing  rocks. 

The  observer  should,  in  the  first  place,  direct  his  attention  to  the 
manner  in  wlm-1:  the  remains  of  terrestrial  life  may  be  entombed. 
Though  wlu-n  i<  i  ,-estrial  plants  die,  the  substances  of  which  they  are 
composed  are,  as  a  mass,  returned  to  the  atmosphere  and  soil  whence 
they  have  been  derived,  the  movements  of  animals  which  nmy  feed  upon 
them  being  regarded  as  so  far  local,  that  keeping  to  the  grounds  where 

*  Pipes  conveying  waters  containing  much  bicarbonate  of  lime,  or  many  other 
substances  in  solution,  are  well  known  to  be  often  coated  all  round. 


AMID    MINERAL    ACCUMULATIONS.  133 

their  food  is  presented  to  them,  their  droppings  restore  to  the  soil  what 
the  plants  had  removed  from  it,  the  carnivorous  animals  which  consume 
the  graminivorous,  returning  that  which  the  latter  did  not  prior  to 
death, — there  are  still  conditions  under  which  parts  of  existing  vege- 
tation may  become  permanently  preserved. 

Exposed  to  atmospheric  influences  after  death,  vegetation  decays  ac- 
cording to  the  structure  of  the  different  plants  and  the  climate  of  the 
locality.  The  rapidity  with  which  decomposition  is  effected  in  certain 
tropical  regions  is  well  worthy  of  attention,  more  particularly  when  the 
outside  of  a  large,  and  sometimes  prostrate  tree  may  retain  its  form, 
and  yet  the  whole  of  the  inside  be  hollow,  filled  with  leaves  that  have 
fallen  into  it,  or  teeming  with  animal  life.  This  kind  of  decay  is  still 
more  instructive  when  upright  stems  of  plants,  in  tropical  low  grounds, 
liable  to  floods,  retain  their  outside  portions  sufficiently  long  to  have 
their  inside  hollows  partially  or  wholly  filled  with  leaves  and  mud  or 
sand,  the  whole  low  ground  silting  up,  so  that  sands,  silt,  and  mud  ac- 
cumulate around  these  stems,  entombing  them  in  upright  positions, 
without  tops,  though  their  roots  retain  their  original  extension.  The 
study  of  the  sedimentary  accumulations  of  river  deltas,  amid  the  rank 
vegetation  of  some  tropical  countries,  is  very  valuable  as  respects  certain 
deposits  in  which  the  remains  of  vegetation  form  a  conspicuous  and  im- 
portant portion.  Behind  mangrove  swamps  much  that  has  a  geological 
bearing  may  be  frequently  seen  ;  and  indeed  amid  them,  the  observer 
not  forgetting  to  direct  his  attention  to  the  mode  in  which  animal  as 
well  as  vegetable  remains  become  mingled  with,  and  finally  covered  over 
by,  sedimentary  matter. 

Not  only  in  the  tropics,  but  in  other  regions,  large  tracts  of  marsh 
land,  interspersed  with  shallow  lakes,  are  highly  favourable  to  the  accu- 
mulation of  vegetable  substances.  The  leaves  of  trees,  growing  in  such 
situations,  falling  upon  the  patches  of  water,  take  a  horizontal  position, 
spreading  in  a  layer  in  certain  climates  and  seasons  over  their  surfaces. 
These  leaves  gradually  soak  up  water,  and  sink  to  the  bottom.  If,  from 
time  to  time,  flood  waters  bring  fine  mineral  matter  in  mechanical  sus- 
pension into  such  situations,  it  settles,  and  thus  the  leaves  may  be  pre- 
served in  thin  layers  alternating  with  the  clayey  sediment.  Should  it 
so  happen  that  waters,  charged  with  calcareous  matter  in  solution,  find 
their  way  either  gradually  and  constantly,  or  by  sudden  rushes  in  floods, 
we  may  have  the  leaves  or  other  remains  of  plants  preserved  in  deposit 
of  carbonate  of  lime,  more  or  less  pure,  according  to  the  presence  of  any 
other  matter  brought  into  the  lakes  in  mechanical  suspension  or  chemi- 
cal solution. 

The  manner  in  which  bogs  are  formed  should  also  be  studied.  Many 
no  longer  exhibit  their  progress  over  shallow  lakes,  while  others  will 
show  it.  In  the  latter  case  we  find  aquatic  plants,  like  the  large  rushes 


134  PRESERVATION    OF    ORGANIC    REMAINS 

and  water  lilies,  accumulating  mud  about  their  roots,  as  also  decaying 
vegetation,  upon  which  finally  the  bog  plants  advance,  the  chief  of  which, 
in  our  climate,  is  the  Sphagnum  palustre.  As  these  decay  beneath,  a 
new  growth  continues  above,  up  to  levels  where  the  requisite  moisture 
can  be  obtained.*  Trees  are  very  frequently  found  in  these  bogs  (some 
of  which  are  very  extensive),  in  a  manner  showing  that  the  conditions 
favourable  for  the  growth  of  oaks,  and  other  trees,  have  from  time  to 
time  obtained,  so  that  distinct  levels  of  them  have  been  found  occasion- 
ally in  the  same  bog. 

The  extent  of  bogs  is  very  variable,  as  also  the  bottoms  on  which  they 
repose.  Sometimes  the  latter  are  formed  of  shell  marls,  accumulated  at 
the  bottoms  of  the  shallow  lakes,  anterior  to  the  advance  of  the  aquatic 
vegetation  over  them.  The  thickness  of  bogs  necessarily  varies :  in  some 
10  to  30  or  40  feet  is  not  uncommon.  Of  the  pauses  in  the  accumula- 
tion of  bogs,  sufficient  to  permit  a  growth  of  trees  upon  them,  as  also  a 
surface  upon  which  habitations  may  be  constructed,  perhaps  as  good  an 
example  as  any  is  that  of  the  ancient  wooden  house  discovered  in  June, 
1833,  in  Drumkelin  Bog,  on  the  northeast  of  Donegal.  It  was  16  feet 
below  the  surface  of  the  bog  before  the  upper  part  was  taken  off,  and  4 
feet  beneath  the  cuttings  of  the  time,  standing  itself  upon  15  feet  more 
of  bog,  so  that  the  total  thickness  at  that  place  had  been  31  feet.  The 
house  itself  was  a  square  of  12  feet  sides,  and  9  feet  high,  and  was  formed 
of  two  floors,  the  roof  constructed  with  thick  planks  of  oak,  the  wood 
employed  for  the  whole  dwelling,  upon  which  no  iron  had  been  used. 
Upon  clearing  away  the  bog  from  the  level  of  the  house,  a  paved  path- 
way was  discovered  extending  several  yards  from  it  to  a  hearthstone, 
covered  with  ashes,  some  bushels  of  half-burned  charcoal,  some  nut- 
shells, and  blocks  of  wood  partly  burned.  Near  the  house  there  were 
stumps  of  oak  trees,  which  grew  at  the  time  it  was  inhabited.  A  layer 
of  sand  had  been  spread  over  the  ground  before  the  erection  of  the  house. 
All  seems  to  have  marked  a  state  of  repose  in  the  growth  of  this  part 
of  the  bog  ;  so  that  a  change  of  conditions  affecting  the  drainage  would 
seem  needful  to  account  for  the  accumulation  of  16  feet  more  above  the 
surface,  after  the  time  when  this  wooden  house  was  constructed.  It  may 
have  been  that  one  of  those  burstings  of  parts  of  a  bog,  some  of  which 
are  recorded,  may  have  overwhelmed  this  locality,  soft  boggy  matter 
having  gradually  accumulated  to  a  higher  level  under  favourable  circum- 
stances in  some  place  adjacent. 

Bogs  are  very  irregularly  dispersed,  forming  unequal  patches  as  to 

*  Those  travelling  in  North  Wales  will  find,  opposite  Cwm-y-glo,  below  the  bridge 
crossing  the  outlet  of  Llyn-Padarn  (the  lower  Llanberis  lake),  a  good  example  of  a  lake 
filling  up,  with  the  advance  of  water  lilies  and  other  aquatic  plants  upon  a  still  remaining 
portion,  while  bog  plants  and  bog  creep  on  behind  them.  At  the  proper  season,  the  local- 
ity is  brilliant  with  thousands  of  water  lilies  thus  advancing.  It  is  easy  to  see  that  this 
was  once  a  third  Llanberis  lake,  but  being  shallow,  was  the  first  to  be  nearly  filled  up. 


AMID    MINERAL    ACCUMULATIONS.  135 

area  and  thickness.  The  surface  occupied  by  the  bogs  of  Ireland  alone, 
has  been  estimated  at  2,800,000  acres.  From  the  tannin  in  them,  ani- 
mal and  vegetable  substances  are  often  found  well  preserved,  and,  in 
consequence,  numerous  relics  of  ancient  times  have  been  handed  down 
to  us,  which,  unless  entombed  in  bogs,  would  have  remained  unknown. 
Other  things  have  evidently  been  lost  in  them,  and  have  been  brought 
to  light  by  the  progress  of  the  turf-cutter.  Many  of  the  beautiful 
bronze  swords,  spear-heads,  and  other  ornaments  and  weapons  of  its 
ancient  inhabitants,  have  been  thus  preserved  in  Ireland.  As  might  be 
expected,  also,  the  remains  of  animals  are  found  which  have  perished  in 
the  bogs. 

Of  bog-like  accumulations  in  a  warm  climate,  the  "  Dismal  Swamp," 
as  it  is  called — 40  miles  long,  from  north  to  south,  and  25  miles  in  its 
greatest  breadth,  from  east  to  west — partly  in  the  State  of  Virginia  and 
partly  in  North  Carolina,  seems  an  excellent  example.  Mr.  Lyell  de- 
scribes this  swamp  as  u  one  vast  quagmire,  soft  and  muddy,  except 
where  the  surface  is  rendered  partially  firm  by  a  covering  of  vegetables 
and  their  matted  roots."*  From  the  nature  of  the  mass,  which  appears 
to  be  chiefly  formed  of  vegetable  matter,  spongy  for  the  most  part,  logs 
and  branches  of  trees  intermingled  in  it,  water  is  so  disseminated  that 
the  central  portions  of  the  swamp  are  the  highest,  rising  on  all  sides 
above  the  surrounding  firm  and  dry  land,  except  for  about  12  or  15 
miles  on  the  western  side,  where  rivers  flow  into  it  from  more  elevated 
ground.  The  greatest  height  of  the  central  part  above  the  sides  is 
estimated  at  about  12  feet,  and  in  such  central  portion  there  is  a  lake,  7 
miles  long,  and  5  miles  wide.  The  greatest  depth  of  this  lake  is  15 
feet ;  the  sides  are  composed  of  steep  banks  of  the  vegetable  mass,  and 
the  bottom  is  chiefly  formed  of  the  same  matter  in  a  highly  comminuted 
state,  with  sometimes  a  white  sand,  about  a  foot  thick.  Rivers  flow  out 
of  the  swamp  from  all  other  parts  of  its  margin  except  that  mentioned. 

It  is  a  highly  interesting  fact  as  connected  with  this  swamp,  one  hav- 
ing many  geological  bearings,  pointed  out  by  Mr.  Lyell,  that  the  sur- 
face supports  a  growth  even  of  trees.  He  mentions  the  juniper  trees 
(Cupressus  thyoides)  as  standing  firmly  in  the  softest  places,  supported 
by  their  long  tap-roots.  With  other  evergreens  these  trees  form  a  shade, 
under  which  grow  a  multitude  of  ferns,  reeds,  and  shrubs.  The  great 
cedar  (Cupressus  disticha)  also  flourishes  under  favourable  conditions. 
Trunks  of  large  and  tall  trees  lie  buried  in  the  swamp.  They  are  easily 
upset  by  extraordinary  winds  and  covered  in  the  mire,  where,  with  the  ex- 
ception of  the  sap  wood,  they  are  preserved.  Much  of  this  timber  is  found 
a  foot  or  two  from  the  surface,  and  is  sawn  into  planks  half  under  water. 
Bears  inhabit  the  swamp,  climbing  the  trees  in  search  of  acorns  from 
the  oaks,  and  gum  berries.  There  are  wild  cats  also,  and  occasionally  a 
*  Lyell's  Travels  in  North  America,  vol.  i.  p.  143. 


136  PRESERVATION    OP    ORGANIC    REMAINS 

wolf  is  seen,  so  that  there  must  often  be  conditions  for  the  loss  of  these 
animals  in  the  mire,  and  favourable  for  the  preservation  of  their  bones. 
Indeed  in  such  a  region  as  this,  occupying  an  area  of  several  hundred 
square  miles,  the  amount  and  mixture  of  animal  and  vegetable  matter, 
which  may  be  collected  in  one  great  extended  sheet,  is  not  a  little  re- 
markable. 

Rivers,  in  some  regions,  carry  forward  not  only  the  small  plants  with 
the  leaves  and  branches  of  the  larger,  but  multitudes  also  of  trees  are 
thus  sometimes  transported,  part  of  them  retained  within  the  sedimentary 
deposits  of  the  rivers  themselves,  part  swept  out  seawards.  It  is  not 
among  the  long-cultivated  lands  that  the  amount  of  plants,  great  and 
small,  carried  downwards  by  rivers,  is  best  observed,  though  during 
floods  in  them  large  trees  are  occasionally  borne  down  their  courses. 
It  is  in  regions  where  man  has  not  by  his  labours  modified  the  growth 
of  vegetation,  or  the  course  of  rivers,  that  the  transport  of  plants  by 
running  waters  can  be  well  studied.  We  then  have  conditions  resem- 
bling those  under  which  vegetable  remains  may  in  this  way  have  been 
mingled  with  the  sedimentary  deposits  of  previous  geological  periods. 
On  this  account,  the  courses  of  rivers,  such  as  those  of  the  Mississippi 
and  its  tributaries,  are  still  highly  instructive,  though  in  various  ways 
other  rivers,  pursuing  their  courses  through  lands  not  yet  cultivated  in 
any  part  by  man,  may  be  still  more  so.  The  snags  of  the  Mississippi, 
or  great  trees  carried  away  from  its  banks,  or  those  of  its  tributaries, 
and  which  are  anchored,  so  to  speak,  by  their  roots  upon  the  bottom  of 
the  ^stream,  their  heads  bending  with  its  strength,  are  well-known 
examples  of  the  partial  stoppage  of  trees  on  their  course  downwards. 
The  same  river,  or  rather  one  of  its  delta  streams,  named  the  Acha- 
falaya,  furnishes  us  with  a  good  instance  of  a  large  accumulation  of 
some  of  these  drift-trees  within  the  last  eighty  years.  About  that  time 
since,  numbers  of  these  drift-trees  got  entangled  in  the  channel,  so  that 
they  no  longer  passed  freely  down  it.  Eventually  they  formed  a  mass, 
termed  the  Raft,  distributed  irregularly,  and  rising  and  falling  with  the 
waters,  for  a  distance  of  twenty  miles,  closely  matted  together  in  some 
localities.  In  1808  the  cubic  contents  of  this  collection  of  drifted  trees 
was  estimated  at  286,784,000  cubic  feet.*  If  by  any  change  of  con- 
ditions the  channel  of  the  Achafalaya  became  little  supplied  with  water, 
and  the  raft  consequently  fell  in  the  channel  and  was  covered  over  with 
fine  sediment  derived  from  muddy  waters  quietly  working  their  way 

*  The  20  miles  of  length  were  estimated  at  10  miles,  this  distance  being  considered 
as  representing  a  close  packing  of  the  trees.  The  average  breadth  was  taken  at  220 
yards,  and  the  depth  at  8  feet. — (Darby,  Geographical  Description  of  the  State  of 
Louisiana.)  Rafts  of  this  description,  but  of  less  size,  are,  as  might  be  expected,  found 
in  other  divisions  of  the  Mississippi  and  its  tributaries.  Captain  Hall  (Travels  in  North 
America,  vol.  iii.  p.  370)  mentions  being  a  witness  of  one  of  those  falls  of  the  banks  of 
the  Missouri,  covered  with  trees,  which  throw  so  much  driftwood  into  the  Mississippi, 
the  banks  of  the  latter  also  contributing  largely  to  the  general  mass. 


AMID    MINERAL    ACCUMULATIONS.  137 

into  the  old  river  course,  a  long  line  of  lignite,  corresponding  with 
twenty  miles  of  the  old  channel  of  this  river,  might  be  the  consequence. 

When  we  regard  the  great  rivers  of  the  world,  we  can  scarcely  avoid 
considering  that  a  large  amount  of  plants  and  trees,  differing  in  kinds 
and  structure  according  to  climates,  must  be  annually  entombed,  in  a 
manner  to  prevent  that  decay  they  would  have  suffered,  if  left,  after 
death,  solely  to  atmospheric  influences.  No  doubt  much  of  this  vegeta- 
tion is  still  decomposed  after  transport  by  the  rivers  to  their  deltas,  yet 
much  also  must  be  entombed  in  deposits  excluding  ordinary  atmospheric 
influences,  and  leaving  the  plants  under  conditions  favourable  for  their 
gradual  alteration  into  lignite,  or  to  the  more  advanced  state  of  coal, 
should  geological  changes  so  permit.  In  deltas,  also,  we  have,  in  the 
pools  and  lakes  formed  by  the  advance  of  the  sediments  thrust  forward 
by  the  rivers,  circumstances  in  many  regions  favourable  to  the  growth 
of  aquatic  and  swamp  vegetation.  In  such  situations,  as  they  fill  up  by 
the  occasional  inflow  of  the  muddy  waters  of  the  rivers  in  flood,  and  by 
the  growth  and  partial  decay  of  the  vegetation,  we  have  also  conditions 
suited  to  the  preservation  of  some  of  the  plants,  or  their  parts,  often  in 
the  positions  in  which  they  grew,  mingled  with  carbonaceous  matter 
and  beds  of  sediment.  It  may  so  happen,  in  rivers  where  sands  as  well 
as  mud  are  forced  forward,  that  by  the  occasional  shifting  of  a  stream, 
or  the  breaking  away  of  a  bank,  previously  barring  the  entrance  of  any 
portion  of  a  main  stream,  sands  may  be  thrust  forward  over  accumula- 
tions of  this  kind,  their  deposit  marked  by  successive  lateral  and  sloping 
additions,  such  as  have  been  previously  mentioned  (p.  55). 

With  regard  to  the  preservation  of  animal  remains  on  dry  land,  or  in 
fresh  water,  we  have  to  recollect  that  the  rapacious  animals  very  fre- 
quently devour  the  bones  of  the  vertebrata  which  they  destroy,  and  the 
scavenger  animals  eat  up  those  which  the  former  may  have  left  uncon- 
sumed,  so  that  few  bones  generally  remain  exposed  on  dry  land  to  be 
decomposed  by  atmospheric  influences.  It  is  very  probable  that  in 
deserts,  the  bones  of  animals  which  have  perished  in  them  may  be  often 
buried  beneath  great  sand-drifts,  there  to  remain,  perhaps,  if  decom- 
posing causes  be  slight  in  such  situations,  until  geological  changes  may 
again  bring  such  deserts  beneath  waters,  and  consolidation  of  the  sands 
be  effected.  We  have  seen  the  bones  of  rabbits  and  birds  exposed  by  a 
shift  of  some  of  our  coast  sand-hills,  by  which  portions  of  old  accumula- 
tions, marked  by  successive  growths  of  vegetation,  have  been  carried 
off  by  the  winds. 

Vertebrate  animals  are,  in  some  countries,  overwhelmed  by  the  fall 
of  parts  of  mountain  sides  or  cliffs,  so  as  to  become  buried  deeply  in 
situations  where  their  bones  are  under  conditions  favourable  for  preser- 
vation. Occasionally,  they  are  destroyed  by  the  partial  fall  of  sea  cliffs 
on  tidal  coasts,  while  wandering  beneath  them  when  the  tide  may  be 


138  PRESERVATION    OP    ORGANIC    REMAINS 

out,  their  harder  parts,  perhaps,  washed  out  to  sea  when  the  breakers 
may  have  subsequently  removed  the  fallen  mass.  Such  harder  parts 
may  thus  become  mingled  with  any  sedimentary  accumulation  which 
may  be  forming,  should  they  not  be  ground  to  pieces  on  the  coast  by 
the  breakers. 

While  studying  the  mode  in  which  the  remains  of  vertebrate  animals 
may  be  preserved  without  the  aid  of  streams,  pools,  or  lakes  of  fresh 
water,  it  will  be  observed  that  the  clefts  of  rocks,  in  countries  where 
such  occur,  are  places  into  which  more  animals  fall  than  might  at  first 
sight  be  thought  probable.  In  some  of  our  limestone  districts,  where 
caverns  are  found  open  to  the  surface,  many  an  animal  is  lost,  notwith- 
standing the  precautions  usually  taken,  so  that  we  are  prepared  to 
expect  that,  in  uncultivated  regions,  animals  chased  by  others,  coming 
suddenly  upon  the  brink  of  a  fissure  and  unable  to  clear  it  at  a  bound, 
often  get  precipitated  into  it.  How  far  their  remains  may  be  preserved 
will  necessarily  depend  upon  circumstances.  While  even  inaccessible 
to  scavenger  quadrupeds,  many  of  these  fissures  are  open  to  scavenger 
birds,  who  may  descend  and  devour  the  flesh,  leaving  the  bones. 
Scavenger  insects  can  readily  also  consume  the  softer  parts.  The 
ultimate  preservation  of  the  bones  from  the  decomposing  effects  of 
atmospheric  influences  would  depend  upon  their  exclusion  from  them. 
The  accumulation  of  clayey  matter  in  the  fissures,  washed  in  from  the 
tops  or  sides  during  rains,  mingled  probably  with  fallen  portions  of 
rocks,  forming  the  sides  of  the  fissure,  will  tend  to  this  end.  Still 
better,  however,  would  be  their  entombment  by  calcareous  stalagmites 
and  stalactites,  where  these  were  found  in  the  fissures  of  limestones. 
In  the  latter  case,  we  might  have  an  ossiferous  limestone  breccia  rising 
to  the  surface  irregularly,  the  width  varying  with  the  form  of  the  walls 
of  the  original  fissure. 

Caves,  inhabited  for  a  length  of  time  by  the  same  kinds  of  animals, 
during  which  they  brought  in  their  prey,  so  that  such  parts  of  them- 
selves or  of  this  prey  which  may  have  remained  unconsumed  accumu- 
lated, would  also  afford  opportunities  for  the  preservation  of  vertebrate 
animal  remains,  according  to  circumstances.  If  these  remains,  even 
teeth,  continued  long  under  the  decomposing  conditions  likely  to  obtain 
in  such  situations,  without  some  protection  afforded  by  clay,  in  limestone 
caverns  by  stalagmites,  or  by  numerous  fallen  fragments,  few  traces 
would  be  expected,  while,  if  these  protecting  influences  existed,  such 
remains  might  often  be  preserved. 

It  is,  however,  to  the  aid  of  water  we  have  to  look  for  the  entomb- 
ment of  vertebrate  remains  in  the  largest  quantities,  though,  no  doubt, 
the  labours  of  Buckland  and  others  have  taught  us  how  much  may  be 
preserved  in  fissures  and  caverns.  We  have  already  noticed  the  loss  of 
animals  in  bogs  and  swamps.  In  some  regions,  the  collective  amount 


AMID    MINERAL    ACCUMULATIONS.  139 

of  those  which  perish  in  this  manner  must  be  considerable.  We  have 
reason  to  believe  that  many  mammals  perish  in  lakes,  sometimes  sink- 
ing into  soft  ground  on  their  borders,  at  others  while  endeavouring  to 
cross  them.  In  the  former  case  they  may  be  preserved,  as  in  bogs  and 
common  swamps,  in  a  nearly  vertical  position,  their  bones  occurring 
relatively  to  each  other  as  in  life.  In  the  latter,  their  bones  may  often 
be  scattered.  After  decomposition  had  sufficiently  advanced,  so  that 
the  dead  body  floated,  it  may  be  either  drifted  to  a  shallow  or  deep  side 
of  the  lake,  supposing,  for  illustration,  that  both  existed.  If  to  the 
latter,  and  decomposition  had  still  further  advanced,  and  probably  also 
the  scavenger  animals,  both  of  the  air  and  water,  had  consumed  no 
small  portion  of  it,  the  body  might  descend  into  deep  water,  with  the 
bones  still,  as  a  whole,  in  their  relative  positions,  so  that  if  detrital  or 
chemical  deposits  were  there  taking  place,  they  would  be  in  the  con- 
dition to  be  so  preserved.  If  drifted  and  stranded  on  a  shallow  part  of 
a  lake,  the  body  would  be  liable  to  be  attacked  with  facility  by  scavenger 
land  quadrupeds,  which  might  not  have  ventured  into  the  water  of  the 
deep  parts  of  the  lake  for  this  purpose.  In  many  instances,  as  those 
who  may  have  seen  the  dead  bodies  of  animals  under  such  circumstances 
are  aware,  the  bones  would  be  eventually  much  scattered,  part  of  them 
pulled  upon  the  dry  land  and  decomposed,  if  not  eaten,  while  another 
part  may)  under  favourable  circumstances,  again  enter  the  lake,  and  be 
there  enveloped  by  deposits  in  the  progress  of  formation. 

Whether  land  animals  floated  or  not  after  being  drowned  in  lakes 
must  often  depend  upon  the  consumption  of  their  flesh  while  submerged. 
The  various  regions  of  the  world  furnish  us  with  different  creatures  in- 
habiting such  pieces  of  water.  In  many  warm  climates,  the  bodies 
would  soon  be  attacked  by  reptiles,  capable  of  easily  destroying  their 
softer  parts.  In  some  countries,  the  crocodilian  family  would  speedily 
proceed  to  devour  them,  and  not  the  less  greedily  that  some  decompo- 
sition had  taken  place.  By  their  aid  some  animals  might  get  dismem- 
bered in  such  a  way  that  the  bones  became  finally  much  scattered,  and 
the  parts  of  the  same  animal  be  somewhat  spread  among  lacustrine  de- 
posits. The  crocodilians  themselves  may  add  not  a  little  to  the  remains 
of  terrestrial  vertebrata  entombed  in  lake  accumulations,  by  seizing 
animals  on  the  shores  and  dragging  them  into  the  water.* 

With  respect  to  the  remains  of  aquatic  reptiles  and  fish  in  lakes,  the 
voracity  of  many  of  these  creatures  is  commonly  so  great,  and  the  sys- 
tem of  mutual  prey  so  incessantly  kept  up  among  them,  that  entire 

*  The  caiman  of  the  great  West  India  Islands  in  this  way  frequently  obtains  dogs, 
and  sometimes  goats,  incautiously  approaching  a  place  where  he  may  be  lurking,  per- 
haps half-depressed  in  mud,  with  the  tip  of  his  snout  at  the  surface  of  the  water.  The 
caiman  is  considered  by  the  negroes  so  fond  of  dogs'  flesh,  that  when  a  bent  mangrove 
tree,  with  a  running  noose,  is  sometimes  placed  to  catch  one,  a  dog  in  a  stout  stockade, 
in  the  line  traced  out  for  the  caiman,  is  thought  one  of  the  best  baits. 


140  PRESERVATION    OF     ORGANIC    REMAINS 

skeletons  would  have  to  be  preserved  under  very  favourable  conditions. 
The  deltas  of  the  great  rivers,  especially  those  in  tropical  regions,  will 
afford  opportunities  for  the  study  of  the  manner  in  which  the  remains  of 
aquatic  reptiles  may  become  embedded  in  detrital  matter.  We  have 
seen  the  caiman  of  Jamaica,  when  pursued,  so  bury  himself  in  the  mud 
of  the  lagoons,  in  which  he  delights  to  live,  that  occasionally  there  must 
be  some  difficulty  of  withdrawal  from  it. 

Floods  in  rivers,  particularly  those  of  large  size,  flowing  amid  great 
plains,  where  the  sudden  rise  of  water  covers  a  large  area  in  a  short 
time,  concealing  the  more  shallow  portions,  would  appear  the  means  by 
which  many  mammals  are  swept  off  their  feeding-grounds,  drowned, 
and  their  dead  bodies  buried  amid  the  detritus  borne  down  at  the  same 
time.  At  such  times,  also,  bones  of  mammals  which  may  remain 
strewed  about  in  the  more  exposed  situations,  not  consumed  or  decom- 
posed, may  get  mingled  with  the  mud,  silt,  or  sands,  carried  forwards, 
and  finally  deposited.  To  delta  accumulations,  whether  in  lakes  or 
seas,  such  floods  must  often  bring  down  terrestrial  mammals  in  certain 
climates,  mingling  their  remains  with  those  of  many  reptiles. 

Though,  from  their  powers  of  flight  and  consequent  escape,  we 
should  not  expect  to  find  birds  caught  by  floods  so  as  to  be  carried 
away,  drowned,  and,  under  favourable  circumstances,  their  harder  parts 
entombed,  yet,  as  we  do  occasionally,  though  rarely,  find  the  body 
of  a  land  bird  borne  down  a  stream  in  countries  and  at  times  of  the 
year  when  we  have  no  reason  to  suppose  that  it  has  been  shot  or 
otherwise  destroyed  by  man,  perhaps  we  may  look  to  this  cause  as 
one,  however  occasional  and  rare,  by  which  remains  of  birds  may  be 
preserved.  It  is  in  districts  where  great  floods  may  suddenly  rise 
over  very  extensive  flat  lands,  particularly  at  times  when  the  young  of 
many  birds  inhabiting  and  breeding  upon  them  may  be  unable  to  fly  far 
or  at  all,  that  we  anticipate  the  more  frequent  surprises  of  this  kind. 
Land  birds  occasionally  fall  into  lakes  and  perish.  We  have  seen 
instances  in  which  land  birds  chased  by  hawks  have  fallen  into 
lakes.  Accidents  causing  death  may  also  now  and  then  happen  to  the 
waders  frequenting  the  margins  of  lakes,  as  also  to  birds  which  live  ha- 
bitually on  their  waters,  either  supporting  themselves  by  fishing  in  the 
shallow  parts,  like  the  swans,  or  by  the  aid  also  of  diving,  like  the  duck 
tribe.  The  preservation  of  their  bones,  once  at  the  bottom,  in  lacustrine 
accumulations,  would  be  the  same  as  with  other  animal  remains. 

Under  all  circumstances,  perhaps,  to  floods  passing  over  extensive 
flats,  raising  to  the  surface  of  the  water  the  dead  bodies  of  birds  which 
have  perished  by  natural  deaths,  as  their  state  of  decomposition  may 
permit,  or  sweeping  forwards  the  bones  of  others,  not  yet  consumed  by 
scavenger  animals,  we  may  look  for  one  of  the  chief  causes  of  the  trans- 


AMID  MINERAL  ACCUMULATIONS.  141 

port  by  water  and  entombment  of  the  remains  of  birds  in  the  resulting 
deposits.* 

During  floods  also  conditions  are  very  favourable  to  the  sweeping  off 
of  numerous  insects,  even  those  having  the  power  of  flight  being  caught 
up  in  the  waters  before  they  could  escape.  Multitudes  of  these  insects 
are  no  doubt  consumed  by  fish,  yet  the  remains  of  others  may  readily 
be  so  mingled  up  with  the  sediment  of  the  flood  waters  where  they  can 
deposit  it,  as  to  remain  permanently  encased  by  mud,  silt,  or  sand. 
Seeing  the  avidity  with  which,  in  general,  insects  cast  by  myriads,  as 
they  sometimes  are,  on  the  surface  of  lakes  or  pools  of  water,  are  de- 
voured by  fish,  when  we  discover  their  remains  embedded  in  calcareous 
matter,  as  they  have  been,  we  should  expect  circumstances  ill-suited  to 
the  habits  of  insectivorous  fish  and  aquatic  reptiles.  It  may  be  that  in 
waters  in  certain  pools  or  lakes  charged  with  large  quantities  of  car- 
bonate of  lime  in  solution  by  means  of  the  needful  carbonic  acid,  the 
latter  may  be  so  abundant  as  to  drive  off  the  insectivorous  fish,  and  pre- 
vent the  breeding  of  insect-eating  aquatic  reptiles,  their  young,  unable 
to  escape  from  the  water,  being  then  as  liable  to  be  injured  by  the 
amount  of  free  carbonic  acid  as  the  fish. 

We  find  the  remains  of  land  molluscs  mingled  with  soils  in  many  lo- 
calities in  sufficient  abundance  to  show  how  capable  the  shells  of  these 
animals  are  of  preservation  when  circumstances  will  permit.  Though 
light  as  regards  the  absolute  weight  of  each  shell,  the  specific  gravity 
of  land  shells  is  considerable,  more  approaching  that  of  arragonite  than 
of  common  calcareous  spar.f  In  soils,  the  shells  are  ill  placed  for  re- 
sisting decomposition  beyond  a  certain  amount  of  time,  the  waters  con- 
taining carbonic  acid  readily  percolating  to  them,  so  that  in  such  situa- 
tions they  are,  if  not  lately  embedded,  usually  brittle,  and  not  unfre- 

*  Neither  should  we  forget,  when  considering  the  manner  in  which  birds'  bones  #nay 
be  preserved  within  the  boundaries  of  land,  that  they  may  get  entangled  among  tra- 
vertines, and  thus  may  be  entombed  in  lines  and  patches  corresponding  with  such  cal- 
careous deposits  as  they  form  in  streams  or  pools,  as  under  favourable  circumstances 
in  Italy. 

In  the  great  deserts  of  the  world,  birds,  such  as  ostriches,  perishing,  their  remains 
may  be  often  covered  over  by  great  sand  drifts,  and  remain  so  long  beneath,  even  sup- 
posing some  change  of  drift  to  expose  them,  as  to  be  no  longer  available  as  food  to  the 
animals  which  would  otherwise  consume  them.  Some  may  remain  permanently  covered, 
until,  as  previously  mentioned,  by  a  change  of  geological  conditions,  these  deserts  may 
be  again  submerged,  and  their  sands  consolidated  into  rocks. 

f  "When  experimenting  some  years  since  upon  the  specific  gravity  of  shells,  we  found 
those  of  the  following  land  molluscs  to  be  : — 

Helix  Pomatia, 2-82 

Bulimus  decollatus,      .     .     .     .     2-85 

undatus, 2-85 

Auricula  bovina, 2-81 

Helix  citrina,  2-S7 


142  PRESERVATION    OF    ORGANIC    REMAINS 

quently  broken.  Among  blown  sands  land  shells  are  often  abundant, 
some  land  molluscs  especially  delighting  in  such  habitats. 

In  volcanic  countries,  or  those  over  which,  from  their  proximity  to 
such  countries,  volcanic  ashes  may  be  scattered,  and  sometimes  abun- 
dantly, land  shells,  and,  indeed,  various  other  land  animals,  may  be 
completely  covered  over  with  coatings  sufficient  not  only  to  kill  them, 
but  to  aid  in  the  preservation  of  their  hard  parts.  The  fall  of  great 
quantities  of  ashes  and  cinders,  discharged  in  some  volcanic  eruption, 
would  appear  to  cause  a  greater  sudden  entombment  of  terrestrial  ani- 
mals, with  the  probability  of  preserving  their  more  solid  parts  entire, 
than  can  be  obtained  without  the  aid  of  water,  even  including  the  moving 
sands  of  deserts.  Volcanic  districts  are,  in  temperate  and  tropical  re- 
gions, often  fertile,  abounding  in  vegetable  and  animal  life,  so  that  in 
regions,  such  as  Sumbawa  and  Java,  for  example,  land  animals,  including 
an  abundance  of  molluscs,  may  be  readily  buried  beneath  discharges  of 
lapilli  and  ash,  such  as  were  vomited  forth  from  the  volcano  of  Tomboro, 
in  Sumbawa,  in  April,  1815.* 

*  The  eruptions  commenced  on  the  5th  April,  and  continued  more  or  less  until  the 
10th,  when  they  became  more  violent.  A  Malay  prahu  was  on  the  llth,  though  distant 
from  Sumbawa,  enveloped  in  utter  darkness  from  the  ashes  in  the  air.  Upon  landing 
afterwards  on  the  island,  the  commander  found  the  country  covered  to  the  depth  of 
three  feet  by  ashes  and  cinders ;  and  difficulty  was  experienced  in  sailing  through  the 
cinders  floating  on  the  sea.  At  Macasar,  217  nautical  miles  from  Tomboro,  the  vol- 
canic discharges  were  heard  to  such  an  extent  that,  supposing  there  was  an  engage- 
ment with  pirates  near  at  hand,  the  East  India  Company's  cruiser,  "  Benares,"  was 
despatched  with  troops  on  board  to  look  after  them.  The  following  account,  by  the 
commander  of  the  «'  Benares,"  obtained  by  Sir  Stamford  Raffles,  will  show  the  amount 
of  ashes  and  cinders  vomited  forth : — 

Proceeding  south  to  ascertain  the  cause  of  the  explosions  heard,  at  8  o'clock  on  the 
morning  of  the  12th,  "the  face  of  the  heavens  to  the  southward  and  westward  had 
assumed  a  dark  aspect,  and  it  was  much  darker  than  when  the  sun  rose ;  as  it  came 
nearer  it  assumed  a  dusky  red  appearance,  and  spread  over  every  part  of  the  heavens ; 
by  ten  it  was  so  dark  that  a  ship  could  hardly  be  seen  a  mile  distant ;  by  eleven  the 
whole  of  the  heavens  was  obscured,  except  a  small  space  towards  the  horizon  to  the 
eastward,  the  quarter  from  which  the  wind  came.  The  ashes  now  began  to  fall  in 
showers,  and  the  appearance  was  altogether  truly  awful  and  alarming.  By  noon  the 
light  that  remained  in  the  eastern  part  of  the  horizon  disappeared,  and  complete  dark- 
ness covered  the  face  of  day.  This  continued  so  profound  during  the  remainder  of  the 
day  that  I,"  continues  the  commander  of  the  "  Benares,"  "  never  saw  anything  to  equal 
it  in  the  darkest  night ;  it  was  impossible  to  see  the  hand  when  held  close  to  the  eyes. 
The  ashes  fell  without  intermission  throughout  the  night,  and  were  so  light  and  subtile 
that,  notwithstanding  the  precaution  of  spreading  awnings  fore  and  aft  as  much  as 
possible,  they  pervaded  every  part  of  the  ship. 

"At  six  o'clock  the  next  morning  it  continued  as  dark  as  ever,  but  began  to  clear 
about  half-past  seven,  and  about  eight  o'clock  objects  could  be  faintly  observed  on 

deck.  From  this  time  it  began  to  clear  very  fast The  appearance  of  the 

ship  when  daylight  returned  was  most  singular ;  every  part  being  covered  with  falling 
matter.  It  had  the  appearance  of  calcined  pumice-stone,  nearly  the  colour  of  wood 
ashes ;  it  lay  in  heaps  of  a  foot  in  depth  on  many  parts  of  the  deck,  and  several  tons 
of  it  must  have  been  thrown  overboard;  for  though  an  impalpable  powder  or  dust 


AMID    MINERAL    ACCUMULATIONS.  143 

The  great  eruption  of  Vesuvius  in  79  furnishes  us  with  an  excellent 
example  of  the  manner  in  which  the  surface  of  a  country  may  be 
covered  up  by  the  discharge  of  volcanic  ashes  and  lapilli,  so  that  various 
works  of  art  and  use  are  preserved  for  our  instruction.  Pompeii  not 
only  shows  us  paintings  still  remaining  on  the  walls  of  the  houses,  but 
also  a  great  variety  of  delicate  articles,  extending  to  those  of  the 
women's  dressing-cases.  At  Herculaneum  we  have  even  the  writings 
of  the  time  on  papyri,  in  part  still  legible.  We  see  an  abundance  of 
men's  works  as  they  were  overwhelmed  by  the  discharge  of  the  ashes 
and  cinders  upon  them,  and  often  in  a  condition,  after  being  thus  buried 
beneath  mineral  matter,  permeable  to  water,  for  1800  years,  which 
might  not  at  first  be  expected.  So  little  general  injury  seems  to  have 
been  sustained  by  the  town,  even  by  the  shocks  of  explosions  so  near, 
or  earthquake  movements,  that  the  crushing  in  of  house-tops  by  means 
of  the  weight  of  ashes  and  cinders,  and  the  filling  up  of  all  corners  by 
the  finer  dust,  seem  to  have  been  the  chief  effects  produced.  Walking 
in  the  street  of  tombs  at  Pompeii  it  seems  to  require  little  else  than  the 
presence  of  persons  clothed  in  the  costume  of  the  place  when  over- 
whelmed by  cinders  and  ashes,  to  have  that  street  presented  to  us  as  it 
appeared  1800  years  since.  As  showing  that  not  only  bones  may  be 
preserved  under  such  conditions,  but  the  form  of  the  flesh  which  clothed 
them,  under  favourable  circumstances,  two  remarkable  instances  have 
occurred  at  Pompeii,  where  parts  of  the  human  form  were  perfectly 
preserved,  the  enveloping  ash  having  sufficiently  consolidated,  before 
the  decomposition  of  the  fleshy  parts,  to  retain  their  external  shape. 
The  thickness  of  the  ashes  and  lapilli  which  covered  up  Stabiae,  Pompeii, 
and  Herculaneum,  in  79,  has  been  estimated  as  varying  from  60  to  112 
feet  in  depth.* 

•when  it  fell,  it  was,  when  compressed,  of  considerable  weight.  A  pint  measure  of  it 
weighed  twelve  ounces  and  three-quarters;  it. was  perfectly  tasteless,  and  did  not 
affect  the  eyes  with  a  painful  sensation;  had  a  faint  smell,  but  nothing  like  sulphur; 
when  mixed  with  water  it  formed  a  tenacious  mud  difficult  to  be  washed  off." 

Approaching  Sumbawa  on  the  18th,  the  "Benares"  encountered  an  immense  quan- 
tity of  pumice,  mixed  with  numerous  trees  and  logs  with  a  burnt  and  shivered  ap- 
pearance. The  fall  of  ashes  at  Bima,  40  miles  from  the  volcano,  was  so  great  as  to 
break  in  the  President's  house  in  many  places.  The  Rajah  of  Saugar  described 
some  of  the  stones  which  fell  there  to  have  been  as  large  as  two  fists,  though  not 
generally  above  the  size  of  walnuts.  A  great  whirlwind  is  mentioned  by  the  Rajah, 
"which  blew  down  nearly  every  house  in  the  village  of  Saugar,  carrying  the  tops 
and  light  parts  along  with  it.  In  the  part  of  Saugar  adjoining  Tomboro  its  effects 
were  much  more  violent,  tearing  up  by  the  roots  the  largest  trees,  and  carrying  them 
into  the  air,  together  with  men,  houses,  cattle,  and  whatever  else  came  within  its  influ- 
ence." Many  thousands  of  lives  were  lost,  and  the  vegetation  of  the  north  and  west 
sides  of  the  peninsula  was  completely  destroyed,  with  the  exception  of  a  high  point  of 
land  where  the  village  of  Tomboro  previously  stood,  and  where  a  few  trees  still  re- 
mained.— Life  of  Sir  Stamford  Raffles. 

*  Daubeny,  "Description  of  Active  and  Extinct  Volcanoes,"  2d  edit.,  1848,  p.  221. 


144  PRESERVATION    OP    ORGANIC    REMAINS 

There  are  few  things  we  can  consider  more  suddenly  destructive  of 
terrestrial  animal  and  vegetable  life  than  these  great  volcanic  eruptions, 
particularly  within  areas  where  several  feet  of  lapilli  and  ashes  can  be 
accumulated  over  a  considerable  area  within  a  few  days.  The  whole 
surface  previously  clothed  with  vegetation,  with  a  multitude  of  land 
molluscs  and  insects,  with  many  birds  and  mammals,  may  be  all  covered 
with  a  thick  coating  of  these  volcanic  products ;  many  of  the  molluscs 
and  insects  close  to  the  plants  on  which  they  may  have  been  feeding. 
In  the  regions  where  bogs  prevail,  large  tracts  of  these  vegetable  accu- 
mulations may  be  buried,  with  any  birds,  insects,  or  molluscs  frequent- 
ing them,  by  a  thick  layer  of  ashes  and  lapilli,  the  consolidation  of 
which,  by  after  geological  causes,  might  produce  the  deceptive  appear- 
ance of  a  molten  rock  having  flowed  over  them  without  producing  those 
effects  which  would,  under  the  latter  supposition,  have  been  anticipated. 
Indeed,  when  we  have  to  study  the  fossil  vegetation  of  some  regions,  a 
reference  to  the  conditions  under  which  trees  and  even  bogs  may  be 
covered  by  volcanic  ashes  is  one  by  no  means  to  be  neglected.* 

In  tideless  seas,  terrestrial  animal  and  vegetable  substances,  borne 
down  floating  on  the  rivers,  necessarily  pass  out  over  the  dense  waters 
of  the  sea  to  various  distances,  according  to  circumstances,  and  may  be 
transported  still  further  than  the  force  of  the  river  waters  have  carried 
them  by  favouring  currents,  should  there  be  such,  or  by  winds,  the 
latter  capable  of  driving  them  about  in  various  directions,  should  they 
change.  The  body  of  a  drowned  animal,  the  decomposition  of  which  is 
sufficiently  advanced  to  give  it  the  specific  gravity  capable  of  floating, 
(and  it  should  be  recollected  that  it  would  float  easier  in  sea  than  in 
fresh  water,  as  regards  its  own  specific  gravity,)  may  be  thus  drifted  a 
considerable  distance  until  eaten,  or  too  much  decomposed  to  float. 
Small  animals  may  be  readily  consumed,  bones  as  well  as  flesh,  by  the 
larger  voracious  fish,  but  the  bones  of  the  larger  mammals  might,  under 
favouring  circumstances,  find  their  way  to  the  bottom,  even  in  deep 
tideless  seas,  like  parts  of  the  Mediterranean,  to  be  there  mingled  with 
the  remains  of  molluscs  or  other  creatures  inhabiting  the  same  depths. 

The  observer  has,  in  like  manner,  to  consider  the  various  land  plants 
and  trees  which  can  be  carried  long  distances,  sometimes  with  live 
creatures  still  upon  them,  parts  of  these  subsequently,  at  least  those 
which  may  escape  the  voracity  of  marine  animals,  scattered  over  various 

*  It  is  stated  that  in  consequence  of  the  great  eruption  of  Skaptar-jakull  in  1783,  the 
atmosphere  over  Iceland  was  impregnated  with  dust  for  a  long  time.  Traces  of  this 
dust  were  observed  in  Holland.  It  is  evident  that  bogs  in  Iceland  may  readily  become 
buried  beneath  volcanic  ashes  and  cinders  under  such  conditions.  Wo  may  t:ike  the 
great  explosion  of  the  Souffrier,  in  Guadaloupe,  in  1812,  as  an  example  of  the  destruction 
of  vegetable  and  animal  life,  and  a  considerable  covering  of  both  in  many  places  in  a 
tropical  region.  It  was  during  this  eruption  that  ashes  were  conveyed  to  Barbudoes 
by  an  upper  current  of  wind,  opposite  to  the  Trade  Wind. 


AMID    MINERAL    ACCUMULATIONS.  145 

depths  of  the  sea  bottom,  many  a  floating  log  of  wood  seized  upon  after 
a  time  by  marine  animals,  and  either  bored  into  or  covered  by  them  as 
their  habits  may  be.  It  will  require  little  attention  to  see  how  often 
the  dead  shells  of  land  molluscs  thus  get  thrust  out  seawards,  their 
modes  of  floatation  at  first  being  such  as  to  keep  them  above  water. 
How  long  they  retain  the  positions  necessary  for  this  purpose,  it  will 
be  observed,  will  depend  upon  the  state  of  the  sea  surface  at  the  time. 
If,  notwithstanding  the  state  of  weather  which  may  have  caused  floods 
in  the  interior  of  adjoining  lands,  lifting  off  the  dead  shells  from  the 
low  grounds  in  multitudes,  the  sea  be  moderately  calm,  the  land  shells 
will  be  carried  on  with  the  river  waters,  but  if  there  be  a  breaking  sea 
they  soon  get  upset  and  sink. 

In  such  situations  we  have  also  to  regard  the  mingling  of  detrital 
with  organic  matter,  which  may  be  effected  by  the  pushing  forward  of 
the  sands  and  gravel  on  the  bottom  of  the  rivers.  Many  a  drowned 
animal  may  thus  become  mixed  up  with  the  delta  advance,  and  many  a 
river  and  land  mollusc  be  included  amid  the  general  subaqueous  drift. 
Trees  often  get  entangled  and  buried  on  the  coast,  as  well  as  floated  off 
seaward. 

Thus  in  tideless  seas  we  have  the  ready  means  of  transporting  terres- 
trial and  fluviatile  vegetable  and  animal  remains  to  various  distances 
seaward,  some,  under  favourable  circumstances,  capable  of  being  embed- 
ded in  marine  deposits  at  various  depths,  while  others  are  included  amid 
the  detrital  accumulations  formed  by  the  action  of  the  rivers,  thrusting 
out  silt,  sand  and  gravel  from  the  shores,  not  forgetting  any  calcareous 
deposits  which  may  sometimes  be  added. 

In  estuaries  we  obtain  a  state  of  things  somewhat  different.  In  them 
a  check  is  afforded  to  all  borne  floating  out  by  rivers  at  each  flood  tide, 
so  that  when  great  freshets  prevail  in  the  rivers,  all  caught  up  by  the 
floods  in  the  interior  and  floated  off  low  grounds,  or  borne  to  the  main 
streams  by  tributaries,  are  arrested  in  their  progress.  The  floating 
bodies  of  animals,  trees,  and  smaller  plants,  are  thus  not  permitted  to 
escape  directly  seaward,  but  are  lifted  by  the  height  of  the  tide  over 
any  low  grounds  bordering  the  estuary,  these  flats,*  at  such  times,  being 
more  than  commonly  covered  with  water.  When  the  ebb  tide  lowers 
the  waters,  the  various  substances  floated  over  the  estuary  lowlands  not 
unfrequently  remain  upon  them,  more  particularly  if  any  wind  prevailing 
at  the  time  forces  them  on  the  edges  of  the  flooded  lands.  There  is 
often  a  curious  mixture  of  terrestrial,  fluviatile,  estuary,  and  more 
marine  animal  and  vegetable  remains  scattered  over  the  estuary  flats 
after  such  floods,  more  particularly  should  it  happen,  as  it  sometimes 
does  on  the  western  parts  of  the  British  Islands,  that  a  heavy  gale, 
accompanied  by  much  rain,  occurs  at  a  time  of  spring  tides,  so  that  the 
high  tides  combined  with  an  on-shore  wind,  raising  the  sea  waters  still 

10 


146  PRESERVATION    OF    ORGANIC    REMAINS 

higher,  are  met  by  strong  freshets  from  the  land.  Under  ordinary 
conditions,  fringes  of  estuary  fuci,  mingled  with  land  plants,  estuary 
crustaceans,  and  molluscs  and  land  shells,  with  here  and  there  the  re- 
mains of  some  creature,  more  strictly  marine,  are  familiar  to  all  visiting 
estuaries. 

Although  amid  the  deltas  of  rivers  delivering  their  waters  into  tideless 
seas,  among  the  lagoons  formed  and  the  coasts  adjoining,  there  may  be 
variable  mixtures  of  fresh  and  sea  waters,  affording  proper  places  for 
the  growth  and  increase  of  vegetables  and  animals  fitted  for  living  in 
brackish  water,  the  conditions  are  different  from  those  of  an  estuary. 
In  the  one  case  the  waters  are  stationary,  except  so  far  as  floods  from 
the  interior  may  force  forward  an  extra  amount  of  fresh  water,  or  a 
prevailing  on-shore  wind  may  drive  in  a  greater  volume  of  sea  water ; 
while  in  the  other,  large  tracts  are  sometimes  bare  at  one  time  and 
covered  by  water  at  another,  the  amount  of  the  saline  mixture  being 
variable  also,  depending  on  the  state  of  the  tide  and  the  volume  of  fresh 
water  falling  for  the  time  into  the  estuary.  And  here  it  is  necessary  to 
remark  that  the  observer  should  not  consider  as  an  estuary  one  of  those 
great  indentations  of  a  coast,  commonly  termed  an  "arm  of  the  sea," 
and  which  is  but  the  consequence  of  the  sea  level  cutting  a  previously 
formed  inequality  of  the  land  surface,  not  unfrequently  the  prolongation 
of  some  valley.  No  doubt  the  one  kind  of  coast  may  sometimes  shade 
into  the  other,  but  as  regards  the  kind  of  life  inhabiting  estuaries,  we 
should  consider  brackish  water  as  essential  to  the  latter,  at  all  events 
to  such  an  extent  that  at  low  tide  a  river,  the  waters  of  which  become 
fresh  or  brackish,  should  occupy  the  channel  left. 

Under  the  conditions  of  an  estuary  silting  up  in  the  manner  previously 
noticed  (p.  108,)  it  must  necessarily  happen  that  the  molluscs  and  other 
creatures  inhabiting  different  surfaces,  or  small  depths  beneath  them, 
died,  such  harder  parts  of  them  as  might  be  preserved  remaining  at 
levels  corresponding  with  such  surfaces,  mingled  here  and  there  accord- 
ing to  circumstances,  with  vegetable  and  animal  remains,  drifted  as 
above  mentioned.  An  observer  will  do  well  to  examine  the  manner  in 
which  the  different  parts  of  an  estuary  surface  may  vary  at  the  same 
time  as  to  the  animal  life  existing  upon  it,  from  the  creatures  inhabiting 
the  little  rills  of  water  which  only  get  checked  at  spring  tides,  otherwise 
meandering  amid  the  higher  estuary  mud  or  clay-flats,  to  those  in  or 
upon  the  sands  in  the  more  exposed  situations,  covered  by  the  tide. 

The  manner  in  which  terrestrial  animals  may  become  caught  in  the 
softer  places  should  also  receive  attention,  especially  where  springs, 
beneath  silt  and  sand,  form  quaking  or  quick  sands  which  engulf  them, 
their  bones  remaining  after  the  flesh  has  been  consumed  by  the  scavenger 
animals,  readily  finding  their  way  amid  such  soft  ground.  An  observer 
should  by  no  means  neglect  the  foot-prints  of  terrestrial  animals,  nor 


AMID    MINERAL    ACCUMULATIONS.  147 

indeed  of  any  leaving  marks  or  trails,  such  having  lately,  and  very 
deservedly,  become  of  geological  importance.  These  foot-prints  are 
often  excellently  well  preserved  upon  the  mud  or  clay-flats,  or  gently 
sloping  grounds  of  estuaries.  Very  many  estuaries  around  the  British 
Islands  afford  abundant  opportunities  for  the  study  of  the  mixed  foot- 
prints of  birds  and  mstmmals  upon  the  mud  or  clay,  more  especially 
during  the  heats  of  summer,  and  at  neap  tides,  when  extensive  surfaces 
covered  at  spring  tides,  may  be  bare  and  exposed  to  the  drying  influence 
of  the  sun.  We  have  often  seen  the  foot-prints  of  common  gulls,  where 
these  birds  have  been  busy  around  some  mollusc,  crustacean,  or  fish 
drifted  on  shore,  sufficiently  in  a  fresh  state  for  their  food,  most  beauti- 
fully impressed  upon  clay  or  mud,  hard  dried  by  the  sun,  the  courses 
of  the  birds,  sometimes  single,  at  others  in  pairs  or  more  numerous,  in 
search  of  more  food,  equally  well  marked,  and  again  other  confused 
foot-prints  where  such  new  food  was  found.  In  the  same  way  the  tracks 
of  other  "birds  are  common,  crossed  here  and  there  by  those  of  rabbits, 
hares,  stoats,  and  weasels,  and  occasionally  of  dogs.  In  some  localities, 
after  an  area  of  mud  or  clay  thus  trod  upon  during  the  difference  of 
time  between  the  springs  and  the  neap  tides,  has  been  well  dried  by  the 
heats  of  the  summer  sun,  deep  cracks  formed  in  clay  by  the  loss  of 
moisture,  pieces  of  the  most  instructive  kind  may  with  care  be  taken 
away,  further  dried  and  preserved,  and  even  baked  into  a  brick-substance, 
if  the  composition  of  the  clay  be  well  suited  to  the  purpose.  Mingled 
with  these  marks  we  have  often  also  the  trails  of  molluscs,  as  also  those 
of  estuary  crustaceans,  striving  to  regain  the  water,  after  finding  them- 
selves left  by  the  tide. 

It  might  at  first  be  supposed  that  the  rise  of  the  tides  over  this,  for 
the  time,  somewhat  hard  surface,  marked  by  the  foot-prints  and  trails 
of  different  animals,  would  entirely  obliterate  all  traces  of  them.  How 
far  this  may  be  effected  will,  however,  depend  upon  circumstances.  If 
the  rise  of  the  tides  from  neaps  to  springs  were  accompanied  by  much  rip- 
ple -or  waves  from  winds,  it  would  scarcely  be  anticipated  that  the  fine 
detritus  constituting  the  mud  or  clay  would  not,  when  remoistened,  be 
readily  caught  up  in  mechanical  suspension,  so  that  all  traces  of  foot- 
prints and  trails  would  be  removed.  In  all  situations  where  such  ripple 
or  waves  could  be  felt  this  would  be  expected.  All  parts  of  estuaries 
are  rarely  exposed  to  such  influences  at  the  same  time :  many  a  nook 
remains  tranquil ;  and  in  those  where  the  accumulation  of  detritus  is  in 
progress,  films  or  fine  layers  of  mud  succeed  each  other,  and  if  one 
becomes  hardened  before  another  is  deposited,  a  line  of  separation  more 
or  less  permanent  may  be  established  between  them.  That  this  may, 
under  favourable  circumstances,  happen,  is  proved  by  being  sometimes 
able  to  separate  the  layers  from  each  other,  after  careful  drying,  so 
that  foot-prints  are  seen  upon  many  surfaces,  beneath  each  other.  We 


148  PRESERVATION    OF    ORGANIC    REMAINS 

have  been  fortunate  in  this  respect  with  some  portions  of  sun-dried  mud 
of  the  Severn  estuary ;  and  Mr.  Lyell  has  pointed  out  the  manner  in 
which  the  foot-prints  of  the  sandpiper  (Tringa  minutd)  are  not  only 
preserved  in  the  red  mud  of  the  Bay  of  Fundy  (a  locality  so  favourable, 
from  its  tides,  for  the  exposure  of  much  ground  at  the  neaps),  but  also 
repeated  upon  the  different  layers  of  accumulation. 

In  some  estuaries,  long  necks  of  sands  and  sand  hills  so,  in  part,  cross 
their  mouths,  that  bays  of  still  or  comparatively  still  water,  occasionally 
of  considerable  area,  occur  behind  them,  the  main  streams  of  tide  flow- 
ing elsewhere.  Let  us  assume,  for  illustration,  that  fig.  50  (p.  82) 
represents  some  estuary  of  this  kind,  and  that,  instead  of  a  shingle 
beach,  d  is  a  tract  of  sandhills,  perhaps  extending  several  miles  in 
length,  then  e  would  be  the  kind  of  bay  noticed,  left  in  comparative  quiet, 
as  regards  the  stream  of  tide,  flowing  chiefly  on  the  opposite  coast. 
Much  would  of  course  depend  upon  conditions  as  to  the  kind  of  deposit, 
effected  at  e,  but  under  the  supposition  that  the  set  of  the  tides  was 
such  as  not  to  cause  a  sweep  of  the  stream  round  this  bay,  it  would  be 
favourable  for  the  occasional  deposit  of  the  finer  sediment  or  mud  borne 
down  the  river,  /,  by  floods.  At  the  same  time  it  would  be  exposed  to 
the  drift  of  sand  from  the  sandhills,  d.  In  such  localities,  we  have  seen 
the  foot-prints  of  mammals  and  birds,  hardened  in  the  sun,  well  strewed 
over  by  the  drift  sand  from  the  sandhills ;  and  it  should  be  observed, 
that  the  same  winds  which  were  powerful  enough  to  disturb  the  sandhills 
and  cause  the  drift,  would  be  prevented  by  the  shelter  afforded  behind 
the  same  hills  from  disturbing  the  bay  waters  near  shore,  these  waters 
being  under  the  lee  of  the  sandhills,  so  that  even  in  the  shore  and 
shallow  waters  the  sand  may  be  drifted  over  the  mud  or  clay,  filling  up 
the  hollows  of  the  foot-prints.  How  far  any  alternate  layers  of  this 
kind  may  remain  undisturbed,  must  depend  upon  circumstances. 

Should  the  general  surface  of  the  land  be  subsiding  gradually,  as 
regards  the  sea  level,  it  will  be  obvious  that  great  estuaries  may  present 
conditions  highly  favourable  to  the  preservation  of  the  foot-prints  of 
animals,  the  actual  remains  of  which,  amid  the  detrital  accumulations, 
may  be  most  rare.  Many  aquatic  birds  frequenting  estuaries  at  parti- 
cular times,  often  when  driven  to  seek  their  food  in  such  situations,  from 
tempestuous  weather  in  their  more  common  sea  haunts,  may  thus  leave 
their  foot-prints,  the  conditions  for  the  preservation  of  whose  bones  in 
the  estuary  deposits  themselves  would  be  of  the  most  rare  kind,  indeed 
not  to  be  expected,  except  under  the  accident  of  some  individual  being 
killed  when  up  the  estuary.  With  the  more  truly  estuary  birds,  those 
which  build  and  commonly  live  on  estuary  shores,  the  case  might  be 
different.  Upon  the  supposition  of  a  gradual  change  in  the  level  of  the 
sea,  the  land  descending,  we  might  have  sands  abundantly  thrust  for- 
ward over  clay  with  foot-prints  and  trails.  A  lowering  of  a  mass  of 


AMID    MINEKAL    ACCUMULATIONS.  149 

sandhills,  partly  barring  the  mouth  of  an  estuary,  would  at  once  place 
much  arenaceous  matter  within  the  transporting  influence  of  the  tidal 
waters,  to  be  drifted  over  mud-flats,  formed  previously  behind  them. 
In  some  regions,  the  mass  of  sand,  either  accumulated  as  partial  and 
subaerial  bars,  or  more  gathered  together  by  the  sides  of  estuary 
mouths,  to  be  again  thrown  into  tides,  however  eventually  other  sand- 
hills and  tracts  might  arise  (conditions  continuing  favourable),  would  be 
considerable. 

That  the  remains  of  cetaceans  should  be  found  amid  estuary  accumu- 
lations, as  also  those  of  numerous  fish,  some  of  them  more  known  as 
purely  marine  than  estuary,  will  not  surprise  those  who  may  have  seen 
the  porpoises  dashing  up  the  estuaries  of  our  coasts  in  chase  of  fish 
which  they  have  driven  before  them,  and  their  occasional  entanglement 
in  shoal  waters,  when  left  by  a  quick-falling  tide.  Other  cetaceans  also 
get  sometimes  stranded.  It  is  more  common  to  find  the  chased  fish, 
especially  the  small  fry,  driven  on  shore.  The  birds,  no  doubt,  then 
pick  up  the  fish  abundantly,  so  that  only  a  minor  portion  may  leave 
their  hard  remains  for  entombment,  and  doubtless,  also,  the  cetaceans 
often  escape  in  the  pools  where  they  may  be  caught,  upon  the  rise  of  the 
tide,  but  there  are  still  many  chances  for  the  preservation  of  the  harder 
parts  of  these  animals  amid  estuary  accumulations,  which  should  not  be 
neglected. 

It  is,  however,  in  connexion  with  the  sea,  looking  at  the  evidence 
afforded  us  by  the  various  fossiliferous  rocks  of  different  geological  ages, 
that  we  should  look  for  the  preservation  of  the  great  mass  of  animal 
remains  amid  the  detrital  and  chemical  deposits  of  the  time.  We  have 
seen  that,  by  means  of  rivers  and  winds,  various  plants  and-  animals,  or 
their  parts,  may  be  borne  into  the  sea,  and  that  in  estuaries  we  may 
have  the  condition's  for  a  mixture  of  terrestrial  and  marine  remains,  and 
of  others  suited  especially  to  such  situations.  In  respect  to  estuaries, 
some  so  gradually  change  into  arms  of  the  sea,  to  be  seen  on  the  large 
scale  in  the  Gulf  and  River  of  St.  Lawrence,  and  other  situations,  and 
equally  well  in  numerous  localities  of  far  less  area,  in  various  parts  of 
the  world,  as,  for  instance,  in  the  Bristol  Channel  and  the  Severn  es- 
tuary, that  no  marked  distinctions  can  be  drawn  between  the  one  and 
the  other. 

Viewing,  therefore,  the  coasts  of  the  world  generally,  we  not  only 
have  to  regard  all  the  modifications  for  the  existence  of  marine  animal 
life  arising  from  the  more  or  less  exposed  or  sheltered  situations  of 
headlands,  bays,  and  other  forms  of  shore,  but  also  the  mingling  of  fresh 
waters  with  the  sea  under  the  various  circumstances  in  which  the  drain- 
age of  the  land  is  thrown  seaward.  Let  us  consider  the  modifications 
of  condition  for  the  existence  and  entombment  of  marine  animal  life 
from  Cape  Horn  to  Baffin's  Bay.  First,  there  is  the  difference  of  cli- 


150  PRESERVATION    OF    ORGANIC    REMAINS 

mate,  producing  modifications  of  no  slight  order,  more  especially  in 
moderate  depths.  From  Cape  Horn  to  the  West  India  Islands,  with  the 
exception  of  the  Straits,  of  Magellan,  there  is  an  unbroken  oceanic  coast, 
subject  to  the  action  of  the  tides,  upon  which  bodies  of  fresh  water  are 
thrown  by  drainage  channels  in  different  places,  the  chief  of  which  are 
the  Rio  de  la  Plata,  the  Rio  de  San  Francisco,  the  Tocantins,  the  Ama- 
zons, and  the  Orinoco  rivers,  delivering  the  portion  of  rains  and  melted 
snows  not  taken  up  by  the  animal  and  vegetable  life,  or  required  for 
the  adjustment  of  springs  or  other  interior  conditions  of  a  large  part 
of  South  America.  After  a  line  of  coast  little  broken  by  rivers,  we 
find  extensive  estuary  conditions  at  the  mouth  of  the  Plata,  and  not  far 
beyond  Lake  Mirim,  about  100  miles  long,  a  body  of  water  apparently 
cut  off  from  the  ocean  by  coast  action,  and  draining  into  another  lake 
or  lagoon,  Lago  de  los  Patos,  having  a  channel  still  open  to  the  main 
sea,  and  about  150  miles  long,  with  an  extreme  breadth  of  about  50 
miles.  In  these  two  bodies  of  water,  receiving  the  drainage  of  the  ad- 
joining land,  there  are  necessarily  modifications  of  the  ocean  conditions 
for  life,  and  for  the  entombment  of  its  remains  outside  in  the  main  sea. 
A  range  of  coast  succeeds,  into  which  comparatively  small  rivers  discharge 
themselves,  until  the  San  Francisco  presents  itself,  and  so  on  afterwards 
until  the  mouths  of  the  Para  and  Amazons  join  in  forming  (and  in- 
cluding between  them,  the  Island  of  Marajo)  great  estuary  conditions, 
the  tides  being  felt  up  the  latter  river,  it  is  stated,  600  miles,  so  that 
there  are  several  in  the  river  at  the  same  time. 

The  mouths  of  the  Orinoco  present  us  with  delta-form  accumulations, 
and  then  comes  the  Caribbean  Sea,  influenced  by  the  ponded-back 
waters  of  the  Gulf  of  Mexico,  so  that  a  kind  of  tideless  sea  shades  into 
one  where  the  tides  are  more  felt.  More  northerly,  the  Gulf  Stream  is 
seen,  transporting  warmer  waters  to  colder  regions,  and  skirted  by  a 
shore,  marked  by  a  line  of  lagoons  for  above  200  miles  on  the  coast  of 
Florida,  one  of  them  named  the  Indian  River,  about  110  miles  in  length, 
with  an  extreme  breadth  of  6  miles ;  another,  the  Mosquito  Lagoon,  being 
about  60  miles  long,  with  the  like  extreme  breadth.  Thence  a  much- 
indented  shore,  on  the  minor  scale,  continues  until  we  come  to  Cape 
Fear  (Carolina),  where  the  lagoon  conditions  obtain,  a  kind  of  barrier, 
broken  by  passages  termed  Met8,  permitting  the  ingress  and  egress  of 
sea  waters.  In  Core,  Pamlico,  Albemarle,  and  Currituck  Sounds,  we 
find  a  great  body  of  water  of  an  irregular  shape,  measuring  along  the 
line  of  barrier  separating  them,  except  where  broken  by  inlets  from  the 
ocean,  about  160  miles  in  length.  Rivers  drain  into  this  body  of  water 
in  various  directions,  so  that  estuary  conditions  obtain  in  different  places, 
while  the  great  barrier  banks,  a  point  of  one  of  which  forms  Cape  II  at- 
teras,  place  it  under  a  modification  of  the  conditions  outside  in  the  main 
sea.  More  northward,  we  obtain  the  great  indentation  of  the  Chesa- 


AMID    MINERAL    ACCUMULATIONS.  151 

peake  Bay,  with  its  minor  breaks  into  the  land,  the  chief  of  which  is  the 
Potomac ;  and  then  the  Delaware  Bay,  with  its  river  extending  inland, 
the  lagoon  coast  and  its  inlets  continuing  from  Cape  Charles  (north  en- 
trance of  Chesapeake  Bay)  towards  the  Delaware,  and  from  near  Cape 
Mary  (Delaware  Bay)  about  85  miles  to  the  northward.  Next  follows 
the  mouth  of  the  Hudson,  and  the  modifications  arising  from  the  shelter 
of  Long  Island  up  the  sound  at  its  back,  the  lagoon  character  still  ap- 
parent on  part  of  its  ocean  coast.  After  shores  variously  indented,  we 
reach  the  Bay  of  Fundy,  with  all  the  modifications  due  to  the  great  rise 
of  tide  (p.  103)  at  its  northern  extremities.  This  is  succeeded  by  the 
great  estuary  conditions  of  the  St.  Lawrence,  and  finally  the  large  in- 
dentations of  Baffin's  Bay  and  Strait,  and  Hudson's  Bay  and  Strait,  and 
all  the  other  channels  of  the  cold  regions  of  North  America  communi- 
cating with  the  Atlantic  Ocean. 

It  is  impossible,  when  directing  our  attention  to  this  long  line  of 
coast,  so  variously  modified  in  character,  and  necessarily  so  different  in 
climate,  not  to  see  how  very  modified  must  also  be  the  conditions  for 
the  existence  of  life  and  the  preservation  of  any  of  its  harder  parts. 
One  contemporaneous  coating  of  sedimentary  or  chemically  deposited 
matter  must  include  the  remains  of  very  different  creatures,  either  living 
upon  or  in  the  surface  accumulations,  as  well  as  the  vegetable  and 
animal  remains  drifted  into  it  from  the  land.  The  molluscs  inhabiting 
the  coasts  of  the  cold  regions  would  be  expected  to  differ  materially 
from  those  in  the  tropics,  and  the  plants  and  terrestrial  animals  and 
amphibious  creatures  of  the  latter  would  vary  from  those  in  the  former. 
The  organic  remains  buried  in  the  deposits  of  the  Gulf  of  Mexico,  though 
entombed  at  the  same  time  as  those  in  Baffin's  Bay,  could  scarcely  be 
expected  to  offer  the  same  characters. 

If,  instead  of  the  eastern  coast  of  America,  we  look  to  the  western, 
the  first  marked  difference  which  presents  itself  is  the  absence  of  great 
rivers  up  the  whole  of  the  southern  continent,  and  the  connecting  land 
joining  it  with  the  wide-spread  northern  part.  Numerous  sheltered 
situations  are  to  be  found  amid  the  islands  and  inlets  extending  from 
Cape  Horn  to,  and  including,  the  island  of  Chiloe ;  after  which,  for 
about  6000  miles  of  coast,  to  the  Gulf  of  California,  the  shores  are 
little  broken  by  indentations,  except  at  Guayaquil  and  Panama,  and  do 
not  present  a  single  estuary  of  importance  as  on  the  eastern  side  of  the 
continent.  The  mixture  of  fresh  water  with  the  oceans  on  either  side 
is  very  different,  as  are  also  the  conditions  for  estuary  life  and  the 
transport  of  terrestrial  and  fluviatile  organic  remains  for  entombment 
in  the  coast  sedimentary  accumulations.  Even  after  we  have  passed 
the  Gulf  of  California,  and  the  Colorado,  delivering  its  waters  at  its 
head,  there  is,  for  about  2000  miles,  from  Cape  St.  Lucas  to  Vancouver's 
Island,  a  slightly  indented  coast  and  a  minor  discharge  of  drainage 


152  PRESERVATION    OF    ORGANIC    REMAINS 

waters,  with  the  exception  of  those  delivered  by  the  Columbia  or  Oregon. 
Subsequently,  more  northward,  for  about  800  miles,  islands  and  inlets 
are  common,  offering  modifications  for  the  existence  of  marine  life,  as 
regards  shelter  and  exposure  to  waves  produced  by  winds,  to  Sitka 
Island  and  Cross  Sound.  After  which  comes  the  variously  indented 
coast  extending  to  the  Aleutian  Islands,  and  so  on  to  Behring's  Straits. 

Though  we  have  the  same  range  through  climates,  the  character  of 
the  two  coasts  of  the  American  continent  varies  so  materially  that  we 
can  scarcely  but  expect  very  important  modifications,  as  well  in  the  life 
as  in  the  physical  conditions  under  which  it  is  placed.  We  have  not 
only  to  regard  the  very  great  difference  in  the  amount  of  fresh  waters 
discharged  on  the  east  and  on  the  west,  with  its  consequences,  but  also 
the  ponded  waters  of  the  Mexican  Gulf  and  their  continuation  into  the 
Caribbean  Sea,  with  the  result,  the  Gulf  Stream,  on  the  one  side  and 
not  on  the  other,  not  neglecting  the  important  difference  presented  by 
the  great  mediterranean  sea  of  Hudson's  Bay  and  Baffin's  Bay  on  the 
east,  and  the  kind  of  coast  found  on  the  west.  To  this  should  also  be 
added  the  great  barrier  offered  by  America  to  the  passage  of  tropical 
marine  animals  from  one  ocean  to  the  other.* 

It  may  be  useful  to  glance  at  the  great  modification  of  conditions  on 
the  western  side  of  the  Pacific.  Though  a  great  portion  of  the  drainage 
of  Asia  is  disposed  of  in  other  directions,  the  surplus  waters  of  a  large 
area  still  find  their  way  to  the  east  coast.  The  Saghalian  River  throws 
its  waters,  derived  from  a  considerable  area,  behind  the  island  of  the 
same  name,  to  be  driven  into  the  Okhotsk  Sea  on  the  north,  or  the 
Japan  Sea  on  the  south,  as  the  case  may  be ;  both  these  seas,  to  a 
certain  extent,  separated  from  the  main  ocean  by  the  range  of  islands, 
composed  of  the  Kourile  and  Japanese  islands,  extending  from  Kamt- 
schatka  to  Corea,  the  Japan  Sea  especially,  from  the  great  mass  of 
island  land  interposing  between  it  and  the  Pacific,  offering  the  character 
of  a  mediterranean  sea. 

Proceeding  southerly,  we  arrive  at  the  Yellow  Sea,  which  receives  the 
abundant  drainage  effected  by  the  Hoang  Ho  and  its  tributaries,  and 

*  According  to  M.  Alcide  d'Orbigny,  of  362  species  of  molluscs  in  the  Atlantic  and 
Great  Oceans,  there  is  only  one  common  to  both,  Siphonaria  Lessoni.  Of  these  362 
species,  omitting  the  last,  156  belong  to  the  Atlantic,  and  205  to  the  Great  Ocean.  He 
also  remarks  that,  if  the  two  sides  of  the  American  continent  be  compared,  the  propor- 
tion, in  the  Atlantic,  of  gasteropod  to  lamellibranchiate  molluscs,  is  85  to  71,  while  in 
the  Pacific,  it  is  129  to  76.  Of  95  genera  considered  to  be  proper  to  the  shores  of  South 
America,  45  only  are  common  to  the  two  seas.  This  M.  d'Orbigny  attributes  to  the 
steep  slopes  of  the  west  side,  the  Cordilleras  rising  near  that  coast,  and  rocks  being 
more  numerous  than  sandy  shores,  so  that  gasteropods  would  be  expected  to  be  more 
common,  while  the  Atlantic  coasts  present  mud,  silt,  and  sand  in  great  abundance,  with 
gently  sloping  shores  for  a  large  proportion  of  its  length. — Recherches  sur  les  lois  qui  Pr£- 
sident  &  la  Distribution  des  Mollusque  Cutiers  Marins.  Comptes  Rendues,  vol.  xix.  (Nov. 
1844).  Ann.  des  Sciences  Naturelles,  Third  Series,  vol.  iii.  p.  193  (1815). 


AMID    MINERAL    ACCUMULATIONS.  153 

more  southerly  still  we  find  the  body  of  fresh  water  discharged  into  the  sea 
by  the  Yang-tse-kiang.  Thence,  to  the  south,  until  the  Si-kiang,  with  its 
tributaries,  presents  itself  in  the  Canton  estuary,  comparatively  minor 
rivers  flow  into  the  ocean,  the  -coast  being  much  indented,  smaller  rivers 
and  streams  often  discharging  in  the  upper  part  of  the  indentations. 

The  Island  of  Hainan,  with  the  great  promontory  stretching  to  meet 
it  from  the  main  Chinese  land,  forms  the  Gulf  of  Tonquin,  into  which 
the  San-koi  and  other  rivers  discharge  their  waters.  The  amount  of 
fresh  water  poured  into  the  sea  on  the  eastern  coast  of  Cochin  China 
is  subsequently  of  no  great  importance,  and  it  is  not  until  we  arrive  at 
the  delta  of  the  Maikiang  or  Camboja  that  the  sea  is  much  influenced 
by  the  influx  of  fresh  waters,  an  influence  again,  however,  to  be  repeated 
at  the  head  of  the  Gulf  of  Siam,  by  the  outpouring  of  the  Meinam,  a 
river  remarkably  parallel  with  the  Maikiang  for  about  700  miles,  the 
latter  holding  a  singularly  straight  course,  as  a  whole,  to  the  N.N.E., 
for  about  1750  miles.,*  The  remaining  portion  of  the  Asiatic  continent, 
formed  by  the  Malayan  promontory,  throws  no  important  body  of  fresh 
waters  into  the  sea  in  the  form  of  a  main  river. 

From  Kamtschatka  nearly  to  the  equator,  we  thus  have  a  continental 
barrier,  for  the  most  part  not  wanting  in  the  outflow  of  bodies  of  fresh 
water,  sufficient  to  produce  marked  influences  on  parts  of  the  coasts, 
and  consequently  upon  the  conditions  under  which  animal  life  may  exist 
along  it,  and  the  remains  of  terrestrial  and  fluviatile  plants  and  animals  be 
drifted  outwards  into  any  sedimentary  or  chemical  deposits  now  forming 
adjoining  it.  Minor  portions  of  the  ocean  are  also,  to  a  certain  extent, 
separated  off  by  islands,  the  range  of  the  Philippines  and  Borneo,  in 
addition  to  those  mentioned,  tending  to  portion  off  the  ocean  down  to 
the  equator,  so  that,  as  a  whole,  a  marked  modification  of  physical 
conditions  is  observable  on  the  east  and  west  coasts  of  the  Pacific 
Ocean. 

From  the  equator  southward  we  have  no  longer  a  mass  of  unbroken 
land  on  the  west  to  compare  with  the  continuous  continent  of  America 
on  the  east.  A  barrier  to  the  free  passage  of  the  tropical  animal  life, 
supposing  other  conditions  equal,  is  not  presented  on  the  west.  Al- 
though much  land  rises  above  the  surface  of  the  sea,  the  mass  of  Aus- 
tralia not  so  very  materially  of  less  area  than  that  of  Europe,  and  Borneo 
and  New  Guinea  exposing  no  inconsiderable  surfaces,  there  are  channels 
of  water  amid  them  permitting  tropical  marine  creatures  to  extend  them- 
selves under  fitting  circumstances.  Though,  with  the  exception  of  Aus- 
tralia, the  various  islands  may  not  offer  areas  sufficient  for  the  accumu- 
lation and  discharge  of  fresh  waters  equal  in  one  locality  to  some  of  the 
great  rivers  of  the  world,  collectively  they  embody  conditions  for  the 

*  Considering  the  inference  to  be  correct,  as  it  appears  to  be,  that  the  Latchou  is 
the  upper  part  of  the  Maikiang. 


154  PRESERVATION    OF    ORGANIC    REMAINS 

outflow  of  much  fresh  water  around  many  of  them,  so  that  estuary  and 
brackish  water  conditions  obtain,  and  consequently  physical  circum- 
stances fitted  for  the  modification  of  life.  So  far  as  the  eastern  coast  of 
Australia  is  concerned,  it  presents  abouk2000  miles  of  shore  not  more 
broken  or  affording  more  fresh  water  than  the  opposite  coast  of  South 
America.  The  western  part  of  the  Pacific  differs  from  the  eastern  por- 
tion in  the  multitude  of  points  and  small  areas  through  which  the  floor 
of  the  ocean  reaches  the  atmosphere,  productive  of  a  combination  of  in- 
fluences affecting  animal  life  and  the  accumulation  of  its  harder  remains. 

While  on  this  subject,  it  may  be  well  to  call  the  attention  of  the  ob- 
server to  the  material  changes  which  would  be  effected  if,  by  any  of  those 
alterations  of  the  level  of  sea  and  land  which  the  study  of  geology  teaches 
may  be  reckoned  by  differences  very  far  exceeding  the  depths  required, 
channels  of  communication  were  established  between  the  Atlantic  and 
Pacific  oceans  by  a  sufficient  subsidence  of  the  Isthmus  of  Panama,  or 
the  communication  cut  off  between  the  Pacific  and  Indian  oceans  by  an 
uprise  of  the  land  and  sea  bottom  between  Australia  and  the  Malayan 
Peninsula,  one  stretching  through  Timor,  Floris,  Java,  and  Sumatra. 
If  the  multitude  of  oceanic  islands  in  the  Western  Pacific  did  not  too 
much  break  up  currents,  we  may  suppose  a  certain  amount  of  ponding 
up  of  waters  inside  the  Moluccas,  Borneo,  and  the  Philippine  Islands, 
somewhat  resembling  that  now  effected  behind  the  West  India  Islands, 
with  perhaps  also  a  modification  of  the  Gulf  Stream,  escaping  along  the 
coast  of  China.  Startling  as,  at  first  sight,  such  changes  may  appear, 
the  geological  student  has  to  accustom  himself  to  consider  modifications 
in  the  distribution  of  land  and  water,  and  elevations  and  depressions  of 
a  far  more  extended  kind,  when  he  comes  to  reason  upon  facts  connect- 
ed with  the  accumulation  and  distribution  of  mineral  and  organic  matter 
constituting  rocks,  formed  at  various  geological  periods. 

In  the  Indian  Ocean  we  have  shores  confined  to  the  tropical  and  tem- 
perate regions.  For  nearly  2000  miles  the  coast  of  Australia,  from  Cape 
Leeuwin  to  Cape  Bougainville,  presents  us  with  no  known  great  river 
pouring  out  a  volume  of  water  sufficient  to  influence  an  extended  area. 
The  same  with  the  island  range  of  Timor,  Floris,  Java,  and  Sumatra, 
and  up  the  Malay  Peninsula,  to  the  head  of  the  Gulf  of  Martaban,  where 
the  Irawady  thrusts  out  its  delta  and  discharges  a  volume  of  fresh  water, 
the  drainage  of  a  large  area.  From  thence  to  the  mouths  of  the  Ganges 
no  important  amount  of  fresh  water  is  carried  out  into  the  sea.  The 
great  volume  thrown  into  the  sea  by  this  river  has  been  already  men- 
tioned, (p.  110.)  Hence  to  Cape  Comorin  we  find  rivers  of  varied  magni- 
tude, the  most  important  of  which  are,  proceeding  southwards,  the 
Mahanuddy,  Godavery,  Kistna,  and  Coleroon,  draining,  with  minor 
streams,  the  great  area  of  Southern  India.  As  a  whole,  the  Bengal  Sea 
and  Martaban  Gulf  receive  a  considerable  quantity  of  fresh  water,  the 


AMID    MINERAL    ACCUMULATIONS.  155 

discharge  of  which  conveys  a  mass  of  detritus  into  the  sea,  and  produces 
conditions  in  the  waters  and  the  sea  bottom,  which,  beyond  Cape  Como- 
rin,  are  not  found  for  about  1000  miles,  until  we  reach  the  Gulf  of  Cam- 
bay,  into  which  the  Nerbudda  and  other  rivers  discharge  themselves. 
We  find  another  volume  of  fresh  water  thrown  into  the  sea  by  the  Indus, 
still  more  northerly,  after  which  we  obtain  the  moderate  outflow  of  fresh 
water  of  the  coast  of  Beloochistan,  the  great  indentation  of  the  Gulf  of 
Oman,  and  in  its  continuation  the  Persian  Gulf,  the  nearly  dry  coast  of 
Arabia,  to  the  Arabian  Gulf  and  its  long-continued  indentation,  the  Red 
Sea.  From  Cape  Guardafui  to  the  Cape  of  Good  Hope,  for  about  4400 
miles,  the  sea  seems  little  influenced  by  any  considerable  discharge  of 
fresh  water  on  the  coast,  excepting  in  such  places  as  at  the  mouths  of 
the  Zambesi  and  two  or  three  other  localities. 

Looking  at  the  Indian  Ocean  as  a  whole,  any  influences  upon  marine 
animal  life  from  fresh  waters  poured  into  the  sea,  with  the  greater  amount 
of  terrestrial  and  fluviatile  plants  and  animals  drifted  into  the  ocean  by 
rivers,  would  be  chiefly  found  in  the  Bengal  Sea  (including  the  Martaban 
Gulf),  and  upon  the  northeast  shores  of  the  Arabian  Sea,  with  one 
or  two  places  on  the  east  coast  of  Africa.  Excepting  Madagascar 
and  Ceylon,  the  area  occupied  by  islands  is  inconsiderable.  The  coasts 
bounding  it  on  the  east  are  those  chiefly  of  considerable  islands  (the  mass 
of  Australia  better  deserving  the  name  of  continent),  so  that  in  the  tro- 
pical regions  there  is  a  free  communication  by  means  of  sea  channels  with 
the  Pacific.  On  the  west,  Africa  bars  all  direct  communication  with  the 
Atlantic,  though  at  the  same  time  the  region  terminated  by  the  Cape  of 
Good  Hope  and  Cape  Agulhas,  trends  southward,  so  comparatively  little 
southward  of  the  tropics,  and  currents  (p.  117)  so  set  from  the  Indian 
Ocean,  round  Cape  Agulhas  and  up  the  southwestern  coast  of  Africa, 
that  there  is  no  great  land  boundary  between  tropical  marine  life  in  the 
one  ocean  and  the  other.*  The  Indian  Ocean  is  now  cut  off  from  marine 
communication  from  northern  regions  (however  this  may  have  been  ef- 
fected in  former  geological  times,  even  as  late  as  the  tertiary  period,  by 
means  of  waters  uniting  the  Bed  and  Mediterranean  seas),  while  it  is 
well  open  to  all  marine  life  which  may  enter  it,  under  fitting  conditions, 
from  the  south  ;  and  herein  it  differs  from  the  Atlantic  and  Pacific  oceans, 
which  range  from  the  Northern  to  the  Southern  Polar  regions. 

In  the  run  of  the  African  coast  which  bounds  the  Atlantic  for  so  long 
a  distance  on  the  east,  fresh  waters  flowing  outwards  through  great  drain- 
age channels  seem  chiefly  to  occur  at  the  Orange  River,  the  Nourse,  the 
Coanza,  and  the  Congo,  or  Zaire,  on  the  south  of  the  equator,  and  at  the 

*  Due  regard  has,  however,  to  be  paid  to  the  temperature  of  the  current,  considered 
to  be  that  of  the  mean  of  the  ocean,  which  flows  for  some  distance  up  the  west  coast  of 
Africa,  from  the  Cape  of  Good  Hope,  as  also  to  that  stated  to  run  from  the  south  end 
of  Africa  some  way  up  the  eastern  coast. 


156  PRESERVATION    OF    ORGANIC    REMAINS 

Quorra,  Gambia,  and  Senegal,  on  the  north.  The  coast  northward  of 
the  Senegal  bounds  for  about  1000  miles  the  Atlantic  on  the  one  side, 
and  the  great  African  Desert  on  the  other.  From  the  Desert  to  Cape 
Spartel  minor  streams  only  fall  into  the  sea.  The  great  indentation  of 
the  Mediterranean  then  succeeds. 

The  European  rivers  discharged  into  the  Atlantic,  or  the  tidal  seas 
and  channels  communicating  with  it,  are  inconsiderable  streams  as  com- 
pared with  the  great  rivers  of  the  world  ;  indeed  a  large  portion  of  the 
European  drainage  finds  its  way  into  the  Mediterranean,  Black,  Caspian, 
Baltic,  and  Arctic  Seas.  Such  drainage  as  falls  into  the  Caspian  is  eva- 
porated in  that  sea,  and  that  not  so  treated  in  the  Black  Sea  is  evaporated 
in  the  Mediterranean ;  with  all  that  directly  finds  its  way  into  the  latter. 
So  that  from  the  Baltic  alone  the  drainage  waters  of  Europe  find  their 
way  into  the  Atlantic,  in  addition  to  those  which  flow  directly  into  it  or 
the  tidal  channels  and  seas  communicating  with  it.  Enough,  however, 
escapes  in  this  way  to  give  a  varied  character  to  the  coast  conditions,  as 
regards  the  mingling  of  fresh  with  sea  waters,  under  which  aquatic  life 
may  be  found,  and  the  remains  of  terrestrial  and  fluviatile  plants  and 
animals  be  accumulated. 

In  the  Arctic  Ocean,  the  coasts  present  us  with  much  mingling  of  fresh 
water  and  sea,  the  drainage  of  a  large  portion  of  Asia  and  of  a  minor 
portion  of  Europe  falling  into  it ;  part  of  the  fresh  water  discharged 
into  great  indentations  or  arms  of  the  sea,  such  as  the  White  Sea  and 
the  Gulfs  of  Obi,  leniseisk,  Khatangskii,  and  Kolima;  part  through 
deltas,  as  the  Petchora  and  Lena ;  and  part  in  a  more  ordinary  form. 
The  fresh  water  so  supplied  to  the  coasts  of  these  regions  is  interrupted 
or  lessened  during  many  months  of  the  year  by  the  climate  ;  much  of  it 
arrested  in  the  form  of  ice,  to  be  let  loose  in  the  warmer  months.  The 
ice,  also,  in  the  seas  of  these  high  latitudes,  necessarily  modifies  the 
coast  conditions  for  life  as  it  exists  in  the  temperate  and  tropical  shores 
of  the  world.  The  drainage  delivered  into  the  same  ocean  from  North 
America  is  less  important  than  from  Europe  and  Asia.  Of  the  North 
American  rivers  flowing  into  this  ocean,  -the  Mackenzie  would  appear 
the  most  important,  succeeded  by  the  Back  and  Slave  Rivers.  The  land 
and  sea  are  so  mingled  on  the  north  coast  of  America,  and  the  ice  and 
snows  so  abundant,  that  the  shore  waters  become  much  influenced  thereby. 

Looking  to  the  Southern  Ocean,  we  find  the  ice  and  snow  of  the  Ant- 
arctic land  most  important,  as  regards  the  shore  conditions.  A  great 
barrier  of  ice,  indeed,  there  occupies  the  position  of  the  coast  for  a  great 
extent,  so  that  both  in  the  Arctic  and  the  Antarctic  regions  we  have  t<> 
regard  ice  accumulated  round  the  land,  or  formed  in  the  sea,  as  most 
materially  influencing  the  existence  of  marine  life  and  the  preservation 
of  its  remains  amid  sedimentary  and  chemical  deposits. 

In  such  regions,  also,  we  see  the  extension  of  marine  life  (vegetable 


AMID    MINEKAL    ACCUMULATIONS.  157 

and  animal),  and  of  air-breathing  creatures  (birds  and  mammals)  feed- 
ing upon  it  beyond  the  range  of  terrestrial  vegetation,  and  of  animals  di- 
rectly consuming  it  or  the  creatures  which  first  feed  upon  it. 

Though  such  is  the  general  fact,  the  conditions  for  the  entombment  of 
the  remains  of  terrestrial  animal  and  vegetable  life  in  the  Arctic  and 
Antarctic  regions  are,  as  respects  the  present  distribution  of  land  and 
sea,  different.  In  the  former,  we  have  the  delivery  of  important  rivers 
into  the  sea,  an  abundance  of  water  discharged  out  during  the  warm  sea- 
son when  the  ice  is  broken  up  at  their  mouths,  and  the  interior  ice  and 
snows  are  melting.  The  Obi  and  its  tributaries  alone  drain  a  large 
Asiatic  area,  extending  from  lat.  47°  to  67°.  The  Jenisei,  rising  from 
the  Tangnou  and  Little  Altai  Mountains,  likewise  flows  through  20°  of 
latitude  to  70°  N.,  while  the  Lena  and  its  tributaries,  considered  to  drain 
785,565  square  (English)  miles,  rises  (in  lat.  57°)  from  the  Jablonnoi  or 
Stannovoi  Mountains  (the  eastern  portion  of  which  looks  upon  the  sea 
of  Okhotsk,  a  branch  of  the  Pacific),  delivering  itself  into  the  Arctic 
Ocean,  in  about  lat.  73°  38'  N.  Other  rivers,  also,  flow  northerly  for 
considerable  distances  from  the  south,  such  as  the  Dvina,  Petchora, 
Khatanga,  Anabara,  Olia,  Olenek,  lana,  and  Kolima.  In  Northern 
America,  also,  the  rivers,  though  not  numerous,  flowing  northerly,  still 
show  a  drainage  extending  to  the  south  for  several  degrees  of  latitude, 
though  much  interrupted  by  lakes.*  Thus  the  Mackenzie,  delivering 
itself  into  the  Arctic  Ocean  in  about  69°  N.,  flows  from  the  Slave  Lake 
by  an  outlet  in  about  61°  N.,  giving  8  degrees  of  latitude  for  this  course, 
during  which  the  river  receives  the  drainage  from  the  Great  Bear  Lake. 
Regarding  the  Slave  Lake  as  a  mere  interruption,  by  which  the  waters 
are  spread  over  a  wider  space  in  a  depression,  the  waters  discharging 
themselves  by  the  Mackenzie  are  derived  from  a  drainage  extending  over 
a  considerable  area  (estimated  at  about  510,000  square  miles),  and 
reaching  down  to  lat.  52°  30'  1ST.,  by  means  of  the  Slave  River  (running 
out  of  the  western  end  of  Athabasca  Lake),  and  the  Athabasca  (flowing 
into  the  same  lake  also  at  its  western  extremity). 

In  the  northern  parts  of  Europe  and  Asia,  3,000,000  square  miles  of 
which  have  been  estimated  as  draining  into  the  Arctic  Ocean,  and  in 
some  portion  of  North  America,  there  are,  therefore,  conditions,  particu- 
larly during  the  floods  caused  by  the  melting  of  the  ice  and  snows,  for 
thrusting  forward  the  remains  of  terrestrial  and  fresh-water  life  into  the 
northern  seas,  there  to  be  mingled  with  detritus,  upon  the  transport  and 
accumulation  of  which  ice  has  an  important  influence.  We  should  ex- 
pect that  amid  the  intermixed  land  and  sea,  terrestrial  animals  may 
often  perish  while  crossing  among  the  ice,  at  times  when  the  latter  is 

*  Collectively,  the  lakes  of  North  America  constitute  a  marked  feature  in  the  physi- 
cal geography  of  that  part  of  the  world.  The  volume  of  water  in  the  chief  lakes  has 
been  estimated  at  11,300  cubic  miles. 


158  PRESERVATION    OF    ORGANIC    REMAINS 

breaking  up  in  the  channels  and  gulfs,  and  their  bones  under  favourable 
conditions  preserved  in  any  sedimentary  matter  accumulating  beneath. 
No  such  conditions  prevail  in  the  southern  continent,  which  navigators 
have  lately  made  known  to  us.  No  great  rivers  there  flow  outwards, 
and  neither  terrestrial  plants  nor  animals,  directly  or  indirectly  living 
upon  them,  furnish  their  remains  for  mixture  with  any  sedimentary  de- 
posits which  may  be  forming.  All  aid  which  great  river  drainages  af- 
ford to  the  latter  is  cut  off,  and  the  little  detritus  that  can  be  obtained 
from  the  land  seems  only  capable  of  being  so  derived  directly  in  the  few 
localities  exposed  to  the  breakers  during  the  short  period  of  the  year 
when  the  shores  are  not  bounded  entirely  by  ice.  For  the  finer  matter, 
not  ice-borne,  entombing  the  remains  of  life,  we  may  probably  look,  as 
affording  the  chief  supply,  to  ashes  and  lapilli  vomited  from  volcanoes, 
and  scattered  over  adjacent  seas. 

Enough  has  been  stated  to  show  the  unequal  conditions  as  to  climate 
and  the  mingling  of  fresh  with  sea  waters  along  coasts.  The  observer 
has  next  to  consider  the  varied  character  of  the  shores  themselves  as 
regards  the  shallowness  or  depth  of  the  adjacent  seas,  and  the  modifica- 
tions of  temperature,  pressure,  access  of  light,  and  conditions  of  inter- 
mixed air  thence  arising.  It  has  been  above  seen  (p.  119),  that  the 
volume  of  ocean  is  so  arranged  as  to  the  specific  gravities  of  its  waters, 
that  an  equal  temperature,  considered  to  be  39-5°  reigns  in  the  sufficient 
deep  parts  from  pole  to  pole,  water  of  higher  temperature  rising  above 
these  more  dense  waters  in  tropical  regions,  and  of  a  lower  temperature 
towards  the  poles.  Though  this  even  temperature  may  prevail  at  the 
proper  depths,  it  is  necessarily  modified  as  the  seas  become  shallow,  or 
currents  may  transport  warmer  or  colder  waters,  as  the  case  may  be, 
from  one  oceanic  area  to  another.  As  the  coasts  are  approached  in  the 
parts  of  the  world  where  warmer  waters  float  above  those  of  39*5°,  we 
there  have  conditions  under  which  the  temperature  decreases  downwards 
below  the  level  of  the  sea  to  7200  feet,  and  upwards  in  the  air  to  the 
greatest  heights  of  land.  Viewing  the  subject  generally,  therefore,  and 
as  far  as  temperature  is  concerned,  marine  animals  which  could  support 
a  decrease  of  temperature  equal  to  about  39-5°,  (the  surface  tempera- 
ture being  taken  at  78°),  could  live  from  the  level  of  the  sea  to  the 
greatest  depths  in  the  equatorial  ocean.*  A  higher  temperature  may 
be  found  under  favourable  conditions  of  shallow  water  and  small  tides  in 
some  tropical  regions.  In  the  polar  areas,  included  within  the  belts  of 
equal  temperatures  from  the  surface  to  the  bottom  of  the  sea,  and  within 
which  colder  waters,  as  a  whole,  float  above  those  of  39*5°,  there  is  a 
different  state  of  things.  Still  regarding  the  subject  merely  with  respect 
to  temperature,  the  animals  capable  of  living  in  the  tropical  regions,  and 

*  It  will  be  at  once  obvious  that  this  difference  of  temperature  is  easily  sustained  by 
many  land  animals  in  different  parts  of  the  world. 


AMID    MINERAL    ACCUMULATIONS.  159 

unable  to  support  lower  temperatures  than  39 -5°,  could  not  occupy  the 
higher  waters. 

While  in  the  equatorial  parts  of  the  world  the  temperature  of  the 
ocean  may  not  be  very  materially  altered  on  its  surface,  it  is  different 
with  those  portions  of  its  higher  waters  exposed  to  the  changes  of  winter 
and  summer,  so  that  the  temperature  of  the  surface  waters  is  there. more 
considerably  modified,  especially  upon  coasts.  The  animals  living  in 
the  shallow  waters  of  such  regions  are,  therefore,  liable  to  an  amount 
of  difference  in  temperature  not  experienced  by  those  inhabiting  the 
seas  of  the  tropics.  This  is  more  particularly  the  case  on  the  shores  of 
tidal  seas,  with  their  estuaries,  where,  even  at  high  water,  large  tracts 
of  coasts  may  only  be  covered  by  shallow  waters,  becoming  dry  at  low 
tide. 

As  regards  mere  temperature,  though  there  may  be  little  doubt  that 
with  respect  to  the  adjustment  of  marine  animal  and  vegetable  life  to 
conditions,  its  differences  are  very  important,  it  will  be  apparent  that  a 
vast  volume  of  the  ocean  might  be  tenanted  by  similar  life,  extended 
over  its  floor  at  any  depths  from  about  7200  feet  at  the  equator,  3600 
in  lat.  45°  S.,  the  surface  in  54°  to  58°  S.,  and  4500  feet  in  lat.  70°  S. ; 
and,  probably,  under  the  needful  modifications,  considering  the  different 
distribution  of  land  and  water  on  the  south  and  on  the  north,  in  a 
similar  manner  towards  the  Arctic  regions.  Modifications,  also,  arising 
in  the  various  seas  communicating  with  the  main  ocean,  and  more  or 
less  separated  from  it,  such  as  the  Mediterranean,  in  the  western  part 
of  which  the  waters  beneath  200  fathoms  have  been  supposed  to  remain 
at  about  a  temperature  of  55°,*  must  also  be  borne  in  mind. 

With  differences  of  depth,  the  observer  has  to  consider  the  differences 
of  pressure  to  which  any  animal  or  vegetable  living  in  the  sea  would 
have  to  be  subjected,  so  that  such  life  would  be  very  differently  circum- 
stanced, though  under  equal  temperatures,  at  the  depth  of  7200  feet  at 
the  equator,  and  in  the  oceanic  regions  where  that  of  39*5°  rises  to  the 
surface.  We  cannot  suppose  an  animal  so  constructed  as  to  sustain  a 
pressure  of  more  than  200  atmospheres  at  one  time,  and  of  2  or  3  at- 
mospheres at  another.  A  creature  inhabiting  a  depth  of  100  feet  would 
sustain  a  pressure,  including  that  of  the  atmosphere,  of  about  60  pounds 
to  the  square  inch,  while  one  at  4000  feet,  no  very  important  depth, 

*  M.  Berard  found,  at  a  depth  of  1200  fathoms  (without  reaching  bottom),  between 
the  Balearic  Islands,  a  temperature  of  53-4°,  the  surface  water  being  at  69-8°,  and  the 
air  at  75-2°.  From  other  observations  in  the  western  part  of  the  Mediterranean, 
at  the  respective  depths  of  600  and  750  fathoms,  and  another  not  stated,  it  was 
found  that  the  water  was  still  at  554°,  though  the  temperature  of  the  surface  water 
varied  materially.  M.  d'Urville  remarks  that  these  experiments  accord  with  some 
made  by  himself,  also  in  the  Mediterranean,  at  300,  200,  250,  600,  and  300  fathoms, 
when  he  obtained  the  respective  temperatures  of  54-5°,  54-1°,  57-3°,  54-6°,  and  54-8°. — 
Geological  Manual,  3d  edit.,  p.  25. 


160        PRESERVATION  OF  ORGANIC  REMAINS 

would  have  to  support  a  pressure  of  about  1830  pounds  to  the  square 
inch. 

Animals,  among  other  conditions  for  their  existence,  are  adapted  to 
a  given  pressure,  or  certain  ranges  of  pressure,  so  adjusted  that  they 
can  move  freely  in  the  medium,  either  gaseous  or  aqueous,  in  which 
they  live.  All  their  delicate  vessels  and  the  powers  of  their  muscles 
are  adjusted  to  it.  When  the  pressure  becomes  either  too  little  or  too 
great,  the  creature  perishes ;  and,  therefore,  when  acting  freely  in  such 
a  medium  as  the  sea,  an  animal  will  not  readily  quit  the  depths  in 
which  it  experiences  ease.  All  are  aware  of  the  adjustment  of  an 
abundance  of  fish  to  the  depths,  to  or  from  which  they  may  frequently 
descend,  by  means  of  the  apparatus  of  swimming-bladders.  This  ar- 
rangement, however,  only  changes  their  specific  gravities  as  a  whole,  the 
relative  volume  occupied  by  the  air  or  gases  in  the  swimming-bladders 
being  the  chief  cause  of  difference,  though,  no  doubt,  also,  the  squeezing 
process  at  great  depths  would  dimmish  the  volume  of  such  other  parts 
of  their  bodies  as  were  in  any  manner  compressible,  the  reverse  hap- 
pening with  a  rise  from  deep  waters  to  near  the  surface.  So  adjusted 
to  given  depths  do  these  swimming-bladders  appear  for  each  kind  of 
fish,  that  it  has  been  observed  that  the  gas  or  air  in  the  swimming- 
bladders  of  fish  brought  up  from  a  depth  of  about  3300  feet  (under  a 
pressure  of  about  100  atmospheres),  increased  so  considerably  in  volume, 
as  to  force  the  swimming-bladder,  stomach,  and  other  adjoining  parts 
outside  the  throat  in  a  balloon-formed  mass.* 

While  thus  some  kinds  of  marine  animals  have  the  power  to  adjust 
their  specific  gravities  to  the  medium  in  which  they  may  be  placed, 
some  molluscs,  such  as  the  nautilus,  possessing  it,  others  appear  unable, 
under  ordinary  conditions,  to  raise  themselves  much  above  the  sea 
bottom.  It  will  be  evident  that  the  more  their  component  parts  are 
incompressible,  and  the  fluids  in  them  agree  with  the  specific  gravity  of 
the  sea  in  which  they  live  (and  the  specific  gravity  of  the  sea  does  not 
appear  to  vary  from  any  increase  of  saline  matters  in  it  to  great  depths, 
though  water  being  slightly  compressible,  it  will  become  more  dense 
according  to  depth),  the  less  they  would  experience  the  difficulties  of  a 
change  of  depth.  On  the  contrary,  the  more  any  parts  may  be  com- 
pressible, and  air  or  gaseous  matter  be  included  in  their  bodies,  the  less 
would  they  suffer  changes  of  depth  with  impunity. 

That  light  should  have  its  effect  upon  marine  as  upon  terrestrial 
vegetation  we  should  expect,  the  light  of  day  being  important  as  well 
to  one  as  the  other,  viewing  the  subject  as  a  whole.  It  would  evidently, 
also,  be  important  to  all  marine  creatures  possessing  the  organs  of 
vision,  so  that  we  should  anticipate  that  the  great  mass  of  fish,  crusta- 

*  Pouillet,  Eldmens  de  Physique  Experimental©,  torn.  i.  p.  188.     Seconde  Edition. 


AMID    MINERAL    ACCUMULATIONS.  161 

ceans  and  molluscs,  which  possessed  eyes,  would  occupy  situations  and 
levels  in  the  sea  where  they  could  obtain  the  light  needful  to  them. 
The  Pomatomus  telescopium,  caught  at  considerable  depths  in  the 
Mediterranean  (near  Nice),  is  considered  to  afford  an  example  of  adjust- 
ment to  the  minor  amount  of  light  reaching  its  ordinary  abode,  its  eyes 
being  remarkable  for  their  magnitude,  and  apparently  constructed  to 
take  advantage  of  all  the  rays  which  can  penetrate  the  depths  at  which 
it  lives.  While,  however,  light  may  be  absolutely  needed  for  the  exist- 
ence of  some  marine  life,  it  is  not  obviously  necessary  to  others,  those 
not  possessing  eyes.  Many  marine  creatures  seem  to  flourish  under 
conditions  in  which  it  can  be  of  little  value,  at  the  same  time  the 
influence  of  light  may  often  be  of  importance  where  it  is  not  suspected. 

It  is  not  improbable  that  to  the  power  of  obtaining  a  proper  amount 
of  disseminated  atmospheric  air  in  waters,  we  may  look  for  a  very 
important  element  in  the  existence  of  animal  and,  indeed,  of  vegetable 
life  in  the  sea.  To  the  one  and  the  other  oxygen  seems  essential.  At 
the  junction  of  the  sea  and  atmosphere,  we  have  the  best  conditions  for 
the  absorption  of  the  air  by  water,  the  agitation  of  the  surface  from  the 
friction  of  the  atmosphere  on  the  sea,  particularly  during  heavy  gales 
of  wind,  being  especially  favourable  for  a  mechanical  mixture  of  the  two, 
assisting  the  absorption  of  the  air.*  Of  the  amount  of  air,  or  rather 
of  the  apparently  needful  element  oxygen,  at  various  depths  in  the  sea, 
we  seem  to  possess  no  very  definite  information,  so  that  researches  on 
this  head  are  very  desirable.  From  observations  by  M.  Biot,  on  the 
gaseous  contents  of  the  swimming-bladders  of  fish,  it  has  been  inferred 
that  such  contents  probably  vary  according  to  the  depths  at  which  such 
fish  live.  He  found  these  swimming-bladders  nearly  filled  with  pure  ni- 
trogen when  they  were  those  of  fish  inhabiting  shallow  waters,  and  with 
oxygen  and  nitrogen,  in  the  proportion  of  T9uths  of  the  former  to  T\th  of 
the  latter,  when  those  of  fish  living  at  depths  of  from  3000  to  3500  feet. 

According  to  M.  Aime',  the  amount  of  air  disseminated  in  the  waters 
of  the  Mediterranean,  opposite  Algiers,  is  nearly  constant  from  the  sur- 
face to  the  depth  of  5250  feet.f 

We  might  assume  that,  from  its  immediate  contact  with  the  air,  sur- 
face waters  would  more  readily  obtain  any  needful  dissemination  of  it 
than  those  situated  at  greater  depths,  so  that  the  mode  of  consuming 
oxygen  would  be  adjusted  to  such  conditions,  animal  life  inhabiting 
great  depths  being  so  formed  as  to  require  it  at  considerable  intervals. 
In  tidal  seas  we  find  certain  molluscs  adjusted  to  live  in  situations  ex- 
posed to  the  atmosphere  during  the  fall  of  every  tide,  while  others  in- 

*  The  friction  of  air  upon  fresh-water  lakes  produces  the  same  result,  intermingling 
the  air  and  water,  as  cascades  and  waterfalls  intermix  them  in  many  rivers,  those 
especially  in  which  fish  swimming  high,  or  inhabiting  minor  depths,  most  nourish. 

f  Comptes  Rendue  de  1' Academic  des  Sciences,  1843,  vol.  xvi.  p.  749. 

11 


162  PRESERVATION    OF    ORGANIC    REMAINS 

habit  places  always  covered  by  sea,  except,  perhaps,  at  equinoxial  spring 
tides.  From  inhabiting  shores  some  molluscs  are  commonly  considered 
as  littoral  species,  while  others  are  well  known  as  rarely  obtained  except 
in  deep  waters. 

Although  general  views  may  have  been  some  time  entertained  with 
respect  to  the  modification  of  marine  life,  depending  upon  the  tempera- 
ture, pressure,  light,  and  ability  to  procure  oxygen  under  which  it  may 
be  placed,*  it  could  scarcely  be  said  that  we  had  sufficient  data  for  the 
philosophical  consideration  of  this  subject,  until  the  labours  of  Professor 
Edward  Forbes  in  the  British  and  ^Egean  seas  supplied  the  necessary 
information. 

Professor  E.  Forbes  pointed  out  that  with  regard  to  primary  influ- 
ences, the  climate  of  the  Eastern  Mediterranean  was  uniform,  and  that 
the  absence  of  certain  species  in  the  -ZEgean  Sea,  characteristic  of  the 
Western  Mediterranean,  was  rather  due  to  a  modification  in  the  compo- 
sition of  the  sea  water,  from  the  inpouring  of  the  less  saline  waters  of 
the  Black  Sea,  than  to  climate,  f  The  influx  of  river  water  produces 
its  consequences ;  and  it  is  remarked  that,  among  46  species  of  testacea 
collected  on  the  shore  at  Alexandria,  there  were  4  land  and  fresh-water 
molluscs,  3  of  which  are  of  truly  subtropical  forms,!  so  that  while  in  one 
part  of  the  Mediterranean  forms  of  this  character  are  mingled  with  the 
ordinary  marine  testacea,  in  another,  as  at  Smyrna  or  Toulon,  the 
Melanopsis  is  mixed  with  them  near  the  former,  and  characteristic 
European  Pulmonifera  near  the  latter.  It  is  also  shown  by  Professor 
E.  Forbes,  that  while  vegetables  of  a  subtropical  character  may  be  borne 
down  by  the  Nile,  into  the  Mediterranean  on  the  one  side,  accompanying 
the  remains  of  crocodiles  and  ichneumons,  the  Danube  may  transport 
parts  of  the  vegetation  of  the  Austrian  Alps,  with  the  relics  of  marmots 
and  mountain  salamanders,  the  marine  remains  mingled  with  these  con- 
temporaneous deposits  retaining  a  common  character. 

With  respect  to  modifications  in  conditions  arising  from  depth,  Pro- 
fessor E.  Forbes  divides  the  Eastern  Mediterranean  into  eight  regions, 

*  The  author  entered  somewhat  at  length  on  this  subject  in  1834,  in  his  Researches 
in  Theoretical  Geology,  chapters  xi.,  xii.,  and  xiii.  To  this  work  a  table  was  appended 
by  Mr.  Broderip,  containing  all  the  information  then  known  (1834)  respecting  the 
depths  and  kind  of  bottom  at  which  recent  genera  of  marine  and  estuary  shells  had 
been  observed. 

f  He  attributes  to  this  cause  the  dwarfish  character  of  the  molluscs,  with  few  excep- 
tions, when  compared  with  their  analogues  in  the  Western  Mediterranean.  "This  is 
seen  most  remarkably  in  some  of  the  more  abundant  species,  such  as  Pecten  oprrcuhtrix, 
Vencrupis  irus,  Venus  fasciata,  Cardita  trapezia,  Modiola  barbata,  and  the  various  kinds  of 
Sulla,  Rissoa,  Fusus,  and  Pleurotoma,  all  of  which  seemed  as  if  they  were  but  miniature 
representations  of  their  more  western  brethren.  To  the  same  cause  may  probably  be 
attributed  the  paucity  of  Meduice,  and  of  corals  and  corallines.  Sponges  only  seem  to 
gain  by  it." — Report  of  the  British  Association,  vol.  xii.  p.  152  (Meeting  of  1843). 

|  Ampullaria  ovata,  Paludina  unicolor,  and  Cyrena  orientalis. 


AMID    MINEKAL    ACCUMULATIONS.  163 

each  considered  to  be  characterized  by  its  fauna,  and  also  by  its  plants, 
where  they  exist.  Certain  species  were  found  confined  to  one  region, 
and  several  were  ascertained  not  to  range  into  the  next  above,  whilst 
they  extended  into  that  beneath,  or  the  reverse.  "  Certain  species," 
he  adds,  "  have  their  maximum  of  development  in  each  zone,  being  most 
prolific  of  individuals  in  that  zone  in  which  is  their  maximum,  and  of 
which  they  may  be  regarded  as  especially  characteristic.  Mingled  with 
the  true  natives  of  every  zone  are  stragglers,  owing  their  presence  to 
the  action  of  secondary  influences  which  modify  distribution.  Every 
zone  has  also  a  more  or  less  general  mineral  character,  the  sea  bottom 
not  being  equally  variable  in  each,  and  becoming  more  and  more  uniform 
as  we  descend.  The  deeper  zones  are  greatest  in  extent ;  so  that  whilst 
the  first,  or  most  superficial,  is  but  12,  the  eighth,  or  lowest,  is  above 
700  feet  in  perpendicular  range."* 

While  tracing  the  first  region  or  littoral  zone,  which  is  thus  limited 
to  12  feet,  all  the  modifications  arising  from  kind  of  bottom,  rock,  sand, 
or  mud,  are  shown  to  have  their  influences,  and  the  effects  of  wave  ac- 
tion, bringing  up  the  exuviae  of  animals  inhabiting  the  next  region  be- 
neath, are  pointed  out.  The  second  region  is  estimated  at  48  feet,  ranging 
from  2  to  10  fathoms  ;  the  third  at  60  feet,  between  the  levels  of  10  and 
20  fathoms ;  the  fourth  at  90  feet  (20  to  35  fathoms) ;  the  fifth  at  120 
feet  (35  to  55  fathoms) ;  the  sixth  at  144  feet  (55  to  79  fathoms) ;  the 
seventh  at  150  feet  (80  to  105  fathoms) ;  and  the  eighth,  all  explored 
below  105  fathoms,  amounting  to  '750  feet,  more  than  twice  the  depth 
of  all  the  other  regions  taken  together,  the  total  depth  amounting  to 
1380  feet. 

So  complete  are  the  modifications  in  invertebrate  life,  produced  by 
the  conditions  in  these  various  zones  or  regions,  that  only  two  species 
of  molluscs  were  found  common  to  the  whole  eight — viz.,  Area  lactea 
and  Oerithium  lima,  "  the  former  a  true  native  from  first  to  last,  the 
latter  probably  only  a  straggler  in  the  lowest."  Three  species  were 
found  common  to  seven  regions  ;f  nine  to  six  regions  :J  and  seventeen 
to  five  regions.  §  With  regard  to  geographic  distribution  and  vertical 

*  British  Association  Reports,  vol.  xii.  p.  154. 

•j-  Nucula  margaritacea,  Marginella  clandestina,  and  Dentaliuih  9-costata  ;  the  second  con- 
sidered to  have  possibly  dropped  into  the  lower  zones  from  floating  sea-weeds. 
J   Corbula  nucleus.  Venus  apicalis.  Columbella  linncei. 

Necera  cuspidata.  Turritella  %-plicata.  Cardita  trapezia. 

Pandora  obtusa.  Triforis  adversum.  Modiola  barbata. 

\  Necera  costellata.  Pecten  hyalinus.  Rissoa  reticulata. 

Tellina  pulchella.  varius.  Trochus  exiguus. 

Venus  ovata.                          Crania  ringens.  Columbella  rustica. 

Cardita  squamosa.                 Natica  pulchella.  Conus  mediterraneus. 

Area  tetragona.                      Rissoa  ventricosa.  Terebratula  detruncata. 

Pecten  polymorpha.  cimicoides. 


164  PRESERVATION    OF    ORGANIC    REMAINS 

range  in  depth,  Professor  E.  Forbes  remarks  that  those  species  which 
possess  the  one  exhibit  the  other,  more  than  one-half  of  those  having  an 
extensive  range  in  depth,  extending  to  distant  localities,  in  nearly  every 
case  to  the  British  seas,  some  still  further  north,  and  some  in  the  At- 
lantic, far  south  of  the  Straits  of  Gibraltar.  He  concludes  "  that  the 
extent  of  the  range  of  a  species  in  depth  is  correspondent  with  its  geo- 
graphical distribution."* 

As  regards  the  influence  of  light,  Professor  E.  Forbes  presents  us 
with  facts  connected  with  the  molluscs  and  other  animals,  deserving 
much  attention  and  extended  research,  due  allowances  being  made  for 
the  modifications  produced,  as  he  points  out,  and  to  be  attributed  in 
many  cases  to  an  abundance  of  nullipores,  and  to  a  beautiful  pea-green 
sea-weed,  Caulerpa  prolifera.  The  majority  of  shells  in  the  lower  zone 
were  found  to  be  white,  or,  when  tinted,  of  a  rose  colour,  few  exhibiting 
any  other  hues.  In  the  higher  zones,  the  shells,  in  a  great  many  in- 
stances, exhibited  bright  combinations  of  colour.  The  animals  also  of 
the  Testacea  and  Radiata,  in  the  higher  zones,  were  much  more  bril- 
liantly coloured  than  in  the  lower,  where  they  are  usually  white,  what- 
ever the  colour  of  the  shell  may  be.f 

The  researches  of  Professor  E.  Forbes  have  led  him  not  only  to  attach 
great  value  to  the  bottom  in  or  on  which  marine  animals  may  live  (and 

*  Reports  of  British  Association,  vol.  ii.  p.  171. 

"If,"  observes  the  Professor,  "we  inquire  into  the  species  of  mollusca  which  are 
common  to  four  out  of  the  eight  ^gean  regions  in  depth,  we  find  that  there  are  38  such, 
21  of  which  are  either  British  or  Biscayan,  and  2  are  doubtfully  British ;  whilst  of  the 
remaining  15,  6  are  distinctly  represented  by  corresponding  species  in  the  North.  Thus 
among  the  Testacea  having  the  widest  range  in  depth,  one-third  are  Celtic  or  northern 
forms :  whilst  out  of  the  remainder  of  JEgean  Testacea,  those  ranging  through  less  than 
four  regions,  only  a  little  above  a  fifth  are  common  to  the  British  seas.  One  half  of 
the  Celtic  forms  in  the  ^Egean,  which  are  not  common  to  four  or  more  zones  in  depth, 
are  among  the  cosmopolitan  Testacea,  inhabiting  the  uppermost  part  of  the  littoral 
zone." 

f  Professor  E.  Forbes  adds,  "In  the  seventh  region,  white  species  (of  Testacea)  are 
also  very  abundant,  though  by  no  means  forming  a  proportion  so  great  as  in  the  eighth. 
Brownish  red,  the  prevalent  hue  of  the  Brachiopoda,  also  gives  a  character  of  colour 
to  the  fauna  of  this  zone ;  the  Crustacea  found  in  it  are  red.  In  the  sixth  zone,  the 
colours  become  brighter,  reds  and  yellows  prevailing,  generally,  however,  uniformly 
colouring  the  shell.  In  the  fifth  region,  many  species  are  banded  or  clouded  with  va- 
rious combinations  of  colours,  and  the  number  of  white  species  has  greatly  diminished. 
In  the  fourth,  purple  hues  are  frequent,  and  contrasts  of  colour  common.  In  the  second 
and  third,  green  and  blue  tints  are  met  with,  sometimes  very  vivid,  but  the  gayest  com- 
binations of  colour  are  seen  in  the  littoral  zone,  as  well  as  the  most  brilliant  whites." 

Respecting  the  colour  of  the  animals  of  Testacea,  the  genus  Trochus  is  selected  as 
"  an  example  of  a  group  of  forms  mostly  presenting  the  most  brilliant  hues  both  of  shell 
and  animal ;  but  whilst  the  animals  of  such  species  as  inhabit  the  littoral  zone  are  gaily 
chequered  with  many  vivid  hues,  those  of  the  greater  depth,  though  their  shells  are 
almost  as  brightly  coloured  as  the  covering  of  their  allies  nearer  the  surface,  have  their 
animals  for  the  most  part  of  an  uniform  yellow  or  reddish  hue,  or  else  entirely  white." 
Reports  Brit.  Assoc.,  vol.  xii.  p.  173. 


AMID    MINERAL    ACCUMULATIONS.  165 

it  will  be  obvious  that  creatures  whose  habits  may  be  suited  to  mud 
would  find  themselves  ill  at  ease  upon  rocky  ground  alone),  but  also  to 
point  out  the  effects  produced  by  the  accumulation  of  the  harder  parts 
of  successive  generations  of  marine  animals  upon  the  same  bottom,  thus, 
in  fact,  altering  its  condition,  so  that  they  may  die  out  from  this  in- 
crease.* He  considers  that  until  the  old  conditions  be  restored  by  a 
new  accumulation  of  detrital  matter  different  from  that  presented  by  the 
animal  exuviae,  the  same  animals  would  not  find  the  kind  of  bottom 
suited  to  them  ;  and  the  geological  bearing  of  this  view  is  shown  to  illus- 
trate the  bands  or  layers  of  fossils  so  frequently  found  interstratified 
with  common  sedimentary  matter. f  In  conclusion,  Professor  E.  Forbes 
adverts  to  the  evidences  of  the  existing  fauna  of  the  .ZEgean  which  would 
be  presented  if  its  bottom  were  to  be  elevated  into  dry  land,  or  the  sea 
filled  up  by  sedimentary  deposits.  While  the  remains  of  some  animals 
would  afford  the  needful  evidence  of  their  existence,  and  occur  under 
circumstances  whence  the  probable  depths  at  which  they  lived  might  be 
inferred,  of  other  animals,  very  abundant  in  the  present  seas,  no  trace 
would  be  found.! 

*  He  illustrates  this  point  by  beds  of  scallops  (Pecten  operations'),  or  of  oysters,  which, 
when  considerably  increased,  give  rise  to  a  change  of  ground,  by  the  accumulation  of 
their  shells,  so  that  the  race  dies  out,  and  the  shelly  bottom  becomes  covered  over  by 
sedimentary  matter. — Edinburgh  New  Phil.  Journal,  vol.  xxxvi.  p.  324. 

j-  In  his  paper  on  the  light  thrown  on  Geology  by  Submarine  Researches,  being  the 
substance  of  a  communication  made  to  the  Royal  Institution  of  Great  Britain,  on  the 
23d  February,  1844  (Edinburgh  New  Phil.  Journal,  vol.  xxxvi.  p.  318,  1844),  Professor 
E.  Forbes,  while  remarking  on  all  varieties  of  sea  bottom  not  being  equally  capable  of 
sustaining  animal  and  vegetable  life,  observes,  "In  all  the  zones  of  depth,  there  are 
occasionally  more  or  less  desert  tracts,  usually  of  sand  or  mud.  Th0*few  animals 
which  frequent  such  tracts,  are  mostly  soft  and  unpreservable.  In  some  muddy  and 
sandy  districts,  however,  worms  are  very  numerous ;  and  to  such  places  many  fishes 
resort  for  food.  The  scarcity  of  remains  of  testacea  in  sandstones,  the  tracks  of  worms 
on  ripple-marked  sandstones,  which  have  evidently  been  deposited  in  a  shallow  sea,  and 
the  fish  remains  often  found  in  such  rocks,  are  explained  in  a  great  measure  by  these 
facts." 

J  The  following  are  the  inferences  on  this  head,  inferences  extremely  valuable  re- 
specting the  animal  life  existing  at  different  geological  periods: — 

"1.  Of  the  higher  animals,  the  marine  Vertebrata,  the  remains  would  be  scanty  and 
widely  scattered. 

"2.  Of  the  highest  tribe  of  Mollusca,  the  Cephalopoda,  which  though  poor  in  species 
is  rich  in  individuals,  there  would  be  but  few  traces,  saving  of  the  Sepia,  the  shell  of 
which  would  be  found  in  the  sandy  strata  forming  parts  of  the  coast  lines  of  the  elevated 
sea-bed. 

"3.  Of  the  Nudibranchous  Mollusca  there  would  not,  in  all  probability,  be  a  trace  to 
assure  us  of  their  having  been;  and  thus,  though  we  have  every  reason  to  suppose  from 
analogy  that  those  beautiful  and  highly  characteristic  animals  lived  in  the  tertiary  pe- 
riods of  the  earth's  history,  if  not  in  older  ages,  as  well  as  now,  there  is  not  the  slightest 
remain  to  tell  of  their  former  existence. 

"4.  Of  the  Pteropoda  and  Nucleobranchiata,  the  shelless  tribes  would  be  equally 
lost  with  the  Nudibranchiata,  whilst  of  the  shelled  species  we  should  find  their  remains 
in  immense  quantity,  characteristic  of  the  soft  chalky  deposits  derived  from  the  lowest 
of  our  regions  of  depth. 


166  PRESERVATION    OF    ORGANIC    REMAINS 

While  Professor  E.  Forbes  was  thus  investigating  the  conditions  under 
which  marine  life  existed  in  the  Eastern  Mediterranean,  it  fortunately 
so  happened  that  Professor  Loven  was  engaged  in  researches  leading  to 

"  5.  The  Brachiopoda  we  should  find  in  deeply-buried  beds  of  nullipore  and  gravel, 
and  from  their  abundance  we  could  at  once  predict  the  depth  in  which  those  beds  were 
formed. 

"6.  The  Lamellibranchiate  mollusca  we  should  find  most  abundant  in  the  soft  clays 
and  muds,  in  such  deposits  generally  presenting  both  valves  in  their  natural  position, 
whilst  such  species  as  live  on  gravelly  and  open  bottoms  would  be  found  mostly  in  the 
state  of  single  valves. 

"  7.  The  testaceous  Gasteropoda  would  be  found  in  all  formations,  but  more  abundant 
in  gravelly  than  in  muddy  deposits.  In  any  inferences  we  might  wish  to  draw  regard- 
ing the  northern  or  southern  character  of  the  fauna,  or  on  the  climate  under  which  it 
existed,  whether  from  univalves  or  bivalves,  our  conclusions  would  vary  according  to 
the  depth  in  which  the  particular  stratum  examined  was  found,  and  on  the  class  of  mol- 
lusca which  prevailed  in  the  locality  explored. 

"8.  The  Chitons  would  be  found  only  in  a  state  of  single  valves,  and  probably  but 
rarely,  for  such  species  as  are  abundant,  living  among  disjointed  masses  of  rock  and 
rolled  pebbles,  which  would  afterwards  go  to  form  conglomerate,  would  in  all  proba- 
bility be  destroyed,  as  would  also  be  the  case  with  the  greater  number  of  sublittoral 
Mollusca. 

"9.  The  Mollusca  tunicata  would  disappear  altogether,  though  now  forming  an  im- 
portant link  between  the  Mediterranean  and  more  northern  seas. 

"  10.  Of  the  Arachnodermatous  Radiata,  there  would  not  be  found  a  trace,  unless 
the  membranous  skeleton  of  the  Velella,  should,  under  some  peculiarly  favourable  cir- 
cumstances, be  preserved  in  sand. 

"  11.  Of  the  Echinodermata,  certain  species  of  Echinus  would  be  found  entire ;  species 
of  Cidaris,  on  account  of  the  depth  at  which  that  animal  lives,  would  not  be  unfrequent 
in  certain  strata,  as  the  region  in  which  it  is  found  bounds  the  great  lowermost  region 
of  chalky  mud ;  the  spines  would  be  found  occasionally  in  that  deposit,  far  removed 
from  the  bodies  to  which  they  belonged.  Star-fishes,  saving  such  as  live  on  mud  or  sand, 
would  be  only  evidenced  by  the  occasional  preservation  of  their  ossicula.  Of  the  extent 
of  their  distribution  and  number  of  species  no  correct  idea  could  be  formed.  Of  the 
numerous  HoJothuriadce  and  Sipunculidce,  it  is  to  be  feared  there  would  be  no  traces.  The 
single  Crinoidal  anima*  would  be  easily  preserved  entire,  but  its  ossicula  and  cup-like 
base  would  be  found  in  the  more  shelly  deposits. 

"12.  Of  the  Zoophyta,  the  corneous  species  might  leave  impressions  resembling  those 
of  Graptolites  in  the  shales  formed  from  the  dark  muds  on  which  they  live.  The  Corals 
would  be  few,  but  perhaps  plentiful  in  the  shelly  beds,  mostly  however  fragmentary. 
The  Cladocora  coespitosat  where  present,  would  infallibly  mark  the  bounds  of  the  sea, 
and,  from  the  size  of  its  masses,  might  be  preserved  in  conglomerates  where  the  tes- 
tacea  would  have  perished.  The  Actinia  would  have  disappeared  altogether. 

"13.  Of  the  sponges,  traces  might  be  found  of  the  more  siliceous  species  when  buried 
under  favourable  circumstances. 

"  14.  The  Articulata,  except  the  shelled  annelides,  would  be  for  the  most  part  in  a 
fragmentary  state. 

"15.  Foraminifera  would  be  found  in  all  deposits,  their  minuteness  being  their  pro- 
tection ;  but  they  would  occur  most  abundantly  in  the  highest  and  lowest  beds,  distinct 
species  being  characteristic  of  each. 

"16.  Tracts  would  be  found  almost  entirely  deficient  in  fossils,  some,  such  as  the  mud 
of  the  Gulf  of  Smyrna,  containing  but  few  and  scattered ;  whilst  similar  muds  in  other 
localities  would  abound  in  organic  contents.  On  sandy  deposits,  formed  at  any  consi- 
derable depth,  they  would  be  very  scarce  and  often  altogether  absent.  Fossiliferous 
strata  would  generally  alternate  with  such  as  contain  few  or  no  organic  remains.  Whilst 


AMID    MINERAL    ACCUMULATIONS.  167 

general  and  similar  conclusions  respecting  the  modifications  in  marine 
life  on  the  coast  of  Norway.  Though  both  localities  are  so  far  similar 
that  the  shores  are  for  the  most  part  rocky,  and  deep  water  to  be  often 
obtained  near  the  coast,  they  differ  as  to  climate,  and  as  to  the  sea 
being  tideless  in  the  Eastern  Mediterranean  and  oceanic  off  Norway. 
While  adverting  to  the  modifications  of  life  at  different  depths,  Professor 
Loven  attributes  much  of  the  character  of  the  submarine  life  off  the 
coast  of  Norway  to  variations  in  the  sea-bottom,  always,  however,  making 
allowances  for  the  depth,*  thus  agreeing  with  the  general  views  of  Pro- 
fessor Forbes. 

While  marine  life  is  thus  found  adjusted  to  different  zones  of  depth 
on  the  ocean  shores  of  Norway  and  the  east  part  of  the  Mediterranean, 
always  carefully  considering  the  local  and  physical  conditions,  it  be- 
comes the  more  interesting  to  have  direct  evidence  of  the  adjustments 
which  may  be  effected  on  the  great  and  gentle  slopes  bounding  some 

at  present  the  littoral  zone  presents  the  greatest  number  and  variety  of  animal  and 
vegetable  inhabitants,  including  those  most  characteristic  of  the  Mediterranean  Sea, 
when  upheaved  and  consolidated,  their  remains  would  probably  be  imperfect  as  com- 
pared with  those  of  the  natives  of  deeper  regions,  in  consequence  of  the  vicissitudes  to 
which  they  are  exposed,  and  the  rocky  and  conglomeratic  strata  in  which  the  greater 
number  would  be  embedded.  A  great  part  of  the  conglomerates  and  sandstones  found 
would  present  no  traces  of  animal  life,  which  would  be  most  abundant  in  the  shales  and 
calcareous  consolidated  muds." — Prof.  E.  Forbes'  Reports,  Brit.  Association,  vol.  xii. 
p.  176. 

*  Professor  Loven  observes,  "As  to  the  regions,  the  littoral  and  laminarian  are  very 
well  denned  everywhere,  and  their  characteristic  species  do  not  spread  very  far  out  of 
them.  The  same  is  the  case  with  the  florideous  Algos,  which  is  most  developed  nearer 
to  the  open  sea.  But  it  is  not  so  with  the  regions  from  15  to  100  fathoms  (90  to  600 
feet).  Here  there  is  at  the  same  time  the  greatest  number  of  species,  and  the  greatest 
variety  of  their  local  assemblages :  and  it  appears  to  me,  that  their  distribution  is  regu- 
lated, not  only  by  depths,  currents,  &c.,  but  by  the  nature  of  the  bottom  itself,  the  mix- 
ture of  clay,  mud,  pebbles,  &c.  Thus,  for  instance,  the  many  species  of  Amphidesma, 
Nucula,  Natica,  Eulima,  Dentalium,  &c.,  which  are  characteristic  of  a  certain  muddy 
ground  at  15  to  20  fathoms,  are  found  together  at  80  to  100  fathoms.  Hence  it  appears, 
that  the  species  in  this  region  have  generally  a  wider  vertical  range  than  the  littoral, 
laminarian,  and  perhaps  as  great  as  the  deep  sea  coral.  The  last-named  region  is  with 
us  characterized,  in  the  south,  by  Oculina  ramea  and  Terebratula,  and  in  the  north,  by 
Astrophyton,  Cidaris,  Spatangus  purpureus  of  an  immense  size,  all  living,  besides  Gor- 
gonise  and  the  gigantic  Alcyonium  arboreum,  which  continues  as  far  down  as  any  fisher- 
man's line  can  be  sunk.  As  to  the  point  where  animal  life  ceases,  it  must  be  somewhere ; 
but  with  us  it  is  unknown.  As  the  vegetation  ceases  at  a  line  far  above  the  deepest 
regions  of  animal  life,  of  course  the  zoophagous  mollusca  are  altogether  predominant  in 
these  parts,  while  the  phytophagous  are  more  peculiar  to  the  upper  regions.  The  ob- 
servation of  Professor  E.  Forbes,  that  British  species  are  found  in  the  Mediterranean, 
but  only  at  greater  depths,  corresponds  exactly  with  what  has  occurred  to  me.  In 
Bohuslan  (between  Gottenburg  and  Norway),  we  found,  at  80  fathoms,  species  which, 
in  Finmark  (on  the  north),  may  be  readily  collected  at  20,  and  on  the  last-named  coast, 
some  species  even  ascend  into  the  littoral  region,  which,  with  us  here  on  the  south, 
keep  within  10  to  11  fathoms." — On  the  Bathy metrical  distribution  of  submarine  life  on  the 
northern  shores  of  Scandinavia. — British  Association  Reports,  Notices,  and  Abstracts,  vol. 
xiii.  p.  50. 


168  PRESERVATION    OF    ORGANIC    REMAINS 

coasts,  such  as  those  so  important  on  the  eastern  coasts  of  America. 
Respecting  these  great  detrital  fringes  off  coasts,  among  which  may  be 
classed,  though  very  small  comparatively,  the  shallow  seas  around  the 
British  Islands,  the  area  of  which  inside  depths,  not  exceeding  600  feet, 
will  be  seen  by  reference  to  fig.  65  (p.  114),  we  should  anticipate  dis- 
turbing conditions  much  affecting  the  distribution  of  some  portion  of 
the  marine  life  upon  them.  With  regard  to  a  knowledge  of  the  distri- 
bution of  marine  life  in  the  British  seas,  we  are  indebted  to  the  re- 
searches of  Professor  E.  Forbes,  commenced  anterior  to  those  under- 
taken in  the  JEgean  Sea.*  It  was  while  prosecuting  these  researches 
that  he  ascertained  the  value  in  these  investigations  of  the  power  of 
mollusca  to  migrate. f  He  has  pointed  out  that  they  do  so  in  their 
larva  state,  ceasing  "  to  exist  at  a  certain  period  of  metamorphosis,  if 
they  do  not  meet  with  favourable  conditions  for  their  development,  i.  e., 
if  they  do  not  reach  the  particular  zone  of  depth  in  which  they  are 
adapted  to  live  as  perfect  animals.  "| 

Professor  E.  Forbes  divides  the  British  seas  into  four  zones  of  depth  : 
1,  the  Littoral;  2,  the  Laminarian  ;  3,  the  Coralline  ;  and  4,  the  Coral. § 
The  littoral  zone  lies  between  high  and  low  water  mark,  varying  in  ex- 
tent according  to  the  rise  and  fall  of  tide,  and  the  shallowness  or  depth 
of  the  shore.  "  Throughout  Europe,  wherever  it  consists  of  rock,  it  is 
characterized  zoologically,  by  species  of  Littorina  ;  botanically,  by  Co- 
rallina ;  where  sandy,  by  the  presence  of  certain  species  of  Cardium, 
Tellina,  and  Solen ;  where  gravelly,  by  Mytilus ;  where  muddy,  by 
Lutraria  and  Pullastra."  The  littoral  is  divisible  into  minor  zones. || 
The  laminarian  zone  is  the  belt  commencing  at  low-water  mark,  and 
extending  to  the  depth  of  7  to  15  fathoms  (42  to  90  feet).  Algae  are 
common,  and  numerous  animals  inhabit  the  forests  composed  of  them. 

*  The  first  notice  of  them  was  published  in  the  Edinburgh  Academic  Annual  for  1840. 

f  In  1840  he  gave  a  summary  of  seven  years'  observations  at  a  particular  season  of 
the  year. — Annals  of  Natural  History,  vol.  iv. 

%  Edinburgh  New  Phil.  Journal,  vol.  xxxvi.  p.  825,  1844.  Speaking  of  the  manner 
in  which  the  larvae  and  eggs  maybe  transported,  it  is  observed  that,  "if  they  (the 
larvae)  reach  the  region  and  ground  of  which  the  perfect  animal  is  a  member,  then  they 
develope  and  flourish ;  but  if  the  period  of  their  development  arrives  before  they  have 
reached  their  destination,  they  perish,  and  their  fragile  shells  sink  into  the  depths  of 
the  sea.  Millions  and  millions  must  thus  perish,  and  every  handful  of  the  fine  mud 
brought  up  from  the  eighth  zone  depth  in  the  Mediterranean,  is  literally  filled  with 
hundreds  of  these  curious  exuviae  of  the  larvte  of  mollusca." 

g  These  zones,  originally  pointed  out  in  1840,  are  considered  to  have  been  established 
by  subsequent  researches  (Memoirs  of  the  Geological  Survey  of  Great  Britain,  vol.  i. 
p.  371,  1846).  Professor  Forbes  remarks  that  the  first  two  regions  had  been  previously 
noticed  by  Lamouroux,  in  his  account  of  the  vertical  distribution  of  sea  weeds ;  by 
Audouin  and  Milne  Edwards  in  their  observations  on  the  natural  history  of  the  coast  of 
France ;  and  by  Sars,  in  the  preface  to  his  Bagtivelser  og  Jagtivelser. 

||  A  table  of  the  characteristic  animals  and  plants,  of  four  sub-zones,  is  given  in  Pro- 
fessor Forbes'  Memoir  on  the  Geological  Relations  of  the  existing  Fauna  and  Flora  of 
the  British  Isles. — Memoirs  of  the  Geological  Survey  of  Great  Britain,  vol.  i.  p.  373. 


AMID    MINERAL    ACCUMULATIONS.  169 

"  Among  the  mollusca,  the  genera  Lacuna  and  Rissoa,  the  Patella  pel- 
lucida  and  Icevis,  Pullastra  perforans  and  vulgaris,  and  various  Modiolce, 
are  especially  characteristic  of  this  zone,  and  numerous  zoophytes  and 
Radiata,  especially  Echinus  sphcera,  Tubularia,  Actinea  senilis,  though 
ranging  both  higher  and  lower,  are  more  prolific  here  than  in  any  of 
the  other  regions."  Lastly  conies  the  Nullipora,  bounding  the  marine 
vegetation  in  depth,  and  rarely  ranging  down  to  more  than  120  feet  in 
our  seas.* 

The  region  of  corallines  is  so  termed  from  the  greatest  abundance  of 
corneous  zoophytes,  which  appear  to  take  the  place  of  plants,  being 
found  in  it.  The  carnivorous  mollusca  are  abundant,  species  of  Fusus, 
Pleurotoma,  and  Buccinum  are  common,  and  many  species  of  Trochus 
are  found ;  Naticce,  Fissurellce,  Emarginulce,  Velutince,  Capulus,  Eu- 
limce,  and  Chemnitzice  are  abundant ;  and  among  bivalves,  Artemis, 
Venus,  Astarte,  Pecten,  Lima,  Area,  and  N'ucula.  "Numerous  and 
peculiar  Radiata,  including  the  largest  and  most  remarkable  species, 
abound,  and,  for  number,  variety,  and  interest  of  the  forms  of  animal 
life  in  the  British  seas,  this  region  transcends  all  others,  "f  This  zone 
extends  from  about  90  to  about  300  feet,  its  greatest  development  being 
between  150  and  210  feet. 

The  fourth  region  is  that  of  deep-sea  corals,  and  is  local.  The  greater 
part  of  the  area  of  the  British  seas  does  not  attain  the  depth  at  which 
this  zone  commences.  Professor  E.  Forbes  considers  this  region  as 
hitherto  but  very  partially  explored.  "As  far  as  we  know,"  he  ob- 
serves, "  it  is  well  characterized  by  the  abundance  of  the  stronger  corals, 
the  presence  in  quantity  of  species  of  the  Dentalium-like  genus  of  An- 
nelides,  called  Ditrupa,  by  a  few  peculiar  Mollusca,  and  by  peculiar 
Ecliinodermata,  as  Astrophyton  and  Oidaris,  and  Amorphozoa,  as  Tethya 
cranium.  All  our  British  Brachiopoda  inhabit  this  zone,  and  probably 
range  throughout  it."J 

*  Professor  E.  Forbes  points  out,  that  the  Nullipora  likewise  bounds  marine  vegetable 
life  in  the  Mediterranean,  -where  it  descends  to  420  and  480  feet.  With  respect  to  the 
depths  to  which  marine  vegetable  life  extends,  he  remarks,  that  it  does  so  further  than 
is  commonly  supposed,  stating  that  in  the  Eastern  Mediterranean,  Codium  flabe lliformce 
is  found  at  30  fathoms,  Microdiclyon  at  30  fathoms,  Rityphlcea  tinctorea  at  50  fathoms, 
Chrysymenia  uvaria  at  50  fathoms,  Dictyomenia  volubilis  at  50  fathoms,  Constantinea  reni- 
formis  at  50  fathoms,  and  Nullipora polymorpha  at  95  fathoms  (570  feet). 

f  Forbes,  Mem.  Geol.  Survey  of  Great  Britain,  vol.  i.  p.  374. 

j  Professor  E.  Forbes  remarks  respecting  the  Brachiopoda,  that  when  found,  in  cer- 
tain localities,  in  more  shallow  water  among  the  corallines,  there  are  reasons  for  be- 
lieving that  their  occurrence  there  may  be  explained  by  geological  changes  affecting 
the  conditions  of  the  sea  bottom. 

We  would  refer  for  a  valuable  view  of  the  characteristic  plants  and  animals  inhabiting 
the  four  zones  into  which  the  area  of  the  British  seas  has  been  divided,  to  the  table 
given  by  Professor  E.  Forbes,  in  his  Memoir  on  the  Geological  Relations  of  the  existing 
Fauna  and  Flora  of  the  British  Isles,  Memoirs  of  the  Geological  Survey  of  Great  Britain, 
vol.  i.  p.  375. 


170  PRESERVATION    OF    ORGANIC    REMAINS 

The  advance  thus  made  will  be  sufficient  to  stimulate  other  observers, 
so  that  at  no  very  distant  period  a  valuable  mass  of  evidence  may  be 
anticipated.*  Probably  the  general  views,  based  on  the  local  investi- 
gations above  noticed,  may  be  found  capable  of  extensive  application. 
However  this  may  be,  it  can  scarcely  but  happen  that  an  accumulation 
of  additional  data  would  most  materially  aid  the  progress  of  the  geolo- 
gical inferences  to  be  deduced  from  the  mode  of  occurrence  of  organic 
remains  in  rocks. 

With  respect  to  the  littoral  zone,  that  most  influenced  by  climate, 
while  in  tideless  seas,  or  those  where  tides  are  of  little  consequence,  the 
marine  animals  inhabiting  it  are  under  conditions  of  slight  change,  as 
regards  the  vertical  rise  and  fall  of  water ;  in  tidal  seas  the  case  is 
different.  In  tidal  seas  many  littoral  molluscs  are  exposed  to  atmospheric 
influences  for  different  periods,  those  near  high-water  mark  the  longest ; 
so  that  while  the  latter  may  remain  uncovered  by  water  six  or  eight 
hours  at  a  time,  those  nearer  low-water  mark  may  be  so  for  only  an 
hour  or  two,  some  merely  for  a  short  time  at  spring  tides.  Neap  tides 
also  leave  a  belt  surrounding  land,  the  higher  part  of  which  is  only 
covered  by  water  for  a  few  days  at  a  time,  and  then  only  at  spring 
tides.  It  thus  happens  that  while  in  the  tropics  the  littoral  zone  may 
not  be  under  very  material  changes  of  temperature  during  the  year, 
this  condition,  looking  at  the  subject  as  a  whole,  gradually  shades  off  on 
either  side  towards  the  polar  regions,  where  the  water  becomes  solid 
along  shore  for  part  of  the  year,  and  the  coasts  are  often  partially 
clear  in  the  summer,  portions  being  still  subject  to  the  occasional  pres- 
sure of  floes  and  masses  of  ice.  In  certain  intermediate  regions,  all 
animals  and  plants  inhabiting  the  distance  between  high  and  low-water 
mark,  with  its  modifications  according  to  the  state  of  the  tide,  must  be 
adjusted  to  sustain  the  extremes  of  a  long  range  of  temperature,  in 
order  to  support  the  atmospheric  changes  to  which  they  are  exposed. 
The  differences  of  temperature  observable  round  the  British  Islands, 
notwithstanding  the  advantage  of  their  position,  are  sufficiently  con- 
siderable to  produce  a  movement  among  many  marine  animals,  as  is 
well  known,  so  that  certain  of  them  are  only  seen  close  in  shore, 
among  the  pools  left  by  the  tide,  in  the  warmer  season.  Others  again 
appear  organized  to  sustain  a  considerable  change  of  temperature.  We 

*  When  we  recollect  that  under  favourable  circumstances  the  officers  of  our  Navy 
and  of  our  Merchant  Service,  may  render  great  assistance  to  this  inquiry,  when  pro- 
perly conducted,  it  is  to  be  hoped  that  we  may  eventually  obtain,  through  their  exer- 
tions alone,  more  extended  facts  connected  with  the  subject.  Under  their  care,  the 
dredge  might  often  be  applied  with  advantage ;  and  if  specimens  of  the  animals  obtained 
were  stowed  away  safely,  properly  ticketed,  for  the  examination  of  competent  natu- 
ralists, far  more  would  be  known  in  the  next  half  century  touching  the  distribution  of 
marine  life,  particularly  at  depths  where  surface  waves  could  not  so  act  as  to  drive  its 
remains  on  shore,  than  could  be  accomplished  by  naturalists  alone,  however  zealous. 


AMID    MINERAL    ACCUMULATIONS.  171 

have  seen  the  common  limpet  (Patella  vulgaris)  apparently  doing  well 
on  our  coasts,  at  temperatures  of  92°  (close  to  the  rock),  and  of  24°, 
a  range  of  68°.  As  far,  therefore,  as  temperature  is  concerned,  such 
a  mollusc  could  live  in  the  ocean  waters,  and  at  any  depths,  in  all 
parts,  except  in  the  higher  portions  of  the  sea  during  the  winter 
months  in  the  icy  regions.  Its  organization  is  no  doubt  adjusted  to 
a  littoral  life,  and  to  changes  of  temperature,  as  part  of  the  littoral 
conditions  in  such  climates  as  that  of  the  British  Islands,  but  the  amount 
of  change  which  it  can  in  this  manner  support,  may  make  us  careful  at 
giving  too  much  importance  to  temperature  alone  in  the  distribution  of 
marine  animal  life.  Once  beneath  a  moderate  depth  of  sea,  the  mass 
of  water  is  less  acted  upon  by  atmospheric  influences,  and  the  adjust- 
ment to  the  specific  gravities  of  water  at  different  temperatures  is  such 
as  to  produce  much  uniformity  in  the  temperature  of  the  deeper  zones, 
and  minor  modifications  in  those  above  them ;  in  the  warmer  regions 
tending  to  keep  the  sea  temperature  beneath  that  of  the  atmosphere, 
and  in  the  colder  to  raise  that  of  the  water  above  it.  As,  therefore, 
the  sea  level  is  approached,  so,  as  a  whole,  must  the  animals  inhabit- 
ing the  higher  zones  be  adjusted  to  support  changes  in  the  tempera- 
ture of  the  sea  in  those  regions  where  the  heat  in  summer  begins  to 
have  an  appreciable  influence  on  the  sea  waters,  as  respects  the  cold  ex- 
perienced in  winter. 

Quitting  coast  conditions,  and  regarding  the  ocean  beyond  the  depths 
of  200  or  300  fathoms,  we  have  a  large  area,  on  the  bottom  of  which 
we  have  no  reason  to  suppose  any  vegetation  exists,  seeing  that  observa- 
tions on  coasts  would  lead  us  to  conclude  that  the  needful  conditions  for 
its  growth  terminated  at  comparatively  very  minor  depths.  All  phy- 
tophagous marine  creatures  would  not  be  expected  beyond  their  ability 
to  obtain  the  food  fitted  for  them,  while  the  carnivorous  animals  have 
necessarily  the  power  to  extend,  vertically  and  horizontally,  far  beyond 
the  growth  of  marine  vegetation,  however  this  vegetation  may  support 
the  mass  of  life  upon  which  the  carnivorous  animals  have,  as  a  beginning, 
to  feed.  In  the  region  of  the  Sargasso  weed,  we  have  an  example  of  a 
floating  vegetation,  tending  to  support  animal  life,  and  forming  the 
abode  of  multitudes  of  marine  creatures  in  the  open  sea.  This,  how- 
ever, is  an  exception  to  the  general  fact  of  the  absence  of  marine  vege- 
tation in  the  open  ocean,  except  so  far  as  stray  portions  of  sea-weed, 
borne  by  currents  from  coasts,  may  be  concerned. 

In  the  oceanic  depths  there  exist,  apparently,  conditions  under  which 
some  portions  of  the  remains  of  the  fish,  crustaceans,  and  molluscs,  to 
be  found  on  the  surface  above,  may  be  preserved.  Although  much  may 
be  consumed  and  continued  in  the  mass  of  life  so  inhabiting  the  sur- 
face, from  time  to  time  some  part  of  the  harder  portions  of  animals 
may  descend  to  the  bottom,  assuming  that  the  specific  gravity  of  such. 


172  PRESERVATION    OP    ORGANIC    REMAINS 

remains  be  such  as  to  permit  their  fall  through  the  water.*  Shells  of 
the  lanthina  communis,  having  a  specific  gravity  of  2 '66,  and  of  the 
Nautilus  umbilicatus  with  that  of  2-64,  would,  after  the  fleshy  matter 
of  these  molluscs  was  decomposed  or  consumed,  and  no  air  entangled  in 
the  interior  of  the  shells,  be  capable  of  descending  to  any  depths  which 
we  may  consider  at  all  probable  in  the  ocean,  supposing  its  saline  con- 
tents not  to  materially  diifer  in  depth,  and  the  compressibility  of  sea 
water  such  as  experiments  upon  fresh  water  would  lead  us  to  infer.  We 
may  thus  have  the  remains  of  marine  animals  scattered  over  the  bottom 
of  the  ocean  floor,  in  certain  localities  especially,  as  also  those  of  stray 
animals  drifted  from  coasts,  attached  to  sea-weeds  or  pieces  of  wood, 
both  of  which  decomposing,  the  harder  portions  of  these  animals  may 
fall  to  the  bottom  at  great  depths.  It  can  scarcely  be  supposed  that  all 
the  logs  of  wood  bored  by  the  Teredo,  or  covered  over  by  the  common 
barnacle,  Anatifa  striata,  are  drifted  on  shore,  and  that  they  do  not 
often  become  so  decomposed  as  to  permit  the  descent  of  the  harder 
parts  of  these  animals  to  the  bottom.  Indeed,  we  might  anticipate  a 
somewhat  singular  mixture  of  the  harder  parts  of  some  marine  animals 
in  different  parts  of  the  ocean,  especially  in  the  vicinity  of  islands  rising 
out  of  considerable  depths,  such,  for  example,  as  near  Hawaii,  Maui, 
and  other  islands  of  the  Sandwich  Group. 

Returning  to  the  coast,  we  find  with  the  plants  the  marine  animal 
life  feeding  upon  it,  from  that  exposed  to  the  atmosphere  at  low  water, 
on  tidal  shores,  to  that  only  known  by  dredging  and  fishing.  Those 
accustomed  to  examine  the  rocky  shores  of  tidal  seas  well  know  how 
much  sea-weed  may  be  cast  on  shore  in  the  little  bays  and  creeks,  or  be 
drifted  to  the  larger  bays,  during  and  after  heavy  gales  of  wind,  pro- 
ducing breakers  on  such  coasts,  and  which  tear  up  marine  plants, 
especially  towards  low-water  mark,  where  during  calmer  times  they  may 
have  been  abundantly  produced.  A  sandy  bay  beyond  a  long  line  of 
steep  rocky  coast,  the  latter  exposed  to  some  heavy  gale  during  the  rise 
and  fall  of  several  successive  tides,  so  that  sea-weeds,  detached  by  the 
breakers  from  it,  are  driven  by  wind  and  tide  into  the  bay,  will  be  often 
seen  by  the  observer  to  have  its  beach  covered  in  various  places  with 
matted  masses  of  these  plants.  Frequently,  as  might  be  expected  from 
the  forces  employed,  these  lines  of  sea-weed  are  cast  up  high  on  the 
beach,  beyond  the  reach  of  calmer  seas  to  float  them  off  again.  They 

*  With  respect  to  the  compressibility  of  the  ocean  waters ;  according  to  Poisson 
(Nouvelle  Th6orie  de  1'Action  Capillaire,  p.  277)  it  would  require  a  pressure  equal  to 
1100  atmospheres  to  reduce  water  six-hundredths  of  its  volume.  In  the  experiments 
of  MM.  Colladon  and  Sturm,  water  not  deprived  of  air,  was  compressed  equal  to 
47*85  millionths  for  each  atmosphere,  and  deprived  of  air,  equal  to  49-66  millionths. 
The  experiments  of  M.  (Ersted  gave  a  compression  of  46-65  millionths  for  each  atmo- 
sphere. Water  containing  salts  in  solution  was  found,  as  might  be  expected,  somewhat 
less  compressible. 


AMID    MINERAL    ACCUMULATIONS.  173 

will  there  be  disposed  of  according  to  climate.  In  warm  countries,  or 
in  the  summer  months  of  the  temperate  regions,  they  soon  decompose, 
and  their  remains,  not  borne  off  in  a  gaseous  form,  become  intermingled 
with  the  beach.  An  observer,  by  studying  the  sections  of  sandy  beaches 
exposed  by  rills  or  small  streams  of  water,  may  occasionally  find 
irregular  layers  of  black  carbonaceous  matter,  the  result  of  the  decom- 
position of  masses  of  sea-weeds  cast  on  shore,  intermingled  with  the 
ordinary  sand,  and  in  some  localities,  parts  of  a  shingle  beach  will  be 
seen  with  an  abundance  of  intermixed  sea-weed  in  a  decomposed  or 
decomposing  state.  He  may  also  find  the  light  matter  of  decomposed 
sea-weeds  borne  to  deeper  waters  in  sheltered  situations,  its  entomb- 
ment in  such  places  depending  upon  the  disturbance  to  which  it  may  be 
subsequently  exposed,  and  the  amount  of  ordinary  sedimentary  sub- 
stances which  may  collect  permanently  over  it.  In  some  localities  much 
mud,  black  with  carbonaceous  matter  thus  derived,  may  be  accumulated. 

Molluscs,  living  among  the  sea-weeds  thus  detached  and  cast  on  shore, 
are  occasionally  observed  to  be  entangled  amid  the  plants,  their  harder 
parts  remaining  intermingled  with  the  sands  or  shingles  after  the 
decomposition  of  the  plants,  so  that  the  shells  of  rock-frequenting 
molluscs  become  embedded  with  those  of  others  living  in  and  upon  sands. 
The  little  Patella  pellucida  is  very  commonly  thrown  on  shore  on  our 
coasts,  adhering  to  the  cavity  it  has  made  for  itself  at  the  root  of  some 
large  fucus,  and  which,  indeed,  has  weakened  the  power  of  the  plant 
to  keep  its  place  when  acted  on  by  the  sea  in  heavy  gales.  It  is  also 
very  common  to  find  drifted  marine  creatures  of  other  kinds  entangled 
in  these  masses  of  detached  sea-weeds ;  on  some  coasts  the  remains  of 
crustaceans  being  abundant. 

With  regard  to  steep  coasts,  vertical  or  nearly  vertical  cliffs  plunging 
suddenly  into  deep  water,  it  may  happen  that  molluscs,  feeding  upon 
marine  plants  growing  at  various  depths,  and  themselves  inhabiting 
different  depths,  according  to  their  kinds,  get  knocked  off  by  the  sea. 
While  those  uninjured  may  again  recover  their  positions,  a  few  perish, 
and  their  shells  be  preserved  in  sand,  silt,  or  mud,  with  the  remains  of 
other  molluscs  living  on  such  bottoms ;  so  that  the  remains  of  littoral, 
shallow,  and  deep-water  molluscs  become  preserved  together  in  the  same 
deposit.  Molluscs  as  they  die  must  have  their  shells  washed  away  by 
the  sea  on  such  coasts,  and  thrown  into  deep  waters.  Some  account 
also  has  to  be  taken  of  birds  picking  the  animals  out  of  shells  which 
they  may  have  obtained  upon  the  rocks  at  low  tide,  or  have  brought 
from  adjacent  bays  where  they  may  have  been  cast  alive  or  recently 
killed  on  shore.  We  have  seen  the  common  oyster-catchers  busy 
knocking  off  and  eating  limpets  upon  projecting  portions  of  steep  coasts, 
leaving  the  shells,  all  of  which,  when  there  is  breaker  action,  must  have 
been  washed  into  deep  water  as  the  tide  rose.  All  such  circumstances 


174 


PRESERVATION    OF    ORGANIC    REMAINS 


have  to  be  considered  upon  the  steep  coasts  of  the  world,  of  which  there 
is  no  want,  many  fathoms  of  depth  being  found,  with  occasionally  a  few 
projections  in  different  places,  close  along  shore,  various  marine  vege- 
tables and  animals  occupying  zones  of  the  depths  best  suited  to  them. 
The  sea  adjoining  some  of  the  ocean  islands,  where  great  depths  are 
obtained  all  round,  may,  perhaps,  afford  some  of  the  best  conditions  for 
collecting  together  the  remains  of  marine  life  which  had  inhabited 
different  zones  of  depth. 

While  the  remains  of  marine  animals  which  have  existed  in  different 
zones  of  depth,  with  the  modifications  due  to  sheltered  and  exposed 
situations  and  other  variations  of  conditions,  may  be  collected  either  in 
the  immediate  vicinity  of,  or  at  no  great  distance  from,  steep  coasts,  it 
is  in  tidal  seas,  to  the  fringes  of  detrital  or  chemically-formed  matter 
around  the  chief  masses  of  land,  rising  above  the  sea,  that  we  look  for 
the  preservation  of  the  great  amount  of  organic  remains.  Indeed,  the 
modifications  of  the  actual  coasts  as  to  depth,  are  commonly  but  varia- 
tions of  the  manner  in  which  these  sub-marine  fringes  join  the  sub-aerial 
portions  of  the  solid  land.  Such  fringes  may  be  regarded  as  forming 
extensive  plains  on  the  margins  of  tidal  seas  (here  and  there  a  project- 
ing mass  of  rock  rising  above  them),  with  usually  a  somewhat  gentle 
slope  to  the  depth  of  600  to  1000  or  1200  feet,  after  which  they  appear, 
as  a  whole,  to  descend  more  abruptly.  Gentle  as  the  slope  may  be,  the 
differences  of  depth  appear  sufficient,  as  above  stated,  for  the  modifi- 
cation of  life  upon  it,  so  that  while  some  animals  live  near  the  coast, 
others  keep  far  out  in  the  deeper  water.  While  some  portion  may  be 
enabled  to  live  at  varied  depths,  there  exists  a  mass  of  life,  the  remains 
of  which  would  be  entombed  far  from  shore  in  one  case,  and  near  it  in 
the  other,  and  not  commingled,  as  in  the  case  of  steep  coasts,  and 
adjoining  deep  seas.  A  glance  at  the  charts  of  a  large  portion  of  the 
eastern  side  of  the  American  continent  will  show  how  far  separated, 
horizontally,  such  masses  of  remains  may  be. 

Let  it,  for  illustration,  be  supposed  that  the  following  map  (fig.  69) 

Fig.  69. 
I   a  b  c  d  e  f 


AMID    MINERAL    ACCUMULATIONS.  175 

represents  an  extended  line  of  coast,  so  that  1,  1 ;  2,  2 ;  and  3,  3,  are 
parallels  of  latitude  sufficiently  distant  from  each  other  to  render  sur- 
face temperature  different  enough  to  be  important  as  regards  marine 
life.  Let  I T  be  a  line  of  coast  extending  from  north  to  south,  and  //' 
the  outer  verge  of  soundings  off  the  same  coast,  a  more  sudden  increase 
of  depth  taking  place  at  this  verge  into  the  area  g  g' ;  equal  depths,  or 
zones  being  represented  by  the  lines  a  a',  b  b',  c  c1,  d  d',  and  e  e'. 

For  still  further  illustration,  we  have  supposed  a  large  river  (r)  to 
deliver  itself  upon  the  coast.  Upon  such  a  subaqueous  area,  we  have 
the  conditions  for  the  entombment  of  the  remains  of  the  life  distributed 
over  it  in  certain  bands,  coinciding  with  depths  ranging  in  lines  with 
the  coast,  and  with  the  power  of  tidal  and  wave  action  upon  the  detritus 
thrust  forward  by,  or  carried  in  mechanical  suspension  out  of,  the  river, 
in  addition  to  any  sedimentary  matter  directly  obtained  from  the  coast. 
The  effect  of  the  river  waters  in  rendering  the  shore  water  brackish 
would  vary  in  depth,  according  to  circumstances,  the  tendency  of  such 
waters,  from  their  relative  specific  gravity,  being  to  float  above  the  sea 
water,  and  not  to  be  much  mingled  with  the  latter  to  any  great  amount 
of  depth,  though,  upon  the  ebb  tide,  brackish  water  might  be  carried 
along  shore  if  the  tide  took  that  course.  Different  states  of  the  weather 
would  modify  the  conditions  for  the  mixture  of  fresh  and  sea  waters. 
Thus  during  heavy  on-shore  gales  of  wind,  and  freshets  in  the  rivers, 
as  are  often  combined  on  the  western  portions  of  the  British  Islands, 
the  conditions  for  mingling  sea  and  river  waters  are  more  favourable 
than  during  calm  weather. 

Let  us  suppose  the  following  section  (fig.  TO)  to  represent  (though 
upon  a  very  exaggerated  scale)  that  of  the  map  (fig.  69)  a  b  being  the 

Fig.  70. 


sea-level,  c,  coast,  and  d,  e,  /,  </,  different  depths  of  sea,  and  h,  the 
more  sudden  descent  into  deep  water.  In  tideless  seas  these  various 
depths  would  remain  undisturbed,  except  by  movements  arising  from 
the  waves  produced  by  the  winds  above,  unless,  indeed,  there  be  cur- 
rents acting  in  such  seas.  In  tidal  seas  the  case  would  be  so  far 
different,  that  the  level  of  the  sea  itself  would  be  altered  during  every 
tide ;  on  some  coasts  making  a  change  of  many  feet.  With  this  change 
of  level,  any  motion  on  the  waters  produced  by  waves  above  would  also 
descend  more  or  less  deep,  supposing  equal  wave  action  on  the  surface. 
In  addition,  the  sweep  of  the  tidal  stream  will  extend  to  the  depths  it 
may,  according  to  conditions,  reach,  and  occasionally  an  ocean  current 
may  range  sufficiently  near  a  coast  to  act  on  the  bottom,  the  shores 


176  PRESERVATION    OF    ORGANIC    REMAINS 

of  ocean  islands  sometimes  offering  conditions  for  the  latter.  We  have 
now  to  consider  that  while  the  shells  of  molluscs  may  often  remain  in 
the  mud,  silt,  or  sand,  which  the  animals  may  frequent,  penetrating  into 
them  to  various  depths,  according  to  their  habits,  so  that  such  remains 
are  preserved  after  their  death  in  the  position  usually  occupied  by  the 
molluscs,  numerous  other  shells  remain  on  the  surface  to  be  acted  upon 
in  the  manner  of  any  inorganic  substance. 

That  shells  are  so  scattered  about,  multitudes  brought  up  by  the 
arming  of  the  sounding  lead  abundantly  attest.  Moreover,  collections 
of  certain  species  are  found  to  mark  particular  portions  of  soundings 
off  given  coasts.  Thus  off  the  shores  of  the  British  Islands,  charts 
give  localities  as  marked  by  Hakes  teeth,  as  they  are  termed ;  com- 
monly nothing  else  than  a  multitude  of  the  shells  of  Dentalium  scattered 
over  particular  areas.  Other  collections  of  shells  are  equally  well  known. 
While  these  shells,  scattered  over  the  sea  bottom,  are  often  either  the 
entire  hard  parts  of  univalves,  or  single  and  uninjured  valves  of  the 
bivalves,  at  other  times  they  are  crushed  or  broken.  Whether  in  the 
one  state  or  the  other,  according  to  their  specific  gravities,  volume,  and 
form,  will  they  be  acted  upon  by  streams  of  tide,  by  ocean  currents 
sweeping  within  sufficient  depths,  or  by  surface  wind-wave  action  trans- 
mitted to  the  bottom.  With  respect  to  specific  gravities,  though  there 
is  apparently  much  variation  in  this  respect,  the  floating  molluscs  being, 
some  of  them  at  least,  provided  with  shells  of  comparatively  minor 
specific  gravity,  the  range  seems  something  between  2 -67  and  2*85.* 
With  equal  forms  and  volumes,  fragments  or  rounded  grains  of  a  great 
proportion  of  marine  shells  would  apparently  be  specifically  heavier 
than  grains  of  quartz  and  rock  crystal  (2-63 — 2*65),  of  common  felspar 
(2-53—2-60),  of  albite  (2-61—2-68),  and  of  chlorite  (2-71),  while  they 
would  be  lighter  than  mica  (2-94).  In  all  sorting  processes  carried  on 
by  surface-wave  action  transmitted  to  the  bottom,  or  in  the  pushing  of 

*  The  author  obtained  the  following  specific  gravities  of  a  few  marine  shells,  some 
years  since. — Researches  in  Theoretical  Geology,  1834,  p.  76. 

Argonauta  tuberculosus,      .     .     .     2-43     Chiton, 2-79 

Nautilus  umbilicatus,      ....     2-64     Pholas  crispata, 2-82 

lanthina  communis, 2-66     Cytherea  maculata, 2-83 

Lithodomus  dactylus,      ....     2-67     Bulla, 2-83 

Teredo  (great,  East  Indies),     .     .     2-68    Voluta  musica, 2-83 

Haliotis  tuberculatus,     ....     2-70     Cassis testiculus, 2-83 

Cyprina  vulgaris, 2-77     Strombus  gibberulus,     ....     2-83 

Mytilus  bilocularis, 2-77     Pyrula  melongena,     .....     2-84 

Strombus  gigas, 2-77     Tellina  radiata 2-85 

It  is  not  improbable,  that  if  experiments  on  this  head  were  much  multiplied,  individual 
differences  would  often  be  found  in  the  same  species.  While  the  shell  of  the  Argonauta 
tuberculosus  is  lighter  than  pure  Sussex  chalk  (2-49),  and  that  of  Ifulintix  ful>,rcnl,ttnx  is 
equal  in  specific  gravity  to  Carrara  marble  (2-70),  the  greater  numbers  exhibit  a  packing 
of  particles  more  approaching  Arragonite. 


AMID    MINERAL    ACCUMULATIONS.  177 

loose  matter  forward  by  streams  of  tide  and  ocean  currents,  this  has  to 
be  considered. 

The  forms  of  shells  or  their  fragments,  except  they  have  been  ground 
down  to  rounded  grains  by  breaker  action  on  beaches,  commonly  agree 
little  with  those  of  the  sedimentary  matter  among  which  they  lie  super- 
ficially mixed.  When,  therefore,  we  have  to  regard  any  movement  of 
water  around  whole  shells  or  their  fragments,  their  forms  become  im- 
portant, as  also  the  mode  in  which  they  may  be  exposed  to  any  moving 
force  employed.  Thus  the  same  shell,  if  a  conical  univalve,  would  offer 
a  different  resistance,  according  as  it  might  be  placed  with  its  apex  or 
its  base  to  the  moving  water,  when  acted  upon,  though  we  might  expect 
that  the  moving  water  would  soon  turn  such  body  so  that  its  apex  would 
be  presented  to  the  line  of  action.  With  the  valve  of  a  bivalve,  its  hold 
on  a  bottom  of  sand  or  silt  would  be  very  different,  whether  it  were 
turned  with  the  margin  of  the  valve  downwards,  or  merely  rested  upon 
some  part  of  its  bombed  surface.  How  far  the  valve  of  a  shell  could 
be  transported  along  the  bottom  without  being  upset,  will  depend  on 
very  obvious  conditions ;  and  in  all  cases  we  have  to  consider  that  shells, 
or  their  fragments,  having  a  specific  gravity  rarely,  perhaps,  exceeding 
2-85,  and  often  presenting  forms  readily  moved,  are  not  difficult  of 
transport  in  a  medium  of  the  specific  gravity  of  1-027 — 1'028. 

Referring  to  the  plan  and  section  above  given  (figs.  69  and  70),  the 
observer  will  have  to  distinguish  between  the  remains  of  those  molluscs 
which  may  die  amid  the  mud,  silt,  or  sand,  and  so  have  their  harder 
parts  preserved  in  the  situations  where  they  lived,  and  the  remains  on 
the  surface  of  the  sea  bottom.  How  far  these  may  retain  their  positions 
relatively  to  the  zones  of  depth  suited  to  their  animals,  will  depend  upon 
the  circumstances  above  noticed.  Looking  at  the  subject  generally,  they 
would  be  liable  to  be  moved  at  the  depth  at  which  surface-wave  action 
could  reach,  and  therefore  to  be  moved  shorewards  in  shallow  waters  ; 
so  that  the  remains  of  molluscs  accumulated  near  the  coast  in  the  zones 
b  a  Z,  b'  a'  I'  (fig.  69),  varying  in  the  depths  b  d,  d  e  (fig.  70),  would,  at  the 
proper  depths,  have  surface-wave  action  added  to  tidal  streams,  which 
were  able  to  transport  the  shells  or  their  fragments,  tending  to  move 
them  on-shore.  In  the  outer  zone  ef  (fig.  69),  and  at  the  depths  f  g 
(fig.  70),  the  effects  of  the  tidal  movement  may  not  only  be  little  felt, 
but  also  any  action  upon  the  bottom  from  surface-waters  be  inappre- 
ciable. Still  further  out,  in  the  deep  waters  g  (fig.  69),  or  A,  (fig.  70), 
there  may  be  no  movement  sufficient  to  produce  transport  of  loose  mat- 
ters on  the  bottom,  even  by  ocean  currents.  There  may,  therefore,  be 
movements  in  the  water  producing  considerable  mixtures  of  the  remains 
of  molluscs  in  shallow  situations,  extending  even  to  the  casting  of  shells 
or  -their  fragments  upon  the  shore,  from  depths  depending  upon  various 
local  modifications  of  the  causes  of  transport  above  noticed. 

12 


178  PRESERVATION    OF    ORGANIC    REMAINS 

On  many  exposed  ocean-coasts  we  have  even  the  accumulation  of 
sandy  dunes,  composed,  for  the  most  part,  of  fragments  of  mollusc 
shells  ground  down  to  sand,  these  cast  on  shore  and  dealt  with  by  winds 
in  the  manner  of  common  sand.  The  western  coasts  of  Ireland,  Scot- 
land, and  of  part  of  England,  afford  good  examples  of  this  fact.* 

The  study  of  the  manner  in  which  the  shells  of  molluscs,  and  the 
harder  parts  of  marine  animals  generally,  are  thrown  on  shore,  the 
depths  from  which  they  may  be  borne  by  the  action  of  on-shore  waves 
and  breakers,  the  various  arrangements  of  whole,  broken,  or  comminuted 
shells  in  layers,  from  their  accumulation  like  ordinary  detrital  matter 
at  various  depths  in  the  sea  to  their  rejection  upon  the  land,  is  one 
which  will  amply  reward  the  observer  anxious  to  compare  the  manner 
in  which  these  remains  are  now  distributed  and  arranged  with  that  of 
the  remains  found  in  the  fossiliferous  rocks.  He  may  at  times  see  the 
pushing  action  of  the  small  wash  of  the  sea  driving  the  larger  shells  and 
their  fragments  before  it  into  convenient  localities,  there  accumulating 
in  a  mass  those  which  may  have  been  distributed  by  breaker  action 
along  a  line  of  coast,  while  at  others  he  will  find  the  shells  jammed  in 
amid  the  joints  and  crevices  of  rocks  so  firmly  that  they  become  difficult 
to  remove. 

The  induration  of  sands  formed  of  comminuted  shells  has  been  pre- 
viously mentioned  (p.  89),  and  we  may  expect  that  such  indurated  sands 
would  occasionally  include  remarkable  mixtures  of  organic  remains. 
The  rock  in  which  the  human  remains  were  discovered  at  Guadaloupe 
would  appear  to  be  of  this  character.  Mr.  Konig  observed  Millepora 
miniacea,  and  shells  referred  to  Turbo  pica  and  Helix  acuta,  in  the 
specimen  preserved  in  the  British  Museum ;  and  Cuvier  mentions  shells 
from  the  neighbouring  sea,  and  terrestrial  shells,  especially  the  Bulimus 
Q-uadaloupensis  (Ferussac),  in  that  in  the  Jardin  des  Plantes,  at  Paris. 
Teeth  of  the  caiman,  with  stone  hatchets  and  other  remains  of  human 
art,  are  mentioned  as  having  been  found  in  this  consolidated  sand. 

Great  as  the  accumulations  of  the  harder  remains  of  molluscs  may  be 
in  the  sea  or  on  its  shores  (and  regarding  the  amount  of  matter,  chiefly 
calcareous,  abstracted  from  the  sea  or  contained  in  their  food,  the  vo- 

*  This  shell-sand  is  often  employed  as  manure ;  it  is  known  to  have  been  so  employed 
in  Cornwall  in  the  reign  of  Henry  III.  A  charter  of  Richard,  King  of  the  Romans, 
granting  the  liberty  of  taking  this  sand  for  manure,  was  confirmed  by  Henry  III. 
(Lysons,  "  Mag.  Brit.,"  Cornwall,  p.  ccciii.,  who  cites  Rot.  Chart.,  45  Hen.  III.)  Carew 
notices  the  use  of  it  in  his  Survey  of  Cornwall  (1602),  and  it  is  largely  employed  for 
agricultural  purposes  to  the  present  day.  Mr.  Worgan,  in  1811,  estimated  the  cost  of 
the  land  carriage  of  this  sand  in  Cornwall  at  more  than  30.000J.  per  annum.  Large 
quantities  are  obtained  at  the  Dunbar  Sands,  in  Padstow  Harbour,  the  annual  amount 
estimated  at  100,000  tons.  It  has  been  calculated  that  5,600,000  cubic  feet  of  sand, 
chiefly  composed  of  comminuted  sea-shells,  is  annually  taken  from  the  coasts  of  Corn- 
wall and  Devon,  and  spread  over  the  land  in  the  interior  as  a  mineral  manure.— Report 
on  the  Geology  of  Cornwall,  Devon,  and  West  Somerset  (1839),  p.  479. 


AMID    MINERAL    ACCUMULATIONS.  179 

lume  of  these  harder  remains  added  annually  to  common  detrital  and 
chemical  deposits  must  be  very  considerable),  the  coral  accumulations 
of  tropical  regions  present  us  with  the  most  striking  additions,  by  means 
of  animal  life,  to  the  mineral  deposits  now  in  progress,  with  which  we 
are  acquainted.  They  have  for  many  years  attracted  the  attention  of 
navigators  and  naturalists,  so  that  much  information  has  been  obtained 
respecting  them.* 

With  regard  to  the  distribution  of  corals,  Mr.  Dana  states,  that  the 
Astrceacea,  Madreporacea,  and  G-emmiporidce  among  the  CaryopJiyl- 
lacea,  are,  with  few  exceptions,  confined  to  the  coral-reef  seas,  a  region 
included  between  the  parallels  of  28°  north  and  south  of  the  equator,  f 
these  corals  forming  the  principal  portion  of  the  reefs,  and  being  con- 
fined to  depths  within  120  feet  from  the  surface.  Other  corals,  as  is 
well  known,  extend  to  far  greater  depths,  and  into  colder  regions.  Sir 
James  Ross,  in  his  voyage  to  the  South  Polar  Regions,  obtained  live 
corals  from  the  depth  of  1620  to  1800  feet  off  Victoria  Land.  Mr. 
Charles  Stokes  notices  a  species  of  Primnoa  (lepadifera),  as  found  from 
900  to  1800  feet  off  the  coast  of  Norway ;  and  Professor  E.  Forbes,  a 
species  of  the  same  genus  from  the  depth  of  1668  feet  off  Staten  Land.f 
As  respects  the  range  of  corals,  Mr.  Dana  observes  that  "  QaryopJiyl- 
lidce  extend  from  the  equator  to  the  frigid  zone,  and  some  species  occur 
at  the  depth  of  200  fathoms  or  more.  The  Alcyonaria  have  an  equally 
wide  range  with  the  Caryophyllidce,  and  probably  reach  still  higher 
towards  the  poles.  The  Hydroidea  range  from  the  equator  to  the  polar 
regions,  but  are  most  abundant  in  the  waters  of  the  temperate  zone."§ 
Regarding  the  distribution  of  species,  Mr.  Dana  states,  that  of  306 
species,  27  only  are  common  to  the  East  Indies  and  Pacific  Ocean, 
while  only  one  species,  and  that  with  doubt  (Meandrina  labyrinthica\ 
is  considered  to  be  common  to  the  East  and  West  Indies. || 

*  We  would  more  especially  call  attention  to  the  labours  of  Mr.  Darwin,  who  has  not 
only  been  personally  engaged  in  the  investigation  of  coral  reefs  and  islands,  but  has 
also  carefully  studied  the  works  of  navigators  and  naturalists  relating  to  the  subject. 
The  results  of  his  investigations  are  contained  in  his  work,  entitled,  "Structure  and 
Distribution  of  Coral  Islands,"  London,  1842.  We  would  also  refer  to  such  portions  of 
the  labours  of  Mr.  Dana  as  have  yet  been  made  public,  and  are  contained  in  his  "  Struc- 
ture and  Classification  of  Zoophytes,"  Philadelphia,  1846.  Mr.  Dana's  views  are  also 
founded  on  the  personal  examination  of  coral  reefs  and  islands. 

f  Locally,  coral  reefs  are  found  further  north  and  south  than  28°.  Mr.  Darwin  ob- 
serves, that  they  extend  in  the  Bermuda  Islands  to  lat.  32°  15'  N.,  the  greatest  distance 
from  the  equator  at  which  they  are  known  to  exist,  and  to  lat.  30°  N.  in  the  Red  Sea ; 
and  that  Houtman's  Abrolhos,  on  the  western  shores  of  Australia,  in  lat.  29°  S.,  are  of 
coral  formation. 

J  Sir  James  Ross,  "Voyage  to  the  Antarctic  Regions." 

g  "  Structure  and  Classification  of  Zoophytes." 

||  Referring  to  the  causes  of  distribution  and  original  sites,  or  centres  of  distribution, 
Mr.  Dana  observes: — "There  is  sufficient  evidence  that  such  centres  of  distribution, 
as  regards  zoophytes,  are  to  be  recognised.  The  species  of  corals  in  the  West  Indies 


180  CORAL    REEFS    AND    ISLANDS. 

Mr.  Darwin  remarks  on  the  entire  absence  of  coral  reefs  in  certain 
large  areas  in  the  tropical  seas.  No  coral  reefs  have  been  found  on  the 
west  coast  of  South  America,  south  of  the  equator,  or  round  the  Gala- 
pagos Islands ;  neither  have  any  been  yet  noticed  on  the  west  coast  of 
America,  north  of  the  equator.  In  the  central  parts  of  the  Pacific  there 
are  islands  free  from  coral  reefs,  and  there  do  not  appear  to  be  any  coral 
reefs  on  the  west  coast  of  Africa,  or  round  the  islands  of  the  Gulf  of 
Guinea.  St.  Helena,  the  Cape  Verde  Islands,  St.  Paul's,  and  Fernando 
Noronha,  are  also  without  such  reefs.*  As  Mr.  Darwin  remarks,  the  causes 
of  the  abundance  of  coral  reefs  in  certain  situations,  and  their  absence  in 
others,  apparently  under  general  similar  conditions,  are  as  yet  not  well 
understood ;  and  the  observer  has  a  wide  field  open  for  the  investigation 
of  what  conditions  essential  to  the  life  of  reef-making  corals  may  be 
absent  in  the  apparently  favourable  situation  where  they  are  not  found, 
including  among  them  the  power  of  distribution  from  any  supposed 
centres  or  sites. 

Regarding  the  occurrence  of  corals  as  a  whole,  we  thus  see  that 
they  may  be  more  or  less  strewed  over  a  very  large  submarine  area, 
one  extending  from  the  polar  to  the  equatorial  regions,  some  of  them 
keeping  to  small  depths  within  a  portion  of  the  general  area  comprised 
between  the  parallels  of  28°  north  and  south  of  the  equator,  and  even 
rising  to  the  surface  of  the  sea  in  certain  parts  of  that  minor  area. 
However  great  occasional  accumulations  of  their  harder  parts  may  be 
under  favourable  conditions  elsewhere  concealed  beneath  the  ocean 
waters,  we  have,  in  the  masses  of  dead  and  living  corals  which  constitute 
islands  and  reefs,  enough  to  show  the  geological  importance  of  these 
animals,  which  thus  from  their  food  and  the  surrounding  waters,  secrete 
a  mass  of  matter  constituting  rocks,  so  acted  upon,  under  fitting  con- 
ditions, by  the  breakers  and  by  atmospheric  and  chemical  influences, 
that  dry  land  rises  sufficiently  above  the  sea  to  support  terrestrial  vege- 
tation and  animal  life. 

It  would  appear  that  the  calcareous  secretionsf  of  corals  only  begin 

are,  in  many  respects,  peculiar,  and  not  one  can  with  certainty  be  identified  with  any 
of  the  East  Indies.  The  central  parts  of  the  Pacific  Ocean  appear  to  be  almost  as  pecu- 
liar in  the  corals  they  afford.  But  few  from  the  Feejees  have  been  found  to  be  identical 
with  those  of  the  Indian  Ocean." — "Structure  and  Classification  of  Zoophytes." 

*  Darwin,  "  Structure  and  Distribution  of  Coral  Reefs,"  pp.  61,  62. 

f  Dana,  " Structure  and  Classification  of  Zoophytes,"  p.  52.  Speaking-of  the  mode 
in  which  the  secretions  are  formed,  Mr.  Dana  observes: — "In  a  Madrepora  the  surface 
between  the  cells  becomes  covered  by  minute  points  by  the  continued  secretions,  and 
then  a  layer  forms,  connected  with  the  preceding,  by  these  points  or  columns.  The 
interior  usually  becomes,  afterwards,  nearly  solid  by  additional  secretions.  This  va- 
riety of  structure  may  be  observed  also  in  the  Dendrophyllice,  and  even  the  compact 
species,  in  which  there  are  no  traces  of  cellules,  will  often  show  evidence  of  having 
been  deposited  in  layers.  I  have  seen  it  brought  out  with  singular  distinctness  in  a 
specimen  half  fossilized.  In  many  corals,  however,  we  fail  to  detect  this  deposition  in 


CORAL    EEEFS    AND    ISLANDS.  181 

to  be  formed  after  the  last  metamorphosis  of  the  young  animal,  one 
effected  when  it  quits  the  swimming  state  and  attaches  itself  to  some 
support.  Until  that  time  the  young  can  move,  by  their  own  powers 
and  the  transporting  action  of  tidal  streams  or  oceanic  currents,  to 
situations  where,  under  the  needful  conditions,  they  can  settle  and 
flourish  as  perfect  corals.  No  doubt  myriads  of  the  young  animals 
perish,  or  are  consumed  as  food,  so  that  a  part  only  is  available  for 
supplying  the  loss  by  death  of  the  old  stock,  for  increasing  the  amount 
of  coral  life  in  localities  where  it  previously  existed,  or  for  the  forma- 
tion of  new  colonies.  Under  all  such  circumstances,  if  there  be  no 
cause  producing  a  removal  of  the  harder  parts  of  the  corals  after  the 
death  of  the  polyps  which  secreted  them,  they  will  accumulate.  Por- 
tions of  the  harder  parts  would  appear  to  be  destroyed  by  the  animals 
which  feed  upon  or  bury  themselves  among  the  corals  while  living, 
other  portions  are  broken  off  by  the  action  of  the  sea,  and  some  por- 
tions would  appear  to  be  taken  up  in  solution.  In  the  first  case,  the 
portion  not  required  for  the  harder  parts  of  the  animals  feeding  upon 
the  corals  appears  to  be  thrown  down  with  their  faeces  amid  the  coral 
reefs ;  in  the  second,  the  fragments  torn  off  by  the  breakers  are  distri- 
buted, like  any  other  detritus,  also  among  the  reefs  ;  and  in  the  third, 
the  part  not  appropriated  by  the  living  corals,  or  by  other  animals,  for 
their  harder  parts,  appears  to  be  deposited  amid  the  matter  of  the  reefs, 
tending  to  bind  them  together,  and  adding  to  their  solidity. 

From  the  chemical  researches  of  Mr.  B.  Silliman,  who  analyzed 
numerous  specimens  of  calcareous  corals  sent  him  by  Mr.  Dana,  it 
would  appear  that,  after  the  animal  matter  had  been  separated,  carbo- 
nate of  lime  formed  from  97  to  99  per  cent,  of  the  inorganic  matter 
which  remained ;  1  to  3  per  cent,  being  composed  of  silica,  lime  (pro- 
bably united  with  the  silica),  carbonate  of  magnesia,  fluoride  of  calcium, 
fluoride  of  magnesium,  phosphate  of  magnesia,  alumina,  and  iron.*  The 

layers.  This  is  the  case  in  the  Astrcea  tribe.  The  Pocilloporce,  and  some  allied  corals, 
have  transverse  plates  crossing  the  cells  internally,  which  are  intermitted  secretions 
from  the  lower  part  of  the  polyp  ;  but  no  appearance  of  layers  has  been  detected  in  the 
spaces  between  the  cells.  The  Favosites,  and  many  Cyathophyllidce,  are  examples  of 
similar  interrupted  secretions  across  the  cells,"  (p.  53.) 

Respecting  the  foot  secretions,  he  remarks : — "  The  foot  secretions  appear  to  be 
entirely  independent  of  the  tissue  secretions.  The  former  are  often  horny  when  the 
latter  are  calcareous,  and  when  they  occur  together  they  constitute  separable  layers, 
one  enveloping  the  other.  The  united  polyps  of  a  branch  have  their  mouths  opening 
outwards  on  every  side,  while  the  bases  are  directed  inward  towards  a  common  central 
or  axial  line.  The  simultaneous  secretions  of  the  bases,  therefore,  must  necessarily 
produce  a  solid  axis  to  the  branch,"  (p.  54.) 

*  Dana,  "  Structure  and  Classification  of  Zoophytes,"  pp.  124-131.  Of  the  35  spe- 
cies of  coral  examined  by  Mr.  B.  Silliman,  Jun.,  9  (specimens  of  them  being  numerous) 
were  analyzed  minutely.  These  were : — 1,  Porites  favosa  (Sandwich  Islands);  2,  Madrepora 
palmatum  (West  Indies) ;  3,  M.  spicifera  (Ceylon) ;  4,  M.  prolifera  (Bermudas) ;  5,  M.plan- 
tagenea  (Ceylon) ;  6,Pocillopora  ligulata  (Sandwich  Islands) ;  7,  Meandrina  phrygia  (Cey- 


182 


CORAL  REEFS  AND  ISLANDS. 


animal  matter  varied  from  2-11  to  9-43  per  cent.  As  a  mass,  there- 
fore, we  may  regard  the  hard  matter  secreted  by  the  coral  polyps  of  a 
reef  as  chiefly  formed  of  carbonate  of  lime,  mingled  with  some  animal 
matter,  and  a  small  percentage  of  other  substances,  among  which  are 
found  fluorine  and  phosphoric  acid,  though  in  very  variable  proportions. 
The  young  of  the  reef-making  coral  polyps  attaching  themselves 
where  the  needful  conditions  obtain,*  and  according  to  the  habits  and 
requirements  of  each  species,  it  becomes  important  to  learn  how  far 
these  may  differ,  and  yet  each  species  aid  in  building  up  the  general 
mass  of  a  reef.  Mr.  Darwin's  detailed  description  of  Keeling,  or  Cocos 
Atoll,  situated  in  the  Indian  Ocean,  in  lat.  12°  5'  S.,  affords  a  valuable 
view  of  the  manner  in  which  the  various  corals  forming  a  reef  in  those 
seas  are  adjusted.  Having,  under  favourable  circumstances,  reached 
the  outer  edge  of  the  reef,  where  the  coral  is  alive,  he  found  that  it 
was  almost  entirely  composed  of  living  Porites,  forming  great  irregular 
rounded  masses,  from  four  to  eight  feet  broad,  and  little  less  in  thick- 
ness. On  the  furthest  mounds  which  he  reached,  and  over  which  the 
sea  broke  with  some  violence,  the  polyps  in  the  upper  cells  were  dead, 
but  three  or  four  inches  lower  down  they  were  living.  In  consequence 
of  the  check  given  to  their  growth  upwards,  the  corals  extend  laterally. 

Ion)  ;  8,  Astrcea  Orion  (Ceylon) ;  and  9,  Astrcea.  After  removing  the  carbonate  of  lime  and 
animal  matter,  these  nine  species  gave  for  the  proportions  of  the  remaining  organic  matter, 


1 

» 

3 

A 

5 

6 

7 

8 

9 

Silica,      

22-00 
13-03 

125 
7-5 

13-50 
10-40 

ln-32 
15-37 

23-74 
35-01 

5-35 
7-17 

11-0 
25-9 

30-01 
17-45 

8-70 
16-74 

7-66 

4-2 

1-63 

39-49 

1-35 

0*49 

0-8 

24-57 

45-19 

Fluoride  of  Calcium,      . 
Fluoride  of  Magnesium, 
Phosphate  of  Magnesia, 
Alumina  and  Iron,         .... 
Oxide  of  Iron,         

7-83 
12-48 
270 
16-00 
18-30 

26-34 
26-62 
8-00 
14-84 

34-85 
1906 
5-87 
14-09 

7-50 
2-62 
0-25 
25-25 

8-88 
20-44 
3-46 
7-12 

4-05 
'4-25 
16-30 
35-00 
27-39 

15-0 
232 
4-7 
19-4 

0-85 
4-31 
0-32 
22-49 

0-71 
2-34 
034 
2597 

Mr.  Silliman  remarks,  "  The  foregoing  results  show  that,  contrary  to  the  expectation 
when  the  research  was  commenced,  fluorine  is  present  in  much  larger  proportion  than 
phosphoric  acid.  The  silica  exists  in  the  coral  in  its  soluble  modification,  and  probably 
is  united  with  the  lime.  The  free  magnesia  existed  as  carbonate,  and  was  thrown 
down  as  caustic  magnesia  by  the  lime  water.  Some  small  portion  of  the  lime  was  pro- 
bably thrown  down  as  carbonate,  in  spite  of  every  precaution  to  the  contrary."  The 
horny  stem  of  Gorgonia  setosa  afforded  Mr.  Silliman  a  considerable  portion  of  alumina 
besides  phosphoric  acid,  some  carbonate  of  lime,  and  93  per  cent,  of  animal  matter. 

*  Respecting  the  needful  conditions  for  the  establishment  and  distribution  of  reef- 
making  cora\s,  Mr.  Couthouy  (Boston  Journal  of  Natural  History,  vol.  iv.  1842,  and 
American  Journal  of  Science,  vol.  xlvii.  1844),  and  Mr.  Dana  (American  Journal  of 
Science,  vol.  xlv.  1843),  independently  of  the  views  of  each  other,  refer  to  the  tempe- 
rature of  the  sea  rather  than  to  its  depth,  as  limiting  the  range  of  the  reef-making 
corals,  and  attribute  the  absence  of  coral  reefs  in  the  inter-tropical  and  eastern  portions 
of  the  Atlantic  and  Pacific  to  the  influence  of  the  cool  and  extra-tropical  currents  which 
there  set  in.  Mr.  Dana  limits  the  distribution  of  the  reef-forming  corals  to  a  tempera- 
ture of,  and  above,  66°  Fahr. ;  and  Mr.  Couthouy  considers  that  they  thrive  best  in 
water,  at  a  temperature  of  between  76°  and  80°  Fahr. 

'  Phosphate  of  Lime. 


CORAL    EEEFS    AND     ISLANDS.  183 

Further  outwards  the  Porites  were  all  seen  to  be  alive.  Next  in  impor- 
tance is  the  Millepora  complanata,  growing  in  thick  vertical  plates,  and 
forming  a  strong  honeycombed  mass,  generally  of  a  circular  form,  the 
marginal  plates  alone  being  alive.  Between  these  plates,  and  in  the 
crevices  of  the  reef,  a  multitude  of  zoophytes  and  other  productions 
nourish,  protected  by  the  Porites  and  Millepora  from  the  breakers. 
Masses  of  living  coral,  apparently  similar  to  those  of  the  margin, 
descend  very  gradually  outwards  to  the  depth  of  60  or  70  feet.  The 
arming  of  the  sounding-lead  brought  up  fragments  of  Millepora  alci- 
cornis  within  these  depths,  and  there  was  an  impression  of  an  Astraea, 
apparently  alive.  Examining  the  fragments  thrown  on  shore  by  the 
breakers,  the  Porites  and  a  Madrepore,  apparently  M.  corymbosa,  were 
the  most  common ;  and  as  this  coral  was  not  found  alive  in  the  hollows 
of  the  reef,  Mr.  Darwin  concludes  that  it  must  occur  abundantly  in  a 
submerged  zone  outside.  Between  the  depth  of  72  and  120  feet,  the 
arming  of  the  lead  came  up  an  equal  number  of  times  marked  by  sand 
and  coral.  Beneath  120  feet,  sand  was  obtained.  After  the  depth  of 
150  feet  the  outward  sides  of  the  reef  plunged,  at  an  angle  of  45°,  into 
the  sea,  the  depth  of  which  was  not  found  at  2200  yards  from  the 
breakers,  with  a  line  of  7200  feet  in  length.* 

Close  within  the  outer  margin  of  the  reef,  where  the  coral  life  ceases, 
three  species  of  Nullipora  flourish,  either  separately  or  mingled  toge- 
ther, forming  by  their  successive  growth  a  layer  two  or  three  feet  in 
thickness,  of  a  reddish  colour.  This  layer  fringes  the  reef  for  about  20 
yards  in  width,  constituting  a  continuous,  smooth,  convex  surface,  when 
the  corals  are  united  into  a  solid  margin,  and  forming  a  protecting 
break  water,  f 

*  Darwin,  "  Structure  and  Distribution  of  Coral  Reefs,"  pp.  6-8.  "  Out  of  25 
soundings,"  observes  Mr.  Darwin,  "taken  at  a  greater  depth'than  20  fathoms,  every 
one  showed  that  the  bottom  was  covered  with  sand  ;  whereas,  at  a  less  depth  than  12 
fathoms,  every  sounding  showed  that  it  was  exceedingly  rugged,  and  free  from  all  extra- 
neous particles.  Two  soundings  were  obtained  at  the  depth  of  360  fathoms,  and  seve- 
ral between  200  and  300  fathoms.  The  sand  brought  up  from  these  depths  consisted  of 
finely  triturated  fragments  of  stony  zoophytes,  but  not,  as  far  as  I  could  distinguish, 
of  a  particle  of  any  lamelliform  genus  :  fragments  of  shells  were  rare. 

"  At  a  distance  of  2200  yards  from  the  breakers,  Captain  Fitzroy  found  no  bottom 
with  a  line  of  7200  feet  in  length ;  hence  the  submarine  slope  of  this  coral  formation 
is  steeper  than  that  of  any  volcanic  cone.  Off  the  mouth  of  the  lagoon,  and  likewise 
off  the  northern  point  of  the  atoll,  where  the  currents  act  violently,  the  inclination, 
owing  to  the  accumulation  of  sediment,  is  less.  As  the  arming  of  the  sounding-lead 
from  all  the  greater  depths  showed  a  smooth  sandy  bottom,  I  at  first  concluded  that 
the  whole  consisted  of  a  vast  conical  pile  of  calcareous  sand;  but  the  sudden  increase 
of  depth  at  some  points,  and  the  circumstance  of  the  line  having  been  cut,  as  if  rubbed, 
when  between  500  and  600  fathoms  were  out,  indicate  the  probable  existence  of  sub- 
marine cliffs."  pp.  8-9. 

f  "These  Nulliporse,"  observes  Mr.  Darwin,  "although  able  to  exist  above  the  limit 
of  true  corals,  seem  to  require  to  be  bathed  during  the  greater  part  of  each  tide  by 
breaking  water,  for  they  are  not  found  in  any  abundance  in  the  protected  hollows  on 


184  CORAL    REEFS    AND    ISLANDS. 

The  form  of  this  atoll  will  be  seen  by  the  subjoined  plan  (fig.  7 1).3 

Fig.  71. 


The  reef  is  broken  by  two  open  spaces,  through  one  of  which  ships  can 
enter ;  it  varies  from  250  to  500  yards  in  breadth,  with  a  level  surface, 
or  one  very  slightly  inclined  towards  the  interior  lagoon,  and  at  high 
tide  the  sea  breaks  entirely  over  those  parts  which  do  not  rise  into 
islets  on  its  surface.  Pocillopora  verrucosa  is  a  common  coral  in  the 
hollows,  as  also  a  Madrepore,  closely  allied  or  identical  with  M.  pocilli- 
fera.  When  the  breakers  are,  by  the  formation  of  an  islet,  prevented 
from  washing  entirely  over  the  reef,  and  channels  and  hollows  fill  up, 
a  hard,  smooth  floor  is  formed,  uncovered  only  at  low  water,  and  strewed 
with  a  few  fragments  torn  off  during  heavy  gales.  The  islets  which  are 
formed  by  an  accumulation  of  fragments,  about  200  or  300  yards  from 

the  back  part  of  the  reef,  where  they  might  be  immersed,  either  during  the  whole  or  an 
equal  proportional  time  of  each  tide.  It  is  remarkable  that  organic  productions  of 
such  extreme  simplicity,  for  the  Nulliporao  undoubtedly  belong  to  one  of  the  lowest 
classes  of  the  vegetable  kingdom,  should  be  limited  to  a  zone  so  peculiarly  circum- 
stanced." p.  9. 

*  The  observer  will  find  an  interesting  selection  of  plans  of  coral  reefs,  cither  sur- 
rounding mountainous  islands  or  forming  atolls  or  lagoon  islands,  among  which  that  of 
Cocos  or  Keeling  Island  is  one,  in  Plates  1  and  2  of  ALv,  Darwin's  work  on  the  Structure 
and  Distribution  of  Coral  Reefs ;  and  a  most  valuable  map  in  the  same  work,  showing 
the  distribution  of  the  different  kinds  of  coral  reefs,  with  the  position  of  active  volcanoes 
in  the  Indian  and  Pacific  Oceans. 


CORAL  REEFS  AND  ISLANDS.  185 

the  outer  edge  of  the  reef,  vary  in  length  from  a  few  yards  to  several 
miles,  with  an  ordinary  breadth  of  less  than  a  quarter  of  a  mile.  On 
the  windward  side  of  the  atoll  the  increase  of  the  islets  is  by  the  addi- 
tion of  fragments  thrown  on  their  outer  sides  by  the  breakers,  the 
highest  part  thus  formed  rising  from  six  to  ten  feet  above  ordinary  high- 
water  mark,  and  upon  this  there  maybe  hillocks  of  blown  sand,  some  of 
which  rise  to  an  elevation  of  30  feet.  On  the  leeward  side  of  the  atoll, 
from  the  sweep  of  the  wind  across  the  lagoon,  the  little  breakers  thus 
formed  cast  up  sand  and  fragments  of  thinly-branched  coral  from  the 
lagoon  on  the  inner  sides  of  the  islets  in  that  part  of  the  atoll,  thus 
adding  to  them  inwards.  These  islands  are  lower  than  those  to  wind- 
ward, though  broader.  The  fragments  beneath  the  surface  are  cemented 
into  a  solid  mass,  so  as  to  form  a  ledge  from  two  to  four  feet  high,  from 
being  worked  by  the  breakers  acting  beyond  ordinary  high-water. 
Chemical  changes  take  place  occasionally  among  the  calcareous  frag- 
ments thus  cemented  together,  so  that  the  altered  coral  passes  gradually 
into  spathose  limestone.* 

The  lagoon  within  is  necessarily  a  sheltered  situation,  and  is  described 
as  much  more  shallow  than  those  of  atolls  of  considerable  size.  About 
half  the  area  consists  of  sediment,  including  mud,  and  half  of  coral 
reefs,  the  corals  composing  the  latter  having  a  very  different  aspect 
from  those  on  the  outside,  and  being  very  numerous  in  kind.f  The 

*  "  The  fragments  of  coral  which  are  occasionally  cast  on  the  '  flat,'  are,  during  gales 
of  unusual  violence,  swept  together  on  the  beach,  where  the  waves  each  day  at  high- 
water  tend  to  remove  and  gradually  wear  them  down  ;  but  the  lower  fragments  having 
become  firmly  cemented  together  by  the  percolation  of  calcareous  matter,  resist  the 
daily  tides  longer,  and  hence  project  as  a  ledge.  The  cemented  mass  is  generally  of  a 
white  colour,  but  in  some  few  parts  reddish  from  ferruginous  matter :  it  is  very  hard, 
and  is  sonorous  under  the  hammer  ;  it  is  obscurely  divided  by  seams,  dipping  at  a  small 
angle  seaward ;  it  consists  of  fragments  of  the  corals  which  grow  on  the  outer  margin, 
some  quite  and  others  partially  rounded,  some  small  and  others  two  or  three  feet 
across  ;  and  of  masses  of  previously  formed  conglomerate,  torn  up,  rounded,  and  re- 
cemented  ;  or  it  consists  of  a  calcareous  sandstone,  entirely  composed  of  rounded  par- 
ticles, generally  almost  blended  together,  of  shells,  corals,  the  spines  of  echini,  and 
other  such  organic  bodies."  "  The  structure  of  the  coral  in  the  conglomerate  has  gene- 
rally been  much  obscured  by  the  infiltration  of  spathose  calcareous  matter ;  and  I  col- 
lected a  very  interesting  series,  beginning  with  fragments  of  unaltered  coral,  and  end- 
ing with  others  where  it  was  impossible  to  discover  with  the  naked  eye  any  trace  of 
organic  structure.  In  some  specimens  I  was  unable,  even  with  the  aid  of  a  lens  and 
by  wetting  them,  to  distinguish  the  boundaries  of  the  altered  coral  and  spathose  lime- 
stone. Many  even  of  the  blocks  of  coral  lying  loose  on  the  beach  had  their  central 
parts  altered  and  infiltrated."  Darwin,  "Structure  of  Coral  Reefs,"  p.  12. 

Mr.  Beete  Jukes  mentions  masses  of  Meandrina,  six  or  eight  feet  in  diameter,  turned 
upside  down,  and  much  worn,  as  torn  by  the  force  of  the  breakers  from  their  places  of 
growth  on  the  weather  edge  of  a  coral  reef,  and  driven  200  to  300  yards  inwards. 
"  Narrative  of  the  Voyage  of  the  Fly,  1847." 

f  "  Meandrina,  however,  lives  in  the  lagoon,  and  great  rounded  masses  of  this  coral 
are  numerous,  lying  quite  or  almost  loose  on  the  bottom.  The  other  commonest  kinds 
consist  of  three  closely  allied  species  of  true  Madrepora  in  thin  branches  ;  of  Seriatopora 


186  CORAL  REEFS  AND  ISLANDS. 

sediment  from  the  deepest  part  of  the  lagoon  was  like  a  very  fine  sand 
when  dry,  though  it  appeared  chalky  when  wet.  Mr.  Darwin  points 
out  that  much  fine  sediment  may  be  supplied  by  means  of  the  excre- 
ments of  the  scarus  and  holothuriae,  which  feed  on  the  coral ;  large 
shoals  of  two  species  of  the  former,  one  of  which  inhabits  the  lagoon 
while  the  other  keeps  outside,  feeding  entirely  on  the  corals,  while 
swarms  of  various  species  of  holothuria  browse  upon  the  lagoon  corals. 
"  The  amount  of  coral  yearly  consumed  and  ground  down  into  the  finest 
mud  by  these  several  creatures,  and  probably  by  many  other  kinds, 
must  be  immense."*  The  tide  flows  in  and  out  of  the  lagoon  through 
the  channels,  and  the  latter  also  carry  out  the  water  thrown  over  the 
reefs  by  the  breakers. 

Thirty-two  coral  islands  in  the  Pacific  Ocean  were  examined  by  Cap- 
tain Beechey;f  they  were  of  various  shapes,  and  29  had  lagoons  in 
their  centres.  The  dry  coral  forming  islets  on  the  reefs  is  rarely  ele- 
vated more  than  two  feet  above  the  sea  when  divested  of  any  sandy 
materials  heaped  upon  it,  and  but  for  the  abrupt  character  of  the  outer 
margin  would  be  inundated  by  the  breakers.  Captain  Beechey  found 
in  the  islands  seen  by  him  no  instance  in  which  the  strip  of  dead  coral 
exceeded  half  a  mile  from  the  usual  wash  of  the  sea  to  the  internal  la- 
goon. In  general  it  was  only  300  or  400  yards.  "  Beyond  these 
limits,  on  the  lagoon  side  in  particular,  where  the  coral  was  less  muti- 
lated by  the  waves,  there  was  frequently  a  ledge,  two  or  three  feet 
under  water  at  high  tide,  30  to  50  yards  in  width ;  after  which  the 
sides  of  the  island  descended  rapidly,  apparently  by  a  succession  of 
inclined  ledges  formed  by  numerous  columns  united  at  their  capitals, 
with  spaces  between  them,  in  which  the  sounding-lead  descended  several 
fathoms."J  The  windward  sides  of  the  reefs  and  islets  upon  them  are 
higher  than  the  others,  the  islets  not  unfrequently  well  wooded,§  while, 

subulata ;  two  species  of  Porites,  with  cylindrical  branches,  one  of  which  forms  circular 
clumps,  with  the  exterior  branches  only  alive  ;  and,  lastly,  a  coral,  something  like  an 
Explanaria,  but  with  stars  on  both  surfaces,  growing  in  thin,  brittle,  stony,  foliaceous 
expansions,  especially  in  the  deeper  basins  of  the  lagoon.  The  reefs  on  which  these 
corals  grow  are  very  irregular  in  form,  are  full  of  cavities,  and  have  not  a  solid  flat 
surface  of  dead  rock,  like  that  surrounding  the  lagoon;  nor  can  they  be  nearly  so  hard, 
for  the  inhabitants  made  with  crowbars  a  channel  of  considerable  length  through  these 
reefs,  in  which  a  schooner,  built  on  the  southeast  islet,  was  floated  out.  It  is  a  very 
interesting  circumstance,  pointed  out  to  us  by  Mr.  Liesk,  that  this  channel,  although 
made  less  than  ten  years  before  our  visit,  was  then,  as  we  saw,  almost  choked  up  with 
living  coral,  so  that  fresh  excavations  would  be  absolutely  necessary  to  allow  another 
vessel  to  pass  through  it."  Darwin,  •'  Structure,"  &c.,  p.  13. 

*  Darwin,  "  Structure  of  Coral  Reefs,"  p.  14. 

f  "  Narrative  of  a  Voyage  to  the  Pacific  and  Behring's  Straits,  &c.,  in  the  years 
1825,  26,  27,  and  28."  London,  1831. 

J  Ibid.  vol.  i.  p.  256. 

£  With  respect  to  the  vegetation  on  Bow  Island,  Mr.  Collie  mentions  that  the  Panda- 
nus  and  Pemphis  grow  in  the  sheltered  parts  of  the  plain  between  the  ridges  ;  that  the 


CORAL  REEFS  AND  ISLANDS.  187 

on  the  opposite  sides,  the  reefs  are  "half  drowned"  or  wholly  under 
water.  The  breaks  or  entrances  into  the  lagoons  generally  occur  on 
the  leeward  side,  though  they  are  sometimes  found  in  a  side  that  runs 
in  the  direction  of  the  wind,  as  at  Bow  Island.  The  points  or  angles 
of  the  islands  were  found  to  descend  less  abruptly  than  the  sides.  The 
lagoons  vary  in  depth,  from  20  to  28  fathoms  being  found  in  those 
which  were  entered,  though  the  appearance  of  the  water  in  others  would 
lead  to  the  inference  that  they  were  very  shallow.  The  accompanying 
figures  are  the  sections  given  by  Captain  Beechey  as  affording  a  general 
view  of  these  coral  islands.  Fig.  72  is  a  section  across  one  about  five 
miles  wide  ;  a  a  being  dry  islets  on  the  reef,  b  6,  lagoon ;  and  c  c,  open 
ocean ;  and  fig.  73  a  section  across  an  islet  and  part  of  a  lagoon,  with 
the  slope  towards  the  sea,  A  B  being  the  habitable  part  of  the  island ; 
a  6,  water  line ;  a  h,  general  descent  seawards  towards  the  points  ;  a  i, 
general  descent  at  the  points  ;  C  C,  part  of  the  lagoon ;  D  D,  coral  knolls 
in  the  lagoon;  Z,  the  ocean ;  s s s,  soundings  on  coral.* 

While  the   coral  reefs   above  mentioned  exhibit  no  traces  of  rocks 

loose  dry  stones  of  the  first  ridge  are  penetrated  by  the  roots  of  the  Tefano,  which  rises, 
into  a  tall  spreading  tree,  accompanied  by  the  Suriana  and  Tournefortia,  under  the 
shelter  of  which  the  Achyranthus  and  Lepidium  thrive  best.  Beyond  the  first  ridge  the 
Scaevola  flourishes.  "  Beechey's  Voyage,"  vol.  i.  p.  248.  At  Ducie's  Island,  the  trees 
are  stated  to  rise  14  feet,  making,  with  the  island,  12  feet  above  the  sea,  26  feet  from 
its  level.  Ibid.  vol.  i.  p.  59. 

*  Captain  Beechey  gives  a  more  detailed  account  of  Matilda  and  Bow  Islands  than 
of  the  others.  The  windward  side  of  the  former  "  is  covered  by  tall  trees,  while  that 
to  leeward  is  nearly  all  under  water.  The  dry  part  of  the  chain  enclosing  the  lagoon 
is  about  a  sixth  of  a  mile  in  width,  but  varies  considerably  in  its  dimensions ;  the  broad 
parts  are  furnished  with  low  mounds  of  sand,  which  have  been  raised  by  the  action  of 
the  waves,  but  are  now  out  of  their  reach,  and  mostly  covered  by  vegetation.  The 
violence  of  the  waves  upon  the  shore,  except  at  low  water,  forces  the  sea  into  the  lake 
at  many  points,  and  occasions  a  constant  outset  through  the  channel  to  leeward. 

"On  both  sides  of  the  chain  the  coral  descends  rapidly  ;  on  the  outer  part  there  is 
from  6  to  10  fathoms,  close  to  the  breakers ;  the  next  cast  is  30  to  40  ;  and,  at  a  little 
distance,  there  is  no  bottom  with  250  fathoms.  On  the  lagoon  side  there  are  two 
ledges;  the  first  is  covered  by  about  three  feet  at  high  water:  at  its  edge  the  lead 
descends  three  fathoms  to  the  next  ledge,  which  is  about  40  yards  in  width;  it  then 
slopes  to  about  5  fathoms  at  its  extremity,  and  again  descends  perpendicularly  to  10 ; 
after  which  there  is  a  gradual  descent  to  20  fathoms,  which  is  the  general  depth  of  the 
centre  of  the  lagoon.  The  lake  is  dotted  with  knolls  or  columns  of  coral,  which  rise  to 
all  intermediate  heights  between  the  bottom  and  the  surface."  "Voyage,"  &c.,  vol.  i. 
p.  218. 

"  Bow  Island  is  30  miles  long  by  an  average  of  5  miles  broad.  It  is  similar  to  the 
other  coral  islands  already  described,  confining  within  a  narrow  band  of  coral  a  spacious 
lagoon,  and  having  its  windward  side  higher  and  more  wooded  than  the  other,  which, 
indeed,  with  a  few  clusters  of  trees  and  heaps  of  sand,  is  little  better  than  a  reef.  The 
sea  in  several  places  washes  into  the  lagoon,  but  there  is  no  passage,  even  for  a  boat, 
except  that  by  which  the  ship  entered,  which  is  sometimes  dangerous  to  boats,  in  con- 
sequence of  the  overfalls  from  the  lagoon,  especially  a  little  after  the  time  of  high  water. 

"  The  bottom  of  the  lagoon  is  in  parts  covered  with  a  fine  white  sand,  and  is  thickly 
strewed  with  coral  knolls,  the  upper  parts  of  which  overhang  the  lower,  though  they 
do  not  at  once  rise  in  this  form  from  the  bottom,  but  from  small  hillocks.  We  found 


188 


CORAL    REEFS    AND    ISLANDS. 


CORAL    REEFS    AND    ISLANDS.  189 

further  than  those  formed  by  the  consolidation  of  the  matter,  chiefly 
calcareous,  secreted  by  the  polyps  or  derived  from  it,  and  distributed 
chemically  and  mechanically,  other  reefs  surround  islands  or  groups  of 
islands  formed  of  different  rocks,  or  range  along  the  shores  of  seas,  such 
as  the  Red  Sea,  or  those  of  large  masses  of  land,  as  on  the  east  coast 
of  Australia.  While  the  reefs  touch  the  land  in  some  places,  they  are 
removed  from  it  in  others ;  and  many  present  the  appearance  of  the 
lagoon  islands — land  either  in  one  mass  or  in  several  masses  rising 
through  the  interior  lagoon.  Mr.  Darwin  has  classed  these  various 
modes  of  occurrence  into  atolls,  or  lagoon  islands,  barrier  reefs,  and 
fringing  or  shore  reefs.* 

The  following  map  (fig.  74)  of  the  Gambier's  group,f  may  be  taken 
in  illustration  of  the  barrier  reefs,  and  as  also  showing  coral  reefs  fring- 
ing the  contained  islands.  All  the  interior  islands  are  steep  and  rugged, 
Mount  Duff,  on  the  largest,  rising  to  the  height  of  1248  feet,  and  they 
would  appear  to  be  of  igneous  origin. J  The  outside  reef  on  the  north- 
east, the  windward  side,  has  portions  raised  above  the  sea,  bearing  trees 
and  other  plants,  while  in  the  opposite  direction  it  dips  30  or  40  feet 

comparatively  few  beneath  the  surface,  though  there  are  some :  at  the  edge  of  such  as 
are  exposed  there  is  usually  six  or  seven  fathoms  of  water ;  receding  from  it,  the  lead 
gradually  descends  to  the  general  level  of  about  20  fathoms.  The  height  of  water  in 
the  lagoon  is  subject  to  the  variations  of  the  tides  of  the  ocean ;  but  it  suffers  so  many 
disturbances  from  the  waves,  which  occasionally  inundate  the  low  parts  of  the  surround- 
ing land,  that  neither  the  rise  of  the  tide  nor  the  time  of  high  water  can  be  estimated 
with  any  degree  of  certainty.  The  strip  of  low  land  enclosing  the  lagoon  is  nearly  70 
miles  in  extent,  and  the  part  that  is  dry  is  about  a  quarter  of  a  mile  in  width.  On  the 
inner  side,  a  few  yards  from  the  margin  of  the  lake,  there  is  a  low  bank  formed  of  finely 
broken  coral ;  and  at  the  outer  edge  a  much  higher  bank  of  large  blocks  of  the  same 
material,  long  since  removed  from  the  reach  of  the  waves,  and  gradually  preparing  for 
the  reception  of  vegetation.  Beyond  this  high  bank  there  is  a  third  ridge,  similar  to 
that  skirting  the  lagoon ;  and  outside  it  again,  as  well  as  in  the  lagoon,  there  is  a  wide 
shelf,  three  or  four  feet  under  water,  the  outer  one  bearing  upon  its  surface  huge  masses 
of  broken  coral,  the  materials  for  an  outer  bank,  similar  to  the  large  one  just  de- 
scribed." "Voyage,"  &c.,  vol.  i.  pp.  245,  246. 

Mr.  Beete  Jukes  ("Narrative  of  the  Voyage  of  the  'Fly'  to  Torres  Straits,  &c., 
1847")  presents  us  with  the  following  description  of  one  kind  of  small  coral  island  as 
seen  from  the  mast-head : — "  A  small  island,  with  a  white  sand  beach  and  a  tuft  of 
trees,  is  surrounded  by  a  symmetrically  open  space  of  shallow  water  of  a  bright  grass 
green  colour,  inclosed  by  a  ring  of  glistening  surf,  as  white  as  snow,  immediately  out- 
side which  is  the  rich  dark  blue  of  deep  water.  All  the  sea  is  perfectly  clear  of  sand 
and  mud  ;  even  where  it  breaks  on  a  sand  beach  it  retains  its  perfect  purity."  "  It  is 
this  perfect  clearness  of  the  water  which  makes  navigation  among  coral  reefs  at  all 
practicable,  as  a  shoal  with  even  five  fathoms  water  on  it  can  be  discovered  at  a  mile 
distant  from  a  ship's  mast-head,  in  consequence  of  its  greenish  hue  contrasting  with 
the  blue  of  deep  water." 

*  We  would  refer  to  Mr.  Darwin's  work,  "  Structure  and  Distribution  of  Coral  Reefs," 
for  great  detail  respecting  the  different  kinds  of  reefs. 

f  Reduced  from  that  given  by  Captain  Beechey,  "Voyage  to  the  Pacific  and  Behr  ing's 
Strait,"  vol.  i. 

J  They  are  described  as  composed  of  porous  basaltic  lava,  sometimes  passing  into  a 
tufaceous  slate,  at  others  into  columnar  basalt.  Dikes  cutting  the  mass  were  observed. 


190 


CORAL    REEFS    AND    ISLANDS. 


beneath  the  sea.  The  outer  sides  plunge,  as  usual,  into  deep  water, 
while  the  inner  descend  gradually  to  120  or  150  feet.  Patches  of  coral 
are  scattered  over  the  lagoon,  and  adhere  as  fringing  reefs  to  the  steep 


Fis>.74. 


islands  rising  out  of  it.  On  the  larger  island  the  coral  reef  rendered 
the  water  so  shallow,  that  the  larger  boats  could  not  come  within  200 
yards  of  the  landing-place. 

The  following  plan  (fig.  75)  of  Ari  Atoll,  one  of  the  Maldiva  Islands,* 
exhibits  a  modification  of  those  coral  islands  which  have  a  general  reef 
surrounding  a  lagoon.  Here  a  number  of  reefs  form  an  outer  line,  and 
the  interior  is  occupied  by  a  number  of  others.  Many  of  these  are 
ring-formed,  so  that  the  general  group  reminds  us  of  many  minor  atolls, 
rising  above  an  area  of  a  tabular  character,  round  which  the  sides 
plunge  rapidly  into  deep  water.  The  common  depth  between  these 
reefs  and  islets,  some  rising  above  the  level  of  the  sea,  varies  from  150 
to  200  feet,  and  in  the  basins  of  the  ring-form  detached  reefs  from  24 
to  60  feet.  According  to  Captain  Moresby,  the  central  and  deepest 
part  of  the  lagoons  in  the  Maldiva  Islands  is  formed  of  stiff  clay,  of 
sand  near  the  border,  and  of  hard  sandbanks,  sandstone,  conglomerate, 

*  Reduced  from  the  chart  of  the  Maldives  by  Captain  Moresby  and  Lieutenant 
Powell. 


CORAL    REEFS    AND    ISLANDS. 


191 


rubble,  and  a  little  live  coral  in  the  channels  of  the  reef.*     The  other 

Fig.  75. 


*  As  stated  by  Captain  Moresby  to  Mr.  Darwin.  "  Structure,"  &c.,  p.  34.  Captain 
Moresby  informed  Mr.  Darwin  that  Millepora  complanata  was  one  of  the  commonest 
kinds  of  corals  on  the  outer  margin  of  reefs  of  the  Maldives.  Ibid.  p.  33. 


192  CORAL  REEFS  AND  ISLANDS. 

large  islands,  or  rather  groups  of  islets  and  reefs,  of  the  Maldives,  pre- 
sent the  same  general  characters,  while  the  smaller,  one  of  which  (Ross 
Atoll)  is  represented  above  (fig.  75  a),  offers  the  usual  atoll  character. 

From  the  observations  of  Mr.  Darwin  on  the  part  of  the  coral  reefs 
of  the  Mauritius,  it  would  appear  that  the  edge  of  the  reef  is  formed  of 
great  masses  of  branching  Madrepores,  chiefly  M.  corymbosa  and  M. 
pocillifera^  mingled  with  a  few  other  kinds  of  coral.  To  the  depth  of 
48  feet,  the  coral  ground  appeared  free  from  sand  ;  but  from  that  depth 
to  90  feet  a  little  calcareous  sand  was  brought  up  by  the  arming  of  the 
sounding-lead ;  more  frequently,  however,  it  came  up  clean.  The  two 
Madrepores  above  mentioned,  and  two  species  of  Astrsea,  with  large 
stars,  seemed  the  commonest  corals  for  the  whole  of  this  depth.  Some 
fragments  of  Millepora  alcicornis  were  brought  up,  and  in  the  deeper 
parts  were  large  beds  of  a  Seriatopora,  allied  to,  but  differing  from,  8. 
subulata.  From  90  to  120  feet  the  bottom,  with  few  exceptions,  was 
covered  by  sand,  or  strewed  with  Seriatopora.  From  120  to  198  feet, 
the  soundings  showed  a  sandy  bottom,  with  one  exception,  at  180  feet, 
when  the  arming  came  up  as  if  cut  by  the  margin  of  a  large  Caryophyl- 
lia.  On  the  beach,  the  rolled  fragments  consisted  chiefly  of  Madrepores 
and  Astrsea  of  the  smaller  depths,  of  a  massive  Porites,  like  that  at 
Keeling  Atoll,  of  a  Meandrina,  Pocillopora  verrucosa,  and  of  numerous 
fragments  of  Nullipora.* 

The  reef  surrounding  the  Mauritius,  excepting  in  two  or  three  parts 
where  the  coast  is  almost  precipitous,  f  generally  ranges  at  a  distance 
of  one,  two,  or  even  three  miles  from  the  shore.  Opposite  every  river 
and  streamlet  the  reef  is,  as  is  common,  breached,  and  the  slope  outside 
the  reef  seems  generally  to  be  moderate,  bearing  a  relation  to  the  slope 
of  the  adjoining  land. 

The  Isle  of  Bourbon  is  also  surrounded  by  coral  reefs,  only  broken 
through  at  the  embouchures  of  the  rivers,  and  opposite  the  chief  ravines. 
M.  Siau,  who  had  excellent  opportunities  of  observing  these  reefs  in 
1839  and  1840,  has  stated]:  that  the  channels  or  passages  through  the 
reefs  are  kept  open  by  the  streams  of  fresh  water  passing  outwards 
through  them,  and  that  they  would  be  otherwise  soon  filled  up.  As  it 
is,  they  are  considered  to  have  decreased  in  size,  in  consequence  of  a 
diminished  quantity  of  rain  having,  of  late  years,  fallen  upon  the  Isle 
of  Bourbon.  These  channels  being,  as  usual  in  such  situations,  the 
passages  to  roadsteads  behind  the  reefs,  their  condition  is  a  constant 
subject  of  attention,  and,  as  illustrative  of  the  quick  growth  of  certain 
at  least  of  the  reef-making  corals  of  that  locality,  M.  Siau  mentions 
that,  in  one  of  the  chnnm-ls  (that  of  the  Riviere  d'Abord),  a  coral  rock 
has  risen  from  the  bottom,  and  in  the  middle  of  it,  to  the  height  of  29 

*  Darwin,  "  Structure  of  Coral  Reefs."  7  I>ar\vin,  ibid. 

+  Comptes  Rendues,  torn,  xii.,  1841. 


CORAL    REEFS    AND    ISLANDS.  193 

feet  (English)  in  12  years.  M.  Siau  presents  us  with  a  very  interesting 
account  of  the  mode  of  growth  of  the  reef-making  corals  of  this  island, 
showing  the  establishment  of  a  series  of  coral  bosses  upon  each  other, 
with  the  admixture  of  coral,  sand,  and  shingle,  in  the  interstices  between 
them,  up  to  the  level  of  the  sea,  where  the  labours  of  the  reef-making 
coral  polyps  terminate.* 

The  Great  Barrier  Reef,  extending  off  the  east  coast  of  Australia  for 
about  1100  miles,  with  a  mean  breadth  of  about  30  miles,  from  Break- 
sea  Spit,  in  lat.  24°  30'  S.,  and  long.  153°  20'  E.,  to  Bristow  Island, 
in  lat.  9°  15'  S.,  and  long.  143°  20'  E.  off  the  coast  of  New  Guinea, 
presents  an  area  of  about  33,000  square  miles,  chiefly  covered  with 
organic,  mechanical,  and  chemical  accumulations  resulting  from  the 

*  M.  Siau  observes,  that  "  the  labours  of  the  coral  polyps  are  as  varied  as  the 
species.  Some  (and  these  are  the  most  widely  spread)  establish  themselves  by  families 
at  the  bottom  of  the  sea,  on  a  volcanic  or  any  other  rock,  unattachable  by  the  action  of 
the  waves.  Each  family  constructs  a  detached  boss  (mamelon),  which  may  rise  to  the 
height  of  two  or  three  yards  by  the  labours  of  many  generations.  These  bosses  are 
known  in  the  country  by  the  name  ofpdtes  de  coraux.  The  bottom  is  thus  covered  by 
bosses,  which  most  frequently  join,  touch,  or  approximate  to  each  other,  sometimes 
leaving  open  spaces  between  them,  into  which  (coral)  sand  and  shingle  are  washed  by 
the  sea.  Such  spaces  are  known  as  rigoles  de  sables. 

"  Upon  this  fresh  bed  new  families  establish  themselves,  constructing  another  bed. 
The  latter  are  independent  of  the  former.  Sometimes  they  entirely  repose  on  the  first 
pates,  sometimes  on  the  rigoles,  so  as  to  conceal  them;  sometimes  an  isolated  pate  com- 
pletely covers  a  primitive  rigole.  The  spaces  between  this  second  bed  are  also  con- 
verted into  rigoles,  the  sea  throwing  in  sand  and  small  shingles.  Above  this  second 
bed  other  generations  raise  a  fourth  and  a  fifth,  and  thus  the  mass  is  formed  of  those 
immense  reefs  so  common  in  intertropical  seas. 

"  It  would  be  wrong  to  conclude,  from  the  description  given,  that  the  beds  thus  formed 
have  a  uniform  thickness.  It  should  be  understood  that  very  great  differences  exist 
in  the  height  of  the  pates,  and  that  the  entire  reef  would  present  a  shapeless  and  divided 
assemblage  of  superimposed  montecules,  the  interstices  between  them  filled  with  sand 
and  shingles,  their  contiguous  portions  joined  together  by  a  coral  cement. 

"  The  corals  of  which  we  have  spoken  are  the  most  common,  forming  the  mass  of  the 
reefs.  The  coral  produced  is  gray,  very  compact,  of  a  very  close  grain,  and  often 
harder  than  marble.  This  coral  is  not  worked  away  by  the  waves,  and  is  not  entirely 
soluble  in  acids.  Upon  the  firm  base  of  the  bosses,  above  described,  a  variety  of  small 
and  delicate  corals,  of  different  kinds,  establish  themselves.  It  is  these  fragile  corals 
which  alone  furnish  the  white  sand  and  shingles  to  the  shore  and  the  rigoles,  and  they 
are  entirely  soluble  in  acids." 

The  same  author  remarks  upon  the  depth  agitated  by  the  waves,  and  infers  (Comptes 
Rendues,  torn.  xii.  p.  775)  that  he  had  evidence  of  that  action  at  the  depth  of  578 
French  feet  (616  English  feet),  on  the  northwest  of  the  roadstead  of  St.  Paul,  Isle  of 
Bourbon.  It  will  be  obvious  that,  in  such  researches,  the  friction  on  the  bottom,  by 
tidal  streams  and  ocean  currents,  has  carefully  to  be  distinguished  from  the  movement 
produced  among  the  particles  of  water  beneath  by  the  action  of  surface  wind-friction 
waves  above.  Whatever  the  cause  of  motion  in  the  superficial  parts  of  the  sea  bottom, 
either  from  surface  wave  action,  or  the  friction  of  tidal  streams,  or  ocean  currents,  the 
observation  of  M.  Elie  de  Beaumont  (appended  to  M.  Siau's  paper),  respecting  an 
inquiry  as  to  the  depths  at  which  fixed  animals  are  found  upon  bottoms  liable  to  this 
motion,  such  animals  depending  for  their  food  upon  the  prey  which  may  pass  them,  is 
equally  important. 

13 


194  CORAL    REEFS    AND    ISLANDS. 

secretions  of  the  coral  polyps.  This  great  mass  is  broken  northwards 
by  the  influence  of  river  waters  discharged  from  the  southeastern  por- 
tion of  New  Guinea,  carrying  detritus  with  them,  and  covering  the 
bottom  of  the  adjacent  seas  with  a  muddy  sediment.  These  conditions 
ceasing,  we  find  the  great  coral  accumulations  continued  to  Louisiade, 
thus  extending  the  surface,  allowing  for  the  great  break  above  men- 
tioned, over  many  more  thousands  of  square  miles. 

The  survey  of  Torres  Strait,  between  Australia  and  New  Guinea, 
by  Captain  Blackwood,  has  added  materially  to  our  knowledge  of  the 
Great  Barrier  Reef,  and  Mr.  Beete  Jukes,  naturalist  to  the  expedition, 
has  afforded  us  very  valuable  information  respecting  it.*  He  divides 
the  coral  accumulation  into — 1st,  linear  reefs,  forming  the  outer  edge, 
or  actual  barrier ;  2d,  detached  reefs,  lying  outside  the  barrier ;  and 
3d,  inner  reefs,  or  those  which  lie  between  the  barrier  and  the  shore. 
'  With  respect  to  the  linear  reefs,  they  are  described  as  generally  long 
and  narrow,  more  or  less  parallel  to  the  coast  of  Australia,  and  sepa- 
rated by  narrow  breaks  or  passages,  varying  from  200  yards  to  a  mile 
in  width,  and  from  half  a  mile  to  15  miles  in  length.  They  have  com- 
monly great  depth  of  water  on  the  ocean  side,  lines  of  100  or  200 
fathoms  rarely  finding  bottom  close  to  the  reefs,  while  the  depths  inside 
generally  vary  from  60  to  120  feet.  The  detached  reefs  occur  only  in 
one  locality — somewhat  in  front  of  Cape  Grenville,  Australia  (if  we 
except  the  reefs  eastward  of  the  Great  Barrier,  eastward  of  Torres 
Strait),  rise  from  deep  water  all  round,  and  have  more  or  less  of  a  cir- 
cular form,  with  lagoons  inside.  The  inner  reefs  are  very  numerous, 
scattered  over  the  platform  beneath  the  more  shallow  water  between 
the  outer  reefs  and  the  coast  of  Australia,  sometimes  leaving  an  open 
channel  between  them  and  the  land  on  the  one  side,  or  the  barrier  on 
the  other.  They  are  of  different  forms,  have  sometimes  gradual  slopes 
around,  and  at  others  are  steep-sided. f 

*  "  Narrative  of  the  Surveying  Voyage  of  H.  M.  S.  Fly,  commanded  by  Captain 
Blackwood,  R.  N.,  in  Torres  Strait,  New  Guinea,  &c."  By  J.  Beete  Jukes,  M.A.,  &c. 
London,  1847. 

t  Beete  Jukes,  "  Surveying  Voyage  of  the  Fly,"  vol.  i.  pp.  317,  18.  Mr.  Beete 
Jukes  gives  a  detailed  account  of  the  range  of  coral  accumulations  from  Breaksea 
Spit  (vol.  i.  pp.  318-332).  Respecting  the  most  southern  portion,  it  is  stated,  that 
«'  from  Sandy  Cape  (Australia),  a  sandy  shoal  runs  out,  partially  covered  by  coral,  as 
it  proceeds  outwards.  .It  is  formed  of  siliceous  sand,  with  10  or  20  fathoms  of  water 
upon  it,  sloping  to  30  fathoms,  after  which  it  plunges  into  deep  water.  At  the  Capri- 
corn Group,  about  50  miles  more  northward,  all — even  the  smallest  grains  of  sand — 
was  calcareous,  and  so  it  seemed  to  continue  to  the  sedimentary  matter  brought  down 
by  the  New  Guinea  rivers,  eastward  of  Torres  Strait. 

"North  of  the  parallel  of  23°  10',  there  is  an  open  space  of  sea,  in  which  no  reefs 
occur,  about  50  miles  wide,  from  north  to  south :  and  the  bank  of  soundings,  instead 
of  being  a  steep,  well-defined  edge,  slopes  out  very  gradually  far  to  the  eastward.  The 
flat  of  about  20  fathoms,  extends  out  as  usual  from  the  mainland  for  about  30  or  40 
miles,  and  then  gradually  deepens,  till  70,  80,  90,  and  100  fathoms  are  successively 


CORAL  REEFS  AND  ISLANDS.  195 

Mr.  Beete  Jukes  observes,  that  up  to  about  lat.  21°  10',  at  Swain's 
Reefs,  it  can  scarcely  be  said  that  any  true  barrier  exists,  there  being 
merely  a  bank  of  soundings  off  the  shore,  "  with  large  masses  of  coral 
reef  settled  upon  it,  and  within  its  outer  boundary, — almost  equally 
large  clear  spaces  intervening  between  the  different  groups  of  reefs. 
In  Swain's  Reefs,  the  individual  reefs  on  the  outer  edge  of  the  group 
can  scarcely  be  distinguished  in  form  from  those  inside  them,  although 
they  may  have  a  little  more  linear  shape,  and  their  greatest  length 
runs  more  invariably  along  the  line  of  the  boundary  of  the  group.  It 
is  only  at  their  northern  extremity  that  they  assume  one  of  the  charac- 
teristics of  a  true  barrier,  that  of  rising  like  a  wall  from  a  deep  and 
almost  fathomless  sea."*  To  the  northward  the  reefs  become  more 
numerous.  Where  the  detached  reefs  occur  opposite  Cape  Grenville 
is  a  great  bay  in  the  barrier,  with  very  deep  water,  a  line  of  1710  feet 
having  failed  to  strike  the  bottom  on  its  southern  side,  four  miles  inside 
the  reefs  forming  the  bay.  Near  this  bay  Yules'  Detached  Reef  rises 
from  an  unknown  depth,  greater  than  100  fathoms,  and  appears  to 
have  a  lagoon  in  its  centre.  The  Great  Detached  Reef  rises  on  the 
northward  of  this  reef,  also  from  a  great  depth,  containing  a  lagoon 
with  30  fathoms  of  water  in  it. 

Raine's  Islet  is  also  another  detached  reef  rising  with  steep  sides  (in 
one  place  at  an  angle  of  55°)  from  deep  water.  Bottom  was  found  at 
160  fathoms  one  mile  north  of  the  islet,  and  at  180  fathoms  two  miles 
and  a  half  northeast  of  it.  On  the  southern  side,  bottom  was  not  found 
until  close  to  the  breakers  of  the  Great  Barrier  Reef,  when  fine  coral 
sand  was  brought  up  from  175  and  200  fathoms. f  Pandora's  Entrance, 

attained,  20  or  30  miles  eastward  of  the  boundary  of  the  line  of  soundings,  as  it  exists 
to  the  southward.  The  character  of  the  bottom  likewise  changes  from  a  coarse  coral 
to  the  finest  possible  mud,  of  a  light  olive-green  colour,  in  which  the  lead  often  wholly 
buried  itself  on  reaching  the  bottom.  This,  when  dried,  was  entirely  calcareous,  and 
wholly  soluble  in  muriatic  acid." — Ibid.  vol.  i.  p.  320. 

*  "Between  Swain's  Reefs  and  the  main  land  there  is  a  space  50  to  60  miles  wide, 
clear  of  reefs,  with  a  depth  of  30  to  50  fathoms." — Beete  Jukes,  "  Surveying  Voyage  of 
the  Fly,"  vol.  i.  p.  321. 

f  Raine's  Island  is  described  as  about  1000  yards  long,  and  500  wide,  rising  in  no 
part  more  than  20  feet  above  high-water  mark.  "  It  is  formed  of  a  plateau  of  calca- 
reous sandstone,  which  has  a  little  cliff  all  round,  4  or  5  feet  high,  outside  of  which  is 
a  belt  of  loose  sand,  forming  a  low  ridge  between  it  and  the  sea.  Some  mounds  of 
loose  sand  also  rest  upon  the  stone,  especially  at  its  western  end.  The  length  of  the 
island  runs  in  about  a  N.N.W.  and  S.S.E.  direction.  It  is  surrounded  by  a  coral  reef 
that  is  narrow  on  the  lee  side,  but  to  windward,  or  towards  the  east,  stretches  out  for 
nearly  two  miles.  The  surface  of  this  reef  is  nearly  all  dry  at  low  water,  and  its  sides 
slope  rapidly  down  to  a  depth  of  150  or  200  fathoms."  "  The  island  is  covered  with  a 
low  scrubby  vegetation,"  and  "  the  central  part  of  the  island  had  a  rich  black  soil 
several  inches  deep."  The  stone  forming  the  base  of  the  island  is  described  as  "made 
up  of  small  round  grains,  some  of  them  apparently  rolled  bits  of  coral  and  shell,  but 
many  of  them  evidently  concretionary,  having  concentric  coats.  It  was  not  unlike 
some  varieties  of  oolite  in  texture  and  appearance.  It  contained  large  fragments  of 


196  CORAL  REEFS  AND  ISLANDS. 

through  the  Barrier  Reef,  occurs  in  11°  10'  S.,  northward  of  the  deep 
bay,  and  the  detached  reefs,  after  which  the  great  reef  is  made  up  of 
long  and  closely  connected  masses,  with  few  and  small  gaps  for  40  miles. 
From  10°  40'  to  Flinder's  Entrance,  in  lat.  9°  40',  the  reefs  consist  of 
numerous  spots  and  patches  (too  close  to  afford  good  entrance  for  ves- 
sels), forming  submarine  pinnacles  or  towers,  rising  from  a  depth  of  90 
or  120  feet,  still,  however,  preserving  the  line  of  the  barrier,  with  deep 
water  outside,  in  which  the  bottom  was  not  found  with  a  line  of  960 
feet. 

From  Cape  Weymouth  and  Restoration  Island,  in  consequence  of  the 
altered  run  of  the  Australian  coast  and  of  the  barrier  reefs,  the  diffe- 
rence between  the  outer  reef  and  the  main  land  in  the  parallel  of  Cape 
York  (the  N.E.  point  of  Australia),  has  increased  to  80  and  90  miles. 
The  whole  of  the  intermediate  distance  has  not  been  surveyed,  but  Mr. 
Beete  Jukes  states,  that  there  appear  to  be  many  inner  reefs  at  a  short 
distance  from  the  land.  Between  which  and  the  great  eastern  barrier, 
the  sea  is  comparatively  free  from  them,  many  sunken  patches  being,  how- 
ever, scattered  about,  and  the  bottom  irregular  in  places.  "  The  gene- 
ral depth  varies  from  12  to  20  fathoms,  the  bottom  being  coarse  sand 
(with  many  foraminifera  and  detached  corals  and  corallines),  gradually 
passing  as  we  approach  the  land  into  finer  sand  and  detritus,  and  from 
that  into  the  finest  possible  mud,  wholly  calcareous  and  lying  close  to 
the  shore."* 

The  outer  barrier  terminates  at  Anchor  Key,  in  lat.  9°  20'  S.,  and 
no  coral  reef  is  found  further  towards  the  coast  of  New  Guinea,  in  this 
direction,  except  the  Bramble  Reef,  described  as  fringing  round  other 
rocks.  The  chart  shows  coral  sand  and  fragments  on  the  bottom  in  38 

corals  and  shells,  and  some  pebbles  of  pumice,  and  it  yielded  occasionally  a  fine  sand 
that  was  not  calcareous,  and  which  was  probably  derived  from  the  pumice.  Some 
parts  of  it  made  a  fair  building  stone,  but  it  got  softer  below,  till  it  passed  downwards 
into  a  coarse  coral  sand,  unconsolidated,  and  falling  to  pieces  on  being  touched.  In 
the  quarries  opened  next  year  for  the  beacon  (constructed  for  the  purposes  of  naviga- 
tion), many  recent  shells,  more  or  less  perfect,  were  found  compacted  in  the  stone,  and 
one  or  two  nests  of  turtle's  eggs,  of  which,  in  some  cases,  only  the  internal  cast  had  been 
preserved,  but  in  others  the  shell  remained  in  the  form  of  white  carbonate  of  lime. 
Some  drusy  cavities  were  also  found  in  the  stone,  containing  crystals  of  gypsum."  "  It 
is  evident  from  the  fossil  turtle  eggs  that  the  consolidation  of  the  stone  had  taken  place 
after  it  was  raised  above  the  sea.  It  was  due,  probably,  to  the  infiltration  of  the  rain- 
water percolating  through  the  calcareous  sand,  that  had  been  gradually  piled  above 
high-water  mark  by  the  combined  action  of  the  winds  and  the  waves.  The  thickness  of 
the  vegetable  soil  in  its  centre  shows  that  it  has  been  above  water  for  a  great  length  of 
time."— Beete  Jukes,  "Voyage  of  the  Fly,"  vol.  i.  pp.  126-128.  The  whole  surface  of 
the  island  was  covered  with  birds,  all  but  one  kind — a  land-rail — sea-birds,  such  as 
frigate-birds,  boobies,  gannets,  &c.  "  On  walking  rapidly  into  the  centre  of  the  island, 
countless  myriads  of  birds  rose  shrieking  on  every  side,  so  that  the  clangour  was  abso- 
lutely deafening,  like  the  roar  of  some  great  cataract."  There  were  turtle  tracks  on 
the  beach,  and  the  shells  and  skeletons  of  dead  turtles  were  scattered  about  the  island. 
*  Beete  Jukes,  "  Voyage  of  the  Fly,"  vol.  i.  p.  88ft, 


CORAL  REEFS  AND  ISLANDS.  197 

fathoms,  increasing  to  54  fathoms,  and  stretching  out  50  miles  to  the 
eastward  of  the  Bramble's  Key,  while  all  the  soundings  on  the  north, 
in  front  of  a  low  coast,  with  a  large  discharge  of  fresh  water  from 
various  channels  in  New  Guinea,  are  of  mud  and  sand.  In  front,  east- 
ward of  Flinder's  Entrance,  Portlock's  Reefs  rise  from  a  depth  of  360 
to  400  feet,  so  that  on  the  north,  as  on  the  south,  as  is  observed  by  Mr. 
Beete  Jukes,  the  corals  rise  from  the  ocean  in  shallow  water  as  compared 
with  the  central  portions.  Between  Cape  York  and  the  opposite  coast 
of  New  Guinea,  extensive  reefs  seem  to  prevail  adjoining  the  latter,  rising 
out  of  30  to  70  feet  of  water  ;  and  a  considerable  reef  connects  Warrior 
Island  with  the  main  land  of  New  Guinea.  All  the  central  parts  of 
Torres  Strait,  from  north  to  south,  between  Cape  York  and  Turtle- 
Back  Island,  are  remarkable  for  a  nearly  uniform  bottom,  9  to  11 
fathoms,  formed  of  sand  and  mud.  No  coral  reefs  were  found  in  this 
central  band,  except  narrow  fringing  reefs  round  islands,  formed  of 
other  materials, — porphyries,  granites,  and  quartz  rocks.* 

*  Beete  Jukes  ("  Voyage  of  the  Fly,"  vol.  i.  p.  331),  from  his  experience  among  the 
great  coral  accumulations  of  Eastern  Australia,  has  given  the  following  account  of  an 
individual  coral  reef: — "A  submarine  mound  of  rock,  composed  of  the  fragments  and 
detritus  of  corals  and  shells,  compacted  together  into  a  soft  spongy  stone.  The  greater 
part  of  the  surface  of  this  mound  is  quite  flat,  and  near  the  level  of  low  water.  At  its 
edges  it  is  commonly  a  little  rounded  off,  or  slopes  gradually  down  to  a  depth  of  2,  3, 
and  4  fathoms,  and  then  pitches  suddenly  down  with  a  very  rapid  slope  into  deep 
water,  20  or  200  fathoms,  as  the  case  may  be.  The  surface  of  this  reef,  when  exposed, 
looks  like  a  great  flat  of  sandstone  with  a  few  loose  slabs  lying  about,  or  here  and 
there  an  accumulation  of  dead  broken  coral  branches,  or  a  bank  of  dazzling  white 
sand.  It  is,  however,  chequered  with  holes  and  hollows  more  or  less  deep,  in  which 
small  living  corals  are  growing  ;  or  has,  perhaps,  a  large  portion  that  is  always  covered 
by  two  or  three  feet  of  water  at  the  lowest  tides,  and  here  are  fields  of  corals,  either 
clumps  or  branching  Madrepores,  or  round  stools  and  blocks  of  Mseandrina  and  As- 
trsea,  both  dead  and  living.  Proceeding  from  this  central  flat  towards  the  edge,  living 
corals  become  more  and  more  abundant.  As  we  get  towards  the  windward  side,  we 
of  course  encounter  the  surf  of  breakers  long  before  we  can  reach  the  extreme  verge  of 
the  reef,  and  among  these  breakers  we  see  immense  blocks,  often  two  or  three  yards 
(and  sometimes  much  more),  in  diameter,  lying  loose  upon  the  reef.  These  are  some- 
times within  reach  by  a  little  wading ;  and  though  in  some  instances  they  are  found  to 
consist  of  several  kinds  of  corals  matted  together,  they  are  more  often  found  to  be 
large  individual  masses  of  species,  which  are  either  not  found  elsewhere,  and  conse- 
quently never  seen  alive  (Mr.  Beete  Jukes  saw  an  irregular  block  of  Mseandrina,  of 
irregular  shape,  12  to  15  feet  in  diameter),  and  which  greatly  surpass  their  brethren 
on  other  parts  of  the  reef  in  size  and  importance.  If  we  approach  the  lee  edge  of  the 
reef,  either  by  walking  or  in  a  boat,  we  find  it  covered  with  living  corals,  commonly 
Mteandrina,  Astroea,  and  Madrepora,  in  about  equal  abundance,  all  glowing  with  rich 
colours,  bristling  with  branches,  or  studded  with  great  knobs  and  blocks.  When  the 
edge  of  the  reef  is  very  steep,  it  has  sometimes  overhanging  ledges,  and  is  generally 
indented  by  narrow  winding  channels  and  deep  holes,  leading  into  dark  hollows  and 
cavities  where  nothing  can  be  seen.  When  the  slope  is  more  gentle,  the  great  groups 
of  living  corals  and  intervening  spaces  of  white  sand  can  be  still  discerned  through  the 
clear  water  to  a  depth  of  40  or  50  feet,  beyond  which  the  water  recovers  its  usual  deep 
blue.  A  coral  reef,  therefore,  is  a  mass  of  brute  matter  living  only  at  its  outer  sur- 
face, and  chiefly  on  its  lateral  slopes." — Ibid.  vol.  i.  pp.  314-316. 


198  CORAL  REEFS  AND  ISLANDS. 

Coral  reefs  are  abundant  in  the  Red  Sea,  fringing  the  coasts  to  a 
great  extent.  Numerous  localities  have  been  examined  for  a  distance 
of  about  200  miles  by  MM.  Ehrenberg  and  Hemprich,  and  about  150 
species  of  corals  were  observed.  According  to  the  former,*  these  reefs 
form  shallow  incrustations  on  the  rocks  of  the  coasts,  from  3  to  12  feet 
beneath  the  surface  of  the  sea,  often  sloping  outwards.  They  do  not 
always  adjoin  the  coast,  but  often  form  narrow  parallel  bands  at  various 
distances  from  it.  The  reefs  are  composed  of  Madrepora,  Retepora, 
Millepora,  Astrsea,  Favia,  Caryophyllia,  Masandrina,  Pocillopora,  and 
Stephanocora,  mixed  with  the  shells  of  molluscs,  the  remains  of  fish, 
&c.  According  to  M.  Ehrenberg,  the  height,  resulting  from  the  accu- 
mulation of  the  same  corals,  is  small.  With  respect  to  the  banks  and 
reefs  lying  some  distance  from  the  shore,  Captain  Moresby  states  that 
they  appear  more  elongated  than  they  really  are  when  correct  plans 
are  constructed  of  them.  Though  many  of  these  reefs  rise  to  the  sur- 
face, the  greater  number  are  found  at  depths  from  30  to  180  feet,  and 
consist  of  sand  and  living  coral,  the  latter  covering  the  largest  part  of 
their  surfaces.  They  run  parallel  with  the  shore,  sometimes  connected 
with  the  mainland  by  transverse  banks.  Deep  water  occurs  close  to 
them.f 

With  respect  to  the  varied  conditions  under  which  coral  reefs  are 
found,  probably  the  observer  may  conveniently  first  consider  the  man- 
ner in  which  different  species  of  coral  have  hitherto  been  known  to 
occur.  As  Mr.  Beete  Jukes  has  remarked,  though  the  reef-making 
coral  polyps  are  only  known  to  us  as  living  at  depths  not  extending 
beyond  20  to  30  fathoms,  there  may  be  others  forming  masses  of  calca- 
reous matter  at  greater  depths  with  which  we  are  unacquainted. J  The 
evidence  respecting  corals  of  various  kinds  would  lead  us  to  infer  that. 
like  the  molluscs  above-mentioned  (p.  161),  while  some  prefer,  or  are 
adjusted,  to  particular  bottoms,  whether  solid  rock,  sand  or  mud,  at 
various  depths,  moderate  or  considerable,  others  are  only  to  be  found 
in  shallow  water.  Viewing  the  subject  in  this  light,  the  corals  living 
at  the  surface  of  the  sea  may  be  compared  with  littoral  molluscs  keep- 
ing situations  peculiar  to  them.  While  some  appear  adjusted  to  the 
nearly  constant  movement  of  ocean  breakers,  others,  even  at  small 
depths,  require  tranquil  water;  so  that  at  nearly  equal  depths  the 
corals,  forming  the  hard  mass  of  the  reef,  or  finding  shelter  amid  its 
cavities,  in  the  leo  of  lagoons,  when  there  are  such,  divide  themselves 
into  two  classes. 

*  "  Uber  die  Natur  und  Bildung  der  Corallen-Biinken  des  Rothen  Meeres,"  Berlin, 
1634. 

f  Darwin  ("Structure  and  Distribution  of  Coral  Reefs,"  p.  192),  from  information 
communicated  to  him  by  Captain  Moresby. 

J  It  would  be  well  carefully  to  examine  the  coral  reefs  which  have  been  undoubtedly 
raised  above  the  sea  by  geological  movements  for  the  species  contained  in  their  lower 
parts. 


CORAL    REEFS    AND    ISLANDS.  199 

Referring  to  the  early  and  swimming  state  of  the  reef-making  coral- 
polyps,  we  may  assume  that,  wherever  fitting  conditions  presented  them- 
selves, they  could  settle,  adhere  to  a  sufficiently  hard  substance,  and 
commence  the  foundation  of  a  reef.  If  we  take  coasts  as  they  are 
variously  presented  to  us,  we  find  that,  as  regards  depth,  we  may  have 
the  20  or  30  fathoms  for  the  reef-making  corals  either  close  to  the 
shore,  or  removed  to  various  distances  from  it.  So  that,  assuming  the 
swimming  germs  to  meet  with  the  requisite  bottom,  they  can  commence 
their  reef-rearing  labours  at  various  distances  from  the  land,  and,  raising 
the  reefs,  form  very  different  lines  around  or  adjoining  it.  Let,  in  the 
annexed  diagram  (fig.  76),  a  a  be  the  surface  of  the  sea  round  an  island, 

Fig.  76. 


b  b  the  level  beneath  that  surface  at  which  the  swimming  coral-germs 
can  attach  themselves  and  begin  their  labours,  then  at  c  the  reef  would 
be  fringing  and  adjoining  the  coast ;  while  at  d,  a  bank  might  be  raised 
up,  forming  a  barrier  reef  to  the  coast  e.  Such  a  bank  once  established, 
the  space  /,  between  the  coast,  e,  and  the  barrier,  d,  becomes  fitted  for 
those  corals  which  require  the  shelter  afforded  by  the  latter.  Whether 
from  being  best  adapted  for  procuring  food,  or  as  affording  conditions 
ill-suited  to  the  coral-eating  animals,  the  surface  reef-making  corals 
flourish  in  the  surf  of  breakers,  so  that  they  grow,  as  a  mass,  outwards. 
With  respect  to  original  bottom,  if  there  be  sufficient  tranquillity  at  the 
depth  of  120  feet  from  wind-wave  action,  either  directly  produced  on 
the  spot  by  winds,  or  transmitted,  as  a  ground  or  ocean-swell,  from  a 
distance,  there  appears  no  reason  why  the  corals  found  at  that  depth, 
in  lagoons  and  other  sheltered  situations  inside  barrier  reefs,  should  not 
live  and  die  under  such  circumstances,  besides  other  corals,  not  yet 
known.  These  would  form  a  base  on  which  the  more  shallow  water  and 
littoral  corals,  among  them  those  able  to  resist  the  breaker-surf  itself, 
would  begin  their  work.  So  long  as  these  keep  at  sufficient  depths,  the 
mechanical  action  of  the  breakers  will  little  affect  them,  but  as  they  rise 
with  the  reef  they  gradually  come  within  its  influence,  so  that  finally 
the  coral  masses  are  dealt  with  as  the  rocks  of  any  other  coast  would 
be  under  similar  conditions. 

While  corals,  thus  forming  a  coast,  may  be,  to  a  certain  extent, 
adjusted  to  the  powers  of  ordinary  breakers,  any  increase  in  the  force 
of  the  breakers  over  the  resisting  powers  of  the  corals  would  break  off 
portions  of  the  latter,  so  that,  during  heavy  gales  of  wind,  the  resis- 


200 


CORAL  REEFS  AND  ISLANDS. 


tance  becoming  very  unequal  to  the  force  employed,  large  masses  of 
the  reef  are  torn  off  and  hurled  over  the  reef  inwards.  This  can  scarcely 
happen  without  minor  portions  being  also  thrown  over,  or  broken  off 
from  the  detached  masses,  and  the  general  action  such  that  fragments 
of  the  coral  mass  fall  outside  the  steep  slope  of  the  outward  growth,  a 
steep  slope  which  we  should  expect  to  have  been  gradually  formed  as 
the  coral  reef  rose  within  the  mechanical  action  of  the  breakers.  Let 
a  b  (fig.  77)  be  the  surface  of  the  sea  in  calm  weather  (for  the  moment 


Fig.  77. 


considered  without  reference  to  changes  of  level  produced  by  tides),  c  d 
a  depth  at  which  reef-making  corals  can,  other  conditions  being  favour- 
able, establish  themselves,  and  0,  e,  the  commencement  of  a  reef,  not 
raised  so  high  as  materially  to  feel  any  of  the  mechanical  effects  arising 
from  any  wave-action,  W,  W,  W,  though  every  successive  addition  to 
the  reef  would  bring  it  more  and  more  within  that  influence.  When, 
by  vertical  increase  in  the  coral  mass,  a  breaker  could  be  formed  by 
sufficient  proximity  to  the  wave,  W,  W,  W,  abrasion  would  commence 
as  the  coral  resistance  became  unequal  to  the  force  employed,  and  the 
detritus  would  be  scattered  on  each  side,  the  inside  probably,  from  the 
direction  in  which  the  force  was  applied,  receiving  the  chief  portion, 
while  some  fell  outwards  towards  b  d.  As  the  coral  growth  rose  to  the 
surface,  under  ordinary  weather,  the  increase  more  than  meeting  the 
loss  by  abrasion,  the  interior  would  be  filling  up  also  by  corals,  some  of 
which  required  the  shelter  there  afforded  them.  Outside,  the  breaker 
action  would  remove  the  smaller  fragments  in  mechanical  suspension, 
leaving  the  larger  blocks,  so  that  hollows  amid  the  latter  would  get 
filled  with  a  portion  of  the  finer  matter,  the  greater  part  of  which  would 
be  carried  out  at  the  base  of  the  reef,  more  or  less  ground  into  sand  by 
the  friction  to  which  it  may  have  been  exposed. 

If  we  suppose  the  reef  to  have  so  risen  that  it  touches  the  surface  of 
the  sea,  the  growth  of  the  coral  still  increasing  the  mass  beyond  the 
power  of  the  surf  to  break  off  portions  of  the  reef,  a  time  would  come 
when,  from  the  usual  breaker  action  upon  coasts  previously  mentioned, 
fragments  of  various  sizes,  with  coral  pebbles  and  sand,  from  continued 
friction  of  the  fragments  in  the  surf,  would  be  thrown  up  in  a  bank  upon 


CORAL    REEFS    AND    ISLANDS.  201 

the  reef,  with  sand  added  by  the  winds.  The  decomposition  of  the 
animal  matter  in  the  more  freshly  broken  pieces  of  coral,  added  to  any 
animal  matter  entangled  amid  the  reef,  would  assist  in  its  consolidation 
by,  among  other  things,  the  production  of  carbonic  acid,  for  combination 
with  the  water  to  act  on  the  carbonate  of  lime  of  the  corals,  so  that 
sufficient  would  be  taken  up  in  solution  to  cement  them  together,  by 
subsequent  deposit  among  the  coral  fragments,  thus  forming  conglome- 
rates and  sandstones.  A  dry  portion  once  above  water,  the  often 
described  vegetation  succeeds,  the  decomposition  of  which  also  affords 
free  carbonic  acid  for  further  solution  of  carbonate  of  lime,  and  an 
additional  consolidation  of  the  mass  beneath  by  chemical  means.  Con- 
sidering the  mixture  of  animal  matter  in  the  coral  mass  itself,  entangled 
among  it  in  various  ways,  and  by  its  decomposition  affording  carbonic 
acid,  and  the  conditions  under  which  this  carbonic  acid  could  be  brought 
to  aid  in  the  solution  of  the  carbonate  of  lime  of  the  coral  polyps,  it  will 
be  seen  that  circumstances  may  often  arise  for  the  obliteration  of  the 
organic  texture,  and  the  substitution  of  calcareous  matter,  presenting 
an  inorganic  character,  such  as  has  been  often  remarked. 

The  nearer  the  surface  the  greater  would  be  the  power  of  the  breaker 
action  to  peel  off  the  upper  coating  of  the  reef,  during  heavy  gales  of 
wind,  and  cast  the  fragments  inwards,  as  well  as  the  rounded  pebbles 
which  may  have  been  formed  in  fitting  situations  at  ordinary  times  by 
the  common  force  of  the  breakers.  We  should  expect  this  to  be  effected 
to  distances  beyond  the -margin  of  the  reef  dependent  upon  circum- 
stances, among  which  the  rise  and  fall  of  the  tide,  both  during  ordinary 
weather  and  at  the  time  of  any  heavy  gale  of  wind,  have  to  be  regarded. 

Assuming  c,  t,  (fig.  78)  to  be  the  difference  of  the  tide  level,  it  will 

Fig.  78. 

9 


be  obvious  that  any  power  which  the  breakers  may  have  at  the  level 
a,  c,  will  be  changed  during  the  rise  and  fall  of  the  tide,  ranging  up  and 
down  all  the  portions  of  the  reef  exposed  within  the  depth  t,  c.  We 
have  assumed,  as  in  the  accompanying  section  (fig.  77),  that  the  coral 
animals  in  their  free  swimming  state  met  with  a  bank  m,  0,  n,  so  that 
at  the  level  b  d,  they  found  the  conditions,  as  to  depth  and  other  things, 
suited  to  them.  Assuming  that  they  would  not  work  beneath  this  level, 
as  the  reef  rose,  and  the  detritus  outside  accumulated,  the  latter  would 
cover  over  the  deeper  part  o  n,  of  the  original  bank,  by  successive  coat- 


202  CORAL  KEEFS  AND  ISLANDS. 

ings,  over  which  the  coral  polyps  would  advance  their  work  laterally,  thus 
covering  horizontally  a  detrital  mass,  laminated  at  an  angle  according 
to  the  slope  on  which  it  may  accumulate.  Taking  the  outside  detrital 
increase  at  any  given  amount  of  cubic  contents,  it  would  follow  that, 
according  to  the  small  slope  of  the  original  bank  would  be  the  rapidity 
of  the  lateral  advance  over  which  the  corals  might  be  disposed  to  work, 
steep  slopes  affording  the  least  ground  at  a  given  level  for  such  increase. 
For  the  sake  of  easy  illustration,  we  have  assumed  a  bank  such  as  that 
near  Breaksea  Spit,  on  the  coast  of  Australia,  and  above-mentioned 
(p.  194),  which  after  retaining  a  certain  general  depth,  and  presenting 
a  rounded  margin,  plunges  into  deep  water. 

It  may  now  be  desirable  to  consider  the  effects  which  would  result,  in 
the  regions  of  coral  reefs,  from  volcanic  action.  We  have  seen  that, 
within  our  own  times,  volcanic  action  has  brought  ashes  and  cinders  to, 
and  above  the  sea  level  in  the  Mediterranean  (p.  95),  and  in  the  Atlantic 
(p.  123),  that  the  islands  so  produced  have  been  temporary,  and  that 
very  probably  the  incoherent  matter  of  which  they  were  composed  has 
been  cut  down  to  the  depths  at  which  breaker  or  wave  action  could  dis- 
turb and  remove  such  matter.  At  least  this  could  scarcely  but  happen, 
supposing  no  subsidence  from  the  pressure  of  the  water  into  the  crater 
in  such  a  manner  as  to  lower  the  volcanic  mass,  independently  of  any 
subsidence  from  volcanic  causes  themselves,  carrying  down  the  ashes 
and  cinders  beyond  the  influences  of  breakers  and  waves. 

If,  in  the  annexed  diagram  (fig.  79),  we  consider,  a,  £,  c,  d,  to  be  a 

Fig.  79. 


section  of  a  volcanic  cone,  the  top  of  which  was  forced  during  some 
eruption  above  the  level  of  the  sea,  e,  /,  that  this  condition  ceasing, 
breaker  and  wave  action  cut  down  the  loose  materials  to  the  level  #,  A, 
one  to  which  their  influence  could  extend,  even  probably  sifting  the 
ashes  and  cinders,  as  in  the  case  of  the  Island  of  Sciacca  (Mediter- 
ranean), so  that  a  somewhat  stony  bottom  might  be  the  result,  we  shouUl 
have  conditions  fitted,  in  the  coral-reef  seas,  for  the  settlement  of  the 
germs  of  the  reef-making  polyps  at  i  and  Jc.  At  those  points  of  the 
section  the  reef-making  corals  would  increase  as  above  noticed,  when 
they  rose  sufficiently  high  to  be  acted  upon  by  the  breakers,  fragments 
broken  off,  and  partly  thrown  down  on  the  outsides,  towards  a  and  dy 
and  the  corals  spreading  over  them  as  previously  noticed.  Inside  there 
would  be  a  lagoon,  which,  as  soon  as  a  general  barrier  of  coral  was 
established  outside,  would  be  filled  in  the  usual  manner  with  corals  and 


CORAL    REEFS    AND    ISLANDS.  203 

other  marine  creatures  suited  to  the  sheltered  conditions  there  found. 
The  overflow  of  the  breaker-waters,  and  the  rise  and  fall  of  tides  com- 
bined, would  tend  to  keep  open  a  channel  or  channels  between  the 
lagoon  and  the  sea  outside,  and,  finally,  terrestrial  vegetation  would 
establish  itself  upon  a  coral  bank  chiefly  raised  into  the  atmosphere  by 
the  piling  influence  of  the  breakers  upon  the  coral  ridge.  The  forms  of 
such  islands  would  necessarily  depend  much  on  the  horizontal  section  of 
the  volcanic  accumulation,  when  cut  down  by  breaker  and  wave  action, 
and  we  should  expect  the  submarine  and  steep  flanks  of  the  mass  to  be 
incrusted  by  coral  sands  and  fragments  in  proportion  to  the  time  during 
which  the  reef-corals  may  have  been  increasing  outwards  in  any  parti- 
cular locality,  so  that  the  sounding-lead  could  bring  up  little  else  around 
the  coral  reefs  and  island  except  coral  detritus,  and  the  marine  animals 
which  could  exist  under  the  needful  conditions  at  various  depths  around 
the  main  mass. 

As  we  have  abundant  proofs  that,  not  only  ashes  and  cinders  have 
been  vomited  out  of  volcanic  vents,  reaching  to  and  beyond  the  sea- 
level,  but  molten  rock  also,  the  whole  even  attaining  considerable  alti- 
tudes, such  as  the  volcanic  heights  of  Hawaii,  and  others  of  the  Sand- 
wich Islands,  with  deep  water  around  them,  it  may  not  be  undesirable 
for  the  observer  to  consider  the  conditions  under  which  coral  reefs 
might  be  gathered  around  such  volcanic  masses.  Let,  in  the  annexed 
section  (fig.  80),  a,  5,  c?,  represent  the  remains  of  a  mixed  volcanic  mass 


of  molten  rock,  and  of  ashes  and  cinders,  cut  away  by  atmospheric 
influences  and  breaker  action,  so  that  a  portion  of  hard  rock  5,  perhaps 
once  molten  matter  in  the  crater  of  a  volcano,  stands  above  the  level  of 
the  sea,  while  at  g  and /incoherent  ashes  and  cinders  are  cut  back  by 
breaker  action  (as  in  fig.  79)  to  this  hard  rock.  We  should  now  have 
conditions  for  the  formation  of  reefs  at/  and  </,  under  the  same  circum- 
stances as  above  noticed  (fig.  79),  with  this  difference,  that  instead  of 
an  uninterrupted  lagoon  in  the  interior  of  the  coral  reefs,  there  would 
be  land  emerging  from  it,  so  that  these  reefs  would  be  encircling.  In 
addition  to  the  usual  causes  of  keeping  channels  open,  the  islands,  if  of 
good  size,  might  contribute  fresh-water  streams,  at  times  charged  with 
detrital  matter,  preventing  the  increase  of  the  coral  reefs  in  the  lines 
which  they  traversed. 


204  CORAL    REEFS    AND    ISLANDS. 

It  would  appear  desirable,  in  the  first  instance,  that  an  observer 
should  direct  his  attention  to  the  conditions  under  which'  coral  reefs  and 
islands  could  be  formed,  either  as  lagoon  islands,  reefs  touching  or  en- 
circling land  composed  of  ordinary  detrital  or  igneous  rocks,  or  upon 
shoals  and  banks  ranging  in  front  of  considerable  lines  of  coast.  It  is 
not  a  little  interesting  further  to  consider  the  mode  in  which  a  general 
mass  of  coral  matter  would  be  composed,  after  a  lapse  of  time  sufficient 
to  complete  the  filling  up  of  lagoons,  with  or  without  the  protrusion  of 
dry  land  formed  of  ordinary  rocks  through  them,  or  the  space  between 
an  outer  line  of  coral  reefs  and  a  considerable  range  of  coast,  such  as 
that  in  a  portion  of  Eastern  Australia. 

As  to  the  height  to  which  corals  may  rise,  Mr.  Beete  Jukes  found 
coral  polyps  alive  six  or  eight  inches  out  of  water,  and  so  remaining 
for  nearly  an  hour,  until  the  return  of  the  tide.  He  often  observed  the 
same  fact,  and  believes  that  an  exposure  to  the  air  and  sun  will  not  kill 
many  of  the  polyps,  so  long  as  the  coral  remains  in  a  position  of 
growth,  the  cells  retaining  their  moisture.  He  has'  seen  blocks  of 
living  Astraea,  the  tops  of  which  were  18  inches  above  water.  This 
shows  that  we  may  take  the  ordinary  tide  level  for  that  to  which  the 
reef-making  coral  polyps  can  work  under  favourable  conditions :  and 
that  there  may  be  a  mass  of  matter  coinciding  with  the  line  of  a  main 
reef  round  a  lagoon-encircling  island,  or  in  front  of  a  long  range  of 
coast,  which  may,  from  the  top  to  the  other  substances  on  which  the 
reef  reposes,  be  chiefly  formed  by  the  growth  of  corals  upon  each  other, 
though  mixed  with  the  hard  remains  of  marine  animals  inhabiting  the 
cavities  amid  the  corals,  or  with  detrital  portions  driven  in  amid  the 
hollows  of  the  rising  mass. 

To  whatever  extent  the  germs  of  coral  polyps  could  settle  upon  any 
surface  beneath  the  sea-level,  suited  to  their  development,  conditions 
would  change,  as  the  reef  portion  rose  seaward,  behind  the  shelter  gra- 
dually afforded  from  the  roll  of  the  waves,  and  their  action  on  the 
bottom  beneath ;  so  that  while  sands  and  fragments  of  corals,  broken 
off  by  the  breakers,  arranged  themselves,  as  above  mentioned,  outwards, 
(the  reef-making  polyps  working  over  this  detritus,)  a  very  complicated 
series  of  deposits  and  coral  growths  would  be  formed  inwards.  In  the 
case  of  coral  lagoon  islands,  there  would  finally  be  calcareous  plateaux 
of  very  variable  areas,  some  many  square  miles  in  extent,  of  equal 
levels,  separated,  in  such  regions  as  the  coral  island  groups  of  the  Pacific 
Ocean,  by  irregular  intervals  of  deep  water.  These  isolated  sheets  of 
matter  of  general  similar  character  would  be,  to  a  certain  extent,  stra- 
tified, though  coral  growths  may  pierce  the  general  mass  in  various 
directions;  the  strata  composed  of  beds  of  coral  sand  and  mud,  as 
these  gradually  accumulated,  mingled  with  the  shells  of  molluscs,  the 
spines  and  coverings  of  echinoderms,  the  hard  remains  of  fish,  with  pos- 


CORAL  REEFS  AND  ISLANDS.  205 

sibly  also  those  of  certain  birds  and  turtles,  even  the  eggs  of  the  latter 
being  preserved  in  the  higher  sand-banks.  There  would  be  deposits  of 
calcareous  mud  outside  also,  at  depths  where  it  could  accumulate  in  an 
undisturbed  manner ;  this  calcareous  mud  borne  out  of  the  outlet  chan- 
nels during  ebb-tides,  and  when  heavy  gales  drove  an  abundance  of 
water  over  the  weather  side  of  the  encircling  reefs,  to  escape  out  of  the 
same  channels.  Such  mud  might  be  widely  spread  by  tidal  streams 
and  ocean  currents,  and  so  far  constitute  a  kind  of  connexion,  envelop- 
ing uneven  and  submarine  ground,  between  the  coral  plateaux. 

In  the  case  of  the  reefs,  more  or  less  encircling  islands  of  varied 
magnitudes,  and  composed  of  ordinary  sedimentary  and  igneous  rocks, 
there  would  be  a  modification  of  the  deposits  inside  the  reefs,  so  far  as 
a  supply  of  decomposed  rocks  from  atmospheric  influences  and  ordinary 
detritus  from  such  lands  would  be  concerned.  The  remains  of  a  larger 
and  more  varied  amount  of  terrestrial  vegetable  and  animal  life  would 
be  there  expected ;  as,  also,  under  favourable  conditions,  the  addition 
of  the  harder  parts  of  fluviatile  creatures.  Where  intermingled  with 
the  simple  lagoon  reefs,  there  would  be  corresponding  modifications  of 
the  interior  deposits  at  the  same  general  level. 

As  respects  the  accumulations,  for  so  many  thousand  square  miles, 
inside  the  Great  Barrier  Reef,  off  the  eastern  coast  of  Australia,  there 
would  be  a  great  sheet  of  matter,  as  a  whole,  having  a  certain  general 
character.  Viewing,  generally,  this  range  of  coast,  there  is  a  great 
absence  of  fresh  waters  draining  from  the  adjoining  land  ;  indeed,  water 
is  scarce  along  it  under  ordinary  conditions.  Hence  no  material  influ- 
ence is  exercised  on  the  growth  of  the  coral  polyps,  and  their  associated 
life,  by  rivers  and  streams  of  fresh  water,  either  clear  or  charged  with 
detritus  in  mechanical  suspension.  Seaward  we  have  the  same  c'ondi- 
tions  as  the  outward  portions  of  the  lagoon  reefs,  for  about  1000  miles ; 
the  southern  portion  ranging  beyond  the  circumstances  fitted  for  the 
development  of  the  reef-making  coral  germs,  and  resting  on  banks  of 
ordinary  siliceous  sand,  while  the  northern  portion  is  terminated  by  the 
influx  of  river  waters,  bringing  down  muddy  matter  from  New  Guinea  ; 
thus  also  preventing  the  same  germs  from  properly  establishing  them- 
selves, though  conditions  would  otherwise  appear  to  be  fitted  for  their 
development,  for  passing  the  outflow  of  the  river  waters,  coral  reefs  are 
again  established  to  the  northward. 

Inside  this  long  line  of  outer  reefs,  accumulations  are  effected  as  in 
the  ordinary  isolated  lagoon  reefs,  until  the  main  line  of  coast  is  ap- 
proached, where  the  observer  would  expect  modifications,  though  on  a 
larger  scale,  of  the  kind  found  around  the  islands,  composed  of  ordinary 
rocks,  inside  encircling  reefs,  and  above  noticed.*  Such  a  small  volume 

*  The  green  mud  off  Cape  Direction,  east  coast  of  Australia,  is  wholly  calcareous. — 
Beete  Jukes,  "  Narrative,"  &c. 


206  CORAL  REEFS  AND  ISLANDS. 

of  fresh  waters  flowing  outwards  from  the  land,  comparatively  little 
detrital  matter  from  the  interior  seems  transported  far  seaward,  so 
that  the  calcareous  detritus  derived  directly  from  the  reefs,  and  ground 
finer  hy  friction  from  breaker  action,  or  passed  through  the  animals 
feeding  on  the  coral  polyps,  readily  becomes  forced  towards  the  land 
from  the  prevalent  action  of  the  waves  in  that  direction.  It  there  min- 
gles near  the  coasts  with  such  detritus  as  may  be  derived  from  the  land 
by  breakers,  however  modified  these  may  be  from  the  shelter  afforded 
by  the  outer  reefs,  or  be  carried  out  into  such  tidal  streams  as  prevail 
by  the  rivers  in  flood.  Viewed  as  a  whole,  we  should  expect  much 
continuity  in  some  of  the  deposits,  particularly  the  finest,  in  many 
parts  of  the  great  area  comprised  between  the  coasts  and  the  outer 
great  barrier  reefs,  in  which  an  abundance  of  molluscs,  radiata,  and 
layers  of  certain  corals,  with  the  harder  parts  of  fish  and  crustaceans, 
would  be  entombed.  Near  the  land,  and  particularly  where  mangrove 
swamps  prevail,  (and  they  appear  not  uncommon,)  there  would  be  modi- 
fications of  these  continuous  deposits,  as  a  whole,  constituting  a  great 
mass  more  or  less  stratified,  intermingled  here  and  there,  especially 
towards  the  outer  barrier  reefs,  with  complicated  mixtures  of  coral 
growth  in  reefs,  the  detrital  matter  derived  from  them,  the  harder  parts 
of  other  marine  animals  living  among  them,  and  with  alterations  of 
structure  produced  by  chemical  means. 

Stratification,  or  an  approximation  to  it,  is  not  confined  to  the  coral 
sands  and  mud,  and  the  layers  of  organic  remains  which  may  be  inter- 
mingled with  them,  for  a  tendency  to  split  into  slabs  is  often  noticed 
in  the  mass  of  the  reefs.  Indeed,  Mr.  Beete  Jukes  not  only  mentions 
such  a  mode  of  occurrence  at  Heron  Island  (part  of  the  eastern  Aus- 
tralian coral  accumulations),  but  joints  in  the  reef  also,  splitting  the 
coral  rock  into  blocks  of  from  one  foot  to  two  feet  in  the  sides.  These 
joints  or  divisional  planes  are  parallel  to  the  dip  and  range  of  the  beds 
respectively,  and  the  coral  beds  dip  seaward  at  an  angle  of  from  8°  to 
10°. 

Having  studied  coral  reefs  and  islands,  with  reference  to  localities, 
and  to  their  present  adjustment  to  levels  beneath  the  surface  of  the  sea, 
as  if  he  could  transport  the  existing  shores  of  Europe,  with  all  their 
modifications  as  to  form  and  depth  of  water,  cutting  back  by  breaker 
action,  drainage  from  the  interior  of  land,  and  even  the  volcanic  shoals 
found  in  the  Mediterranean,  to  regions  where  the  germs  of  reef-making 
polyps  could  settle  and  be  developed ;  the  observer  has  next  to  turn 
his  attention  to  the  consequences  which  would  follow  any  of  those 
changes  of  the  relative  levels  of  sea  and  land,  both  on  the  small  and 
large  scale,  and  to  be  subsequently  further  noticed,  which  the  study  of 
geology  teaches  us  has  so  frequently  occurred. 

There  can  be  little  doubt  of  coral  bank*  and  reefs  similar  to  those  in 


CORAL    REEFS    AND    ISLANDS.  207 

the  seas  of  our  times,  and  in  coral-reef  regions,  having  been  raised  above 
the  surface  of  the  sea,  like  other  marine  accumulations,  forming  dry 
land.  Such  have  been  long  known.  MM.  Quoy  and  Gaimard,  who 
accompanied  the  expedition  of  M.  Freycinet,  and  who  remarked  on  the 
moderate  depths  to  which  the  reef-making  corals  appeared  to  extend,* 
mention  that  on  the  coasts  of  Timor,  coral  banks  so  occur  above  the  sea 
level  as  to  have  induced  M.  Peron  to  consider  the  whole  land  formed  of 
them.f  At  Oahu,  and  other  places  in  the  Sandwich  Islands,  coral  banks 
have  been  long  known  to  extend  inland,  and  more  modern  researches 
have  confirmed  these  observations.  Mr.  Couthouy,  in  particular,  gives 
an  account  of  ancient  reefs,  now  raised  above  the  sea  level,  at  the  islands 
of  Maui,  Morokai,  Oahu,  and  Tauai.J  We  had  occasion  to  remark,  also, 
some  years  since,  on  the  raised  coral  reefs  on  parts  of  the  coast  of 
Jamaica. §.  Elizabeth  Island,  off  the  eastern  side  of  the  low  archipelago, 
(between  Ducie  and  Pitcairn  Islands),  has  been  considered,  from  the 
description  of  Captain  Beechey,||  to  be  a  good  case  of  a  raised  coral 
island,  its  flat  summit  80  feet  above  the  sea.  Mr.  Darwin  has  accumu- 
lated a  mass  of  information^  from  the  personal  communications  of  the 
Rev.  J.  Williams,  Mr.  Martens  (of  Sydney),  and  Mr.  G.  Bennett,  and 
from  numerous  voyagers,  and  other  authors,  showing  coral  banks  ele- 
vated to  various  heights  above  the  level  of  the  sea  in  the  Cook  and 
Austral  Islands,  Savage  Islands,  the  Friendly  Islands,  the  Navigator 
Group,  the  New  Hebrides,  New  Ireland,  the  Marianas,  the  East  India 
Archipelago,  the  Loo-Choo  Islands,  Ceylon,  Mauritius,  Madagascar, 
part  of  the  eastern  coast  of  Africa,  the  Red  Sea,  and  the  West  India 
Archipelago.  In  fact,  this  list  comprises  examples  in  all  seas  where 
coral  reefs  and  islands  have  been  noticed,  and  leaves  little  doubt  that 
since  coral  reefs  and  islands  were  formed,  as  they  now  are,  in  the  fitting 
regions,  many  throughout  those  regions  have  been  raised  above  the  level 
of  the  sea  into  the  atmosphere. 

Lafu  Island,  one  of  the  Loyalty  Group,  has  also  been  noticed  by  the 
Rev.  W.  B.  Clarke  as  a  raised  coral  island.  It  is  about  90  miles  in 
circumference,  and  surrounded  by  a  fringing  reef,  upon  which  the  depth 
gradually  increases  outwards  for  a  quarter  of  a  mile,  the  reef  then 
plunging  into  deep  water.  The  whole  island  is  composed  of  dead  coral. 
Its  average  height  above  the  sea  is  about  120  feet ;  and  it  attains,  at 
points  on  the  eastern  side,  an  elevation  of  250  feet.  There  is  a  ledge 

*  Quoy  and  Gaimard,  Sur  1'Accroisement  des  Polypes  Lithophytes  consider**  geolo- 
giquement,  Annales  des  Sciences  Naturelles,  torn.  vi. 

f  Upon  proceeding  inland  a  short  distance,  MM.  Quoy  and  Gaimard  found  these  coral 
banks  resting  on  vertical  beds  of  slate. 

J  Remarks  on  Coral  Formations. 

\  Geological  Manual,  3d  edit.  1833,  p.  165. 

||  Beechey,  Voyage  to  the  Pacific. 

\  Darwin,  Structure  and  Distribution  of  Coral  Reefs,  pp.  132 — 137. 


208  CORAL  REEFS  AND  ISLANDS. 

or  shelf,  like  that  now  surrounding  the  island,  at  70  or  80  feet  above 
the  sea.  The  surface  is  table  land,  with  hollows  and  elevations,  just 
such  as  characterize  a  coral  reef.  Mr.  Clarke  infers  that  this  island 
has  been  elevated  at  two  distinct  periods ;  at  the  first,  to  the  amount  of 
170  feet,  at  the  second,  to  80  feet  additional  height.* 

In  considering  the  elevation  of  coral  reefs  above  the  sea-level,  the 
observer  should  also  take  into  account  the  portions  of  a  sea-bottom,  which 
may,  by  the  same  means,  be  brought  within  such  a  distance  of  the  sur- 
face water,  that  the  germs  of  the  various  coral  polyps,  which  aid  in  the 
establishment  of  a  reef,  could  find  the  needful  conditions  for  establishing 
themselves.  He  has  to  bear  in  mind  that  inequalities  of  the  sea-bottom 
exist  as  much  in  coral  regions  as  in  others ;  indeed,  the  igneous  cha- 
racter of  many  islands  in  the  tropics,  particularly  in  the  Pacific  and 
Indian  Oceans,  would  lead  us  to  expect  no  slight  variations  in  this 
respect.  Many  a  boss  or  extended  collection  of  volcanic  inequalities 
may  be  raised  by  the  same  movements  as  those  which  have  elevated  the 
coral  banks  to  various  altitudes  above  the  sea ;  and  while  some  pierced 
the  surface-level  of  the  water,  to  be  dealt  with  by  the  atmosphere  and 
the  breakers,  as  far  as  their  varied  resistances  to  the  destructive  action 
of  the  one  or  the  other  might  permit,  others  would  be  differently  cir- 
cumstanced. Some,  formed  of  incoherent  cinders  and  ashes,  would 
readily  be  cut  down  to  the  level  to  which  breaker  action  could  extend ; 
while  others  would  only  just  reach  the  needful  depth  beneath  the  surface- 
water  for  the  establishment  of  coral  reefs. 

As  respects  inequalities  of  sea-bottom,  if  the  Great  Bank  of  New- 
foundland were  in  coral  regions,  and  were  elevated  from  its  present 
relative  level,  so  that  its  broad  platform  with  its  common  depth  of  from 
40  to  50  fathoms,  one  small  portion  of  the  area  being  occupied  by  the 
Virgin  Rocks,  were  raised  about  twenty  fathoms,  by  which  coral  reef- 
making  germs  could  fix  and  develope  themselves  under  fitting  conditions, 
we  should  have  an  area  of  between  35,000  to  40,000  square  miles,  around 
the  irregular  margin  of  which  there  would  be  conditions  as  represented 
beneath  (fig.  81),  for  an  extended  border  of  coral  reefs.  The  sea  around 
the  margin  would  often  be  suddenly  deep.  The  new  Admiralty  Chart 
of  the  North  Atlantic  gives  106,  137,  147,  132,  107,  and  149  fathoms, 
as  now  found  close  off  the  southeastern  side  of  the  Great  Bank.  There 
would  be  an  island  of  small  size,  now  the  Virgin  Rocks,  above  water, 
with  still  20  fathoms  close  to  it ;  and  supposing  a  somewhat  questionable 
shoal  (with  3  J  fathoms  upon  it),  about  40  miles  to  the  eastward  of  the 
Virgin  Rocks,  to  be  really  existing,  there  would  be  another  small  island 
in  the  same  area.  The  Great  Bank,  with  its  continuation,  the  Green 
Bank,  would  be  separated  by  a  channel,  then  55  to  79  fathoms  deep, 
from  the  St.  Pierre  Bank,  round  the  edges  of  which  there  would  be 

*  Clarke,  Quarterly  Journal  of  the  Geological  Society  of  London,  vol.  iii.  p.  01.  1847. 


CORAL    REEFS    AND    ISLANDS. 


209 


conditions  for  a  fringe  of  coral  reefs,  enclosing  a  large  area  of  water 
with  no  land  above  its  surface.  Indeed,  the  St.  Pierre  Bank  would 
then  bear  an  external  resemblance  to  a  great  atoll,  about  140  miles 

Fig.  81. 


across  from  southeast  to  northwest,  with  a  maximum  breadth  from 
southwest  to  northeast  of  about  70  miles,  and  having  a  somewhat  steep 
slope  outside,  on  the  southwest  side,  into  118,  160,  and  149  fathoms, 
the  change  from  the  present  depths  being  taken  into  account.* 

*  The  extensive  submarine  area  of  the  Newfoundland  banks  is  also  highly  interesting, 
as  exhibiting  a  very  slight  difference  in  level.  From  250  to  300  feet  beneath  the  sur- 
face water  seems  a  very  common  depth,  though  there  appear  to  be  gradual  swelling 
portions  bringing  the  bottom  more  upwards.  If  these  banks  were  elevated  above  the 

14 


210  CORAL  REEFS  AND  ISLANDS. 

In  the  Bermudas  we  seem  to  have  an  instance  of  an  isolated  bank  in 
the  Atlantic,  far  distant  from  land,  and  rising  from  deep  water,  upon 
the  upper  part  of  the  crown  of  which  coral  reefs  have  established  them- 
selves, mingled  with  others  which  have  been  described  as  chiefly  com- 
posed of  Serpulse,  Nulliporae  incrusting  the  work  of  the  marine  animals 
as  upon  the  coral  reefs  of  the  Pacific  (p.  183).  The  remarks  of  Captain 
Nelson,  of  the  Royal  Engineers,  having  chiefly  reference  to  the  geo- 
logical structure  of  these  islands,  there  is  yet  much  to  be  accomplished 
by  the  experienced  naturalist  respecting  the  reefs  themselves,  which 
are  especially  interesting  from  their  geographical  position,  and  the 
marine  life  connected  with  it. 

Although  deep  water  is  reported  to  surround  the  bank  upon  which 
the  reefs  and  isles  of  Bermuda  are  situated,  the  reefs  themselves  are 
immediately  bounded  outwards  by  shallow  water,  only  6  and  7  fathoms 
being  marked  on  the  charts  as  a  somewhat  common  depth  immediately 
beyond  the  reef,  deepening  somewhat  further  distant  to  12  and  15 
fathoms.  Captain  Nelson  describes*  the  Bermudan  group  to  consist  of 
about  150  islets,  lying  in  a  northeast  and  southwest  direction,  within 
a  space  of  15  by  5  miles,  and  containing  altogether  an  area  of  about 
21  square  miles.  This  group  is  situated  very  near,  and  conformably 
to,  the  southeast  side  of  a  belt  of  reefs,  partly  formed  by  corals,  and 
partly  by  Serpulae,  of  a  rude  elliptical  form,  25  miles  long  by  13  miles 
broad.  The  channels  amid  the  islets  are  shallow,  and  the  depth  of 
water  within  the  boundary  reefs  rarely  exceeds  12  to  14  fathoms.  The 
highest  land  rises  to  about  260  feet  above  the  sea  at  Sears  Hill,  and 
Gibbs  Hill  has  an  elevation  of  245  feet. 

Captain  Nelson  describes  the  islands  as  altogether  calcareous,  the 
beds  varying  from  loose  sand  to  limestone,  so  compact  as  to  receive  a 
good  polish,  the  whole  derived  from  animal  secretions,  chiefly  marine, 
though  the  remains  of  land  shells  and  birds'  bones  are  also  mentioned. 
From  the  mode  of  occurrence  of  the  calcareous  beds,  and  especially 
from  the  saddle-shaped  sections  observable  throughout  the  islets,  Cap- 
tain Nelson  infers  that  the  deposits  have  been  effected  by  means  of  the 

sea,  they  would  present  an  irregularly  bounded  platform,  divided  by  one  main  channel, 
many  thousand  square  miles  in  extent,  the  chief  height  above  which  would  be  a  rocky 
eminence,  about  240  feet  above  the  general  surface,  where  the  Virgin  Rocks  now  occur  ; 
and,  if  the  questionable  shoal  on  the  eastward  really  exists,  a  boss  of  ground  of  about 
the  same  altitude  in  that  direction  also.  If  these  banks  have  been,  in  previous  geolo- 
gical times,  raised  into  the  atmosphere,  all  traces  of  considerable  hills  and  valleys, 
which  may  then  have  existed,  have  been  obliterated.  And  this  may  readily  have  hap- 
pened from  the  levelling  effects  of  breaker  action,  combined  with  the  distribution  of 
the  detritus  by  tidal  streams  and  ocean  currents,  as  the  land  may  have  slowly  subsided. 
Be  this  as  it  may,  detritus  would  not  readily  be  now  borne  to  these  banks  from  the 
adjoining  coasts  of  Newfoundland  by  any  drifting  action  along  the  bottom,  since,  as 
previously  mentioned,  deep  water  occurs  between  the  banks  and  that  land. 

*  "Nelson,  Transactions  of  the  Geological  Society  of  London,"  2d  series,  vol.  v. 


CORAL    REEFS    AND    ISLANDS.  211 

wind,  driving  the  calcareous  sands,  including  fragments  of,  and  whole 
shells,  in  the  usual  way  before  it,  and  heaping  them  up  irregularly  into 
sand-hills,  the  component  parts  of  which  have  been  variously  consoli- 
dated. A  foot  of  red  earth,  containing  vegetable  matter,  commonly 
covers  the  calcareous  accumulations.  Fragments  of  coral  and  shells 
are  noticed  as  common,  and  the  remains  of  Lucina  (Venus)  Pensyl- 
vanica  are  especially  pointed  at  as  frequent.  Turbo  pica  is  also  com- 
mon; and  Captain  Nelson  is  inclined  to  refer  its  occurrence  on  the 
heights  to  the  hermit  crabs,  which  he  has  seen  running  about  with  these 
shells.*  Coral  reefs  occur  inside  the  main,  or  outside  reefs,  and  do  not 
rise  above  low  water,  except  at  spring-tides.  Over  the  bottom  of  this 
basin,  calcareous  sand  and  chalky  clay  (the  best  anchoring  ground)  are 
distributed.  The  tides  average  a  rise  and  fall  of  about  4J  feet,  and  at 
low  water  the  main  reefs  stand  about  2  feet  above  the  sea. 

Although  there  may  be  good  evidence  of  much  of  the  calcareous  ac- 
cumulations of  these  islets  having  been  effected  by  means  of  the  wind, 
piling  up  sand  and  fine  calcareous  particles,  driven,  in  the  usual  way, 
by  breaker  action  at  high  tides,  and  by  gales  of  wind,  and  as  above 
noticed  (p.  86),  within  its  influence,  f  still  there  would  also  appear  evi- 
dence, in  a  bed  of  the  remains  of  the  Lucina  Pensylvanica,  5  feet  thick, 
and  now  about  6  feet  above  water,  having  an  even  range  from  Phyllis 
Island  to  Harris  Island,  apparently  corresponding  also  with  another, 
but  thinner,  bed  of  the  same  remains,  that  there  may  have  been  some 
elevation  of  the  general  mass.  Under  this  hypothesis,  a  mixed  accumu- 
lation, by  means  of  both  wind  and  water,  would  not  appear  inconsistent 
with  the  sections  given  by  Captain  Nelson.  The  following  (fig.  82)  is 
one  similar  to  many  sections  of  sandstone  deposits  formed  beneath 
water. 

Fig.  82. 


a,  6,  c,  Ordinary  friable  calcareous  rock. 
d,  Recent  loose  deposit  in  front  of  cliff. 

Having  so  much  evidence  of  the  elevation  of  coral  reefs  in  various 
parts  of  the  world,  and  seeing  that  depressions  of  ordinary  rock-accu- 
mulations (to  be  hereafter  noticed)  have  been  effected,  often  on  the 
large  scale,  also  in  various  regions,  the  observer  would  expect  that  coral 

*  Mellita  (Scutdla)  quinquefora  is  noticed  as  found,  the  pores  of  the  crusts  filled  with 
crystalline  carbonate  of  lime,  like  the  echinites  in  the  European  chalk.  Turtles'  bones 
have  been  discovered  in  the  accumulations,  as  also  the  remains  of  Cypreea  and  Bulla. 

f  Sand  drifts  are  now  in  progress,  and  Captain  Nelson  especially  refers  to  one  en- 
croaching on  the  land,  and  arising  from  works  executed  a  few  years  since,  by  which  a 
protecting  vegetation  was  removed,  and  the  wind  acted  on  a  sufficient  area  of  free  sand 
to  work  its  destructive  way  into  a  more  considerable  mass. 


212  CORAL    REEFS    AND    ISLANDS. 

reefs,  and  even  extended  areas  in  which  they  occur,  may  in  like  manner 
have  been  subjected  to  the  like  movements.  Mr.  Darwin  has  very  ably 
sustained  this  view,  both  as  respects  single  coral  reefs,  and  extended 
regions  in  which  they  may  be  found.*  To  account  for  barrier  reefs 
and  atolls,  which  have  been  produced  by  the  subsidence  of  land,  around 
which  fringing  coral  reefs  only  were  first  attached,  he  gives  the  follow- 
ing illustration  :f 

Pig.  83. 


Let  A,  A,  be  the  outer  edges  of  fringing  reefs,  on  two  opposite  sides 
of  an  island,  L,  at  a  sea-level,  S,  S;  B,  B,  shores  of  the  island;  A',  A', 
outer  edges  of  the  fringing  reef,  after  its  upward  growth,  during  the 
gradual  subsidence  of  the  island  L,  by  which  the  relative  sea-level  be- 
comes transferred  to  S',  S';  then  A'B',  B' A',  are  sections  of  the  lagoons 
inside  barrier  reefs  on  each  side  of  the  land,  after  this  subsidence,  and 
B'  B'  the  new  shores  of  the  island.  Should  the  gradual  subsidence  con- 
tinue, so  that  the  relative  level  of  the  sea,  as  regards  the  island  L,  be 
changed  to  S"  S",  then  the  original  island  round  which  the  corals  first 
formed  a  fringing  belt,  would  be  completely  concealed,  A"  A"  consti- 
tuting the  outer  reefs  of  an  atoll,  and  C  its  contained  lagoon.  In  this 
manner  the  original  mass  of  land,  which  may  be  a  volcanic  cone,  or 
some  modification  of  that  form,  would  become  encrusted  by  the  remains 
of  marine  animals,  or  the  detrital  and  chemical  accumulations  arising 
from  such  remains,  including  the  faeces  of  the  various  reptiles,  fish, 
crustaceans,  molluscs,  and  other  marine  creatures  which  inhabited  the 
reefs  and  lagoons.  This  would  be  contained  within  a  general  crust,  due 
chiefly  to  the  work  of  the  outer  reef-making  polyps ;  this  crust  again 
covered,  after  a  certain  depth,  by  the  debris  of  the  reefs,  broken  away 
by  breaker  action,  as  the  subsidence  continued,  and  accumulated  over 
the  first  formed  reefs  in  the  usual  talus,  at  the  same  time  affording,  by 
such  accumulation,  a  certain  amount  of  lateral  extension  to  the  general 
mass.  With  the  exception  of  certain  portions  of  this  outside  distribu- 

*  Darwin,  Structure  and  Distribution  of  Coral  Reefs,  chap.  vi.  On  the  distribution 
of  coral  reefs  with  reference  to  the  theory  of  their  formation. 

f  In  this  section  the  two  diagrams  given  by  Mr.  Darwin  (Structure  of  Coral  Reefs, 
pp.  98  and  100),  have,  for  convenience,  been  thrown  into  one ;  in  other  respects 
they  are  the  same.  As  Mr.  Darwin  points  out,  the  sections  of  the  lagoons  are  exagge- 
rated. 


CORAL    BEEFS    AND    ISLANDS.  213 

tion  of  the  debris  from  breaker  action,  there  would  be  a  general  hori- 
zontal arrangement  of  the  rest ;  even  the  crust  of  the  outer  reef 
exhibiting,  to  a  certain  extent,  this  mode  of  accumulation,  from  the 
intermingling  of  sheets  or  disconnected  patches  of  Nulliporse  with  the 
corals,  with  any  patches  of  islands,  and  with  the  remains  of  their  vege- 
tation and  of  amphibious  or  terrestrial  life,  as  from  time  to  time  con- 
ditions for  their  production  may  have  obtained  during  the  subsidence  of 
the  general  mass.  No  doubt  a  large  volume  of  calcareous  matter, 
obtained  by  marine  animals  from  the  sea  and  their  food,  mingled  with 
some  terrestrial  vegetable  and  animal  matter,  would  be  thus  accumu- 
lated ; — and  no  small  amount  would  be  required  to  fill  in,  as  it  were, 
the  space  between  the  outer  crust  of  the  rising  reefs  and  the  original 
land ;  but  the  former,  with  their  shelter  for  numerous  marine  animals 
being  given,  the  required  volume  of  calcareous  matter  might  follow, 
supposing  a  very  gradual  subsidence  continued  through  a  long  lapse 
of  time. 

Assuming  the  hypothesis  good  for  the  single  case  adduced,  there 
would  appear  no  difficulty  in  applying  it  to  a  variety  of  modifications, 
either  in  the  form  of  the  original  land,  which  may  be  either  of  small 
or  considerable  extent,  mountainous  or  hilly  in  one  part,  and  more  level 
at  others  ;  or  with  reference  to  the  altered  and  changing  arrangements 
of  the  surface  distribution  of  land  and  water  at  different  times  as  the 
subsidence  continued,  was  more  sudden  at  one  time  than  others,  or  was 
interrupted  by  pauses  of  greater  or  less  duration.*  The  Maldives  are 
considered  as  affording  a  good  example  of  the  effects  of  the  submer- 
gence of  the  land,  after  the  first  incrustation  of  its  shores  by  the  reef- 
making  corals,  so  that  a  considerable  fringing  reef  round  a  large  island, 
like  that  of  New  Caledonia,  became  divided  up  into  numerous  rings  of 
coral  reefs,  crowning  different  heights  of  the  original  land,  the  general 
outline  of  the  latter  still  preserved  from  the  upward  increase  of  the 
general  mass  of  the  corals.  The  Great  Chagos  Bank,  on  the  south  of 
the  Maldives,  presents  peculiarities  well  worthy  of  attention  ;f  and  Mr. 

""  The  varied  effects  of  submergence  of  coral  reefs  and  islands  will  be  found  treated 
at  length,  and  with  reference  to  reefs  and  islands  considered  to  bear  out  this  view,  in 
Mr.  Darwin's  Structure  of  Coral  Reefs,  chap,  v.,  entitled,  Theory  of  the  formation  of 
the  different  classes  of  coral  reefs. 

-{•  "  The  longest  axis  is  ninety  nautical  miles,  and  another  line  drawn  at  right  angles 
to  the  first,  across  the  broadest  part,  is  seventy.  The  central  part  consists  of  a  level, 
muddy  flat,  between  forty  and  fifty  fathoms  deep,  which  is  surrounded  on  all  sides, 
with  the  exception  of  some  breaches,  by  the  steep  edges  of  a  set  of  banks,  rudely  ar- 
ranged in  a  circle.  These  banks  consist  of  sand,  with  a  very  little  live  coral ;  they 
vary  in  breadth  from  five  to  twelve  miles,  and  on  an  average  lie  about  sixteen  fathoms 
beneath  the  surface ;  they  are  bordered  by  the  steep  edges  of  a  third  narrow  and  upper 
bank,  which  forms  the  rim  of  the  whole.  The  rim  is  about  a  mile  in  width,  and  with 
the  exception  of  two  or  three  spots  where  islets  have  been  formed,  is  submerged  between 
five  and  ten  fathoms.  It  consists  of  smooth,  hard  rock,  covered  with  a  thin  layer  of 


214  CORAL  REEFS  AND  ISLANDS. 

Darwin  points  it  out  as  an  instance,  in  which  the  corals  of  the  main 
reef  perished  before  or  during  a  submergence,  now  such  that  the  great 
outer  reef,  instead  of  being  within  the  break  of  the  sea,  is  sunk  from  5 
to  10  fathoms  beneath  the  surface  of  the  water,  two  or  three  spots  only 
rising  into  islets.  As  the  depth  of  the  outer  reef  does  not  appear  such 
as  to  prevent  reef-making  corals  from  developing  themselves,  and  as 
interior  knolls  present  themselves  at  the  same  depth  with  luxuriantly- 
growing  corals,  there  would  appear  some  other  reason  than  mere  depth 
of  water,  with  its  consequences,  preventing  the  establishment  of  more 
than  a  slight  amount  of  living  coral  polyps  on  these  reefs.  Supposing 
the  outer  reef  to  have  once  flourished  in  the  common  manner,  at  and 
near  the  surface  (and  there  are  still  two  or  three  islets  above  water), 
perhaps  the  somewhat  sudden  submergence  of  an  extended  range  of 
islets,  thickly  studded  over  the  outer  reef,  with  their  vegetation  and 
sands,  would,  for  a  long  time  at  least,  be  very  unfavourable  to  conditions 
well  suited  for  the  re-establishment  of  the  upper  reef-making  corals. 
Wave  and  tidal  action  would  tend  to  distribute  and  move  about  the 
sands  over  the  sunk  reef  in  a  manner  scarcely  fitted  to  the  habits  of 
the  upper  reef-making  coral  polyps,  or  the  firm  establishment  of  their 
germs. 

With  regard  to  the  incrusting  of  islands  by  coral  masses,  including 
the  accumulations  mechanically  and  chemically  obtained  from  the  stony 
matter,  chiefly  calcareous,  secreted  by  the  polyps  and  other  marine 
creatures  forming  or  inhabiting  coral  reefs,  if  we  can  have  a  growth 
and  accumulation  adjusted* to  the  submergence,*  the  geological  results 
would  be  such  that  upon  again  being  elevated  above  the  sea-level  (as 
has  happened  so  often  with  many  regions  during  the  lapse  of  geological 
time  after  submergence),  in  areas  such  as  that  of  the  corallian  portions 
of  the  Pacific,  numerous  masses  of  calcareous  accumulations  would 

sand,  but  with  scarcely  any  live  coral ;  it  is  steep  on  both  sides,  and  outwards  slopes 
abruptly  into  unfathomable  depths.  At  a  distance  of  less  than  half  a  mile  from  one 
part  no  bottom  was  found  with  190  fathoms ;  and  off  another  point,  at  a  somewhat 
greater  distance,  there  was  none  with  210  fathoms.  Small  steep-sided  banks  or  knolls, 
covered  with  luxuriantly-growing  coral,  rise  from  the  interior  expanse  to  the  same 
level  with  the  external  rim,  which,  as  we  have  seen,  is  formed  only  of  dead  rock." 
— Darwin,  Structure  and  Distribution  of  Coral  Reefs,  p.  39. 

*  If  the  submergence  were  so  rapid  that  the  growth,  and  consequent  accumulations 
inside  the  reefs  did  not  become  adjusted  to  it,  and  supposing  the  reef-making  corals 
only  able  to  nourish  in  certain  minor  depths,  it  is  obvious  that  the  reefs  could  not 
increase  upwards,  but  remain  beneath  like  any  mass  of  inorganic  matter,  the  reef- 
making  polyps  perishing. 

With  respect  to  the  rate  of  growth  of  reef-making  corals,  the  evidence  is  at  present 
somewhat  uncertain  and  contradictory.  Some  contend  that  the  growth  is  very  slight, 
reefs  having  been  known  in  their  present  state  for  a  long  time  ;  while  others  consider 
their  increase  as  more  rapid.  There  is  evidently  a  want  of  more  information  on  this 
subject,  especially  as  respects  the  conditions  under  which  the  appearances  supporting 
these  different  views  may  have  been  caused. 


CORAL    BEEFS    AND    ISLANDS.  215 

present  themselves,  often,  perhaps,  corresponding  in  general  character 
at  equal,  or  nearly  equal  levels,  and  having  the  appearance  of  being 
the  remains  of  limestone  deposits,  once  continuous,  though  in  reality 
they  had  never  been  united.  If  the  Cape  de  Yerde  Islands,  the  Cana- 
ries, and  the  Azores,  were  to  be  incrusted  with  coral  reefs,  and  be 
gradually  depressed  beneath  the  level  of  the  sea,  so  that  the  reefs  and 
the  consequent  accumulations  inwards  could  be  adjusted  to  the  rate  of 
submergence,  and  were  again  raised  above  the  sea  (as  at  least  some  of 
them  would  appear  to  have  been,  since  notwithstanding  their  general 
igneous  character,  sea  bottoms  and  shores  around  them,  of  the  more 
recent  geological  times,  termed  the  tertiary,  are  uplifted),  these  falla- 
cious appearances  would  be  very  marked.* 

The  observer  would  readily  expect  to  find,  in  regions  where  coral 
reefs  abound,  and  volcanoes  are  now,  or  have  been  active  during  their 
formation,  that  there  are  occasional  mixtures  of  igneous  products  with 
the  coral  accumulations.  In  Mr.  Beete  Jukes'  account  of  the  Great 
Barrier  Reefs  of  Australia,  he  mentions  mingled  substances  of  this 
kind  at  Murray  and  Erroob  Islands,  where  beds  are  found  containing 
variable  portions  of  trachytic  lava  and  calcareous  rocks,  some  of  the 
lumps  of  lava  and  limestone  being  apparently  rounded  by  attrition. 
There  are  also  beds  of  volcanic  ash,  or  sand,  in  which  calcareous  grains 
are  dispersed.  In  Erroob,  igneous  rocks  cover  the  sandstones  and  con- 
glomerates. In  this  region,  also  pumice  would  appear  to  have  been  at 
one  time  much  drifted  about,  arising  probably  from  volcanic  eruptions 
in  directions  whence  a  portion  of  this  light  substance  could  be  driven 
by  prevalent  winds  and  currents.  It  seems  to  have  become  mingled 
with  the  coral  deposits.  Portions  of  it  are  embedded  in  the  coral  rock 
of  Raine's  Islet,  and  frequent  in  the  coral  conglomerate  on  the  northeast 
coast  of  Australia. f  Captain  Wilkes  describes J  portions  of  vesicular 

*  There  are  suddenly  very  considerable  depths  around  the  Cape  de  Verde  Islands. 
Even  in  the  channel  between  Sal  and  Bonavista,  a  line  of  232  fathoms  found  no  bottom. 
The  same  with  the  Canaries.  There  is  no  bottom  at  309  fathoms  close  on  the  north  of 
Palma.  The  like  with  the  Madeira,  off  the  west  end  of  which  a  line  of  280  fathoms 
does  not  reach  the  bottom.  Very  deep  water  surrounds  the  various  islands  of  the 
Azores.  There  is  a  depth  of  300  fathoms  close  on  the  south  of  Santa  Maria,  and  no 
bottom  with  320  fathoms  of  line  between  that  island  and  the  Formigas,  on  the  northeast. 
Around  Pico,  Fayal,  San  Jorgo,  and  Terceira,  there  are  depths  of  200  and  300  fathoms 
near  the  land  ;  and  there  is  very  deep  water  around  Flores,  the  most  western  isle. 

f  Beete  Jukes,  Narrative  of  the  Voyage  of  the  Fly.  He  describes  flats  of  coral 
conglomerate,  half  a  mile  wide,  as  frequent  along  shore  on  the  northeast  coast  of  Aus- 
tralia. Upon  all  these  flats,  and  about  10  feet  above  high  water,  there  is  an  abundance 
of  pumice  pebbles.  They  occur  on  the  east  coast  of  Australia,  under  similar  condi- 
tions, for  2000  miles ;  are  rarely  seen  on  the  present  beach,  or  found  floating  at  sea ; 
and  Mr.  Beete  Jukes  infers,  that  this  proves  either  the  stationary  character  of  the  coast, 
or  that  it  has  been  equally  affected,  for  this  distance,  by  elevation  or  depression.  He 
allows  for  the  piling  action  of  the  breakers,  and  considers  it  as  not  improbable  that 
the  coast  has  been  slightly  elevated,  or,  at  least,  has  not  suffered  any  depression  through 
a  long  lapse  of  time. 

•J  United  States  Exploring  Expedition,  vol.  ii.  p.  64. 


216  TRANSPORTAL    OF    MINERAL    MATTER    BY    ICE. 

lava  as  found  among  blocks  of  coral  conglomerate  at  Rose  Island,  a 
small  and  low  coral  island,  forming  the  most  eastern  of  the  Samoan 
Group.  We  should  expect  many  mixtures  of  volcanic  rocks  with  coral 
sands  and  pebbles  on  the  beaches  of  volcanic  islands,  fringed  by  coral 
reefs,  as  appears  often  to  be  the  case,  and  also  an  occasional  overflow 
of  lava  on  reefs  adjoining  land  liable  to  volcanic  eruptions.* 

Transportal  of  Mineral  Matter  "by  means  of  Ice. — Very  considerable 
attention  has,  of  late  years,  been  directed  to  the  influence  of  ice  in  the 
distribution  of  detritus,  both  upon  dry  land  and  over  the  bottom  of  the 
sea,  and  to  the  mechanical  effects  ice  may  produce  on  hard  rocks,  or 
loose  accumulations,  on  or  against  which  it  may  move  or  be  thrown, 
upon  the  land  or  beneath  the  sea. 

We  observe  the  influence  of  the  sun's  heat  to  be  now  such,  (whatever 
view  may  be  taken  of  any  supposed  heat  in  the  body  of  the  earth  itself, 
sufficient,  in  previous  times,  to  prevent  the  formation  of  ice  on  its  sur- 
face,) that  the  cold  of  the  planetary  space,  as  it  has  been  termed,  so 
acts  upon  the  earth,  that  it  is,  as  it  were,  encased  in  a  spheroidal  space, 
outside  which,  water  remains  permanently  solid ;  this  space  having  a 
spheroidal  form  more  oblate  than  the  earth,  so  that,  at  the  equator, 
there  is  a  difference  of  from  16,000  to  17,000  feet  between  the  two,  and 
that  it  cuts  beneath  the  poles  of  the  earth  in  the  Arctic  and  Antarctic 
regions.  Above  this  space,  it  is  inferred  that  the  temperature  continues 
to  decrease  in  the  atmosphere  until,  finally,  that  of  the  planetary  space 
alone  prevails. f 

Taking  thus  the  heat  derived  from  the  sun  as  so  influencing  the  pre- 
sent surface  temperature  of  the  earth,  that  the  cold  of  the  planetary 
space  does  not  render  the  waters  solid  over  the  whole  face  of  the  world, 
we  should,  from  the  conditions  under  which  it  could  prevail,  anticipate 
many  minor  modifications  in  its  action. J  These  would  arise  from  its 
different  absorption  and  radiation  according  as  the  heat  fell  upon  land 
or  water,  and  in  different  latitudes ;  from  the  varied  relief  and  cha- 

*  A  coral  bed,  10  feet  thick,  is  stated  to  occur  between  two  lava  streams  at  the  Isle 
of  France  ;  the  coral  bed  elevated,  since  its  formation,  above  the  level  of  the  sea. 

f  Fourier  inferred  that  the  temperature  of  the  planetary  space  was  — 50°  centigrade 
(—68°  Fahr.),  and  Svanberg  held  it  was  — 49-85°  centigrade,  employing  another  method. 
Observing  this  near  approach  to  the  result  given  by  Fourier,  the  latter  calculated  the 
temperature  according  to  Lambert's  statements,  and  obtained  —50-35°. 

J  Respecting  the  temperature  of  our  atmosphere,  M.  Arago  has  remarked,  (Ann.  de 
Phys.  et  de  Chim.,  torn.  27,)  that,  "1st,  in  no  part  of  earth  on  land  will  a  thermometer, 
raised  from  two  to  three  metres  (6-5  to  10  English  feet)  above  the  ground,  and  pro- 
tected from  all  reverberation,  attain  46°  centigrade  (114-8°  Fahr.) ;  2dly,  in  the  open 
sea,  the  temperature  of  the  air,  whatever  be  the  place  and  season,  never  attains  31° 
centigrade  (87-8°  Fahr.)  ;  3dly,  the  greatest  degree  of  cold  which  has  ever  been  observed 
upon  our  globe,  with  the  thermometer  suspended  in  the  air,  does  not  descend  50  centi- 
grade degrees  below  zero  ( — 58°  Fahr.)."  To  this  he  adds,  "  4thly,  the  temperature  of 
the  water  of  the  sea,  in  no  latitude,  and  in  no  season,  rises  above  30°  centigrade  (86° 
Fahr.)." 


LINE    OF    PEKPETUAL    SXOW. 


217 


racter  of  the  land,  and  its  intermixture  with  surface  waters  ;  from  the 
variation  in  the  waters  as  to  depths,  and  the  motion  of  some  portions  of 
them  from  colder  to  hotter  regions,  or  the  reverse,  from  the  movement 
of  the  atmosphere  and  its  varied  conditions ;  and  from  the  periodical 
change  in  the  position  of  portions  of  the  earth's  surface,  according  as 
one  hemisphere  or  the  other  becomes  most  exposed  to  the  influence  of 
the  sun. 

Numerous  observations  have  shown  the  exact  regularity  of  the  sphe- 
roidal space,  in  which  water  commonly  remains  liquid,  to  be  much  dis- 
turbed by  the  modifications  noticed  ;  so  that,  for  all  the  purposes  required 
by  the  animals  and  vegetables  of  our  planet,  certain  regions  are  ren- 
dered habitable  which  would  otherwise  scarcely  support  life.  A  very 
marked  instance  of  this  kind  is  found  on  the  north  flank  of  the  Hima- 
laya, where  the  perpetual  snow-line,  as  it  is  termed,  is,  from  a  combina- 
tion of  physical  conditions,  more  elevated  by  4,000  feet  than  on  the 
southern  side  of  the  same  great  range  of  mountains.*  Minor  modifica- 

*  Humboldt  (Fragmens  Asiatiques,  p.  549)  has  given  the  following  table  of  the 
snow-line  on  certain  mountain  ranges  : — 


Mountains. 

Latitude. 

Height  above 
the  Sea. 

Cordillera  of  Quito     .     . 
Bolivia  .     . 
Mexico  .     . 
Himalaya:  — 
Northern  Flank      .     . 
Southern  Flank 
Pyrenees      

0° 
16 
19 

30| 

to      l£c 

31 
43 

S. 
S. 

N. 

N. 
N 

English  Feet. 

15,730 
17,070 
15,020 

16,620 
12,470 
8  950 

42^ 

43 

N 

10  870 

Alps    

45f 

46 

N 

8  760 

49 

491- 

N. 

8  500 

Altai  

49 

51 

N 

6  400 

61 

62 

N 

5  400 

67 

N 

3  800 

M 

70 

70^ 

N 

3  500 

Coast                                 . 

71 

r,      4 

N 

2  340 

<    2 

To  these  may  be  added  the  following  observations : — 


Locality. 

Latitude. 

Height  above 
the  Sea. 

Authority. 

Bolivia      

16°  to  18°  S. 
33°  S. 
40°  to  43°  S. 
54°  S. 
57°  N. 
74°  30'  N. 

English  Feet. 
16,263 
14,500 
6,000 
3,750 
5,308 
590 

Pentland. 

Gillies. 
Fitzroy. 
King. 
Erman. 
Durocher. 

Cordillera  of  Chili  .     . 
Chiloe  

Terra  del  Fuego     .     . 
Kamtschatka      .     .     . 
B'aren  Island      .     .     . 

M.  Durocher  (Mdmoire  sur  la  limite  des  neiges  perpdtuelles.     Voyage  de  la  Recher- 


218  GLACIERS. 

tions  of  the  same  kind  are  abundant,  as  also  from  the  influence  of  great 
surfaces  occupied  by  the  sea,  and  from  prevalent  winds  sweeping  over 
it  and  reaching  land ;  thus  producing  marked  elevations  of  the  general 
temperature  above  that  at  which  ice  would  be  common. 

To  obtain  the  snow  reposing  on  the  regions  or  elevated  mountains, 
piercing  through  the  space  above  noticed  into  those  portions  of  our 
atmosphere  where  the  temperature  is  such  that  snow  more  or  less 
encrusts  them  during  the  whole  of  the  various  climatal  changes  of  the 
year,  we  have  to  infer  evaporation  from  the  land  and  water,  modified 
according  to  their  various  states,  surfaces,  and  localities,  sufficient  to 
afford  the  needful  falls  of  water  in  this  form.  And  this  would  be  re- 
quired up  to  any  altitude  on  which  we  find  the  snow,  unless  we  suppose 
any  change  of  relative  level  of  the  regions  or  of  mountains,  so  that  they 
were  elevated,  after  the  production  and  deposit  of  the  snow  at  minor 
altitudes,  into  atmospheric  heights  where  evaporation  did  not  carry  the 
watery  vapour  for  the  production  of  snow. 

From  the  polar  regions,  where  we  find  such  a  great  amount  of  cli- 
matal change,  that  the  influence  of  the  sun,  as  far  as  it  can  be  there 
experienced,  is  uninterrupted,  or  nearly  so,  during  one  half  of  the  year, 
and  unfelt  during  the  remainder,  to  the  tropical  regions,  where  portions 
of  mountain  masses  may  rise  so  high  into  the  atmosphere  as  to  support 
a  covering  of  snow,  there  are  necessarily  great  variations  of  tempera- 
ture, the  latter  becoming  less  changeable,  as  a  whole,  in  the  equatorial 
portions  of  the  earth. 

When  attention  is  directed  to  the  effects  arising  from  these  variations 
of  temperature,  it  is  found  that  the  production  of  glaciers  stands  some- 
what prominently  forward  among  those  which  have  a  geological  bear- 
ing. In  the  Alps,  Europeans  have  been  long  familiar  with  the  elongated 
masses  of  ice,  so  called,  descending  from  the  regions  of  snows,  through 
ravines  and  rocky  depressions  of  various  forms,  even  into  fertile  valleys, 
where  ripening  crops  and  ice  may  be  almost  in  contact  under  the  heats 
of  summer  and  autumn,  in  latitudes  ranging  from  44°  to  47°.  De  Saus- 
sure,  though  not  the  first  to  examine  them,  by  the  charm  of  his  writings 
directed  no  little  attention  to  glaciers,  and  to  the  effects  produced  by 
them.  Other  authors  have,  at  various  times,  since  described  them  ;  and 
among  those  of  late  years,  M.  Charpentier*  and  M.  Agassizf  have 
written  much  in  support  of  a  particular  hypothesis  as  to  the  mode  in 
which  these  masses  of  ice  moved  outwards  from  the  mountain  heights 
whence  they  originated,  and  as  to  their  former  more  considerable  range 

che,  1845)  places  the  line  of  perpetual  snow  in  the  Arctic  Ocean  in  78°  N.  ;  so  that,  at 
Spitzbergen  (N.  W.  coast),  it  descends  to  the  level  of  the  sea. 

*  "  Essai  sur  les  Glaciers  et  sur  le  Terrain  Erratique  du  Bassin  du  Rhone,"  1841. 
Lausanne. 

f  "  Etudes  sur  les  Glaciers,"  1840.     Neuchatel. 


GLACIERS.  219 

and  extension  than  at  present,  pointing  to  many  circumstances  connected 
with  this  subject,  and  of  geological  value,  though  the  hypothesis  itself 
may  not  be  adopted. 

The  progress  of  researches  respecting  glaciers  and  their  geological 
effects,  affords  a  fair  example  of  the  necessity  of  careful  observation  in 
a  right  direction  ;  so  many  assertions  connected  with  the  mode  of  occur- 
rence and  advance  of  these  masses  of  ice,  upon  which  hypotheses  were 
based,  having  been  found,  upon  actual  investigation,  unsupported  by 
facts.  Though  this  has  been  the  case,  many  observations  have,  from 
time  to  time,  been  recorded,  which  have  borne  the  test  of  careful  inves- 
tigation ;  and  no  one  would  appear  more  desirous  of  admitting  the  value 
and  importance  of  real  additions  to  our  information  on  this  subject,  than 
Professor  James  Forbes,  to  whom  so  much  of  our  present  knowledge  of 
the  Alpine  glaciers  is  due.* 

A  glacier  commences  near  the  line  of  perpetual  snow,  but  lower  some- 
what than  that  on  the  adjacent  ground.  "  There  is  often  a  passage, 
nearly  insensible,  from  perfect  snow  to  perfect  ice  ;  at  other  times,  the 
level  of  the  superficial  snow  is  well  marked,  and  the  ice  occurs  beneath 
it.  No  doubt  the  transition  is  effected  in  this  way  : — the  summer's 
thaw  percolates  the  snow  to  a  great  depth  with  water ;  the  frost  of  the 
succeeding  winter  penetrates  far  enough  to  freeze  it  at  least  to  the  thick- 
ness of  one  year's  fall,  or,  by  being  repeated  in  two  or  more  years,  con- 
solidates it  more  effectually,  "f  The  part  of  a  glacier,  where  the  surface 
begins  to  be  annually  renewed  by  the  unmelted  accumulation  of  each 
winter,  is  commonly  known  as  neve,  and  true  stratification  has  been  here 
recognised  by  De  Saussure  and  other  writers.  Professor  Forbes  agrees 
with  M.  de  Charpentier^  in  thinking  that  this  stratification  becomes 
entirely  obliterated  as  the  neve  passes  into  complete  ice.§  The  crevasses, 
or  great  fissures,  in  the  neve  are  considered  to  differ  from  those  lower 
down  the  glacier  in  their  greater  width  and  irregularity,  and  the  caverns 
in  it  to  be  more  extensive  and  singular  in  their  forms,  from  the  greater 
facility  with  which  the  neve  is  thawed  and  water-worn. 

*  See  his  Travels  through  the  Alps  of  Savoy  and  parts  of  the  Pennine  Chain,  with 
observations  oh  the  Phenomena  of  Glaciers,  2d  edit.,  Edinburgh,  1845  ;  and  his  papers 
printed  in  the  Philosophical  Transactions,  for  1846. 

f  Forbes'  Travels  through  the  Alps  of  Savoy,  2d  edit.,  p.  31. 

j  For  his  views  respecting  glaciers,  consult  M.  de  Charpentier's  Essai  sur  les  Glaciers 
et  sur  le  Terrain  Erratique  du  Bassin  du  Rhone.  Lausanne,  1841. 

g  "  The  granulated  structure  of  the  neve*  is  accompanied  with  the  dull  white  of  snow 
passing  into  a  greenish  tinge,, but  rarely,  if  ever,  does  it  exhibit  the  transparency  and 
hue  of  the  proper  glacier.  The  deeper  parts  are  more  perfectly  congealed,  and  the 
bands  of  ice,  which  often  alternate  with  the  hardened  snow,  are  probably  due  to  the 
effect  of  thaw  succeeding  the  winter  coating,  or  any  extraordinary  fall.  On  exposed 
summits,  where  the  action  of  the  sun  and  the  elements  is  greater,  the  snow  does  not  lie 
so  long  in  a  powdery  state,  and  the  exposed  surface  becomes  completely  frozen." 
Forbes'  Travels  through  the  Alps,  &c.,  2d  edit.,  p.  32. 


220  GLACIERS. 

Further  down  the  valley,  or  ravine,  in  which  the  glacier  finds  its  way, 
much  will  necessarily  depend,  as  to  its  form  and  appearance,  upon  the 
general  character  of  the  ground  traversed.  The  ice  changes  its  cha- 
racter :  it  is  not  like  that  produced  by  the  freezing  of  still  water  in  a 
lake,  but  "  laminae,  or  thin  plates  of  compact  transparent  blue  ice,  alter- 
nate, in  most  parts  of  every  glacier,  with  laminae  of  ice  not  less  hard 
and  perfect,  but  filled  with  countless  air-bubbles,  which  give  it  a  frothy 
semi-opaque  look."*  "  The  alternation  of  bands,  then,  is  marked  by 
blue  and  greenish-blue  or  white  curves,  which  are  seen  to  traverse  the 
ice  throughout  its  thickness  whenever  a  section  is  made.  It  is,  there- 
fore, no  external  accident ;  it  is  the  internal  structure  of  a  glacier,  and 
the  only  one  which  it  possesses,  and  may  be  expected  to  throw  light 
upon  the  circumstances  and  formation  of  these  masses. "f 

Below  the  neve,  the  glacier  commonly  finds  its  way,  amid  various  de- 
pressions of  different  forms,  to  the  lower  ground,  far  beneath  the  line 
which  marks  the  usually  constant  presence  of  snow  throughout  the  year. 
The  accompanying  view  (fig.  84)  of  Mont  Blanc,  taken  from  the  Breven, 
a  mountain  rising  high  above  the  valley  of  Chamonix,  which  separates 
the  BreVen  from  Mont  Blanc,  will  give  a  better  idea  of  the  passage 
of  the  glacier  downwards  into  the  lower  valley,  than  a  verbal  descrip- 
tion, and  more  especially  as  the  altitude  and  position  of  the  Breven 

*  "This  peculiar  structure,"  continues  Professor  Forbes,  "which  gives  to  glacier- 
ice  its  extreme  brittleness,  (which  makes  the  formation  of  steps  with  a  hatchet  a  very 
easy  task  compared  to  what  it  would  be  in  common  ice,)  may  be  compared  to  what  the 
geologists  call  the  slaty  cleavage  of  many  rocks,  rather  than  to  stratification,  properly 
so  called.  The  distinction  is  important,  and  amounts  to  this  :  that  strata  are  deposited 
in  succession,  and  owe  their  form  and  separation  to  that  circumstance  only ;  whereas, 
slaty  cleavage,  or  structural  planes,  occur  in  rocks,  and,  in  many  bodies,  wholly  irre- 
spective of  stratification  or  deposition,  and  may  be  communicated  to  a  mass  after  com- 
plete or  partial  consolidation."  Forbes'  Travels  through  the  Alps,  &c.,  2d  edit.  p.  27. 

f  Forbes'  Travels  through  the  Alps,  &c.,  2d  edit.,  p.  28.  It  is  remarked,  respecting 
this  structure,  that  it  is  the  consequence  of  the  viscous  condition  of  the  mass  and  its 
movement.  It  is  observed  that  it  "has  all  the  appearance  of  being  due  to  the  forma- 
tion of  fissures  in  the  aerated  ice  or  consolidated  ne've',  which  fissures  having  been  filled 
with  water  drained  from  the  glacier,  and  frozen  during  winter,  have  produced  the 
compact  blue  bands  ;"  (p.  372).  Professor  Forbes  considers,  that,  as  the  viscous  mass 
moves  onward,  the  central  parts  faster  than  the  sides,  these  fissures,-  filled  with  ice, 
take  a  more  horizontal  position  in  the  general  mass,  with  such  modifications  as  may  be 
expected  on  the  sides  and  bottom  where  the  friction  is  greatest,  accompanying  his 
remarks  by  ideal  sections  of  glaciers  and  real  sections  of  viscous  bodies  experimented 
upon  for  illustration.  He  observes,  "  that  this  ribboned  structure  follows  a  very  pecu- 
liar course  in  the  interior  of  the  ice,  of  which  the  general  type  is  the  appearance  of  a 
succession  of  oval  waves  on  the  surface,  passing  into  hyperbolas,  with  the  greater  axis 
directed  along  the  glacier.  That  this  structure  is  also  developed  throughout  the  thick- 
ness of  a  glacier,  as  well  as  from  the  centre  to  the  side,  and  that  the  structural  sur- 
faces are  twisted  round  in  such  a  manner,  that  the  frontal  dip,  as  we  have  called  it,  of 
the  veins,  as  exhibited  on  a  vertical  plane  cutting  the  axis  of  a  glacier,  occurs  at  a 
small  angle  at  its  lower  extremity,  and  increases  rapidly  as  we  advance  towards  the 
origin  of  the  glacier."  (p.  372.) 


GLACIERS. 


221 


itself  prevents  that  foreshortening  and  less  instructive  view  obtained 
from  beneath. 

As  the  great  icy  mass  descends  from  the  region  of  the  neve  to  the 
lower  ground,  -the  crevasses  vary  much  in  length  and  breadth,  sometimes 


222  GLACIERS. 

extending  across  the  whole  glacier,*  and  this,  as  might  be  expected, 
according  to  the  character  of  the  surface  on  which  it  may  repose.  As 
it  descends  into  warmer  regions,  the  glacier  is  necessarily  exposed  to 
the  influence  of  higher  temperature,  and  if  it  did  not  obtain  the  needful 
supply  from  above,  it  would  there  diminish  in  bulk  and  disappear.  As 
this  supply  varies,  the  extension  of  a  glacier  will  correspond  with  the 
kind  of  seasons  experienced,  so  that  it  may  descend  further  into  the 
lower  valleys  at  one  time  than  another  ;f  and  thus  its  actual  amount  of 
protrusion  into  a  valley  may  depend,  for  the  time,  upon  effects  pro- 
duced through  many  seasons,  and  be  liable  to  frequent  change. 

The  turbid  waters,  rushing  out  from  beneath  the  glaciers  of  the  Alps, 
will  be  familiar  to  all  who  have  visited  those  mountains,  as  also  the 
caverns  of  ice  through  which  these  waters  commonly  find  their  way 
when  they  are  most  abundant.  With  respect  to  such  waters,  Professor 
Forbes  has  pointed  out  that  they  may  not  only  be  due  to  the  ice  melted 
by  contact  with  the  rocks  on  which  it  moves,  to  the  fall  of  rain  upon 
the  ice  drained  by  the  glacier  valley,  in  the  season  when  rain  falls,  and 
to  the  waste  of  the  glacier  itself  by  the  sun  and  rain,  but  also  to  the 
natural  springs  rising  from  beneath  the  ice,  as  in  any  other  locality. J 

With  respect  to  the  cause  producing  the  motion  of  glaciers,  different 

*  In  the  account  of  his  passage  over  the  Col  de  Ge"ant,  Professor  Forbes  mentions  an 
immense  chasm  or  crevasse,  extending  wholly  across  a  glacier  in  the  descent  on  the 
Chamonix  side,  and  at  least  600  feet  in  width.  "It  terminated  opposite  to  the  preci- 
pices of  the  Aiguille  Noire  in  one  vast  enfoncement  of  ice,  bounded  on  the  hither  side  by 
precipices  not  less  terrible."  Travels  through  the  Alps,  &c.,  p.  238. 

f  Among  the  numerous  examples  of  the  varied  extension  and  volume  of  glaciers 
known  in  modern  times,  there  would  appear  none  more  illustrative  than  that  of  the 
Brenva,  on  the  Italian  side  of  Mont  Blanc.  In  1818  it  attained  a  height  different  from 
that  found  by  Professor  Forbes,  in  1842,  of  at  least  300  feet,  as  proved  by  that  of  a 
rock,  upon  which  a  well-known  chapel  (Chapelle  de  Berrier)  was  placed,  which,  with 
the  rock  on  which  it  stood,  was  heaved  and  fissured  by  the  rise  of  the  ice.  This  great 
increase  of  volume,  and  its  decrease  in  the  24  years,  is  well  attested.  The  Professor 
remarks,  that  the  mean  temperature  for  the  five  years  preceding  1818,  when  the  glacier 
was  thus  of  such  increased  volume,  presented  no  marked  change,  the  mean  temperature 
at  Geneva  being  for  that  time  7-61  Reaumur  (49-12°  Fahr.) ;  the  mean  for  the  last 
40  years,  in  the  same  town,  being  7-75°  (49-44°  Fahr.)— Travels,  &c.,  p.  205. 

J  With  respect  to  the  waste  of  the  glacier  by  the  sun  and  rain,  Professor  Forbes  re- 
marks, that  it  is  "a  most  important  item,  and  which  constitutes  the  main  volume  of 
most  glacier  streams,  except  in  the  depth  of  winter.  It  is  on  this  account  that  the 
Rhine  and  other  great  rivers,  derived  from  Alpine  sources,  have  their  greatest  floods 
in  July,  and  not  in  spring  or  autumn,  as  would  be  the  case  if  they  were  alimented  by 
rain-water  only.  On  the  same  account,  the  mountain  torrents  may  be  seen  to  swell 
visibly,  and  roar  more  loudly,  as  the  hotter  part  of  the  day  advances,  to  diminish 
towards  evening,  and  in  the  morning  to  be  smallest."  "Winter  is  a  long  night  amongst 
the  glaciers.  The  sun's  rays  have  scarcely  power  to  melt  a  little  of  the  snowy  coating 
which  defends  the  proper  surface  of  the  ice;  the  suin-rfk-i.-il  waste  is  next  to  nothing, 
and  the  glacier  torrent  is  reduced  to  its  narrowest  dimensions." — Travels  through  the 
Alps  of  Savoy,  &c.,  2d*edit.,  pp.  20,  21. 


MOVEMENT    OF    GLACIERS.  223 

views  have  been  taken:*  Professor  James  Forbes  considers  it  as  "con- 
vincingly proved,f  that  the  motion  of  a  glacier  varies  not  only  from 
one  season  to  another,  but  that  it  has  definite  (though  continuous) 
changes  of  motion,  simultaneous  throughout  the  whole,  or  a  great  part 
of  its  extent,  and  therefore  due  to  some  general  external  change;"  and 
that  "this  change  has  been  shown  to  be  principally  or  solely  the  effect 
of  the  temperature  of  the  air,  and  the  conditions  of  wetness  or  dryness 
of  the  ice."J  With  regard  to  the  movement  itself,  the  Professor  has 
pointed  out  "that  the  ice  does  not  move  as  a  solid  body, — that  it  does 
not  slide  down  with  uniformity  in  different  parts  of  its  section, — that 
the  sides,  which  might  be  imagined  to  be  most  completely  detached 
from  their  rocky  walls  during  summer,  move  slowest,  and  are,  as  it 
were,  dragged  down  by  the  central  parts. "§  His  theory  is,  that  "a 
glacier  is  an  imperfect  fluid,  or  a  viscous  body,  which  is  urged  down 
slopes  of  a  certain  inclination  by  the  mutual  pressure  of  its  parts. "|| 
He  does  not,  however,  "doubt  that  glaciers  slide  on  their  beds,  as  well 
as  that  the  particles  of  ice  rub  over  one  another,  and  change  their 
mutual  positions. "T 

*  The  chief  of  these  views  will  be  found  in  the  works  of  MM.  de  Saussure,  De  Char- 
pentier,  Agassiz,  Elie  de  Beaumont,  Mr.  William  Hopkins,  and  of  Professor  James 
Forbes.  In  the  latter  they  will  be  seen  discussed  in  much  detail,  and  the  Professors 
own  views  advocated,  especially  in  his  Travels  through  the  Alps  of  Savoy,  &c.,  and  in 
chap.  xxi.  (entitled  "An  attempt  to  explain  the  leading  Phenomena  of  Glaciers,")  and 
in  his  papers  entitled  "Illustrations  of  the  Viscous  Theory,"  published  in  the  Philo- 
sophical Transactions  for  1846.  A  very  detailed  account  of  the  works  and  views  re- 
specting glaciers  will  also  be  found  in  the  Histoire  des  Progres  de  la  Geologic,  de  1834- 
1845,  by  the  Vicomte  d'Archiac,  Paris,  1847. 

|  Travels  through  the  Alps  of  Savoy,  &c.,  and  alluding  to  chap.  vii. 

J  Ib.,  chap,  xxi.,  p.  363. 

\  Ib.  p.  363.  As  to  the  different  rates  of  motion  of  a  glacier,  it  is  observed  that  a 
glacier,  "like  a  stream,  has  its  still  pools  and  its  rapids.  Where  it  is  embayed  by 
rocks  it  accumulates — its  declivity  diminishes,  and  its  velocity,  at  the  same  time.  When  it 
passes  down  a  steep,  or  issues  by  a  narrow  outlet,  its  velocity  increases.  The  central 
velocities  of  lower,  middle,  and  higher  regions  of  the  Mer  de  Glace  are — 1-398,  -574, 
and  -925 ;  and  if  we  divide  the  length  of  the  glacier  into  three  parts,  we  shall  find  these 
numbers  for  its  declivity,  15°,  4£°,  and  8°." — Forbes,  Travels,  &c.,  p.  371. 

j|  Ib.,  p.  365.  It  would  be  somewhat  out  of  place  in  this  work  to  enter  more  fully 
into  the  theory  of  glacier  movements.  Respecting  the  theory  of  the  viscous  condition 
of  a  glacier,  Professor  Forbes  alludes  to  its  spreading  as  a  viscous  body  would  do,  when 
a  glacier  passes  out  of  a  narrow  gorge  into  a  wide  valley,  stating  that  this  fact  had 
been  first  brought  prominently  forward  by  M.  Rendu,  now  Bishop  of  Annecy  (Travels, 
p.  367).  M.  Rendu  (The'orie  des  Glaciers  de  la  Savoie,  Chambery,  1840),  divides 
glaciers  into  glaciers  reservoirs  and  glaciers  d1  ecoulement,  the  former  in  the  high  regions, 
and  the  latter  descending  into  the  lower  valleys.  He  estimates  the  height  of  the  sepa- 
ration between  the  two  in  Savoy  at  2,923  metres  (9,590  English  feet).  He  points  to  the 
accumulation  of  snow  in  the  higher  regions,  the  rain,  when  it  falls  there,  freezing,  and 
to  the  feeding  of  the  lower  glaciers  by  the  descent  of  this  snow  and  ice. 

^[  "  But,"  he  adds,  "I  maintain  that  the  former  motion  is  caused  by  the  latter,  and 
that  the  motion  impressed  by  gravity  upon  the  superficial  and  central  parts  of  a  glacier 
(especially  near  its  lower  end),  enables  them  to  pull  the  lateral  and  inferior  parts  along 


224  GLACIER    MORAINES. 

.  The  movement  of  glaciers  is  important  as  regards  the  transportal  of 
mineral  substances,  inasmuch  as  by  it  they  bear  onwards  upon  their 
surfaces  any  fragments  of  rock  that  may  fall  upon  them  from  the 
heights  amid  which  they  pass  ;  thrust  before  them  any  loose  accumula- 
tions of  blocks,  gravel,  sand,  and  earth,  which  may  oppose  their  course, 
and  even  break  off  portions  of  rocks  where  the  resistance  of  the  latter 
is  less  than  the  force  of  the  glacier,  divisional  planes,  such  as  joints  and 
cleavage,  with  the  natural  bedding  of  rocks,  often  rendering  the  mass 
of  such  rocks  less  resistant  than  it  would  otherwise  be.  The  observer, 
accustomed  often  to  see  the  steep  cliffs  of  many  a  mountain  region 
covered  towards  their  bases  by  the  debris  detached  by  atmospheric  in- 
fluences from  above,  and  especially  in  climates  or  regions  where  frosts 
and  thaws  often  alternate,  would  readily  expect  these  fragments  to 
move  onwards  with  the  glacier  on  the  edges  of  which  they  may  fall. 
Instead,  therefore,  of  accumulating  in  a  talus  of  debris,  as  can  be  well 
studied  in  the  more  mountainous  parts  of  the  British  Islands,  the  mass 
of  fragments  moves  slowly  onwards,  and  the  protection  from  atmospheric 
influences  afforded  by  this  talus  to  the  solid  rocks  beneath  it  (in  some 
mountain  regions  collectively  very  considerable),  is  removed  precisely 
in  localities  where  the  vicissitudes  of  climate  are  often  so  great  that  it 
can  be  the  least  spared. 

The  blocks  and  smaller  fragments  (necessarily  very  variable  in  form 
and  volume,  according  to  the  character  of  the  overhanging  rocks,  and 
the  amount  of  their  decomposition  anterior  to  their  fall),  and  thus 
strewed  upon  the  glaciers,  are  well  known  as  moraines.*  These  mo- 
raines also  necessarily  differ  in  general  volume,  according  to  the  amount 
of  matter  which  may  be  detached  from  the  heights  above  the  glacier, 
and  the  rate  of  movement  of  the  glacier  itself  on  the  sides  adjoining 
the  sources  of  the  detached  fragments.  Two  lines  of  moraine  will  mark 
the  edges  of  a  glacier,  should  the  heights  on  either  side  of  it  afford  the 
needful  supply,  as  also  a  mass  of  rock  rising  through  a  glacier,  should 
it  also  afford  fragments,  as  has  been  pointed  out  by  Professor  Forbes. 
When  two  or  more  streams  of  glaciers  unite,  each  bearing  its  two,  or 
even  as  we  have  seen,  three  lines  of  rock  fragments,  the  union  will  so 

with  them.  One  proof,  if  I  mistake  not,  of  such  an  action  is,  that  a  deep  current  of 
water  flows  under  a  smaller  declivity  than  a  shallow  one  of  the  same  fluid.  And  tins 
consideration  derives  no  slight  confirmation,  in  its  application  to  glaciers,  from  a  cir- 
cumstance mentioned  by  M.  Elie  de  Beaumont,  which  is  so  true  that  one  wonders  that 
it  has  not  been  more  insisted  on — namely,  that  a  glacier,  where  it  descends  into  a 
valley,  is  like  a  body  pulled  asunder  or  stretched,  and  not  a  body  forced  on  by  superior 
pressure  alone"  (p.  370).  In  a  note  to  this  passage,  the  Professor  remarks,  "that  a 
state  of  universal  distension,  or  a  state  of  universal  compression,  is  equally  incom- 
patible with  the  existing  phenomena  of  most  glaciers,  and  that  compression  in  some 
parts  and  distension  in  others  are  plainly  indicated  by  their  natural  features." 

*  This  name  has  become  common  with  us  from  the  works  of  De  Saussure  and  others 
writing  in  French.  Guffer  is  the  German  term  for  them. 


GLACIER    MORAINES. 


225 


dispose  of  the  lines  as  to  form  a  less  number  for  the  remaining  course 
of  the  glacier,  as  in  fig.  85,  where  the  glaciers  coming  down  the  valleys 


Fig.  85. 


A  and  B,  and  uniting  the  four  moraines,  two  on  the  sides  of  each 
glacier,  become  three  (#),  (£),  (<?),  by  the  union  of  the  lateral  moraines 
2  and  3  into  a  central  moraine  (b).  Various  other  unions,  easily 
imagined,  are  produced,  as  minor  contribute  to  main  glaciers.  A  great 
central  moraine  may  be  established  by  the  junction  of  two  long  lines  of 
glacier  sides,  unbroken  for  a  considerable  distance,  and  upon  which  a 
great  fall  of  fragments  may  take  place,  while  the  opposite  sides  may  be 
marked  with  slighter  lines  of  moraine,  derived  from  tributaries  receiving 
a  less  amount  of  fragments. 

Fig.  86. 


The  above  view  (fig.  86),  representing  the  upper  part  of  the  glacier 

15 


GLACIER    MORAINES. 

of  the  Aar,*  well  shows  the  lines'of  moraine  coming  down  from  the 
glacier  of  Finsteraarhorn,  on  the  left,  and  from  that  of  the  Lauteraar- 
hbrner,  on  the  right.  It  also  illustrates  the  formation  of  a  single  line 
of  moraine  in  the  centre,  by  the  union  of  the  two  lateral  moraines  of 
the  glaciers  above  noticed.  Examples  are  also  seen  of  the  mushroom- 
like  appearance  produced  by  the  unequal  melting  of  the  surface  of  a 
glacier,  so  that  protection  being  afforded,  as  long  since  pointed  out  by 
De  Saussure,  by  a  block  of  rock  (particularly  if  it  has  so  fallen  on  the 
glacier  as  to  rest  in  a  tabular  manner),  the  ice  beneath  has  not  dis- 
appeared so  rapidly  as  around  it,  and  thus  the  block  is  raised  upon  a 
stem  of  ice.  Some  of  the  blocks  thus  supported  are  very  large,  f  It 
is,  in  the  same  manner,  to  the  protection  from  the  sun  and  rain  afforded 
to  the  ice  beneath  by  the  mass  of  the  moraine,  that  it  often  rises  above 
the  ice.J 

The  next  view§  (fig.  87),  of  the  upper  part  of  the  glacier  of  Zermatt, 
also  shows  the  effects  produced,  as  regards  moraines,  by  the  union  of 
glaciers.  On  the  left,  the  lines  of  moraine  are  derived  from  the  glacier 
of  Monte  Rosa  and  of  the  Gornerhorn,  and  the  lateral  moraine  of  the 
foot  of  the  Riffelhorn  with  the  great  moraine  of  the  Breithorn  are  seen. 
On  the  right  are  the  glaciers  of  the  Little  Cervin  and  of  the  Furke-nue, 
and  the  crevasses  across  the  united  glaciers  are  well  exhibited  in  front, 

*  Reduced  from  a  view  in  the  Etudes  sur  les  Glaciers,  by  Agassiz.    Neuchatel,  1840. 

f  A  large  one,  observed  by  Professor  Forbes,  in  1842,  is  represented  in  his  Travels 
through  the  Alps,  &c.,  pi.  1,  and  he  gives  the  following  instructive  account  of  it: — "There 
lies  on  the  ice  a  very  remarkable  flat  block  of  granite,  which  particularly  attracted  my 
attention  on  my  first  visit  in  1842  to  that  part  of  the  glacier.  It  is  a  magnificent  slab, 
of  the  dimensions  of  23  feet  by  17,  and  about  3£  in  thickness.  It  was  then  easily 
accessible,  and  by  climbing  upon  it  and  erecting  my  theodolite,  I  made  observations  on 
the  movement  of  the  ice ;  but  as  the  season  advanced  it  changed  its  appearance  re- 
markably. In  conformity  with  the  known  fact  of  the  waste  of  the  ice  at  its  surface, 
the  glacier  sunk  all  round  the  stone,  while  the  ice  immediately  beneath  it  was  pro- 
tected from  the  sun  and  rain.  The  stone  thus  appeared  to  rise  above  the  level  of  the 
glacier,  supported  on  an  elegant  pedestal  of  beautifully  veined  ice.  Each  time  that  I 
visited  it,  it  was  more  difficult  of  ascent,  and  on  the  6th  of  August,  the  pillar  of  ice  was 
thirteen  feet  high,  and  the  broad  stone  so  delicately  poised  on  the  summit  of  it  (which 
measured  but  a  few  feet  in  any  direction),  that  it  was  almost  impossible  to  guess  in 
what  direction  it  would  ultimately  fall,  although  by  the  progress  of  the  thaw,  its  fall 
in  the  course  of  the  summer  was  certain.  During  my  absence  in  the  end  of  August,  it 
slipped  from  its  support,  and  in  the  month  of  September  it  was  beginning  to  rise  on  a 
new  one,  whilst  the  unmelted  base  of  the  first  was  still  very  visible  on  the  glacier." 
(p.  92.) 

J  The  glacier  cones,  as  they  are  called,  are  accounted  for  on  the  same  principle  of 
protection  from  the  influence  of  the  sun,  sand  washed  by  rain-water  into  cavities  on 
the  glacier  finally  so  accumulating  that  it  prevents  the  melting  of  the  ice  beneath  at 
the  rate  experienced  around,  so  that  the  sand  still  remaining  on  the  ice,  the  latter  takes 
the  form  of  a  cone  with  a  sandy  covering.  They  have  been  found  20  to  30  feet  in 
height,  and  80  to  100  feet  in  circumference. — Agassiz,  Etudes  sur  les  Glaciers,  chap. 
x.,  and  Forbes,  Travels,  &c.,  chap.  ii.  p.  26. 

g  Also  taken  from  the  Etudes  sur  les  Glaciers,  by  Agassiz. 


GLACIER    MORAINES. 


227 


as  also  the  rise  of  the  ice  above  the  side  of  the  glacier,  showing  that 
the  blocks  and  other  rock  fragments,  there  borne  onwards,  would  have 
a  tendency  to  fall  over  and  accumulate  in  a  lateral  moraine,  off  the  ice, 
and  upon  the  adjoining  lower  ground. 

Fig.  87. 


If  the  rate  of  movement  of  a  glacier  depends  upon  the  slope  and  form 
of  the  subjacent  and  boundary  rocks,  all  other  conditions  being 
equal,*  we  should  expect  it  to  vary  very  materially  in  the  course  of  the 
same  glacier,  and  in  different  glaciers.  The  very  careful  investigations 
of  Professor  James  Forbes  have  proved  the  correctness  of  the  view 
taken  by  M.  Rendu,f  that  the  central  portions  move  faster  than  the 
lateral,^  so  that  the  blocks  and  fragments  of  the  medial  lines  of  moraine 

*  When  the  rates  of  advance  of  different  glaciers  are  compared  with  the  slopes  on 
which  they  move,  it  is  very  essential  to  take  all  other  conditions  into  account,  a  pre- 
caution which  does  not  appear  to  have  been  always  adopted. 

f  The'orie  des  Glaciers  de  la  Savoie,  p.  63. 

J  Travels  through  the  Alps  of  Savoy,  &c.,  chap,  vii.,  entitled  "  Account  of  Experi- 
ments on  the  Motion  of  the  Ice  of  the  Mer  de  Glace  of  Chamouni."  The  means  adopted 
were  of  an  order  to  insure  success.  The  Professor  selected  a  point  on  the  ice,  and  de- 
termined its  position  with  respect  to  three  fixed  co-ordinates,  having  reference  to  the 
fixed  objects  around.  He  found,  after  the  observations  of  four  days,  that  the  ice  on 
which  his  instrument  was  placed  moved  during  each  24  hours  at  the  rate  of 
15-2  :  —  16-3  :  —  17-5  :  —  174  inches, 


228   CENTRAL  PORTIONS  OF  GLACIERS  MOVE  FASTEST. 

descend  further  in  less  time  than  those  on  the  sides,  even  when  the 
latter  are  not  thrown  over,  and  left  in  the  ground  bounding  the  sides  of  a 
glacier.  From  the  nature  of  the  transport,  any  enormous  mass  of  rock, 
detached  from  a  height  ahove  a  glacier,  will  move  as  readily  onwards 
as  a  small  fragment ;  indeed,  from  its  protecting  influence  against  the 
action  of  the  sun  and  rain,  it  would  tend  to  preserve  the  ice  beneath  far 
more  effectually,  considering  the  subject  generally ;  not,  however,  for- 
getting that  from  the  unequal  melting  of  the  ice  around  and  partly  be- 
neath, it  may  be  tilted  off,  not  only  into  a  crevasse,  where  it  might 
advance  with  the  general  march  of  the  glacier,  but  also  into  some  situa- 
tion where  its  progress  may,  for  a  time  at  least,  be  arrested.  Some  of 
the  blocks  observed  on  the  glaciers  are  of  very  considerable  dimensions. 

a  variation  which  he  considered  due  to  the  increasing  heat  of  the  weather.  On  trying 
the  rate  of  nocturnal  motion,  as  compared  with  the  diurnal,  the  Professor  found 
exactly  one-half,  the  night  having  been  cold.  The  general  motion  was  not  by  fits  of 
advance  and  halts,  but  orderly  and  continuously.  By  well-considered  arrangements, 
he  also  found  that  the  somewhat  common  opinion  of  the  sides  of  a  glacier  moving  faster 
than  the  centre  was  incorrect,  and  that,  on  the  contrary,  their  motion  was  slower. 
From  the  29th  June  to  the  1st  July  (1842),  while  the  sides  of  the  part  of  the  Mer  de 
Glace  experimented  upon,  moved  at  a  rate  of  17-5  inches  for  each  24  hours,  the  centre 
advanced  27*1  inches.  Other  experiments  on  other  parts  of  the  glacier  led  to  similar 
results.  It  was  found  that  "  (1)  The  motion  of  the  higher  parts  of  the  Mer  de  Glace 
is,  as  a  whole,  slower  than  that  of  its  lower  portion,  but  the  motion  of  the  middle  region 
is  slower  than  either.  (2)  The  Glacier  de  Gdant  moves  faster  than  the  Glacier  de  Le*- 
chaud.  (3)  The  centre  of  the  glacier  moves  faster  than  the  sides.  (4)  The  difference 
of  motion  of  the  centre  and  sides  of  the  glacier  varies  with  the  season  of  the  year,  and  at 
different  parts  of  the  length  of  the  glacier ;  and  (5)  The  motion  of  the  glacier  generally 
varies  with  the  season  of  the  year  and  the  state  of  the  thermometer."  Subsequent  in- 
vestigations enabled  Professor  Forbes  to  state  (Philosophical  Transactions,  1846,  "  Illus- 
trations of  the  Viscous  Theory  of  Glacier  Motion,"  parts  1,  2,  and  3),  that  the  movement 
of  the  Mer  de  Glace  went  on  continuously  for  17  days,  and  he  gives  a  valuable  table  of 
the  apparent  and  relative  motion  of  45  points,  two  feet  apart,  in  a  line  traversing  the 
axis  of  this  glacier,  in  1844  (p.  171). 

The  motion  of  a  particular  stone,  named  the  Pierre  Platte,  on  the  Mer  de  Glace,  was 
observed  to  be  as  follows : — 

From  the  17th  September,  1842,  to^!2th  September,  1843,  the 

advance  in  360  days  was 256-8    feet. 

Reduced  to  the  year  of  365  days 260-4      " 

Mean  daily  motion 8-56  inches. 

From  12th  September,  1843,  to  19th  August,  1844,  342  days  .  270      feet. 

Proportional  motion  for  865  days 288-3      " 

Mean  daily  motion .        .        .  9-47  inches. 

There  are  also  important  tables  of  the  motion  observed  at  two  stations  on  the  Glacier 
des  Bois  (one  observed  from  the  2d  October,  1844,  to  the  21st  November,  1845,  and  the 
other  from  4th  December,  1844,  to  21st  November,  1845) ;  and  at  two  stations  on  the 
Glacier  des  Bossons  (one  from  20th  November,  1844,  to  22d  November,  1845,  and  the 
other  from  2d  October,  1844,  to  22d  November,  1845),  showing  the  variable,  but  con- 
tinued progress,  of  these  glacfers  during  the  intervals.  Among  the  results,  it  appeared 
that  "in  both  glaciers  the  summer  motion  exceeds  the  winter  motion  in  a  greater  pro- 
portion as  the  station  is  lower,  that  is,  exposed  to  more  violent  alternations  of  heat  and 
cold." 


LARGE    BLOCKS    OF    ROCKS    CARRIED    B.Y    GLACIERS.      229 

Professor  Forbes  mentions  having  seen  one  on  the  ice  of  the  glacier  of 
Viesch,  in  the  Vallais,  nearly  100  feet  long,  and  40  or  50  feet  high.* 

While  thus  fragments  of  all  dimensions,  and  in  great  abundance,  find 
their  way  with  an  unequal  rate  of  movement,  according  to  their  position 
on  a  glacier,  to  lower  levels,  numerous  others  are  arrested  in  their  pro- 
gress, tilted  off,  and  left  on  the  ground  adjoining  its  sides,  should  cir- 
cumstances permit.  When  a  glacier  so  changes  its  volume  as  to  occupy 
a  higher  relative  level  at  one  time  than  another,  amid  the  mountain 
depressions  and  ravines  over  and  through  which  it  may  move,  and  the 
conditions  for  leaving  marginal  accumulations  of  rock  fragments  on  the 
outside  of  it  obtain,  such  accumulations,  should  the  ice  afterwards 
decrease  in  volume,  would  remain  to  attest  this  previous  state  of  the 
glacier. f  No  marks  of  this  kind  would  be  left  where  the  sides  of  a 
ravine  or  cliff  were  so  steep  that  the  blocks  could  not  find  rest.  The 
fragments  would  either  rise  or  descend  with  the  glacier,  some  probably 
falling  into  any  space  left  between  the  ice  and  the  wall  of  rock,  and 
open  either  from  a  certain  amount  of  melting  of  the  glacier  at  its  con- 
tact with  the  rock,  or  from  the  passage  of  the  mass  of  ice  along  the 
uneven  front  of  a  cliff,  cavities  of  different  kinds  thus  presenting  them- 
selves. 

From  fragments  of  rock  becoming  jammed  between  the  ice  of  a  gla- 
cier and  its  rocky  walls,  as  cannot  fail  often  to  be  the  case,  and  indeed 
is  well  known,  the  friction  of  these  fragments,  pressed  by  the  great 
force  of  the  glacier,  grooves  and  furrows  the  adjoining  rocks  in  lines 
corresponding  with  their  motion.  Professor  Forbes  gives  the  following 
interesting  view  (fig.  89)  of  the  "Angle,"  Mer  de  Glace,  where  granite 
blocks  are  jammed  in  between  the  ice  and  the  rock,  wearing  "  furrows 
in  the  retaining  wall,  which  is  all  freshly  streaked,  near  the  level  of  the 
ice,  with  distinct  parallel  lines,  resulting  from  this  abrasion.  The  juxta- 
position of  the  power,  the  tool,  and  the  matter  operated  on,  is  such  as 
to  leave  not  a  moment's  doubt  that  such  striae  must  result,  even  if  their 
presence  could  not  be  directly  proved."J  This  friction  alone  would 

*  Travels,  &c.,  p.  46.  A  very  large  granite  block,  also  seen  by  the  Professor  upon 
the  Mer  de  Glace,  in  1842,  is  figured  by  him  in  the  same  work,  p.  57. 

f  Professor  Forbes  (Travels,  &c.,  p.  24)  has  given  a  very  illustrative  section  (fig.  88), 
showing  the  manner  in  which  fragments  (c)  of  rock  may  be  left  by  the  decrease  of  a 


glacier,  and  in  which  a  part  of  a  lateral  moraine  may  fall  into  a  cavity  (a)  between  the 
ice  and  the  boundary  rock,  or  be  left  stranded,  on  an  inclined  shore  (b).  The  section 
of  a  central  moraine  is  seen  at  (d). 

%  Travels,  &c.     The  wood-cut  is  a  reduced  sketch  from  pi.  3,  p.  76. 


230 


ROCKS  GROOVED  AND  SCRATCHED 


tend  to  reduce  the  fragments  to  less  size,  and  even  to  fine  powder. 
Looking  at  the  general  conditions  of  glacier  movements,  the  kind  of 
ground  these  masses  of  ice  pass  over,  and  to  the  introduction  of  frag- 


Fig.  89. 


ments  from  the  sides,  and  even  through  the  crevasses  to  the  bottom,  we 
should  expect  that  the  grooving  and  scratching  would  be  considerable 
on  the  bottom  and  sides,  mingled  with  an  extensive  smoothing  of  sur- 
face, as  if,  in  the  application  of  a  huge  polishing  apparatus,  acting,  as 
a  whole,  with  minor  deviations,  in  one  direction,  harder  grains  were 
strewed  about,  so  that  scratching  as  well  as  polishing  was  effected.* 
This  scratching  and  smoothing  by  glaciers  has  been  chiefly  observed, 
with  reference  to  their  geological  value,  in  modern  times,  though  the 
rounded  and  polished  surfaces  frequently  seen  have  been  long  known 
by  the  name  of  Rockes  Moutonn£e8,  that  assigned  them  by  De  Saussure. 
From  the  general  grinding  of  glaciers  on  their  beds,  the  friction  of 
the  fragments  on  each  other,  and  the  decomposition  of  many  kinds  of 
rock  in  regions  where  the  alternations  of  frost  and  thaw  are  so  common, 
particularly  in  the  warmer  parts  of  the  year,  much  finely  comminuted 

*  Though  the  grooves  are  usually  long,  parallel,  and  polished,  the  minor  scratches 
often  cross  each  other. 


BY    GLACIER    ACTION.  231 

mineral  matter  could  scarcely  fail  to  be  exposed  to  the  action  of  any 
running  water,  finding  its  way  amid  the  glacier,  and  along  its  sides  and 
bottom.*  The  streams  and  rivers  derived  from  glaciers  have  commonly 
a  marked  character,  as  above  noticed,  from  the  quantity  of  fine  mineral 
matter  in  mechanical  suspension.  These  sometimes  fall  into  lakes,  and 
leave  the  fine  sedimentary  matter  behind  them,  as  is  the  case  with  many 
amid  and  on  the  skirts  of  the  Alps,  while  some  have  a  considerable 
course,  as  for  example,  the  Durance  (bearing  the  glacier  waters  of  Monte 
Viso),  and  many  tributaries  of  the  Po,  fed  by  glacier  streams  from  the 
southern  side  of  Mont  Blanc,  and  other  Italian  portions  of  the  high 
Alps  on  either  side  of  that  mountain. 

Independently  of  the  mass  of  fragments  which  may  be  borne  forward 
by  a  glacier,  when  it  is  on  the  increase  outwards,  from  a  fitting  combi- 
nation of  conditions,  it  ploughs  up  the  ground  before  it,  thrusting  for- 
ward the  loose  substances,  no  matter  how  accumulated,  and  with  them, 
should  they  come  in  its  course,  fields,  woods,  and  houses.  We  remember 
seeing  the  Glacier  des  Bois  thus  crushing  and  forcing  all  before  it 
during  its  advance  in  1819.  f  These  accumulations,  to  which  the  trans- 
ported blocks  and  minor  fragments  of  rock  are  being  added,  as  the  ice 
melts,  which  once  supported  and  carried  them  onwards, J  are  known  as 
terminal  moraines,  and  by  their  position  a  glacier  is  inferred  to  be,  for 
the  time,  either  retreating,  advancing,  or  stationary. §  That  glaciers 
advance  and  decrease  is  well  known,  and  this  to  considerable  distances, 
so  that  many  a  terminal  moraine  left  at  one  time,  may  be  again  forced 

*  There  is  much  finely  comminuted  mineral  matter  distributed  over  some  parts  of 
many  Alpine  glaciers.  It  is  sometimes  so  fine  as  to  enter  the  interstices  of  the  more 
porous  ice,  thus  distinguishing  the  latter  from  the  more  compact  bands.  These  "  dirt 
bands,"  as  Professor  Forbes  terms  them,  were  of  much  service  to  him  in  his  examina- 
tion of  the  structure  of  glaciers.  Alluding  to  the  discoloration  from  this  finely  com- 
minuted detritus,  the  Professor  observes,  "  The  cause  of  the  discoloration  was  the  next 
point,  and  my  examination  satisfied  me,  that  it  was  not,  properly  speaking,  a  diversion 
of  the  moraine,  but  that  the  particles  of  earth  and  sand,  or  disintegrated  rock,  which 
the  winds  and  avalanches  and  water-runs  spread  over  the  entire  breadth  of  the  ice, 
found  a  lodgment  in  those  portions  of  the  glacier  where  the  ice  was  most  porous,  and 
that  consequently  the  '  dirt  bands'  were  merely  indices  of  a  peculiarly  porous  veined  struc- 
ture traversing  the  mass  of  the  glacier  in  these  directions" — Travels,  &c.,  p.  163.  Upon 
careful  examination  these  "  dirt  bands"  were  found  to  be  quite  superficial. 

•}•  In  1820  it  attained  its  greatest  known  modern  advance  into  the  valley  of  Chamonix. 

J  Respecting  the  blocks  and  fragments  of  rocks  thus  carried  outwards,  M.  Rendu  has 
remarked  that  some  of  them  can  be  occasionally  traced  to  the  very  commencement  of  a 
glacier. — Theorie  des  Glaciers  de  la  Savoie. 

g  Professor  Forbes,  after  quoting  M.  Venetz  (vol.  i.  of  the  Transactions  of  the  Swiss 
Nat.  Hist.  Society),  as  pointing  out  "  that  passes  the  most  inaccessible,  traversed  now 
perhaps  but  once  in  twenty  years,  were  frequently  passed  on  foot,  sometimes  on  horse- 
back, between  the  eleventh  and  fifteenth  centuries,"  considers  the  evidence  important, 
as  "showing  that  a  very  notable  enlargement  of  these  boundaries  (glacier  boundaries), 
was  consistent  with  the  limits  of  atmospheric  temperature,  which  we  know  that  the 
European  climate  has  not  materially  overpassed  within  historic  times." — Travels,  &c., 
pp.  43,  44. 


232  ADVANCE    AND    DECREASE    OF    GLACIERS. 

forward  at  another,  part  of  it  so  caught  in  the  advance  of  the  ice  as  to 
be  employed  in  grooving  and  scratching  the  solid  rocks  beneath,  then 
bared  and  passed  over  by  the  glacier.  Enormous  blocks*  are  often  left 
by  glaciers  in  their  retreat ;  indeed,  under  such  circumstances,  they 
would  not  only  leave  the  terminal  moraines,  marking  their  extension 
for  the  time,  and  during  periods  of  increase,  but  also  their  whole  load 
of  blocks  and  fragments,  up  to  the  new  limits  of  the  decreased  glaciers. 

Supposing  a  glacier  to  advance  and  retreat,  from  causes  which, 
though  variable  on  the  minor  ^cale,  are  constant  for  considerable  in- 
tervals of  time,  there  would  be  no  small  amount  of  blocks  and  frag- 
ments of  rock,  too  considerable  to  be  borne  onwards  by  river  action, 
left  either  perched  on  various  parts  of  the  mountain  sides,  or  distributed 
over  the  valleys,  within  the  range  of  increase  and  decrease  of  these 
masses  of  ice  in  glacier  regions.  This  great  and  constant  general 
action,  continued  through  a  long  time,  would  scarcely  otherwise  than  very 
considerably  modify  the  state  of  the  area  from  that  original  condition, 
when  the  glaciers  were  first  formed,  even  supposing  no  alteration  in 
the  relative  level,  as  respects  the  sea,  of  the  mountain  masses  amid 
which  they  occur.  Under  this  view,  and  without  inferring  any  altera- 
tion of  general  climate,  further  than  that  brought  about  by  the  accumu- 
lations of  snow  and  ice  upon  the  rocks  so  thrust  up,  by  geological 
causes,  into  the  cold  part  of  the  atmosphere  that  they  can  there  remain, 
no  slight  modification  of  surface  would  arise  from  the  fall  of  fragments 
of  rock,  some  remaining  stranded  and  perched  about  in  various  direc- 
tions, while  multitudes  of  others  were  borne  outwards  amid  surrounding 
valleys.  Avalanches  aid  in  the  general  descent  of  fragments  of  rocks, 
carrying  many,  with  their  snows,  to  lower  levels,  sometimes  falling  on 
glaciers,  sometimes  into  deep  valleys,  where  the  fragments  are  merely 
exposed  to  the  ordinary  action  of  rivers. 

Taking  the  general  causes  and  movements  of  glaciers  in  the  Alps  for 
his  guides,  the  observer  is  enabled  to  infer  how  far  glaciers  would  be 
found  in  other  regions.  M.  Elie  de  Beaumont  has  pointed  out,  thatf 
from  the  little  variation  of  climatal  conditions  in  tropical  regions,  gla- 
ciers would  not  be  expected  among  the  mountains  there  situated,  and 
sufficiently  high  to  be  clothed  with  perpetual  snow.  Where  the  alterna- 
tions of  frost  and  thaw,  snow  and  rain,  would  be  insufficient  to  produce 
the  needful  amount  of  neVe*,  assuming  this  to  be  the  storehouse  whence 

*  Professor  Forbes  mentions  one  of  green  slate,  pushed  forward  by  the  glacier  of 
Swartzberg,  valley  of  Saas,  and  now  left  at  a  distance  of  about  half  a  mile  from  the 
glacier  by  its  retreat,  estimated  by  M.  Venetz  to  contain  244,000  cubic  feet.  This  mass, 
if  about  14  cubic  feet  be  taken  to  the  ton,  would  weigh  no  less  than  17,428  tons. 

f  Remarques  sur  deux  points  de  la  Th6orie  des  Glaciers,  Anhales  des  Sciences  Gdo- 
logiques,  1842.  He  observes  that  glaciers  being  due  to  annual  and  not  merely  to 
diurnal  conditions,  there  could  be  only  perpetual  snows,  and  not  glaciers,  under  the 
equator,  where  the  variations  of  temperature  are  only  diurnal. 


ARCTIC    GLACIERS    REACHING    THE    SEA.  233 

the  glaciers  are  supplied,  these  would  not  be  found.  Looking,  there- 
fore, at  the  different  known  regions  of  the  world,  their  varied  relief,  as 
regards  the  distribution  of  high  and  low  land,  the  different  amount  of 
water  supply  from  the  atmosphere,  either  in  the  shape  of  snow,  hail,  or 
rain ;  changes  of  temperature  during  various  times  of  the  year,  and 
their  amount ;  prevalent  or  periodical  winds — one  set  dry,  the  other 
bringing  abundant  moisture,  and  proximity  or  distance  from  the  sea — 
the  observer  finds  no  want  of  modifying  conditions  for  the  presence  or 
absence,  and  geological  importance  of  glaciers.  At  one  time  glaciers 
were  somewhat  doubted  among  the  great  range  of  the  Himalaya,  but 
several  are  now  known.  The  height  of  the  lowest  part  of  the  Finder 
glacier  is  estimated  at  about  11,300  feet  above  the  sea,  and  that  of  the 
Kuplinee  glacier  at  12,000,  which,  the  height  of  the  perpetual  snow 
line  near  them  being  considered  at  about  15,000  feet,  would  give  a 
glacier  descent  of  3,700  feet  for  the  former,  and  3,000  feet  for  the 
latter.*  The  lowest  part  of  the  glacier  of  the  Ganges  is  12,914  feet 
above  the  sea,  according  to  Captain  Hodgson. 

Proceeding  from  the  temperate  parts  of  the  world,  where  high  lands 
rise  sufficiently  high  into  the  atmosphere  to  obtain  a  constant  covering 
of  snow,  and  the  fitting  conditions  permit  glaciers  to  descend  amid  the 
adjacent  valleys  at  lower  levels, f  to  the  Arctic  and  Antarctic  regions, 
we  find  the  glaciers  not  only  covering  various  portions  of  land,  but 
jutting  into  the  sea,  the  line  of  perpetual  snow  having  descended 
towards  its  level.  If  the  observer  will  in  imagination,  and  by  reference 
to  the  view  of  part  of  it  previously  given  (fig.  84),  fill  up  the  valley  of 
Chamonix  with  sea  to  the  height  of  about  4,000  fee!  above  the  village 
of  Chamonix  (3,425  feet  above  the  sea),  and  therefore  so  that  the  per- 
petual snow  line  descended  (in  round  numbers)  to  within  about  1,000 
feet  from  the  sea  level,J  it  will  readily  be  seen  that  numerous  glaciers 
would  jut  into  the  sea,  resting  upon  and  grating  along  the  rocks  forming 
their  bases  and  sides,  until  the  emersion  in  the  water  became  such  that 
they  floated  at  their  extremities,  the  transport  of  fallen  fragments  being 
continued  in  the  manner  that  they  now  are,  until  the  glacier  reached 
the  sea.  Here  the  conditions  for  their  further  transport  would  be 
modified.  Instead  of  terminal  moraines,  the  blocks  would  be  thrown 
into  deep  water,  and  those  which  now  fall  off  the  lateral  moraines  would 
be  distributed  at  greater  or  less  distances  from  the  new  shores.  Modi- 
fications would  also  arise  from  the  increase  or  decrease  of  the  mass  of 

*  Lieutenant  Strachey,  Bengal  Engineers,  Jameson's  Edinburgh  New  Phil.  Journal, 
vol.  xliv.  p.  119,  and  Journal  of  the  Asiatic  Society  of  Bengal,  No.  viii.  p.  794. 

|  In  the  Pyrenees,  the  conditions  for  the  production  of  glaciers  would  appear  to  be 
such,  that,  where  they  occur,  they  are  almost  always  found  on  the  northern  slopes  of 
the  mountains. 

J  Taking  8,500  feet  above  the  sea  as  the  snow  line  for  the  Alps,  the  altitude  inferred 
by  Professor  Forbes. 


234 


ARCTIC  GLACIERS  REACHING  THE  SEA. 


the  glaciers,  assuming  the  nee.dful  climatal  changes.  If  we  now  add 
wave  and  breaker  action,  and  tides,  it  will  be  seen  that  there  would  be 
a  tendency  to  have  the  protruding  portions  of  the  glaciers,  where  they 
floated,  broken  away  by  the  one  and  the  other,  more  particularly  when 
the  glaciers  were  weakened  by  lines  of  crevasses,  formed,  as  now,  upon 
the  land,  before  the  protrusion  seaward  was  effected.  Great  masses  of 
ice  would  thus  be  borne  away,  supporting  their  moraines,  gathered  and 
transported  outwards,  as  at  present. 

This  imaginary  case  may  be  considered  as  realized,  from  the  near  ap- 
proach of  the  perpetual  snow  line  to  the  sea,  with  certain  obvious  modifi- 
cations, in  portions  of  the  Arctic  regions.  Glaciers  formed,  necessarily, 
at  minor  altitudes  above  the  sea,  there  descend  to  the  shores  in  various 
situations,  as,  for  example,  in  parts  of  Greenland  and  Spitsbergen,* 
even  advancing  beyond  them,  so  that  their  extremities  become  separated 
and  are  borne  away  by  tidal  streams  and  sea  currents,  the  masses  of 
ice  often  loaded  with  the  fragments  of  rock  detached  from  the  cliffs  and 
heights  amid  which  the  glaciers  moved  outwards,  as  in  the  Alps.  Let 
#,  £>,  c,  d,  and  e  (fig.  90),  represent  the  section  of  a  portion  of  coast, 
along  a  ravine  or  hollow,  in  which  a  glacier,  /,  </,  c,  h,  finds  its  way 

Fig.  90. 


outwards  to  the  sea,  s,  so  that  at  A,  it  has  a  tendency  to  float  at  its  ex- 
tremity, from  its  relative  specific  gravity,  as  regards  the  sea,  and  it 
should  be  recollected  that  glacier  ice  would  sink  less  deeply  in  sea  than 
in  fresh  water.  And  let  t  be  the  level  of  ordinary  high  water  in  a  tidal 
sea,  and  1 1'  the  difference  of  level  between  high  and  low  water.  The 
ordinary  glacier  movements  and  their  consequences  would  go  on  unin- 
terruptedly, as  in  the  Alps,  allowing  for  the  modifications  due  to  an 
Arctic  climate,  from  /to  g,  where  the  sea  line  cuts  the  coast  and  glacier  ; 

*  With  respect  to  the  alternations  of  temperature  productive  of  glaciers,  it  would 
appear  that  in  these  regions  there  is  no  want  of  the  needful  alternations  of  frost  and 
thaw.  In  Greenland  the  heat  of  the  days  in  the  summer  months  is  considerable,  thaw- 
ing the  snow  and  ice,  while  the  nights  are  commonly  cold,  with  frosts.  Even  during 
the  winter  at  Spitzbergen,  when  strong  southerly  winds  prevail,  thaws  are  known. 
The  temperature  of  the  warmest  months  at  Spitzbergen  is  estimated  at  34-5°,  and  the 
longest  day  lasts  four  months,  the  northern  portion  of  these  islands  being  within  10° 
of  the  North  Pole. 


ARCTIC    GLACIERS    REACHING    THE    SEA.  235 


while  from  g  towards  J,  a  change  in  the  polishing,  grooving,  and 
scratching  of  the  rocky  sides  and  bases  would  gradually  be  effected  as 
the  final  floating  of  the  ice  removed  its  pressure  from  them.  Still  much 
of  the  polishing,  grooving,  and  scratching  would  take  place  beneath  the 
sea  level,  and  the  fragments  which  may  have  fallen  between  the  glacier 
and  its  sides,  or  through  crevasses  of  sufficient  depth,  while  above 
the  level  of  the  sea,  would  be  squeezed  out  beneath  the  ice  under 
that  level,  accompanied  by  the  finer  detrital  matter,  derived  in  the 
manner  above  mentioned  (p.  230),  which  is  borne  away  amid  dry 
land,  and  in  mechanical  suspension,  by  the  glacier  rivers.  As  the  ice 
moved  seawards,  instead  of  the  terminal  moraine  of  an  inland  gla- 
cier, the  blocks  and  fragments  of  rock  of  the  lateral  and  central 
moraines,  should  there  be  such,  would  fall  over  into  the  sea,  accumu- 
lating in  different  ways  beneath  it,  according  to  the  depth  of  water  and 
configuration  of  the  coast.  It  is  assumed,  for  illustration,  that  at  d 
such  blocks  do  accumulate.  With  respect  to  the  finer  detritus,  instead 
of  being  removed,  amid  dry  land,  by  running  waters,  as  in  the  Alps, 
its  outward  movements  by  such  means  would  be  checked  at  the  sea 
level,  t,  with  the  difference  due  to  the  fall  of  tide  to  t' .  Its  further 
course  outwards  would  depend  upon  the  specific  gravity  of  the  water 
loaded  with  this  matter  in  mechanical  suspension,  and  the  general 
motion  of  the  glacier.  We  have  seen  that  the  turbid  waters  of  the 
Rhone  readily  sink  beneath  the  clear  water  of  the  Lake  of  Geneva, 
spreading  over  the  bottom  (p.  72),  and  we  should  anticipate  that  the 
turbid  waters  under  notice,  finding  their  way  beneath  Arctic  glaciers 
in  the  usual  manner  above  the  sea  level,  would  also  be  discharged  out- 
wards beneath  the  glacier,  particularly  when  we  regard  the  head  of 
water  formed  inland,  between  the  glacier  and  its  rocky  sides  and  base, 
and  the  movement  of  the  glacier  itself,  tending  to  carry  off  any  mud  or 
clay  so  accumulated  that  it  could  interrupt  the  free  course  of  the  turbid 
water.  We  have,  moreover,  to  recollect,  that  from  the  melting  of  the 
glacier  by  the  sea,  the  saltness  of  the  latter  is  usually  found  much 
diminished  in  such  situations.  Taking  all  the  circumstances  into  con- 
sideration, there  would  appear  much  probability  of  the  finer  detritus 
finding  its  way  beneath  the  glacier  into  the  sea,  to  be  distributed  over 
its  bottom  according  to  conditions,  tidal  streams  and  sea  currents  pro- 
ducing their  usual  effects.  Along  steep  coasts,  such  as  those  of  Green- 
land, where  glaciers  are  so  common,  much  mud  may  be  thus  distributed 
under  the  deep  water  which  usually  adjoins  them,  and  into  this  mud 
glacier-borne  fragments  of  rock,  sometimes  of  considerable  volume, 
would  from  time  to  time  be  discharged,  so  that  the  resulting  mixture 
would  be  a  clay  without  apparent  stratification,  amid  which  fragments 
of  rocks,  of  very  varied  form  and  volume  were  dispersed. 

The  transport  of  fragments  by  glacier  ice,  the  latter  jutting  into  the 


236  ARCTIC    GLACIERS    REACHING    THE    SEA. 

sea,  does  not  cease  in  the  cold  regions  of  the  glohe  with  the  extension 
of  the  glacier  itself;  not  only  is  it  subject,  at  its  seaward  extremity,  to 
the  breaker  action,  which  observers  inform  us  undermines  its  base,  and 
finally  brings  down  huge  fragments  into  the  water,  but  also  to  the  pres- 
sure of  tidal  streams  or  sea  currents,  and  to  the  fracturing  influence  of 
the  up  and  down  motion  produced  by  the  rise  and  fall  of  tides  in  tidal 
seas.  Some  of  the  masses  of  ice  thus  broken  off  and  floated  away,  as 
at  m  (fig.  90),  with  any  load  of  blocks  and  minor  fragments  of  rock, 
which,  in  the  ordinary  inland  glaciers  of  temperate  climates  would  be 
carried  towards  the  terminal  moraines,  would  contribute,  as  at  e  (fig.  90), 
by  their  melting,  and  during  a  long  lapse  of  time,  no  small  amount  of 
blocks,  which  might  be  dispersed  amid  the  clay  or  mud,  even  of  deep 
waters,  such  as  those  in  Baffin's  Bay. 

Greenland  has  been  considered  as  a  mass  of  land  nearly  covered  by 
perpetual  snows,  and  interlaced  with  glaciers,  many  of  the  latter  pro- 
truding beyond  the  ordinary  coasts  into  the  sea.  Their  seaward  extre- 
mities are  well  known,  after  having  been  detached  from  their  main 
masses,  to  be  floated  away,  often  bearing  fragments  of  rock  in  and  upon 
them,  even  to  and  beyond  Newfoundland.*  In  the  western  and  moun- 
tainous part  of  Spitzbergen,  glaciers  reach  and  protrude  into  the  sea, 
exposing  ice-cliffs  from  100  to  400  feet  in  height.  A  little  northward 
of  Horn  Sound,  a  great  glacier  is  noticed  as  occupying  11  miles  of  the 
sea-coast,  the  highest  portion  rising  in  a  cliff  of  400  feet  above  the 
water.  On  the  east  coast  of  Northeast  Land  great  glaciers  are  also 
found. 

M.  Ch.  Martiusf  mentions  that  the  glaciers  of  Spitzbergen  are  com- 
monly even,  and  not  much  broken,  and  that  the  ice  resembles  that  of 
the  upper  glaciers  of  Switzerland,  pointing  out  that  of  Aletsch  as  a  good 
illustration  of  the  Spitzbergen  glaciers.  There  are  lateral,  but  no  cen- 

*  The  current  from  the  northward  bears  a  mass  of  ice  with  it  to  the  southward  along 
the  east  coast  of  Greenland ;  sea  ice,  as  well  as  the  glacier  ice  noticed  above.  The  ice 
is  described  as  sometimes  extending  across  from  Greenland  to  Iceland ;  polar  bears 
being  occasionally  ice-borne  to  the  latter,  where  they  commit  great  havoc  until  destroyed. 
The  accumulation  of  ice  is  stated  to  extend  occasionally  from  120  to  160  miles,  sea- 
wards, around  Cape  Farewell.  Its  movement  thence  is  described  as  northward  to 
Queen  Anne's  Cape,  passing  afterwards  to  the  western  side  of  Davis's  Strait,  and  from 
Cape  Walsingham  (Cumberland  Island)  along  the  American  shore  to  Newfoundland. 

Mr.  Redfield  (American  Journal  of  Science,  vol.  xlviii.,  1845)  gives  a  valuable  chart, 
illustrative  of  a  paper,  on  the  Drift  Ice  and  Currents  of  the  North  Atlantic.  Touching 
the  general  quantity  of  drift-ice,  it  is  stated  to  vary  considerably.  "  It  is  sometimes 
seen  as  early  in  the  year  as  January,  and  seldom  later  than  the  month  of  August. 
From  March  to  July  is  its  most  common  season.  It  is  found  most  frequently  to  the 
west  of  longitude  44°,  and  to  the  eastward  of  longitude  62°,  but  icebergs  are  sometimes 
met  with  as  far  eastward  as  longitude  40°,  and  in  some  rare  cases  even  still  further 
towards  Europe."  p.  378. 

|  Observations  sur  les  Glaciers  du  Spitzberg  compare's  a  ceux  de  la  Suisse  et  de  la 
Norwe"ge.  Bull,  de  la  Soc.  Ge"ol.,  vol.  xi.  1840 ;  Bibliothfcque  Universelle  de  Geneve,  1840. 


NORTHERN    ICEBERGS.  237 

tral  moraines,  the  former  proceeding  with  the  glacier  to  the  sea.*  The 
cliffs  of  ice  rising  above  the  sea  he  estimates,  as  previous  observers  have 
done,  as  varying  in  height  from  30  to  120  metres  (98  to  393  English 
feet),  and  he  states,  that  the  seaward  terminal  portions  of  the  glaciers 
rest  on  water.  Respecting  the  height  and  slope  of  the  Spitzbergen 
glaciers,  he  estimates  the  difference  between  the  foot  and  the  summit  of 
a  Bell  Sound  glacier  at  1150  feet,  and  its  slope  at  10°.  The  principal 
glacier  of  Bell  Sound  is  also  stated  to  be  nearly  horizontal,  in  conse- 
quence of  its  great  length.  M.  Eugene  Robert,  who  likewise  visited 
Spitzbergen,  remarks  on  the  destruction  of  the  ice  by  the  breakers,  and 
considers  that  where  this  is  not  effected,  the  masses  of  ice  are  very  sta- 
tionary. M.  Durocher,  who  has  also  visited  these  lands,  observesf  that 
the  glaciers  do  not  there  rise  more  than  from  1300  to  1650  (English) 
feet  above  the  sea ;  the  snows  above  not  taking  the  character  of  ne've', 
being  too  much  elevated  above  the  needful  conditions  for  its  production. 
The  masses  of  ice  detached  from  the  land,  floating  about,  and  com- 
monly known  as  icebergs,  are  sometimes  of  very  considerable  dimen- 

Fig.  91. 


sions.     The  accompanying  view  (fig.  91)  is  of  one  seen  by  Sir  Edward 
ParryJ  in  his  first  voyage,  and  is  interesting,  not  only  as  showing  the 

I 

*  Respecting  the  moraines  of  Spitzbergen,  M.  Martins  observes  that  the  bases  of  the 
nearly  vertical  cliffs  bounding  the  glaciers  are  covered  with  a  mass  of  debris,  fallen 
from  the  heights.  Between  these  heights  and  the  glacier  there  is  sometimes  a  small 
valley  or  depression.  The  great  glacier  of  Bell  Sound  is  thus  separated  from  its  boun- 
dary heights.  This  glacier  was  merely  stained  with  earth  in  its  lateral  portions. 
Those  of  Madalina  Bay  were  covered  with  stones  at  their  lower  portions,  occupying 
about  an  eighth  part  of  their  breadth.  Not  only  were  blocks  seen  in  their  upper  sur- 
faces, but  also  imbedded  in  the  ice.  M.  Martius  never  saw  them  in  the  front  of  the 
glaciers  bordering  the  sea. 

|  Memoire  sur  la  limite  des  neiges  perpe'tuelles,  sur  les  glaciers  du  Spitzberg  com- 
pare's a  ceux  des  Alpes — Partie  de  Gdographie  Physique  du  Voyage  de  la  Recherche, 
1845.  Scoresby  gives  the  height  of  the  Horn  Sound  glacier  as  1300  feet. 

J  Reduced  from  a  plate,  in  Parry's  First  Voyage,  4to.  edit. 


238         GEOLOGICAL    EFFECTS    OF    NORTHERN    ICEBERGS. 

magnitude  of  this  mass  of  ice  (the  far  greater  portion  being  concealed 
beneath  the  sea),  but  also  as  exhibiting  something  of  its  structure.  It 
may  be  here  observed,  that  such  masses  of  ice,  remaining,  as  they  are 
often  known  to  do,  stranded  for  a  long  time  in  some  high  latitude,  might 
become  covered  with  snows,  marked  by  alternations  of  frosts  and  thaws, 
and  even  frozen  rain,  so  that  their  upper  parts  may  be  in  the  condition 
of  ne've',  thus  covering  over  the  remains  of  old  moraines,  resting  on  more 
ordinary  glacier  ice.  Indeed,  as  respects  the  latter  itself,  in  regions 
where  the  perpetual  snow  line  closely  approximates  to,  and  even  cuts 
the  level  of  the  sea,  we  might  expect  the  neVe*  condition  more  and  more 
to  prevail,  and  it  has  been  considered  that  icebergs  are  frequently  of 
that  character. 

The  northern  icebergs  may  be  regarded  as  the  great  carriers  of  rock 
fragments,  often  of  great  size,  from  the  lands  where  the  bergs  have 
been  formed,  as  portions  of  glaciers,  over  a  part  of  the  Northern 
Atlantic,  distributing  them  upon  the  bottom  in  various  directions,  and 
upon  parts  of  it  to  which  no  other  cause  now  contributes  detritus.* 
Blocks  and  minor  fragments  may  even  be  thus  dropped  upon  bare 
rocks  beneath,  and  upon  every  kind  of  inequality.  Should  a  constant 
supply  of  block-bearing  icebergs,  regarding  the  subject  generally,  be 
thrown  into  any  constant  current,  corresponding  lines  of  deposit  would 
result,  assuming  the  melting  of  masses  of  ice,  of  various  sizes,  at  dif- 
ferent times  and  distances  during  their  progress  in  such  current ;  these 
lines  having  no  reference  to  the  form  of  the  bottom,  or  its  modifications 
from  any  other  deposits  accumulated  now,  or  at  previous  geological 
times.  Stranded  near  shores,  or  upon  mud  or  sand-banks,  these  though 
somewhat  deep  in  the  sea,  still  catching  their  submerged  portions,  ice- 
bergs would  tend  much  to  disturb  detrital  deposits  beneath  them,  par- 
ticularly when  moved  by  the  waves  produced  during  heavy  gales  of 
wind,  as  also  by  the  rise  and  fall  of  tides.  The  heavy  thumping  of 
such  huge  masses,  as  some  of  these  icebergs  are,  would  cause  great 
derangement  of  deposits  effected  tranquilly ;  and  in  many  situations, 
blocks  and  fragments  of  rocks,  with  gravels,  sands,  and  clays,  would  be 
irregularly  mixed  by  the  application  of  such  force — singular  inter- 
mixtures, and  contortions  of  any  previously  bedded  structure  being 
produced.  The  icebergs  which  ground  upon  the  Banks  of  Newfound- 
land can  scarcely  fail  to  produce  much  disturbance  of  the  bottom,  often 
adding  to  it  great  blocks  and  minor  fragments  of  rocks,  borne  by  them 
from  more  northern  regions. f 

*  Mr.  Couthouy  mentions  an  iceberg,  -with  apparently  boulders  upon  it,  as  low  down 
as  latitude  36°  10'  N.,  and  longitude  39°  W.  The  same  author  states  that  he  had  often 
met  with  icebergs  between  the  parallels  of  36°  and  42°  N.,  in  his  voyages  to  and  from 
America  and  Europe.  American  Journal  of  Science,  vol.  xliii.,  1842. 

f  Mr.  Couthouy  (American  Journal  of  Science,  vol.  xliii.,  1842,  p.  155)  mentions 
having  seen  (in  September,  1822)  a  large  iceberg  aground  on  the  eastern  edge  of  the 


ANTARCTIC    ICE-BARRIER.  239 

As  is  well  known,  glaciers  reaching  the  sea  are  not  confined  to  the 
northern  hemisphere  ;*  they  are  also  found  in  the  Antarctic  regions. 
Sir  James  Ross  mentions  a  great  glacier,  at  -ZEtna  Islet,  South  Shet- 
land, as  descending  from  a  height  of  1200  feet  into  the  ocean,  where  it 
presented  a  vertical  cliff  of  100  feet.  Adjoining  the  termination  of  the 
glacier,  Sir  James  found  the  largest  aggregation  of  icebergs,  evidently 
broken  from  it,  he  had  ever  seen  collected  together.  Glaciers  are  also 
noticed  by  Sir  James  Ross  as  descending  from  nearly  the  summit  of 
the  Admiralty  Range  (mountains  7,000  to  10,000  feet  high)  in  Victoria 
Land,  and  projecting  many  miles  into  the  sea,  bare  rocks  in  a  few 
places  inland  breaking  through  the  covering  of  ice.  As  in  the  Arctic 
regions,  such  glaciers  may  be  expected  to  bring  down  with  them  those 
fragments  of  rock  which  can  fall  upon  them,  to  grate  over  the  hard 
rocks  on  which  they  move,  and  to  aid  in  contributing  fine  detritus  to 
the  adjacent  sea-bottom,  should  the  temperature  be  such  that  water 
could  flow  between  the  ice  and  the  supporting  rock.  Moreover,  when 
we  consider  the  volcanic  character  of  so  much  of  the  great  southern 
land  as  has  been  seen,  we  should  expect  that,  as  in  Iceland,  volcanic 
eruptions  and  the  heating  of  the  ground  would  occasionally  produce  the 
sudden  melting  of  snows  and  descent  of  the  water  which  could  remain 
fluid  sufficiently  long  to  find  its  way  to  the  sea.  In  this  manner,  not 
only  the  transport  of  ashes  and  cinders,  and  the  larger  volcanic  sub- 
stances vomited  out  of  craters,  may  be  moved  to  the  lower  ground,  or 
into  the  sea,  but  also  the  fragments  of  rock  which  might  have  fallen 
upon  snow  or  ice  from  any  cliffs  or  steep  places  wherever  atmospheric 
influences  could  detach  them  ;  not  forgetting  the  effects  of  earthquakes 
(so  common  in  great  volcanic  countries)  upon  the  glaciers  and  snows, 
especially  in  localities  where  great  avalanches  could  be  produced. 

Though  from  its  general  mode  of  occurrence,  the  great  icy  barrier 
of  the  Antarctic  regions  might  not,  at  first,  appear  any  important  agent 

Great  Bank  of  Newfoundland,  and  considered  to  be  in  about  720  feet  water  (120 
fathoms),  soundings  three  miles  inside  giving  630  feet  (105  fathoms).  A  fresh  wind 
from  the  eastward  kept  forcing  it  on  the  bank,  the  sea  causing  it  to  rock  with  a  heavy 
grinding  noise.  On  another  occasion  (August,  1827)  he  observed  another  iceberg 
aground  upon  the  Great  Bank,  in  between  480  and  540  feet  water  (80  to  90  fathoms). 
The  huge  mass  rocked  with  the  swell,  going  at  the  time,  and  even  turned  half  over 
when  struck  by  the  breakers.  The  sea,  for  about  a  quarter  of  a  mile  around,  was  dis- 
coloured by  mud  worked  up  from  beneath.  Above  water  the  iceberg  was  50  to  70  feet 
high,  and  about  1200  feet  long.  It  suddenly  fell  over  on  its  side,  with  much  disturb- 
ance of  the  sea. 

*  Although  glaciers  are  so  common  in  Iceland,  they  do  not  appear  actually  to  reach 
the  sea.  Those  descending  from  the  high  Jokulls  are  noticed  as  separated  from  it  by 
great  moraines.  Some  of  the  glaciers  are  described  as  black  in  parts,  from  the 
quantity  of  volcanic  cinders  and  ashes  with  which  they  are  covered.  The  sudden 
melting  of  snows  and  glaciers  from  volcanic  action  in  Iceland  is  represented  as  pro- 
ducing great  rushes  of  water,  bearing  large  accumulations  of  volcanic  products 
outwards. 


240  ANTARCTIC    ICE-BARRIER. 

in  the  transportal  of  mineral  matter,  it  has  been  found  that,  under  cer- 
tain conditions,  portions  of  the  ice,  detached  from  it,  may  bear  no  in- 
considerable amount  of  mud,  sand,  and  rock  fragments  of  various  sizes 
into  milder  climates,  depositing  their  loads  over  the  bottom  of  the  sea 
upon  which  they  may  be  carried.  This  icy  barrier  presents  a  very 
singular  appearance,  stretching  over  a  vast  distance,  with  ice-cliffs 
rising  from  150  to  200  feet  above  the  sea,  large  fragments  of  them  and 
minor  pieces  of  ice  floating  in  front  of  it,  as  shown  in  the  annexed  view* 
(fig.  92),  representing  a  great  detached  mass  in  a  long  creek  or  bay  in 

Fig.  92. 


the  barrier  itself.  From  the  relative  specific  gravity  of  the  ice  and  sea- 
water,  the  former  necessarily  descends  from  beneath  the  level  of  the 
sea  to  a  depth  which  might  be  estimated  if  the  ice  were  of  a  uniform 
kind,  with  a  known  specific  gravity.  This  is,  however,  far  from  being 
the  case,  for  the  layers  of  which  it  is  composed  would  appear  to  present 
somewhat  the  character  of  the  neV^  of  the  higher  parts  of  glaciers  in 
temperate  regions,  being  formed  of  alternations  of  snow,  sleet,  frozen 
mist  and  rain,  with  the  refreezing  of  portions  which  in  the  summer 
months  may  be  thawed  at  times  by  the  influence  of  the  sun.f  As  de- 
tached portions  of  this  barrier  were  found  by  Sir  James  Boss  aground, 
60  miles  from  its  main  edge,  and  200  miles  from  Victoria  Land,  in 
1,560  feet  of  water,  the  ice  was  there  at  least  of  that  thickness. 

*  Taken  from  Captain  Wilkes's  "United  States  Exploring  Expedition,"  vol.  ii.  The 
vessel  represented  is  the  "Peacock,"  which  had  been  driven  against  this  great  mass  of 
ice.  The  view  will  at  the  same  time  afford  an  idea  of  the  great  barrier  itself,  which 
would  be  but  an  extension  of  a  similar  range  of  ice-cliffs.  A  long  illustrative  view  of 
the  great  Antarctic  ice-barrier  is  given  in  Ross's  "Voyage  of  Discovery  and  Research 
in  the  Antarctic  Regions,"  vol.  i.  p.  232. 

f  Sir  James  Ross  describes  gigantic  icicles  depending  from  the  projecting  parts  of 
the  ice-cliffs,  proving  that  thaws  sometimes  took  place.  Notwithstanding  that  the  time 
of  the  observation  (February  9,  1841)  corresponded,  as  respects  season,  with  August 
in  England,  the  temperature  was  at  12°  (Fahr.),  and  did  not  rise  above  14°  at  noon. 


ANTARCTIC    ICE-BARRIER.  241 

The  depth  of  water  obtained  not  far  distant  from  the  barrier*  would 
show,  as  Sir  James  Ross  has  observed,  that  much  of  it  must  be  up- 
borne by  the  sea,  and  not  rest  on  the  sea  bottom,  however  the  general 
mass  may  be  held  fast  by  adhering  to  land,  or  by  reposing  upon  mud, 
sand,  gravel,  or  solid  rock,  at  minor  depths.  It  will  be  obvious  that 
the  ice  must  be  limited  in  depth  by  the  temperature  of  the  water  to 
which  it  descends.  We  have  seen  (p.  120)  that  at  the  depth  of  4,500 
feet,  the  most  dense  water,  with  its  temperature  of  39-5°,  appears  to 
remain  somewhat  fixed  in  these  regions,  the  waters  of  the  upper  parts 
of  the  sea  necessarily  varying  in  temperature  according  to  the  seasons. 
In  January  (1841),  consequently  in  the  summer  of  that  portion  of  our 
globe,  Sir  James  Ross  found,  about  12  or  14  miles  from  the  barrier,  a 
temperature  of  33°  at  a  depth  of  900  feet,  one  which  could  not  fail, 
widely  spread  beneath  as  we  might  expect  it  to  be,  to  act  upon  the 
lower  part  of  the  great  mass  of  ice  descending  into  the  sea.f 

Seeing  that  numerous  and  large  masses  of  ice  are  annually  detached 
from  the  great  ice-barrier  adjoining  Victoria  Land,  and  are  floated  off 
into  milder  regions,  the  question  arises  of  whence  the  needful  supply 
for  this  loss  is  obtained,  assuming  a  certain  general  icy  frontier  to  bound 
the  barrier,  and  due  allowance  being  made  for  the  variation  of  seasons. 
The  great  thickness  of  the  detached  masses  would  lead  us  to  consider 
that  they  were  not  portions  formed  on  the  outskirts  of  the  main  mass 
during  certain  seasons  as  additions  to  it,  and  were  subsequently  broken 
off,  to  be  replaced  by  other  additions ;  but  rather  that  they  were  essen- 
tial portions  of  the  main  mass,  formed  at  the  same  time  and  in  the  same 
manner  with  it.  Under  this  view  there  would  be  a  motion  outwards  of 
this  mass,  sufficient  to  supply  the  annual  waste  of  icebergs  at  the  outer 
edge.  Such  a  movement,  though  very  slow,  would  yet  produce  a  cor- 
responding effect  on  the  bottom  of  the  sea  over  which  this  great  mass  of 
ice  passed,  grating  over  it,  heavily  pressing  upon  and  scratching  bare 
rocks  and  shingle  beds,  in  the  manner  of  a  common  glacier,  though  over 
a  far  wider  area.  Shingle  beds,  produced  by  some  previous  condition 
of  land  and  sea,  might  thus,  as  well  as  any  supporting  rock,  be  scratched 

*  Sir  James  Ross  found  (lat.  77°  66'  S.,  long.  190°  15/E.)  a  depth  of  1,980  feet  (380 
fathoms),  within  a  quarter  of  a  mile  of  the  barrier,  the  bottom  green  mud.  He  also 
obtained  2,400  feet  (400  fathoms)  12  or  14  miles  off  the  icy  barrier  in  another  situation, 
about  100  miles  from  Victoria  Land,  the  bottom  being  also  a  green  mud,  so  soft  that 
the  sounding-lead  descended  into  it  2  feet. — "Voyage  of  Discovery  and  Research  in  the 
Southern  and  Antarctic  Regions,"  vol.  i. 

f  The  temperature  at  1,800  feet  was  34-2°,  at  900  feet  33°,  at  the  surface  31°,  and 
of  the  air  28°.  In  another  situation  (lat.  77°  49/  S.,  and  long.  162°  36/  W.),  and  about 
one  mile  and  a  half  from  the  barrier,  Sir  James  Ross  found  the  temperature  of  the 
bottom  (green  mud)  at  1,740  feet  (290  fathoms)  to  be  30-8°,  only  2°  lower,  he  observes, 
than  would  be  obtained  at  a  more  considerable  distance  from  the  barrier,  and  showing 
the  small  influence  of  the  mass  of  ice  upon  the  sea  adjoining  it. 

16 


242  ICEBERGS    FROM    THE    ICE-BARRIER. 

throughout,  pebbles  moved  against  pebbles,  in  lines  of  a  general  parallel 
character,  over  very  extended  areas. 

As  the  various  layers  of  which  the  ice-barrier  is  formed  indicate  accu- 
mulations from  atmospheric  causes,  unless  the  melting  of  the  beds* 
beneath  were  equal  to  the  deposit  of  snow,  sleet,  fog,f  and  rain  (frozen 
upon  its  fall)  above,  there  would  be  a  continued  increase  of  icy  matter. 
The  marked  general  uniformity  in  height  of  the  ice-cliffs,  and  the  tabular 
character  of  the  surface  of  the  barrier  inwards,  J  would  point  to  some 
cause  having  an  extended  and  uniform  action,  so  modifying  any  accu- 
mulation of  the  kind  as  to  keep  the  mass  at  a  general  uniform  thickness. 
The  temperature  of  the  sea  at  a  fitting  depth  would  appear  sufficient  to 
effect  this,  any  addition  from  above  to  the  general  mass,  so  long  as  it 
plunged  into  water  and  did  not  rest  on  the  sea  bottom,  being  compen- 
sated by  the  melting  of  the  lower  surface,  pressed  down  by  the  increased 
accumulation  above. 

Captain  Wilkes  refers  the  formation  of  the  ice  in  the  first  place  to 
ordinary  field  ice,  upon  which  layers  from  rain,  snow,  and  even  fog  so 
accumulate,  that  the  mass  descending,  takes  the  ground,  part  of  it 
trending  outwards  into  deeper  water,  and  floating  when  conditions 
permit.  § 

Huge  masses  of  this  barrier,  detached  from  it,  float  to  more  tempe- 
rate regions,  borne  onwards  by  currents  and  prevalent  winds.  The 
following  sketch 1 1  (fig.  93)  will  afford  an  idea  of  the  tabular  character 
of  numerous  icebergs  before  they  have  been  much  melted  in  more  tem- 
perate climates,  and  also  will  show  the  stratified  appearance  noticed. 
Sir  James  Ross  found  many^f  in  about  63°  30'  south,  rising  with  tabular 

*  Respecting  these  layers,  Captain  Wilkes  (United  States  Exploring  Expedition,  yol. 
ii.)  observes,  "that  80  different  beds,  on  the  average  2  feet  thick,  were  counted  in  the 
large  icebergs,  detached  from  the  main  ice,  and  30  in  the  smaller."  Assuming  similar 
beds  beneath  the  sea  level,  the  whole  would  constitute  no  small  amount  of  ice  and  snow 
accumulated  in  horizontal  layers  and  beds,  in  part  supported  like  beds  of  solid  mineral 
matter  by  subjacent  ground. 

f  Respecting  fog,  Captain  Wilkes  remarks,  "  that  it  may  make,  when  frozen,  a  marked 
addition  to  the  ice  accumulations,  since  he  has  known  it  frozen  to  the  depth  of  a  quarter 
of  an  inch  upon  the  spars  and  rigging  of  the  ships  in  a  few  hours." 

J  Where  an  opportunity  occurred  of  seeing  over  the  ice-cliff  (about  50  feet  high),  Sir 
James  Ross  describes  the  mass  as  quite  smooth  in  its  upper  part,  and  looking  like  "  an 
immense  plain  of  frosted  silver." 

\  Wilkes,  "United  States  Exploring  Expedition,"  vol.  ii.  Respecting  that  portion  of 
the  mass  which  reposes  on  the  bottom  beneath  the  level  of  the  sea,  we  have  also  to  con- 
sider the  effect,  for  any  value  it  may  have,  which  may  be  due  to  terrestrial  heat  be- 
neath, the  ground  protected  from  great  atmospheric  depressions  of  temperature  by  the 
mass  of  ice  and  snow  above. 

||  Taken  from  Wilkes's  "  United  States  Exploring  Expedition,"  vol.  ii. 

\  27th  December,  1840.  "Voyage  of  Discovery,"  &c.  They  extend  often  with  a 
similar  tabular  character,  according  to  particular  seasons,  more  northerly.  According 
to  such  seasons  also,  the  icebergs  generally  of  the  southern  regions  range  to  very 
different  warmer  latitudes.  Upon  returning  from  the  Antarctic  regions  in  1840,  the 


GEOLOGICAL    EFFECTS     OF    ANTARCTIC    ICEBERGS.        '243 

summits  to  the  height  of  from   1-0  to   ISO  feet,  several  more  than  '2 
:u  circumference.     They  were  falling  rapidly  to  pieces,  and  their 

Pip.  93. 


course  was  marked  by  the  portions  of  ice  detached  from  them.  Re- 
specting the  mode  in  which  icebergs  are  separated  from  the  main  mass 
of  the  ice  barrier,  and  from  the  few  he  observed  near  it  during  the  sum- 
mer months.  Sir  James  Ross  infers  that  they  are  chiefly  detached  during 
the  winter,  the  temperature  of  the  sea  and  the  air  being  then  so  different, 
whereas  it  more  closely  approximates  during  the  summer.  He  points 
to  the  great  cracks,  some  many  miles  in  length,  observed  in  the  ice  of 
Arctic  regions  upon  a  sudden  fall  of  30°  or  40°  in  the  temperature,  and 
more  especially  well  seen  in  the  great  fresh-water  lakt-s.  where  the  sudden 
rents  are  accompanied  by  loud  reports.  The  unequal  expansion  of  the 
ice  exposed  to  40°  or  50°  below  zero  (Fahrenheit Vwhile  beneath,  the 
temperature  is  'JS^  to  30°  above  it,  could  not,  Sir  James  Koss  infers, 
but  produce  the  separation  of  large  masses  of  ice.  However  little  the 
action  of  the  waves  could  affect  a  mass  descending  s<5  low  beneath,  the 
surface  of  the  sea.  we  should  expect  that  the  iniluence  of  a  rise  and  fall 
of  tide  would  be  felt,  tending  alternately  to  lift  and  depress  much  of  it, 
especially  at  spring  tides,  so  that  supposing  fissures  formed,  this  very 
constant  up  and  down  movement  would  also  tend  to  separate  masses  at 
the  outer  edge  of  the  barrier. 

AVhile  numerous  icebergs  are  but  the  detached  portions  of  the  great 
ice  barrier,  which  have  not  rested  on  a  sea-bottom,  and  therefore  trans- 
porting no  mineral  matter  to  milder  regions,  beyond  any  volcanic  ashes 
or  cinders  discharged  over  the  icy  area,  of  which  they  may  have  formed 
a  part,  from  such  volcanic  vents  as  Mount  Erebus,  and  be  interstratiiied 
with  the  layers  of  ice  and  snow,*  others  carry  onwards  no  small  amount 

different  vessels  of  the  United  States  Exploring  Expedition  saw  the  last  in  "M°  S..  «M° 
S..  and  68°  S.  They  were  known  to  range  so  much  northerly  in  18;>2.  that  vessels 
bound  round  Tape  Horn  t'rom  the  Pacific  were  obliged  to  put  back  to  Chili  for  a  time, 
in  order  to  avoid  them. 

*  Sir  .lames  Koss  v Antarctic  Voyage)  mentions  "that  having  observed  new-formed 
ice  off  Victoria  Land,  covered  with  some  colouring  matter,  a  portion  of  the  ice  was 
melted  and  filtered,  and  an  impalpable  powder  collected,  considered  as  volcanic  dust," 


244      ICE-DISTRIBUTED    DETRITUS    IN    SOUTHERN    OCEAN. 

of  mud,  sand,  and  rock  fragments  of  different  sizes.  We  have  accounts 
of  some  covered  with  such  detritus,  blocks,  so  found,  weighing  several 
tons.*  The  detached  portions  of  the  glaciers,  such  as  those  descending 
from  the  Admiralty  Range,  would  be  expected  to  transport  the  frag- 
ments which  could  fall  upon  them,  as  in  the  Arctic  regions.  It  would 
appear  that,  in  addition  to  whatever  may  be  thus  carried,  large  icebergs 
which  have  rested  upon  the  sea  bottom  are  often  capsized,  so  that  the 
mud,  sand,  and  pieces  of  rock  adhering  to  them  beneath  are  suddenly 
upturned,  a  very  great  change  in  the  relative  position  of  such  detritus 
being  in  this  manner  quickly  produced.  Sir  James  Ross  mentions  one 
suddenly  capsized  off  Victoria  Land,  bringing  up  a  portion  of  the  bottom 
100  feet  above  the  surface  of  the  sea,  so  that  it  was,  for  the  moment, 
supposed  to  be  an  island  not  previously  seen.f  In  this  manner  detritus 
may  not  only  be  transported  directly  from  the  land  upon  detached  por- 
tions of  glaciers,  but  also  the  mud,  sand,  and  stones  of  a  sea  bottom  be 
uplifted  several  hundred  feet,  and  carried  great  distances  into  milder 
climates. J  A  somewhat  constant  supply  and  a  general  course  of  the 
floating  ice,  from  currents  and  prevalent  winds,  would  cause  a  vast 
quantity  of  the  detritus,  thus  obtained  and  floated  away,  to  be  distributed 
over  the  sea  bottom,  mud,  sand,  and  fragments  of  varied  sizes  mingled 
together.  Though  the  finer  matter  would  take  longer  to  sink  through 
the  sea,§  and  so  far  become  strewed  over  the  bottom  more  widely  and 
in  a  more  even  form,  enveloping  various  inequalities  that  may  occur  (as 
well  covering  the  tops  as  the  sides,  if  not  too  steep,  of  submarine  hills), 

*  Ross,  "  Voyage  in  the  Antarctic  Regions,"  vol.  i.  p.  173.  Mr.  Couthouy  observed 
masses  of  rock  embedded  in  an  iceberg  seen  in  lat.  53°  20'  S.,  long.  104°  50'  W.,  1,450 
miles  from  Tierra  del  Fuego,  and  1,000  miles  from  St.  Peter's  and  Alexander's  Islands, 
•whence  he  supposes  the  ice  to  have  drifted.  One  of  the  rock  masses  seemed  to  show  a 
face  of  about  20  square  feet.  When  within  half  a  mile  of  this  iceberg,  the  temperature 
of  the  air  -was  35°,  and  of  the  water  34°.  The  water  to  leeward  of  the  ice  was  7°  colder 
than  4£  miles  to  windward  of  the  berg. — "  American  Journal  of  Science,"  vol.  xliii., 
1842. 

f  "  Antarctic  Voyage,"  vol.  i.  p.  196. 

J  Captain  Wilkes  ("  United  States  Exploring  Expedition")  considered  that  he  landed 
upon  an  upturned  iceberg,  part  of  the  icy  barrier  weathered  by  storms,  about  eight 
miles  from  the  main  land,  in  latitude  65°  59'  40"  S.  Upon  it  were  boulders,  gravel, 
sand,  and  mud  or  clay.  The  larger  specimens  were  of  basalt  and  red  sandstone.  One 
piece  of  rock  was  estimated  at  5  to  6  feet  in  diameter.  The  stones  were  cemented  by 
very  compact  ice,  thus  forming  an  icy  conglomerate. 

As  regards  the  distances  to  which  the  icebergs  from  the  southern  ice  are  carried, 
Captain  Wilkes  infers  that  they  are  conveyed  westward  the  first  season  by  the  southeast 
winds,  about  70  miles  north  of  the  barrier,  being  the  second  season  driven  northwards 
until  they  reach  00°  S.,  after  which  they  rapidly  move  more  northward  and  disappear. 
Sir  James  Ross  mentions  a  tabular  iceberg,  rising  130  feet  above  the  sea,  and  three- 
quarters  of  a  mile  in  circumference,  in  about  58°  36'  S. 

§  Sir  James  Ross  ("Antarctic  Voyage")  considers  the  bottom  as  usually  to  be  found 
in  the  Antarctic  Ocean  at  12,000  feet.  Inequalities  to  a  considerable  amount  also 
exist.  No  bottom  was  obtained  by  a  line  of  24,000  feet,  in  latitude  68°  38'  S.,  and 
longitude  12°  49'  W. 


ICE-DISTRIBUTED    DETRITUS    IN    SOUTHERN    OCEAN.        245 

the  larger  fragments  would  fall  more  irregularly  upon  and  into  the  finer 
sediment.  Submarine  hill-tops  would  be  as  much  covered  by  them  as 
any  depressions,  and  they  would  often  be  plunged  into  mud,  in  the  same 
manner  as  the  sounding-lead  above  mentioned  (p.  241),  and  which  de- 
scended two  feet  into  the  fine  green  mud  beneath  2400  feet  of  sea,  at  a 
distance  of  100  miles  from  Victoria  Land.  This  fine  mud  would  not 
appear  an  uncommon  sea  bottom  off  Victoria  Land,*  and  as  icebergs 

*  This  mud  seems,  from  the  soundings  obtained  by  Sir  James  Koss  ("Antarctic 
Voyage"),  to  be  common  for  about  400  miles  along  the  great  icy  barrier  near  Victoria 
Land.  It  has  been  noticed  previously  (p.  241)  that  a  detached  portion  of  this  barrier 
was  found  aground  upon  it,  beneath  1560  feet  of  water,  200  miles  from  that  land.  Ee- 
specting  its  composition,  those  minute  bodies,  the  Diatomacece,  which  were  considered 
by  Ehrenberg  and  many  naturalists  as  infusorial  animals,  and  by  others  as  vegetables, 
and  which  seem  now,  especially  from  the  researches  of  Mr.  Thwaites  (of  Bristol),  to  be 
admitted  by  Dr.  Hooker,  Dr.  Harvey,  and  other  highly  qualified  persons  as  the  latter, 
would  appear  to  form  no  inconsiderable  portion  of  it.  At  the  same  time,  as  no  rivers 
of  Victoria  Land  bear  out  fine  sediment,  and  great  volcanoes  are  there  in  activity,  we 
may  look  to  the  distribution  of  ashes  and  cinders  vomited  forth  from  the  latter  as  add- 
ing such  products  from  time  to  time  to  this  mud. 

"The  water  and  the  ice  of  the  South  Polar  ocean,"  observes  Dr.  Hooker  ("Flora 
Antarctica,"  vol.  ii.  p.  503),  "  are  alike  found  to  abound  with  microscopic  vegetables 
belonging  to  this  order  (Diatomaceae).  Though  much  too  small  to  be  discerned  with 
the  naked  eye,  they  occurred  in  such  countless  myriads  as  to  stain  the  berg  and  pack 
ice  wherever  they  were  washed  by  the  swell  of  the  sea ;  and  when  enclosed  on  the  con- 
gealing surface  of  the  water  they  imparted  to  the  brash  and  pancake  ice  a  pale  ochreous 
colour.  In  the  open  ocean  northward  of  the  frozen  zone,  this  order,  though  no  doubt 
almost  universally  present,  generally  eludes  the  search  of  the  naturalist,  except  when 
its  species  are  congregated  amongst  that  mucous  scum  which  is  sometimes  seen  floating 
on  the  waves,  and  of  whose  real  nature  we  are  ignorant,  or  when  the  coloured  contents 
of  the  marine  animals  which  feed  on  these  Algce.  are  examined.  To  the  south,  however, 
of  the  belt  of  ice  which  encircles  the  globe,  between  the  parallels  of  50°  and  70°  S.,  and  in 
the  waters  comprised  between  that  belt  and  the  highest  latitude  ever  attained  by  man, 
this  vegetable  is  very  conspicuous,  from  the  contrast  between  its  colour  and  the  white 
snow  and  ice  in  which  it  is  embedded,  insomuch  that,  in  the  eightieth  degree,  all  the 
surface  ice  carried  along  by  the  currents,  the  sides  of  every  berg,  and  the  base  of  the 
great  Victoria  Barrier  itself,  within  reach  of  the  swells,  are  tinged  brown,  as  if  the 
polar  waters  were  charged  with  oxide  of  iron. 

"As  the  majority  of  these  plants  consist  of  very  simple  vegetable  cells,  enclosed  in 
indestructible  silex  (as  other  Algce  are  in  carbonate  of  lime),  it  is  obvious  that  the  death 
and  decomposition  of  such  multitudes  must  form  sedimentary  deposits,  proportionate 
in  their  extent  to  the  length  and  exposure  of  the  coast  against  which  they  are  washed, 
in  thickness  to  the  power  of  such  agents  as  the  winds,  currents,  and  sea,  which  sweep 
them  more  energetically  to  certain  positions,  and  in  purity  to  the  depth  of  the  water 
and  nature  of  the  bottom.  Hence  we  detected  their  remains  along  every  ice-bound 
shore,  in  the  depths  of  the  adjacent  ocean,  between  80  and  400  fathoms.  Off  Victoria 
Barrier  the  bottom  of  the  ocean  was  covered  with  a  stratum  of  pure  white  or  green 
mud,  composed  principally  of  the  siliceous  cells  of  Diatomaceos  ;  these  on  being  put  into 
water  rendered  it  cloudy,  like  milk,  and  took  many  hours  to  subside.  In  the  very  deep 
water  off  Victoria  and  Graham's  Land  this  mud  was  particularly  pure  and  fine ;  but 
towards  the  shallower  shores  there  existed  a  greater  or  less  admixture  of  disintegrated 
rocks  and  sand,  so  that  the  organic  compounds  of  the  bottom  frequently  bore  but  a 
small  proportion  to  the  inorganic," 

Respecting  the  distribution  of  the  Diatomaccce,  Dr.  Hooker  remarks  (ibid.  p.  505), 


246      SOUTH    GEORGIAN    GLACIERS    REACHING    THE    SEA. 

discoloured  by  mud  seem  not  unfrequent  in  these  southern  latitudes, 
such  mud  may  be  widely  distributed  and  be  irregularly  supplied  with 
sand,  stones,  and  large  fragments  of  rock,  as  the  icebergs  melt  away 
and  drop  their  loads  of  mineral  substances.* 

Captain  Cook  long  since  (1777)  made  known  the  fact  that,  at  the 
mountainous  island  of  South  Georgia,  included  between  latitude  53°  57' 
and  54°  57'  S.,  glaciers  descended  into  the  sea,  detached  masses  from 
which  floated  outwards,  to  be  distributed  by  ocean  currents  and  preva- 
lent winds,  in  given  directions.  The  following  view  of  Possession  Bayf 

Fig.  94. 


(latitude  54°  5'  S.),  in  that  island,  presents  us  with  a  glacier  reaching 

that  many  species  are  found  from  pole  to  pole,  "  while  these  or  others  are  preserved  in 
a  fossil  state  in  strata  of  great  antiquity.  There  is  also  probably  no  latitude  between 
that  of  Spitzbergen  and  Victoria  Land,  where  some  of  the  species  of  either  country  do 
not  exist:  Iceland,  Britain,  the  Mediterranean  Sea,  North  and  South  America,  and  the 
South  Sea  Islands,  all  possess  Antarctic  Diatomacece.  The  siliceous  coats  of  species 
only  known  living  in  the  waters  of  the  South  Polar  Ocean  have,  during  past  ages,  con- 
tributed to  the  formation  of  rocks,  and  thus  they  outlive  several  successive  creations  of 
organized  beings.  The  phonolite  stones  of  the  Rhine  and  the  tripoli  stone  contain 
species  identical  with  what  are  now  contributing  to  form  a  sedimentary  deposit  (and 
perhaps  at  some  future  period  a  bed  of  rock),  extending  in  one  continuous  stratum  for 
400  measured  miles.  I  allude  to  the  shores  of  the  Victoria  Barrier,  along  whose  coast 
the  soundings  examined  were  invariably  charged  with  diatomaceous  remains,  constitu- 
ting a  bank  which  stretches  200  miles  north  from  the  base  of  Victoria  Barrier,  while 
the  average  depth  of  water  above  it  is  300  fathoms,  or  1,800  feet." 

*  As  respects  sand  intermingled  with  ice  and  carried  away,  Captain  Wilkes  mentions 
("  United  States  Exploring  Expedition")  a  floating  mass,  composed  of  alternate  layers 
of  snow  and  ice,  the  former  mixed  with  sand.  Upon  this  pieces  of  granite  and  red  clay 
were  also  found. 

f  Taken  from  the  plate,  vol.  ii.  p.  213,  of  Cook's  Voyage  to  the  South  Pole,  4to., 
1777. 


SOUTH    GEORGIAN    GLACIERS    REACHING    THE    SEA.      247 


the  sea,  the  depth  of  which  was  more  considerable  than  that  of  an  ordi- 
nary sounding-line  (204  feet)  employed  at  the  time.  Captain  Cook 
says,  "  The  head  of  the  bay,  as  well  as  two  places  on  each  side,  was 
terminated  ^y  perpendicular  ice-cliffs  of  considerable  height.  Pieces 
were  continually  breaking  off,  and  floating  out  to  sea  ;  and  a  great  fall 
happened  while  we  were  in  the  bay  (January  17,  1775),  which  made  a 
noise  like  cannon."  He  also  calls  attention  to  the  bottoms  of  the  bays 
generally  in  this  land  being  filled  by  glaciers,  supplying  an  abundance 
of  icebergs  ;  and  it  is  easy  to  infer  that,  from  amid  the  mountain  cliffs 
among  which  these  glaciers  find  their  way  to  the  coast,  many  a  frag- 
ment of  rock  may  be  ice-borne,  and  deposited  at  the  bottom  of  the  sea, 
remote  from  South  Georgia.  Not  a  stream  or  a  river  could  be  seen 
throughout  the  whole  coast  explored,  though  it  was  visited  in  the  sum- 
mer of  that  region.  Captain  Cook  also  mentions  bays  full  of  glaciers, 
descending  from  the  heights  of  Sandwich  Land,  discovered  by  him  upon 
leaving  South  Georgia,  on  the  southeast  of  that  island.* 

Quitting  the  far  southern  land  and  remote  islands,  the  climate  is 
such  in  Tierra  del  Fuego,  although  comprised  between  latitude  52°  30' 
and  56°  S.  (a  range  corresponding  in  the  northern  hemisphere  with  the 
position  and  distance  between  Birmingham  and  Edinburgh),  that  the 
line  of  perpetual  snow  occurs,  according  to  Captain  King,  at  between 
3500  and  4000  feet  above  the  sea  in  the  Straits  of  Magellan,  and  that 
glaciers  descend  into  the  sea.f  Mr.  Darwin  states  that  on  the  north 
side  of  the  Beagle  Channel  (a  remarkable  strait,  running  east  and  west 
across  the  southern  part  of  Tierra  del  Fuego),  the  mountains  are  covered 
with  perpetual  snow,  whence,  in  many  places,  magnificent  glaciers 
descend  to  the  water's  edge,  fragments  falling  from  them  into  the  sea, 
and  floating  about  as  miniature  icebergs.J  He  remarks  that  glaciers 
occur  at  the  head  of  the  sounds  along  the  whole  western  coast  of  the 
southern  part  of  South  America. §  It  would  appear  that  as  far  north 

*  Cook's  Voyage  to  the  South  Pole,  vol.  ii.  p.  224.  He  remarks  also  upon  the  flat 
surfaces,  and  even  heights,  of  the  icebergs  in  that  region,  some  two  or  three  miles  in 
circumference,  reminding  us  of  the  character  of  those  off  the  great  ice  barrier  near 
Victoria  Land. 

f  Mr.  Darwin  gives  the  following  table  of  the  climate  of  Port  Famine,  Straits  of 
Magellan,  and  of  Dublin: — 


Latitude. 

Summer 
Tempera- 
ture. 

Winter 
Tempera- 
ture. 

Difference. 

Mean 
of  Summer 
and 
Winter. 

Dublin  

53°  21'  N 

59.540 

39-2° 

20-34° 

40.070 

Port  Famine  .     .     . 

53    38   S. 

50- 

33-08 

16-92 

41-54 

Difference    .     . 

0    17 

9-54 

6-12 

3-42 

7-83 

Darwin,  "Voyage  of  Adventure  and  Beagle,"  vol.  iii.  p.  243. 

Ibid.,  p.  282.     Mr.  Darwin  observes  (p.  283),  "In  the  Canal  of  the  Mountains  no 


248     TRANSPORTAL  OF  DETRITUS  BY  RIVER  ICE. 

as  latitude  48o  30'  S.  glaciers  advance  into  the  sea.  Eyre's  Sound  is 
terminated  by  glaciers  descending  from  the  range  of  the  Sierra  Nevada 
on  the  east.  Mr.  Bynoe  saw  numerous  detached  masses  of  ice  floating 
about,  20  miles  from  the  head  of  the  sound ;  and  upon  one,  drifting  out- 
wards, found  an  angular  block  of  granite,  described  as  a  cube  of  nearly 
two  feet,  partly  imbedded  in  it,  the  ice  thawed  around.*  Mr.  Darwin 
directs  attention  to  the  occurrence  of  a  glacier  at  the  level  of  the  sea, 
even  in  latitude  46°  40'  S.,  in  the  Gulf  of  Penas,  reaching  to  the  head 
of  Kelly  Harbour,  pointing  out  that  thus  "  glaciers  here  descend  to  the 
sea  within  less  than  nine  degrees  of  latitude  from  where  palms  grow, 
less  than  two  and  a  half  from  arborescent  grasses ;  and,  looking  to  the 
westward,  in  the  same  hemisphere,  less  than  two  from  orchideous  para- 
sites, and  within  a  single  degree  of  tree  ferns. "f 

The  transportal  of  mineral  matter  by  floating  ice  is  not  limited  to 
portions  of  glaciers,  broken  off  where  they  have  protruded  into  the  sea, 
or  to  masses  detached  from  great  continuous  ranges  of  ice,  such  as  the 
barrier  off  Victoria  Land,  and  which  have  rested  upon  the  bottom,  and 
have  been  subsequently  upset,  then  carrying  rock  fragments,  sand,  and 
mud  upwards,  or  which  scraped  away  a  part  of  the  sea  bottom  as  they 
floated  off,  transporting  detritus,  adhering  beneath,  to  various  distances. 
Rivers,  in  regions  where  the  temperature  descends  sufficiently  low, 
remove  no  small  portion  of  such  matter  by  means  of  ice  down  their 
courses,  and  coast  ice  distributes  no  inconsiderable  amount  of  it  in 
various  directions.  As  regards  the  mode  in  which  detritus  may  be 
conveyed  by  rivers,  it  may  often  be  studied  in  our  brooks  and  streams, 
when  a  sudden  thaw  suddenly  fills  them  with  water,  lifting  away  ice 
which  may  bind  gravel,  sand,  or  pieces  of  frozen  mud  together,  by  their 
sides  or  in  shallow  places.  According  to  the  relative  specific  gravities 
of  the  detached  portions  of  ice,  stones,  sand,  and  mud,  will  they  be 
seen  to  move,  some  larger  pebble,  perhaps,  deeply  set  in  its  support  of 
ice,  trailing  along,  and  leaving  the  mark  of  its  passage  on  the  bottom. 
Other  portions  will  float  more  freely  onwards,  some  acquiring  rotatory 
motion,  and,  by  grinding  against  each  other,  parting  with  some  parts  of 
their  load,  especially  the  heaviest,  while  here  and  there  they  become 
jammed  in  the  narrower  parts  of  the  stream,  and  stranded  upon  shoals, 

less  than  nine  (glaciers)  descend  from  a  mountain,  the  whole  side  of  which,  according 
to  the  chart,  is  covered  with  a  glacier  of  the  extraordinary  length  of  21  miles,  and  with 
an  average  breadth  of  1 J  mile.  It  must  not  be  supposed  that  the  glacier  merely  ascends 
some  valley  for  the  21  miles,  but  it  extends  apparently  at  the  same  height  for  that 
length,  parallel  to  the  sound,  and  here  and  there  sends  down  an  arm  to  the  sea-coast. 
There  are  other  glaciers  having  a  similar  structure  and  position,  with  a  length  of  10  or 
16  miles  (Tierra  del  Fuego)." 

*  ''Voyage  of  Beagle,"  vol.  iii.  p.  283.  Mr.  Darwin  calls  attention  to  this  sound 
being  in  a  latitude  corresponding  in  the  north,  with  that  of  Paris,  and  also  to  an  "  Ice- 
berg Sound,"  as  given  in  the  charts  still  further  north. 

f  Ibid.,  p.  285. 


TRANSPORTAL  OF  DETRITUS  BY  RIVER  ICE.     249 

there  remaining,  in  great  part,  until,  the  thaw  proceeding,  the  ice  melts, 
and  the  detrital  matter  is  dealt  with  by  the  stream  in  the  usual  manner.* 
The  transportal  of  mineral  matter  which  may  often  and  easily  be  seen 
in  this  minor  manner,  under  the  fitting  conditions,  is  but  carried  out 
upon  a  larger  scale  in  many  great  rivers,  where  the  relative  magnitude 
of  the  effects  produced  more  engages  our  attention,  especially  when  those 
objects  to  which  we  attach  interest  are  endangered  or  sustain  injury. 
In  the  regions  where  ice  is  common  upon  great  rivers  during  part  of 
the  year,  and  that  part  of  the  year  the  time  when  the  water  supply  is 
the  least,  and  the  river  level  the  lowest,  the  fragments  of  rocks,  pebbles, 
sand,  and  mud  of  the  sides  and  shoal  grounds  become,  as  it  were,  a  piece 
of  the  main  sheet  of  ice,  should  it  extend  entirely  over  the  river,  or  of 
such  portions  of  one  as  may  exist.  These  are  ready  to  be  broken  off, 
lifted,  and  borne  down  the  stream  as  the  waters  of  the  river  rise  before 
any  general  increase  of  temperature  melts  the  ice  upon  the  banks,  shoals, 
or  general  surface  of  the  river.  It  will  be  obvious  that  the  transportal 
of  detritus  will  depend  upon  circumstances,  as  in  the  little  brooks,  and 
that  while  some  portions  are  carried  long  distances,  others  will  be  left 
in  various  situations,  according  to  conditions ;  sometimes  fragments  of 
rock  being  carried  to,  and  accumulated  in,  situations  where  the  ordinary 
force  of  the  river  cannot  readily  dislodge  them,  and  indeed  sometimes 
be  altogether  insufficient  for  the  purpose.  We  have  various  accounts 
of  detritus  so  borne  downwards  in  rivers  by  means  of  ice.  In  the  St. 
Lawrence  there  would  appear  to  be  good  opportunities  of  studying  the 
transportal  of  mineral  matter  on  the  large  scale.  Captain  Bayfield  has 
pointed  out  that  there,  when  the  temperature  in  winter  sometimes  de- 
scends 30°  below  zero  (Fahr.,)  large  boulders  are  entangled  in  the  ice, 
and  carried  considerable  distances  upon  the  surface  of  the  water  in  the 
spring.  Shoals  are  thickly  strewed  with  them.f  Conditions  being 
favourable  for  keeping  blocks  and  fragments  of  rock  in  the  lower  part 

*  It  is  while  studying  the  effects  of  ice  in  the  brooks  and  minor  streams  that  an 
observer  may  sometimes  see  the  formation  of  ice  at  the  bottom.  M.  Arago,  whose 
attention  this  subject  has  engaged,  remarks  respecting  it  ("  Annuaire  du  Bureau  des 
Longitudes  pour  1833,"  p.  244),  that  the  movement  of  these  running  waters  mixes 
those  of  different  temperatures  and  densities,  so  that  when  the  whole  is  at  the  freezing 
point,  the  pebbles  and  other  substances  at  the  bottom  of  the  brook  constitute  so  many 
projections,  as  in  a  saline  solution,  and  thus  ice  is  formed  upon  them.  The  ice  thus 
produced  is  spongy,  from  the  crossing  and  confused  grouping  of  its  crystals,  the  move- 
ment of  the  water  preventing  a  uniform  arrangement  of  parts.  The  ice  accumulates, 
and  gradually  envelopes  numerous  pebbles  and  other  substances,  and  will  rise  to  the 
surface  with  its  mineral  load  if  the  general  specific  gravity  of  the  whole  will  permit. 
M.  Leclercq  has  observed  ("  Memoires  Couronnes  par  I'Acad&nie  de  Bruxelles,"  torn, 
xiii.  1845)  that  the  ice  'is  first  formed  upon  the  face  of  the  pebbles  or  other  objects 
opposed  to  the  current  of  water,  that  although  a  rapid  flow  of  water  contributes  to  the 
first  production  of  the  ice,  the  increase  of  ice  is  in  proportion  as  the  movement  of  the 
water  is  moderate,  the  extreme  cold  considerable,  and  the  sky  clear. 

f  Bayfield  "  Proceedings  of  the  Geological  Society  of  London,"  (1836,)  vol.  ii.  p.  223. 


250        GEOLOGICAL  EFFECTS  OF  RIVER  ICE. 

of  the  river  ice,  thus  carried  onwards,  and  indeed  often  driven  forwards 
rapidly,  wherever  the  general  masses  grated  upon  any  bottom,  over 
which  they  could  be  forced  by  the  volume  of  water  behind  (and  heavy 
piles  of  ice  sometimes  accumulate,  obstructing  the  free  flow  of  the 
waters),  much  scratching  and  furrowing  would  be  expected,  according  to 
the  relative  hardness  of  the  rocks  passed  over  and  of  the  ice-borne  frag- 
ments, to  the  pressure  of  the  mass  of  ice  and  detritus,  and  to  the  velo- 
city with  which  that  mass  may  be  driven  upon  the  rocky  ledge  or  shoal. 
Fragments  of  rock,  set  in  the  ice,  and  grating  against  vertical  cliffs 
rising  from  comparatively  deep  water,  such  as  frequently  occur  on  the 
bends  of  rivers,  would  also  horizontally  scratch  and  abrade  the  rocks, 
according  to  their  relative  hardness,  the  ordinary  river  action  not  re- 
moving these  marks,  though  they  may  become  obliterated  by  atmospheric 
influences  at  lower  states  of  the  river,  especially  where  the  cliiF-rocks 
were  composed  of  somewhat  incoherent  materials.  Thus  while  some 
ice-supported  boulders  and  fragment  of  rocks  were  grooving  and  furrow- 
ing the  horizontal  surface  of  a  ledge  of  rocks  at  b  (fig.  95),  and  others, 
encased  in  ice,  were  borne  down  the  river  at  the  same  time,  scratching 
and  wearing  away  the  vertical  cliff  at  <?,  another  collection  might  be 
leaving  permanent  traces  of  its  passage  upon  previously  ice-borne  boul- 
ders, accumulated  from  local  causes  at  a. 

Fig.  95. 


It  is  interesting  to  an  observer  to  consider  that  by  such  means  large 
rounded  portions  of  rock,  with  minor  pebbles,  may  thus  be  borne  to- 
wards the  Gulf  of  St.  Lawrence,  and  be  thrown  down,  after  being 
scratched  in  their  passage  over  hard  ledges  of  rock,  or  over  boulders  in 
shallow  water,  in  situations  where  such  marks  would  not  be  removed  by 
any  attrition  to  which  they  would  be  exposed  under  existing  circum- 
stances, there  accumulating  with  finer  detritus,  even  mud  deposited 
from  water  in  which  it  had  been  held  in  ordinary  mechanical  suspen- 
sion. Thus  the  scratching  of  the  ledges  of  solid  rock  and  heavy  stranded 
boulders  in  shallow  situations  might  be  accomplished,  and  the  boulders 
and  pebbles  by  which  this  was  effected  be  themselves  often  also  scratched, 
carried  onwards  under  favourable  circumstances,  and  be  deposited,  with 
these  marks  still  upon  them,  amid  fine  sediment  in  depths  beyond  the 
reach  of  wave  or  breaker  action  for  the  attrition  necessary  to  remove 
such  scratches. 

The  great  rivers  of  Northern  Europe,  Asia,  and  America  delivering 
themselves  into  the  Arctic  Sea  (p.  157),  flowing  as  they  do  from  milder 
into  colder  climates,  present  us  with  the  conditions  for  the  formation  of 


GEOLOGICAL  EFFECTS  OF  RIVER  ICE.        251 

ice  sooner,  and  its  continuance  later  at  their  embouchures  than  towards 
their  origin.  The  effects  produced  are  especially  interesting,  inasmuch 
as  when,  from  the  melting  of  the  snows  and  ice  on  the  southward,  floods 
are  produced,  these  meet  with  the  obstruction  of  the  ice  towards  the 
mouths  of  the  rivers.  In  consequence,  it  not  unfrequently  occurs  that 
the  resistance  of  the  ice  being  suddenly  overcome,  it  is  violently  up- 
heaved and  broken,  and  in  parts  thrown  aside,  with  any  masses,  or  minor 
fragments  of  rocks  attached  to  it.  Sir  Roderick  Murchison  has  pointed 
out  the  banks  of  rock-fragments  thus  produced  on  the  sides  of  rivers  in 
Russia,  and  especially  notices  the  fluviatile  ridges  of  angular  blocks 
towards  the  mouth  of  the  Dwina.  White  carboniferous  limestone  there 
occurs  (about  110  versts  from  Archangel),  and  the  waters  of  the  river 
entering  amid  its  chinks  and  joints,  separates  them  when  frozen,  so  that 
subsequently  they  are  entangled  in  the  ice  adjoining  the  banks,  and  are 
thus  carried  with  it.*  By  the  sudden  rise  of  waters  thus  caused,  many 
a  block  of  rock  must  be  borne  over  low  ground,  stranded  on  shoal  water, 
or  be  occasionally  carried  seawards,  and  thrown  down  amid  fine  sedi- 
ment, the  conditions  for  the  transport  of  which  outwards  would  be  in- 
creased during  these  sudden  discharges  of  water.  The  crashing  and 
jamming  together  of  the  broken  masses  of  ice  would  be  highly  favour- 
able to  the  scratching  and  scoring  of  blocks  and  fragments  of  rocks 
entangled  among  them,  and  such  blocks  and  fragments  may  also  be 
often  transported  to  situations  where,  under  existing  circumstances,  the 
markings  thus  produced  would  not  be  obliterated. 

When  we  consider  the  state  of  sea-coasts  in  those  regions  where  the 
temperature  falls  sufficiently  low  during  a  part  of  the  year  that  ice  is 
formed  upon  them,  entering  amid  the  substances  of  which  they  are  com- 
posed, and  binding  blocks  of  rock,  shingles,  sand,  and  even  mud,  with 
the  remains  of  any  marine  animals  there  occurring,  into  one  solid  mass, 
we  see  that  when  the  warmer  season  in  such  regions  comes  round,  mi- 
neral matter  may  be  readily  removed  from  one  place  to  another  upon 
the  breaking  up  of  the  coast  ice. 

Upon  the  breaking  up  of  this  coast  ice,  which  sometimes  rests  on 
shallow  ground,  and  at  others  covers  deep  water,  we  should  expect  much 
grinding  of  the  masses  on  the  shore,  scratching  and  grooving  the  sides 
of  cliffs  and  shallow  rocky  bottoms,  when  shingles  or  other  fragments 
of  rock  are  frozen  into  the  ice,  so  as  to  be  brought  into  contact  with  the 
one  or  the  other. f  The  force  employed  would  appear  to  be  often  very 

*  Murchison,  "  Geology  of  Russia  in  Europe  and  the  Ural  Mountains,"  vol.  i.  p.  567. 
He  quotes  M.  Bohtlingk  as  noticing  large  granitic  boulders,  weighing  several  tons,  en- 
tangled in  the  branches  of  pine  trees,  30  or  40  feet  above  the  level  of  the  streams. 
Speaking  of  blocks  of  rocks  ice-borne  down  rivers,  Sir  Roderick  Murchison,  after 
noticing  their  modes  of  transport  and  deposit,  remarks,  that  old  drift  from  the  north 
may  thus  be  brought  back  to  the  northward  by  the  rivers,  p.  565. 

f  M.  Weibye,  of  Kragero,  is  quoted  by  M.  Frapolli  ("Bulletin  de  la  Societe'  G6olo- 


252         GEOLOGICAL  EFFECTS  OF  COAST  ICE. 

considerable,  great  sheets  of  ice  being  set  in  motion,  and  being  driven 
with  tremendous  crashes  against  the  land,  so  as  not  only  to  act  upon 
shore  ice,  in  which  rock  fragments  and  shingles  may  be  imbedded,  thus 
pressing  them  heavily  against  bare  rocks,  but  also  forcing  beaches  before 
them,  grinding  the  pebbles  and  boulders  against  each  other,  and  upon 
exposed  rocks,  by  which  both  may  be  scored  and  marked.  In  this  man- 
ner friction-marks  may  be  produced,  which  in  some  situations  may  not 
be  very  readily  removed  by  the  ordinary  rounding  and  smoothing  of 
breaker  action. 

When  an  observer  studies  the  maps  and  charts  which  we  as  yet  pos- 
sess of  the  northern  seas  of  America,  Europe,  and  Asia,  he  will  find 
enough  to  show  him  that  portions  of  beaches  may  readily  be  removed 
upon  the  breaking  up  of  ice  from  the  coasts,  and  be  transported  to 
other  situations,  where,  upon  the  melting  of  that  ice,  they  may  be 
thrown  down  in  depths  amid  any  fine  detritus  there  accumulating. 
Should  any  of  their  component  pebbles  or  fragments  of  rock  have  been 
so  acted  upon  as  to  be  scratched  before  they  were  thrown  down,  they 
would  retain  those  marks  amid  the  fine  deposits  in  such  depths.  As 
ice  adheres  to  coasts  in  many  localities  during  winter,  upon  which,  from 
the  ordinary  action  of  the  sea  on  shores,  breakers  throw  whole  and 
broken  shells  of  molluscs  and  other  marine  animal  remains  during  the 
summer,  these  remains  would  be  liable  to  be  entangled  in  portions  of 
beach  removed  by  the  ice,  and  be  scattered  over  various  depths  of 
water,  in  the  same  manner  as  the  transported  mineral  matter,  and  thus 
the  remains  of  littoral  molluscs,  often  in  fragments,  may  be  dispersed 
amid  a  mixture  of  mud,  and  ice-borne  blocks,  and  fragments  of  rock 
accumulating  in  deep  water. 

In  tidal  seas  account  has  to  be  taken  of  the  movement  of  ice  in 
estuaries,  and  in  those  long,  deep  loughs  or  arms  of  the  sea,  in  Norway 
termed  fiords,*  up  and  down  which  the  flood  and  ebb  tides  are  felt 

gique  de  France,"  1847),  as  inferring,  respecting  the  marks  left  by  the  block-and- 
shingle-bearing  ice  of  the  Scandinavian  coasts,  that  on  those  bordering  the  sea  in  the 
Bradsbergsamt,  "the  scratches  and  furrows  on  horizontal,  or  nearly  horizontal  sur- 
faces, take  a  direction  always  perpendicular  to  the  general  line  of  coast  in  open  bays, 
and  always  parallel  to  the  range  of  the  channels  in  narrow  fiords,  that  the  horizontality 
or  the  greater  or  less  inclination  of  the  scratches  on  the  inclined  or  vertical  surfaces 
depends  on  the  relief  of  the  coasts  of  the  locality,  and  always  corresponds  with  the 
relief  and  with  the  action  of  the  different  winds."  M.  Frapolli  himself  also  calls  atten- 
tion to  the  effects  of  coast  ice  armed  with  blocks  and  pebbles  of  rock,  driven  about  in 
numerous  fragments  by  the  storms  of  winter  and  spring,  and  grinding  against  the  cliffs 
of  Scandinavia,  polishing  and  scratching  the  rocks  according  to  their  surfaces  and  posi- 
tion, the  cliffs  scratched  in  horizontal  lines  along  the  fiords  and  in  other  similar 
positions. 

*  The  channels  which  divide  Tierra  del  Fuego  into  its  many  islands,  and  the  Straits 
of  Magellan  separating  it  from  the  mainland  of  America,  with  the  very  numerous  inden- 
tations and  channels  found  between  the  east  entrance  of  the  Straits  of  Magellan  and 
the  Gulf  of  Perias,  and  into  which  glaciers  often  descend,  and  ice  floats  about,  would 


GEOLOGICAL    EFFECTS    OF    COAST    ICE.  253 

according  to  circumstances.  Coast  ice,  borne  backwards  and  forwards 
by  the  tide,  and  having  pebbles  and  fragments  of  rock  so  set  in  it  that 
they  can  grind  upon  or  against  bare  rocks,  spread  horizontally  or  rising 
vertically,  or  nearly  so,  in  the  estuaries  and  fiords,  could  scarcely  fail 
to  become  an  instrument  of  importance  in  the  scratching  and  grooving 
of  such  bare  rocks,  these  markings  being  also,  especially  in  the  case  of 
the  cliffs,  not  easily  removable.  This  action  continuing  through  many 
successive  ages,  certain  kinds  of  rocks  might,  in  favourable  localities, 
retain  marked  scratches  and  grooves  thus  produced,  independently  of 
the  influence  of  winds  driving  the  fractured  coast  ice  about  against  lines 
of  coast,  upon  the  breaking  up  of  such  ice.  Fragments  of  ice  and  any 
mineral  matter  they  may  sustain  are  thus  piled  up  at  the  bottom  of  bays 
or  in  shoal  water,  a  combination  of  a  heavy  on-shore  gale  of  wind  and 
a  spring  tide  leaving  many  a  fragment  of  rock  in  a  situation  whence  it 
could  not  readily  be  removed  under  ordinary  circumstances. 

No  small  amount  of  rounded  boulders  and  pebbles  of  various  sizes 
may  thus  become  strewed  near  coasts,  or  be  mingled  beneath  deep 
water  with  the  angular  fragments  which  have  either  been  transported 
by  icebergs,  broken  off  the  terminal  portions  of  glaciers,  or  which  may 
have  fallen  from  cliffs  upon  coast  ice,  with  the  addition  even  of  the 
remains  of  littoral  or  shallow-water  molluscs,  or  of  other  marine  animals, 
such  as  the  bones  of  fish,  whales,  and  seals  carried  off  by  the  coast  ice. 
A  good  example  of  the  removal  of  a  block  of  rock  by  coast  ice,  so  far 
from  the  polar  regions  as  Denmark,  is  mentioned  by  Dr.  Forchhammer, 
who  states  that  one,  about  four  to  five  tons  in  weight,  and  resting  on 
the  shore,  was  encased  in  coast  ice  during  the  winter  of  1844,  and  car- 
ried out  to  sea  with  the  ice  in  the  following  spring,  leaving,  as  it  moved 
seaward,  a  deep  furrow  in  the  sandy  clay  of  the  shore,  not  quite  oblite- 
rated six  months  afterwards.* 

As  modifying  the  accumulations  which  may  be  formed  on  the  bottoms 
of  seas  liable,  from  time  to  time,  and,  sometimes,  as  a  whole,  periodi- 
cally, to  sustain  icebergs  grounded  upon  them,  the  observer  has  to  bear 
in  mind  that  not  only  may  the  icebergs,  by  being  forced  against  banks, 

appear  to  be  frequently  very  deep  and  steep-sided.  In  mid-channel,  eastward  of  Cape 
Forward,  Captain  King  found  no  bottom  in  the  Straits  of  Magellan,  with  a  line  of  1536 
feet. 

*  Forchhammer,  "  Bulletin  de  la  Societe  Ge*ologique  de  France,"  1848.  He  observes, 
respecting  the  transport  of  blocks  and  pebbles  on  the  coast  of  Denmark  by  coast  ice, 
that  although  the  latter  envelopes  the  blocks  and  pebbles  on  the  shore,  to  enable  these 
to  be  borne  away,  it  is  necessary  that  the  thaw  or  rupture  of  the  ice  should  coincide 
with  the  rise  of  the  waters.  Respecting  blocks  and  fragments  of  rock  borne  out  by  the 
ice  from  the  Baltic,  by  means  of  the  current  setting  through  the  Kattegat  in  the  spring, 
Dr.  Forchhammer  mentions  that,  in  1844,  a  diver  found  the  remains  of  an  English 
cutter,  blown  up  during  the  bombardment  of  Copenhagen  in  1807,  covered  by  blocks, 
some  of  which  measured  from  six  to  eight  cubic  feet.  The  same  diver  affirmed  that  all 
the  wrecks  he  had  visited  in  the  roadstead  of  Copenhagen  were  more  or  less  covered  by 
rock  fragments. 


254  EFFECTS    OF    GROUNDED    ICEBERGS. 

jumble  together,  and  singularly  mingle  beds  of  clay  and  sand,  even 
occasionally  adding  transported  fragments  to  the  disturbed  mass,  but 
also  act  as  rocks  around  and  amid  which  streams  of  tide,  or  sea-currents, 
may  become  for  the  time  modified.  We  should  expect  this  to  be  most 
experienced  in  the  regions  where,  from  the  general  intensity  of  the  cold, 
the  icebergs  could  the  longest  remain.  Sir  James  Ross  mentions  that 
the  streams  of  tide  were  so  strong  amid  grounded  icebergs  at  the  South 
Shetlands,  that  eddies  were  produced  behind  them,*  so  that,  as  far  as 
such  streams  were  concerned,  they  acted  as  rocks.  Navigators  have 
observed  icebergs  sufficiently  long  aground  in  some  situations,  that  even 
mineral  matter  might  be  accumulated  at  their  bases  in  favourable  situa- 
tions, while  streams  of  tide  may  run  so  strongly  between  others,  that 
channels  might  be  cut  by  them  in  bottoms  sufficiently  yielding,  and  at 
depths  where  the  friction  of  these  streams  could  be  experienced.  Much 
modification  of  sea  bottoms  might  be  thus  produced  by  grounded  ice- 
bergs, not  forgetting  those  seasons  of  the  year  when  many  become 
joined  together  by  ordinary  sea  ice,  constituting  part  of  a  mass  to  be 
dealt  with  on  the  large  scale,  when  such  ice  is  broken  up.  However 
firm  the  icebergs  may,  like  so  many  anchors,  often  tend  to  hold  the 
main  mass,  it  is  not  difficult  to  conceive  that  conditions  might  arise  by 
which  many  were  dragged,  cutting  and  ploughing  up  the  sea  bottoms  in 
their  courses. 

Ice  thus  transports  portions  of  rocks,  either  in  the  shape  of  glaciers, 
descending  under  the  needful  conditions  in  various  extra-tropical  regions, 
or  as  floating  ice  down  rivers,  as  coast  ice,  as  fragments  of  glaciers  de- 
scending into  the  sea,  or  as  masses  which,  having  been  aground,  cap- 
size, and  bring  up  a  portion  of  the  bottom  on  which  they  previously 
rested.  Huge  fragments  of  rock  are  by  these  means  moved  to  distances 
from  their  parent  masses,  of  which  no  other  known  power,  now  in  force 
on  the  surface  of  our  globe,  appears  capable.  It  has  been  seen  that 
glaciers  increase  and  decrease  according  to  the  variations  of  the  cli- 
mates under  which  they  are  formed.  What  the  amount  of  that  increase 
and  decrease  may  be,  under  the  conditions  now  existing,  and  where 
glaciers  have  been  noticed,  seems  not  well  ascertained,  though  the  diffe- 
rences in  their  volume  and  extent  would  appear  to  have  been  greater 
than  was  once  supposed.  Be  that  as  it  may,  they  distribute  rock  frag- 
ments outwards  from  mountain  regions,  these  generally  angular,  unless 
ground  between  the  glacier  sides  and  bottom,  the  larger  blocks  and 
fragments  remaining  where  the  glaciers  left  them,  while  minor  portions 
and  finely  comminuted  mineral  matter  are  thrown  into  the  torrents  and 
rivers,  to  be  disposed  of  by  them  according  to  their  powers.  River  ice 
may  carry  detritus  entangled  in  it,  distributing  the  mineral  matter 

*  Ross,  "Antarctic  Voyage." 


GENERAL     GEOLOGICAL    EFFECTS    OF    ICE.  255 

over  areas  corresponding  with  their  courses,  and  which  may  be  suffi- 
ciently flooded  by  them,  transporting  many  a  block  and  fragment 
which  the  power  of  the  stream  could  not  othewise  have  moved.  With 
the  exception  of  rock  fragments,  which  may  have  fallen  from  cliffs  over- 
hanging the  rivers,  and  not  afterwards  have  been  rounded,  which  may 
have  been  broken  up  from  the  sides  in  the  manner  previously  noticed 
(p.  251),  or  which  may  have  been  left  by  some  prior  geological  condi- 
tion of  the  area,  we  should  expect  much  of  the  detritus  borne  down  by 
river  ice  to  be  composed  of  the  ordinary  pebbles,  sand,  and  mud  of  river 
courses. 

The  sea  deals  with  any  ice-borne  detritus  received  from  rivers,  or 
from  the  coasts,  according  as  it  is  tideless  or  tidal,  and  as  the  portions 
into  which  these  are  carried  may  be  in  movement  as  sea  and  ocean  cur- 
rents, or  the  ice  be  acted  on  by  the  wind.  Looking  at  the  northern 
regions,  where  rivers  of  sufficient  importance  discharge  themselves, 
carrying  ice  outwards,  and  coast  ice  is  common,  it  may  be  anticipated 
that  much  coast  shingle,  with  rounded  river  pebbles,  lumps  of  the  frozen 
mud,  and  sands  of  estuaries,  the  occasional  remains  of  marine  animals, 
and  now  and  then  those  of  terrestrial  animals,  suddenly  swept  outwards 
by  the  river  floods,  would  be  strewed  about  upon  the  sea  bottom. 
Many  a  bone  of  elephants,  rhinoceroses,  and  other  animals,  imbedded 
in  the  mud,  sand,  and  gravel,  of  these  regions,  may  also,  after  having 
been  washed  out  of  the  beds  which  contained  them,  be  ice-borne  into 
the  sea,  and  be  mingled  with  remains  of  existing  animals.  To  these 
may  be  added  angular  fragments  carried  out  by  the  ice  of  rivers,  or 
borne  by  coast  ice  from  beneath  cliffs  whence  such  fragments  have 
fallen  upon  it,  independently  of  those  carried  into  parts  of  the  same 
seas  by  icebergs  detached  from  the  terminal  part  of  glaciers. 

Notwithstanding  the  Arctic  seas  are  so  shut  in  by  the  lands  of 
America  and  Asia,  a  comparatively  small  opening  (Behring's  Strait) 
only  occurring  between  them,  a  space  sufficiently  open  exists  between 
America  and  Europe,  notwithstanding  the  interruption  presented  by 
Iceland,  to  permit  the  escape  outwards  of  a  certain  portion  of  ice.  We 
have  seen  that  over  the  bottom  of  part  of  the  North  Atlantic  blocks 
and  fragments  of  rocks,  with  minor  detritus,  are  now  being  strewed, 
without  reference  to  its  inequalities.  In  the  Antarctic  seas  very  dif- 
ferent conditions  present  themselves.  Great  rivers,  bearing  ice-borne 
blocks  and  fragments  of  rocks,  with  minor  detritus,  are  not  found.  The 
land,  now  commonly  supposed  to  occupy  so  large  an  area  in  the  South 
Polar  regions,  supports  little  else  than  water  in  its  solid  form,  and  the 
coast,  for  the  most  part,  seems  so  encased  by  huge  icy  barriers,  that 
common  coast  ice  would  there  appear  considerably  limited,  as  compared 
with  the  Arctic  regions,  in  its  power  to  carry  off  rounded  boulders  and 
shingles.  Such  glaciers  as  reach  the  sea,  transporting  fragments  from 


256  GENERAL    GEOLOGICAL    EFFECTS    OF    ICE. 

the  inland  cliffs  amid  which  they  may  move,  would  appear  the  principal 
agents  in  carrying  mineral  matter  directly  from  the  land,  allowing  for 
a  portion  transported  by  coast  ice.  The  ice  aground  off  Victoria  Land 
would  nevertheless  appear  to  have  the  power  of  transporting  much 
detritus  when  broken  up  into  icebergs  and  upset,  strewing  blocks  and 
minor  fragments,  sand,  and  mud,  over  a  part  of  the  Southern  Pacific. 
The  South  Shetlands,  South  Orkneys,  South  Georgia,  Sandwich  Land, 
and  the  lands  more  or  less  encased  with  ice  between  the  South  Shet- 
lands and  Victoria  Land,  doubtless  also  contribute,  by  means  of  glaciers, 
coast  ice,  and  probably  also,  as  capsized  grounded  ice,  blocks  and  frag- 
ments of  rock  (some  rounded),  sand,  and  mud,  to  the  bottom  of  the 
Southern  Atlantic,  and  the  ocean  southward  of  Africa  and  Australia. 
The  southern  portion  of  America  adds  its  glacier-borne  fragments,  and 
thus,  both  on  the  north  and  on  the  south,  portions  of  rocks,  formed  in 
the  colder,  are  ice-borne,  and  left  beneath  the  seas  of  the  more  tempe- 
rate regions  of  the  earth. 

Such  being  the  geological  effects  now  due  to  ice,  it  becomes  desirable 
to  consider  those  which  would  probably  arise,  either  from  a  general 
diminution  of  temperature  on  the  surface  of  the  globe,  or  from  partial 
changes  of  that  temperature.  With  respect  to  the  first  we  have  to  look 
to  some  general  cause  common  to  the  whole  globe.  Whatever  the  con- 
ditions for  the  distribution  of  temperature  may  have  formerly  been,  we 
see  that  the  influence  of  the  sun  now  causes  the  heat  of  the  tropics,  and 
the  different  exposure  of  the  polar  parts  of  the  earth's  surface  to  it,  the 
great  variations  of  seasons  there  experienced.  Any  changes  of  suffi- 
cient importance,  therefore,  in  the  influence  of  the  sun,  which  should 
produce  a  corresponding  change  on  the  face  of  the  earth,  so  that  the 
spheroidal  space  above  noticed  (p.  216),  surrounding  which  water  re- 
mains solid,  would  descend  lower  towards  the  sea  in  the  equatorial,  and 
cut  its  level  at  less  high  latitudes  in  the  polar  regions,  would  materially 
alter  the  climates  of  many  parts  of  the  world.  Geological  effects  due 
to  ice  would  be  more  widely  spread  than  they  now  are,  and  the  equa- 
torial space  within  which  ice-transported  masses  of  rock  and  other 
detritus  could  not  be  borne,  would  be  more  limited.  Glaciers,  where 
they  could  be  formed,  would  not  only  become  more  extended  than  they 
now  are  in  certain  mountainous  regions,  but  ranges  of  mountains,  amid 
which  they  do  not  at  present  occur,  the  line  of  perpetual  snow  not 
descending  sufficiently  low,  would  contain  them;  so  that,  in  the  one 
case,  mineral  matter  would  be  distributed  by  them  over  a  wider  area ; 
and,  in  the  other,  over  districts  where  no  transportal  of  the  kind  exists 
at  the  present  time.  Fragments,  angular,  subangular,  and  rounded, 
would  be  distributed  by  river-ice  and  coast-ice,  where  none  such  are 
now  formed,  and  sea  bottoms  would  then  be  strewed  over  by  them, 
where  previously  nothing  of  the  kind  had  been  carried.  Animal  and 


EFFECTS    OF    GENERAL    INCREASE    OF    COLD.  257 

vegetable  life  would  be  adjusted  to  the  new  conditions  (that  adapted  to 
the  colder  climates  of  the  earth  moving  more  towards  the  equator),  its 
remains,  at  least  such  as  were  preserved,  spreading  over  those  of  the 
animals  and  plants  which  flourished  in  the  same  regions  under  higher 
temperatures. 

The  like  general  effects  would  be  expected  if,  without  supposing  a 
diminished  influence  of  the  sun,  our  whole  solar  system,  moving  through 
space,  should  pass  from  the  temperature  now  inferred  to  be  that  of  the 
portion  amid  which  that  system  takes  its  course  (p.  217)  to  one  less 
high.  And  it  may  well  deserve  the  attention  of  the  geologist  to  con- 
sider the  effects  which  would  follow  such  a  change,  even  to  the  amount 
of  a  few  degrees,  as  commonly  measured  by  thermometers.  In  his 
observations  on  the  distribution  of  masses  of  rock,  apparently  ice-borne 
to  their  present  positions,  and  about  to  be  noticed,  it  is  very  desirable 
that  he  should  regard  the  subject  generally  as  well  as  locally,  so  that 
whatever  may  eventually  appear  the  right  inference  to  be  drawn  from 
the  facts  recorded,  such  as  may  bear  upon  the  former  should  not  be 
omitted  in  the  search  for  the  latter.  As  regards  the  evidence  of  many 
climates  having  remained  much  the  same,  with  certain  modifications, 
during  those  comparatively  few  revolutions  of  our  planet  round  the 
sun,  of  which  we  have  any  records,  and  from  which  we  may  infer  that 
the  climates  generally  of  the  surface  of  the  globe  have  not  suffered 
material  alteration  since  the  historical  period,  as  it  has  been  termed, 
the  geological  observer  will  soon  perceive  that  he  is  forced  to  consider 
it  as  affording  him  very  limited  aid  in  his  inquiries  respecting  the 
former  climatal  conditions  of  the  earth. 

The  present  different  conditions  as  to  the  production  of  ice  capable 
of  transporting  mineral  matter,  in  the  manner  above  noticed,  in  the 
northern  and  southern  cold  regions  of  the  globe,  are  sufficient  to  prove 
that  partial  changes  of  great  importance  may  arise  from  differences  on 
the  surface  of  the  earth  itself.     Every-day  experience  in  geological  re- 
search will  show  the  observer  that  he  has  to  consider  the  surface  of  the 
earth  to  have  been  in  an  unquiet  state  from  remote  geological  times  to 
the  present,  and  that  while  he  so  often  stands,  amid  stratified  deposits, 
on  ancient  sea  bottoms  now  elevated  to  various  altitudes  above  the  ocean 
level,  many  a  region  shows  that  its  area  has  more  than  once  been 
beneath  that  level  and  above  it.     Thus,  although  a  mass  of  land  may 
now  rise  above  the  sea-level  at  the  South  Pole,  separated  by  a  broad 
band  of  ocean  from  other  great  masses  of  land  to  the  northward,  pro- 
ducing certain  effects  as  regards  the  climate  of  that  part  of  the  globe, 
and  the  northern  polar  regions  are  otherwise  circumstanced,  it  by  no 
means  follows  that  such  has  always  been  the  case,  even  in  more  recent 
geological  times.    If  we  change  the  conditions  of  the  two  polar  regions, 
a  difference  of  results  is  obtained  of  an  important  geological  character. 

17 


258         EFFECTS    OF    PARTIAL    INCREASE    OF    COLD    FROM 

Mr.  Darwin  has  skilfully  touched  upon  the  effects  which  would  follow 
such  a  modification  of  conditions,  and  which  require  to  he  home  in 
mind  in  researches  of  this  kind.* 

In  like  manner  any  elevation  or  depression  of  a  considerable  area  of 
dry  land,  which  should  raise  parts  of  it  ahove,  or  lower  others,  now 
above,  beneath  the  line  of  perpetual  snow,  would  produce  modifications 
in  the  transportal  of  mineral  matter  which  could  be  effected  by  ice.  If 
the  region  comprising  the  Alps  was  raised  3000  feet  above  its  present 
relative  level,  the  area  fitted  for  the  formation  of  glaciers  would  be. 
greatly  extended,  many  a  valley  would  be  filled  with  ice,  and  many  a 
mountain  would  contribute  its  glacier,  not  so  filled  or  contributing  at  the 
present  moment.  Blocks  and  minor  fragments  of  rocks  would  be  ice- 
borne  over,  and  left  at  distances  from  the  main  range  not  now  attained  ; 
and,  under  the  supposition  of  a  gradual  rise  of  land,  many  modifica- 
tions would  attend  the  change  in  the  perpetual  snow  line,  whence  the 
glaciers  for  the  time  took  their  rise.  Many  a  ravine  and  mountain 
side  would  be  grooved  and  scratched,  not  now  touched  by  glaciers,  and 
huge  masses  of  rock  be  accumulated  in  heaps  or  lines,  in  localities  where 
no  ice  now  transports  such  masses.  Assuming  a  depression  of  the  same 

*  He  transports,  in  imagination,  parts  of  the  southern  region  to  a  corresponding 
latitude  in  the  north.  "On  this  supposition,"  he  observes,  "in  the  southern  provinces 
of  France,  magnificent  forests,  intwined  by  arborescent  grasses,  and  the  trees  loaded 
•with  parasitical  plants,  would  cover  the  face  of  the  country.  In  the  latitude  of  Mont 
Blanc,  but  on  an  island  as  far  eastward  as  Central  Siberia,  tree-ferns  and  parasitical 
Orchideae  would  thrive  amidst  the  thick  woods.  Even  as  far  north  as  Central  Denmark, 
humming-birds  might  be  seen  fluttering  about  delicate  flowers,  and  parrots  feeding 
amidst  the  evergreen  woods,  with  which  the  mountains  would  be  clothed  down  to  the 
water's  edge."  Nevertheless,  the  southern  part  of  Scotland  (only  removed  twice  as  far 
to  the  eastward)  would  present  an  island  "  almost  wholly  covered  with  everlasting 
snow,  and  having  each  bay  terminated  by  ice-cliffs,  from  which  great  masses  yearly 
detached,  would  sometimes  bear  with  them  fragments  pf  rock.  This  island  would  only 
boast  of  one  land-bird,  a  little  grass,  and  moss ;  yet,  in  the  same  latitude,  the  sea 
might  swarm  with  living  creatures.  A  chain  of  mountains,  which  we  will  call  the  Cor- 
dillera, running  north  and  south  through  the  Alps  (but  having  an  altitude  much  in- 
ferior to  the  latter),  would  connect  them  with  the  central  part  of  Denmark.  Along 
this  whole  line  nearly  every  deep  sound  would  end  in  'bold  and  astonishing  glaciers.' 
In  the  Alps  themselves  (with  their  altitude  reduced  by  about  half),  we  should  find 
proofs  of  recent  elevations,  and  occasionally  terrible  earthquakes  would  cause  such 
masses  cf  ice  to  be  precipitated  into  the  sea,  that  waves,  tearing  all  before  them,  would 
heap  together  enormous  fragments,  and  pile  them  up  in  the  corner  of  the  valleys.  At 
other  times,  icebergs,  charged  with  no  inconsiderable  blocks  of  granite,  would  be 
floated  from  the  flanks  of  Mont  Blanc,  and  then  stranded  in  the  outlying  islands  of  the 
Jura.  Who,  then,  will  deny  the  possibility  of  these  things  having  taken  place  in 
Europe  during  a  former  period,  and  under  circumstances  known  to  be  different  from 
the  present,  when,  on  merely  looking  to  the  other  hemisphere,  we  see  they  are  under 
the  daily  order  of  events?"  Mr.  Darwin  then  calls  attention  to  the  island  groups, 
"situated  in  the  latitude  of  the  south  part  of  Norway,  and  others  in  that  of  Ferroe. 
These,  in  the  middle  of  summer,  would  be  buried  under  snow,  and  surrounded  by  walls 
of  ice,  so  that  scarcely  a  living  thing  of  any  kind  would  be  supported  on  the  land."— 
Narrative  of  the  Surveying  Voyages  of  the  Adventure  and  Beagle,  vol.  iii.  p.  291. 


CHANGES    IN    LAND    AND    SEA    OF    NORTHERN    REGIONS.     259 

area,  if  we  take  the  present  relative  levels  only  into  consideration,  the 
transport  of  glacier-borne  blocks  and  fragments  of  rock,  with  the 
polishing,  grooving,  and  scratching  of  valleys  and  their  sides  by  the 
moving  ice,  would  be  limited  to  the  areas  now  occupied  by  glaciers, 
duly  allowing  for  their  extension  and  contraction  within  the  range  of 
the  present  climatal  condition. 

Thus,  by  the  elevation  and  depression  of  large  areas  of  dry  land 
very  varied  conditions  for  the  existence,  extension,  or  contraction  of 
glaciers,  with  their  geological  consequences,  may  arise  without  reference 
to  those  due  to  floating  ice,  excepting  such  as  could  be  formed  in  great 
lakes,  such  as  that  of  Geneva,  for  example,  where  effects  similar  to 
those  observed  in  northern  America  would  be  produced.  On  the  shores 
of  such  lakes  coast  ice  would  be  formed,  inclosing  fragments  of  the 
rocks  and  shingles  of  beaches,  to  be  borne  away,  should  circumstances 
permit,  if  raised  to  an  altitude  permitting  a  depression  of  temperature 
sufficient  for  the  production  of  such  ice.  There  is  also  no  difficulty  in 
imagining  conditions  under  which  glaciers  could  protrude  into  large 
fresh-water  lakes,  carrying  rock  fragments  with  them,  and  having  their 
extremities  broken  off  and  floated  away  with  their  detrital  loads,  under 
proper  depths  of  water,  as  now  takes  place  in  the  sea  in  the  polar 
regions.  Such  masses  of  ice,  though  not  moved  onwards  by  streams  of 
tide  or  ocean  currents,  would  still  be  under  the  influence  of  the  winds, 
to  be  driven  to,  and  stranded  in  minor  depths,  where  the  ice  could 
melt,  and  leave  any  blocks  or  fragments  entangled  in  or  resting  upon 
them. 

With  respect  to  the  distribution  of  ice-borne  blocks  of  rock  upon 
lakes,  Sir  Roderick  Murchison  has  called  attention  to  effects  which 
would  follow  the  lowering  of  lakes  in  regions  where  ice  could  be  formed 
of  sufficient  thickness  and  importance  for  the  transportal  of  detritus.* 

When  the  depression  of  an  area  of  dry  land,  with  the  needful  modi- 
fications of  surface,  in  climates  where  glaciers  had  been  formed,  is  such 
that  the  sea  enters  amid  the  valleys  in  which  these  streams  of  ice  oc- 
curred, the  change  may  or  may  not,  according  to  the  general  climatal 
conditions  produced,  affect  the  glaciers.  Should  the  change  in  the 
northern  be  of  an  order  to  introduce  the  climate  of  the  southern  hemi- 
sphere, it  has  been  above  seen  (p.  247),  the  cold  might  be  so  increased, 
that  Alpine  glaciers  would  become  more  extended,  delivering  icebergs 
into  surrounding  seas,  so  that,  as  Mr.  Darwin  has  remarked  (note,  p. 
258),  they  might  float  away,  and  be  stranded  on  the  Jura,  then  an 
island  range. 

Hitherto  we  have  regarded  these  alterations  of  level  as  slowly  pro- 
duced, so  that  the  changes,  of  whatever  kind,  were  gradual,  causing  no 

*  "  Geology  of  Russia  in  Europe  and  the  Ural  Mountains,"  vol.  i.  p.  568. 


ERRATIC    BLOCKS. 


sudden  alteration  of  conditions.  This,  however,  is  far  from  necessary 
in  geological  reasoning,  there  being  evidence  connected  not  only  with 
actual  mountain  ranges,  but  also  with  many  a  district  wherein  the  rocks 
are  broken  and  contorted,  which  would  lead  us  to  infer,  with  every 
allowance  for  the  repeated  effects  resulting  from  the  multiplied  applica- 
tion of  minor  forces,  that  considerable  forces  had  often  been  somewhat 
suddenly  called  into  action.  The  waves  produced  during  the  disturbances 
of  the  land,  known  to  us  as  earthquakes,  and  which  will  be  noticed 
hereafter,  are  sufficient  to  show  how,  in  that  mode  alone,  glaciers,  pro- 
truding into  the  sea,  or  great  lakes  of  fresh  water,  may  be  lifted  at 
their  ends,  and  their  fragments,  with  any  load  of  detritus  they  may 
sustain,  whirled  about  and  stranded  in  unusual  situations.  Greater 
waves  would  produce  greater  results,  and  when  we  unite  them  with 
land  suddenly  depressed  beneath  the  sea-level,  even  only  a  few  hundred 
feet,  in  such  regions  as  those  of  Victoria  Land  and  South  Georgia,  or 
of  Greenland  and  Iceland,  we  have  the  means  of  removing  ice,  and 
producing  a  complicated  mixture  of  blocks  and  minor  fragments  of  rock 
of  great  geological  importance.  In  like  manner,  the  sudden  elevation 
of  land,  covered  by  snow  and  glaciers,  if  accompanied  by  the  transmis- 
sion of  heat  through  fissures  then  formed,  or  by  the  increased  tempera- 
ture of  the  supporting  mineral  matter  from  the  protrusion  of  igneous 
rocks  among  it,  so  that  the  snow  and  ice  were  suddenly  and  in  part 
melted,  would  be  productive  of  no  slight  geological  effect,  more  espe- 
cially if  the  glaciers  of  the  land  so  acted  upon,  protruded,  or  nearly  so, 
into  the  sea.  « 

Huge  blocks  of  rock,  often  angular,  are  found  scattered  in  such  a 
manner  over  parts  of  the  northern  portions  of  Europe  and  America, 
and  again  in  part  of  South  America,  and  amid  and  around  mountainous 
regions,  such  as  the  Alps,  that,  comparing  their  mode  of  distribution 
with  that  now  known  to  be  taking  place  by  means  of  ice,  attention  has 
of  late  been  very  generally  given  to  this  explanation  of  their  mode  of 
occurrence.  The  masses  of  rock  so  found  are  commonly  termed  Erratic 
Blocks,  and  correct  observations  respecting  the  conditions  under  which 
they  are  found  are  material  to  a  right  understanding,  particularly  as 
respects  the  northern  hemisphere,  of  the  manner  in  which  they  have 
been  accumulated. 

As  there  are  occasionally  blocks  of  rocks  scattered  over  a  country, 
which  are  merely  portions  of  some  harder  beds,  interstratified  with 
more  yielding  substances,  or  are  the  remains  of  dykes  and  veins  of 
igneous  rocks,  the  continuity  and  mode  of  occurrence  of  which  may 
not  be  clear,  the  more  readily  disintegrated  rocks  having  been  removed 
by  the  effects  of  atmospheric  influences,  or  breaker  action  at  some  prior 
geological  time,  the  observer  has  in  some  districts  to  employ  much 
caution  as  respects  their  origin.  This  is  especially  needed  where  the 


ERRATIC    BLOCKS. 


261 


dykes  or  veins  of  the  igneous  rocks  may  have  decomposed,  as  often 
happens,  in  an  irregular  manner,  so  that  portions  of  the  more  unyield- 
ing, or  harder  parts,  are  scattered  about,  while  traces  of  the  softer  are 
not  easily  found.  From  the  liability  of  certain  igneous  rocks  to  de- 
compose in  spheroidal  forms  (fig.  2,  p.  35,  and  fig.  7,  p.  40)  such  blocks 
will  sometimes  present  the  false  appearance  of  having  been  rounded  by 
attrition,  as  if  worn  on  some  coast.  Let,  for  illustration,  a,  #,  be  a 


dyke  of  greenstone,  liable  to  unequal  decomposition  in  different  parts,x 
at  a  decomposed  in  spheroidal  portions,  then  during  the  loss  of  general 
surface  upon  the  hillside  e  /,  the  harder  parts  of  the  disintegrated 
portion,  a  e,  might  fall  over  towards  e,  and  present  the  appearance  of 
rounded  boulders  of  greenstone  resting  upon  some  other  rock.  Again, 
on  the  other  side  of  the  hill,/ </,  there  might  also  be  angular  fragments 
of  rock  h  7i,  detached  from  the  harder  beds  above  them,  during  a  loss 
of  matter  from  an  old  surface,  /  Jc.  This  kind  of  precaution  has  fre- 
quently to  be  taken  in  granitic  regions,  the  blocks  of  granite  often  de- 
composing in  a  rounded  form,  so  as,  when  scattered  about  amid  bogs,  and 
much  disintegrated  rock,  to  present  the  appearance  of  boulders  rounded 
by  attrition. 

This  disposition  to  decompose  in  spheroidal  forms  has  also  to  be  some- 
times well  considered  when  it  is  inferred  that  such  rocks,  even  when  they 
are  true  erratic  blocks,  have  been  rounded  by  attrition  before  they  were 
ice-transported.  A  block  of  granite,  for  example,  such  as  that  repre- 
sented beneath,  a,  (fig.  97,)  though  now  rounded,  may  have  been  trans- 
Fig.  97. 


ported  in  a  more  angular  condition,  the  removal  of  the  angular  parts 
having  been  effected  by  decomposition,  from  atmospheric  influences, 
since  it  occupied  its  present  position.  In  this  manner,  rounded  blocks 
of  granite  may  be  scattered  down  a  mountain  side,  as  in  the  following 


262  EFFECTS    OF    GRADUAL    RISE    OF    SEA    BOTTOM 

section  (fig.  98),  where  granite,  £,  rising  in  a  tor,  c?,  above  certain  stra- 
tified deposits,  b,  has  fallen  in  blocks,  down  the  slope,  a  large  rounded 
block  presenting  itself  at  a.  Although  it  may  have  so  happened  that 

Fig.  98. 


such  a  state  of  things  had  been  brought  about  by  the  motion  of  a  gla- 
cier, leaving  lateral  moraines  (other  fitting  conditions  obtaining),  or  by 
coast  ice  carrying  blocks  of  rock,  it  still  becomes  needful  to  ascertain 
that  such  are  not  blocks  fallen  from  the  heights,  and  simply  rounded 
by  decomposition,  which  a  careful  examination  of  the  granite  at  d,  would 
aid  in  showing. 

As  under  the  hypothesis  of  cold  having  once  prevailed  in  the  northern 
hemisphere,  greater  than  at  present,  much  of  the  land  then  submerged 
is  now  raised  above  the  level  of  the  sea,  and  consequently  an  upward 
movement  of  a  large  portion  of  Northern  Europe,  Asia,  and  America 
inferred,  it  becomes  of  no  slight  interest  to  see  how  far  ice,  in  its  various 
modes  of  occurrence,  could  be  the  means  of  producing  the  distribution 
of  the  rock  fragments,  often  of  great  magnitude,  there  found.  Assuming 
the  submergence,  it  becomes  desirable  to  see  if  its  amount  can  be  ascer- 
tained. There  is  always  the  difficulty  of  knowing  how  much  portions 
of  rock,  of  various  sizes,  may  have  been  rounded  and  left  on  coasts 
and  in  river  courses  over  the  older  accumulations,  anterior  to  this  sup- 
posed ice  or  glacial  period  in  the  northern  hemisphere.  Giving  this, 
however,  its  full  value,  we  should  expect,  as  the  land  rose  and  the  tem- 
perature became  gradually  elevated  to  that  which  we  now  find,  that, 
under  certain  favourable  circumstances,  glaciers  which  were  previously 
cut  off  by  the  sea,  floating  away  their  terminal  portions,  might  for  a 
time  become  more  extended  over  dry  land,  thrusting  forward  their  mo- 
raines further  than  formerly.  Thus  the  levels  at  which  the  remains  of 
true  terminal  moraines  could  be  found,  might  not  give  the  amount  of 
submergence  sought,  even  supposing  that  they  could  be  fairly  separated 
from  other  accumulations  of  rocks  which  they  may  more  or  less  resemble. 
Coast  accumulations  of  the  time,  if  they  could  be  traced,  would  be  more 
certain  guides. 

Still  assuming  a  gradual  disappearance  of  ice,  up  to  the  amount  now 
found  in  the  northern  regions,  and  consequently  the  entire  disappear- 


STREWED    WITH    ICE-TRANSPORTED    DETRITUS.          263 

ance  of  many  glaciers  on  lands,  such,  for  example,  as  in  the  British 
Islands,  where  they  are  supposed  to  have  occurred  at  the  glacial  period, 
the  various  moraines,  as  also  the  polished  surfaces,  grooves,  and  scratches 
formed  by  the  glaciers,  would  be  gradually  left  to  be  dealt  with  by 
atmospheric  influences,  and  the  modifications  and  changes  brought 
about  by  them,  vegetation  spreading  over  the  land  as  the  snow  and  ice 
disappeared. 

The  land  rising,  and  the  deeper  parts  becoming  more  shallow,  mud, 
previously  beyond  the  action  of  the  wind-waves  moving  on  the  surface, 
would  be  caught  up  in  mechanical  suspension,  to  be  carried  to  more 
quiet  situations  by  streams  of  tide  (in  tidal  seas),  or  sea  currents,  where 
these  began  to  act.  The  same  with  the  other  portions  of  the  sea  bottom : 
fragments  of  rock,  of  various  forms  and  sizes,  thrown  down  from  por- 
tions of  glaciers,  river  ice,  and  coast  ice,  as  they  floated  above,  and  gra- 
dually parted  with  them,  rising  with  the  rest.  While  much  fine  sediment 
would  be  separated  from  the  larger  detritus,  as  the  wind-wave  action 
became  more  and  more  felt,  so  that  much  of  this  sediment  might  be 
removed  from  amid  the  larger  detritus,  bringing  the  portions  of  the 
latter  gradually  into  closer  contact,  it  would  be  when  the  sea  bottom 
came  within  the  action  of  the  breakers,  that  the  chief  modifications  of 
such  previous  sea  bottom  would  be  effected.  The  new  coasts  would  be 
adjusted  to  the  conditions  arising  from  their  exposure  to  the  force  of 
the  breakers,  and  the  rise  and  fall  of  tides,  where  these  were  felt,  and 
the  angular  fragments  which  had  reposed  quietly  at  the  bottom,  in  the 
manner  above  noticed  (p.  235),  would  be  brought  within  the  action  of 
the  breakers,  to  be  rounded  by  attrition,  large  blocks  standing  out  as 
many  rocks  now  do  on  the  sea-coasts.  While  previously  ice-borne  and 
rounded  blocks  and  shingles  would  again  be  more  worn,  the  angular 
fragments  would  be  more  or  less  rounded  by  the  same  action,  according 
to  their  exposure  to  the  breakers.  Lines  of  beach  would  be  thrown  up 
in  the  usual  manner,  sandy  or  shingly  according  to  circumstances,  and 
be  left  and  be  modified  by  atmospheric  influences  as  the  land  rose,  and 
the  drainage  of  the  old  sea  bottom  became  adjusted  to  its  various  levels 
and  inequalities  of  surface. 

Under  such  circumstances,  very  variable  results  would  be  produced 
as  conditions  changed,  and  the  component  portions  of  the  old  sea  bottom 
were  partly  removed  and  partly  left ;  dispersed  ice-borne  fragments  of 
rock,  rounded  or  angular  as  the  case  may  have  been,  brought  together, 
the  angles  of  the  latter  sometimes  completely  rounded  by  breaker  action, 
at  others,  not  much  injured ;  the  shells  of  molluscs  and  the  harder  parts 
of  other  marine  animals  sometimes  removed  and  redeposited  in  a  nearly 
uninjured  state,  at  others,  broken  into  fragments,  and  variously  arranged 
amid  the  new  accumulations  of  mud,  sand,  shingles,  and  boulders. 
Should  there  have  been  a  tendency,  under  the  old  conditions  of  the 


264         BRITISH    ISLANDS    DEPRESSED    ONE    THOUSAND 

sea  bottom,  to  have  glacier  ice,  loaded  with  rock  fragments,  or  coast 
ice,  bearing  away  shingles,  boulders,  and  also  angular  blocks  floated 
away  in  particular  directions,  dropping  their  mineral  burdens  in  lines, 
upon  that  bottom,  such  lines,  as  it  rose,  would  be  preserved  according 
to  circumstances.  However  separated  large  blocks  might  be  by  any 
other  deposits  effected  during  their  gradual  accumulation,  there  would 
be  a  tendency  to  remove  the  finer  sediment  from  among  them,  so  that 
they  would  finally  present  the  aspect  of  lines,  often,  when  the  blocks 
were  very  thickly  thrown  down  from  the  ice,  forming  ridges.  Such 
ridges  would,  however,  be  acted  upon  by  breakers  during  the  rise  of  the 
land,  so  that  detritus  might  be  strewed  upon  them  in  the  manner  of 
beaches,  and  thus  a  complicated  arrangement  of  parts  be  produced. 

During  such  changes,  icebergs  derived  from  glaciers  would  float 
about  until  the  parent  glaciers  either  disappeared  or  became  separated 
from  the  sea,  and  the  coast  ice  formed  would  become  gradually  limited 
in  its  production  up  to  its  present  adjustment.  Various  new  modifica- 
tions would  arise  from  the  formation  of  coast  ice,  as  also  from  river  ice, 
as  the  drainage  of  the  old  land  found  its  way  amid  the  new  land,  with 
the  rain  and  spring  waters  of  the  latter,  to  the  sea.  Many  blocks  of 
rock  would  be  caught  up  on  the  coast,  and  be  transported  elsewhere,  as 
was  the  case  with  the  block  on  the  coast  of  Denmark  mentioned  by  Pro- 
fessor Forchhammer  (p.  253),  and  rivers  flowing  in  certain  directions 
might  carry  back  blocks  of  rock  towards  their  parent  masses,  as  noticed 
by  Sir  Roderick  Murchison*  in  the  manner  that  blocks  are  now  moved 
northwards  by  the  Volkof  and  Msta. 

Under  the  hypothesis,  therefore,  of  lower  temperature  accompanied 
by  more  sea,  the  bottom  of  much  of  which  has  since  become  dry  land  in 
the  northern  hemisphere,  the  observer  has  not  only  to  study  a  wide 
range  of  country  for  evidence  of  the  land  supposed  to  be  originally 
above  the  water,  variously  snow-clad,  and  furnishing  glaciers,  the  ter- 
minal parts  of  which,  from  time  to  time,  floated  away,  with  the  coast 
ice  and  extension  probably  of  ice  barriers,  but  also  the  modifications 
which  the  old  sea  bottom  has  undergone  in  its  rise  above  the  sea.  Thus 
he  would  often  have  to  separate,  and  duly  weigh,  much  evidence  which 
might,  at  first,  appear  somewhat  contradictory  as  to  erratic  blocks 
having  been  transported  by  land  ice  or  sea  ice — as  to  the  polisliini:, 
grooving,  and  scratching  of  subjacent  rocks  by  the  one  or  the  other, 
and  as  to  the  original  arrangement  and  rearrangement  of  many  detrital 
accumulations. 

It  may  be  instructive  for  the  observer  to  consider  the  effects  which 
would  follow  the  submergence  of  the  British  Islands,  and  of  an  adjoin- 
ing portion  of  France,  to  1000  feet  beneath  the  level  of  the  seas  which 

*  "Geology  of  Russia  in  Europe  and  the  Ural  Mountains,"  vol.  i.  p.  565. 


FEET    UNDER    CONDITIONS    OF    INCREASED    COLD.       265 

now  surround  and  adjoin  them.  And  it  should  be  noticed  that  of  a 
submergence  to  this,  and  even  a  larger  amount  at  a  comparatively 
recent  geological  period,  there  would  appear  good  evidence.  A  glance 
at  the  accompanying  map  (fig.  99),  which  represents  the  land  that 

Fig.  99. 


would,  under  this  hypothesis,  be  above  water,  will  show  numerous  islands 
and  islets  variously  distributed.  The  largest  amount  of  dry  land  would 
be  found  in  Northern  Scotland,  and  be  divided  into  two  main  portions 
by  a  strait,  now  occupied  by  the  low  ground  and  lakes  between  the 
Murray  Frith,  and  Loch  Linnhe.  Off  these  principal  islands  there 


266         BRITISH    ISLANDS    DEPRESSED    ONE    THOUSAND 

would  be  many  minor  islets,  chiefly  on  the  south  and  southwest.  In 
Southern  Scotland  there  would  also  be  a  patch  of  dry  land,  of  some 
size,  and  in  Cumberland  and  Westmoreland  another ;  while  a  somewhat 
comparatively  large  island  would  extend,  in  a  north  and  south  direction, 
from  Westmoreland  by  Yorkshire  into  Derbyshire.  In  Wales  there 
would  be  much  land  above  the  level  of  the  sea,  with  many  detached 
islets  there  and  in  some  parts  of  England ;  among  them  the  tops  of  the 
Malvern  Hills,  which  now  at  a  distance  present  so  much  the  appearance 
of  an  island.*  In  Ireland  there  would  be  numerous  islets,  the  chief 
island  being  formed  by  the  Wicklow  Mountains  and  their  continuation. 
From  them,  to  the  westward,  many  islets  would  rise  above  the  sea.  As 
a  whole,  the  Irish  islets  would  be  principally  gathered  into  two  groups, 
one  on  the  north,  the  other  on  the  south. 

Taking  this  submergence,  with  a  climate  resembling  that  of  Tierra 
del  Fuego  and  South  Georgia,  so  that  such  islands  as  were  sufficiently 
high  were  snow-clad,  glaciers  would  descend  into  the  valleys,  even 
occasionally  reaching  the  sea,  their  terminal  portions  loaded  with  blocks 
and  fragments,  these  floated  off  by  the  ice,  and  strewed  over  the  bottoms 
of  the  neighbouring  seas  according  to  circumstances.  And  respecting 
the  heights  of  the  islands,  many  would  rise  to  sufficient  altitudes  for 
these  effects  to  be  produced,  Lugnaquilla  being  still  2039  feet  above 
the  sea,  Ben  Nevis  3373  feet,  Skiddaw  2022  feet,  and  Snowdon 
2571  feet.  If  to  this,  we  add  the  coast  ice,  with  its  effects  as  above 
noticed  (p.  251),  there  would  be  no  want  of  conditions  for  the  distribu- 
tion, by  means  of  ice,  of  blocks  of  rock  of  various  sizes  and  kinds,  and 
of  fragments  of  all  forms  over  the  area  now  presented  by  the  British 
Islands,  at  various  levels  beneath  that  corresponding  with  an  altitude 
of  1000  feet  above  the  present  sea  level.  While  this  was  being  accom- 
plished, the  formation  of  moraines,  and  the  polishing,  grooving,  and 
scratching  of  rocks,  through  the  instrumentality  of  glaciers,  would  be 
effected  above  that  level,  up  to  altitudes  where  glacier  action  of  that 
kind  could  be  then  felt.  At  the  sea  level,  and  at  such  depths  beneath 
it  as  its  influence  could  be  felt,  coast  ice  would  be  the  means  of  polish- 
ing, grooving^  and  scratching  rocks  exposed  to  its  action;  icebergs 
would  ground,  producing  their  effects,  and  such  rivers  as  moved  rocks 
by  means  of  ice  would  add  their  ice-transported  detritus. 

A  submergence  of  the  British  Islands  to  1000  feet  beneath  the  pre- 
sent level — a  change  in  the  relative  level  of  sea  and  land  which,  how- 

*  A  study  of  the  Malvern  district  is  not  only  interesting  as  showing  how  long  the 
Malvern  Hills  retained  their  insular  character  during  the  emergence  of  the  British 
Islands  to  their  present  relative  level,  but  also  as  regards  the  island  state  of  the  same 
hills  at  a  far  more  remote  geological  period,  one  anterior  to  the  accumulation  of  the 
rocks  commonly  known  to  British  geologists  as  the  New  Red  Sandstone.  A  detailed 
account  of  this  district  is  given  by  Professor  John  Phillips,  Memoirs  of  the  Geological 
Survey  of  Great  Britain,  vol.  ii.  part  1. 


FEET    UNDER    CONDITIONS    OF    INCREASED    COLD.       267 

ever  startling  it  may  be  to  those  unaccustomed  to  geological  investiga- 
tions, the  observer  will  soon  learn  to  consider  as  one  of  a  minor  kind, — 
could  scarcely  fail  to  be  accompanied  with  a  submergence  of  various 
portions  of  Europe.  It  is  not  needful  to  infer  that  the  relative  change 
of  level  was  of  equal  amount  through  a  very  considerable  area.  It  may 
have  been  greater  in  some  regions,  less  in  others ;  but  let  this  have 
been  as  it  may,  such  a  change  would  probably  bring  about  a  very  mate- 
rial difference  in  the  distribution  of  land  and  sea,  as  we  now  find  it. 
Among  other  modifications,  the  Scandinavian  regions  would  be  brought 
under  conditions  by  which,  should  currents  permit,  blocks  and  fragments 
of  rocks,  and  of  various  sizes  and  forms,  could  be  borne  by  icebergs  or 
coast  ice,  and  be  distributed  over  the  bottoms  of  the  seas  then  on  the 
southward  of  them,  some  even  being  drifted  to  the  area  of  the  British 
Islands,  mingling  here  and  there  with  their  own  ice-distributed  detritus. 

In  such  changes,  not  only  has  the  observer  to  bear  in  mind  the  diffe- 
rent distribution  of  sea  and  land,  but  also  the  modification  of  tidal 
action  and  sea  currents  effected,  duly  giving  attention  to  the  probable 
extension  of  coast  ice,  even,  perhaps,  sometimes  amounting  to  great  icy 
barriers.  Though  some  value  would  have  to  be  attached  to  the  influ- 
ence of  the  outstanding  group  of  islands  and  islets  then  rising  above 
the  area  now  more  extensively  occupied  by  the  British  Islands,  the 
waves  of  the  Atlantic  would  roll  over  a  large  tract  now  forming  a  por- 
tion of  Northern  France,  with  Belgium,  Holland,  Denmark,  Northern 
Germany,  and  an  extended  area  in  Russia.  The  conditions  producing 
the  action  of  tides  surrounding  the  British  Islands  being  changed, 
others  would  arise  suited  to  the  new  arrangement  of  land  and  sea,  and 
many  a  mass  of  ice  in  the  Scandinavian  regions,  so  long  as  it  rested  on 
sea  bottoms,  would  act  as  land  in  the  modification  of  tidal  streams  and 
sea  currents. 

How  far  the  outlines  of  the  land  may  have  generally  resembled  the 
present  at  the  commencement  of  these  changes  it  would  be  difficult  to 
say,  since  many  modifications  have  been  produced  while  such  changes 
were  effected,  and  the  submergence  may  have  commenced  when  more 
land  was  above  the  sea  level  than  at  present,  somewhat  more  corre- 
sponding with  the  line  of  600  feet  now  beneath  the  sea,  around  the 
British  Islands,  as  in  the  plans,  fig.  65  (p.  114),  and  fig.  99  (p.  265). 
Taking,  however,  the  present  distribution  of  sea  and  land  as  a  guide, 
and  looking  chiefly  to  the  production  of  ice  (other  consequences  of  sub- 
merging and  emerging  land  being  reserved,  in  a  great  measure,  for 
subsequent  notice),  we  have  to  consider  an  increase  of  cold  on  the  one 
side,  and  a  decrease  of  dry  land,  accompanied  by  a  loss  of  height,  on 
the  part  still  above  water,  on  the  other.  For  convenience  we  may 
regard  these  changes  as  gradual,  the  modifications  arising  from  more 
rapid  change  being  readily  appreciated. 


268  EXTENSION    OF    ALPINE    GLACIERS. 

The  gradual  increase  of  cold  would  tend  to  lower  the  line  of  perpetual 
snow  over  the  dry  land,  while  the  rate  of  its  descent  down  any  moun- 
tain range  would  depend  upon  the  rate  of  submergence  of  the  land. 
They  might  balance  each  other.  Should  the  rate  of  decrease  of  tempe- 
rature be  more  rapid  than  would  be  compensated  by  the  submergence, 
pre-existing  glaciers  would  increase  even  during  the  descent  of  the 
land,  and  new  glaciers  would  establish  themselves  elsewhere  under  the 
needful  conditions.  Assuming,  however,  the  continued  increase  of  cold, 
a  time  would  come,  even  if  the  pre-existing  glaciers  did  not  much 
increase  during  the  submergence  of  the  land,  when  those  formed  in 
Scandinavia  could  reach  the  sea,  as  now  in  Greenland,  distributing 
detritus  by  their  detached  portions,  bearing  rock  fragments  to  the  adja- 
cent seas.  This  might  also  have  been  the  case  with  the  portions  of  the 
British  Islands  then  above  water. 

Looking  to  other  portions  of  Europe  with  reference  to  this  submer- 
gence of  1000  feet,  or  thereabouts,  it  may  not  be  uninstructive  to  con- 
sider the  effects  of  the  cold  inferred  upon  the  glaciers  of  such  regions 
as  the  Alps,  and  the  establishment  of  new  glaciers  in  other  mountainous 
districts  where  the  needful  conditions  may  have  been  produced.  In  the 
Alps  the  glaciers  would  increase,  as  they  now  do,  under  the  influence 
of  certain  seasons,  but  instead  of  that  decrease  which  brings  them  back 
to  a  certain  state  from  a  modification  of  the  seasons  in  another  direc- 
tion, the  increase  would  continue,  an  extension  of  the  sea,  from  the 
Atlantic,  being  not  unfavourable  for  this  purpose,  independently  of  the 
greater  cold  produced.  Under  such  circumstances,  glacier-borne  blocks 
and  other  rock  fragments,  which  would  have  been  left  in  many  a 
locality,  or  carried  forward  to  the  terminal  moraines,  would  continue  to 
advance  with  the  augmented  length  and  volume  of  the  glaciers,  until 
they  were  finally  arrested  in  their  progress  by  the  conditions  affecting 
the  extent  of  the  glaciers  themselves.  If  the  observer  will  study  the 
occurrence  of  existing  glaciers  upon  maps  or  models  of  the  Alps  and 
adjoining  districts,*  he  will  perceive  that  the  outward  courses  of  exist- 
ing glaciers  would  be  greatly  extended,  while  many  a  new  glacier  would 
contribute  its  ice  to  the  general  mass,  sometimes  carrying  its  own 
moraines,  and  at  others  modifying  the  courses  of  the  main  streams  of 
ice  into  which  it  might  merge.  With  a  change  of  temperature  and  of 
relative  level  of  sea  and  land,  which  should  bring  down  the  altitude  of 
the  present  line  of  perpetual  snow  in  the  Alps  to  that  of  Chiloe  (between 
40°  to  43°  S.,  the  Alps  being  between  42°  and  47°  N.),  it  would  descend 
about  2500  feet,  and  with  it  the  neve  of  the  glaciers.  This  descent  of 

*  The  map  accompanying  Travels  in  the  Alps  of  Savoy,  &c.,  by  Professor  James 
Forbes,  upon  which  the  glaciers  of  the  districts  visited  are  very  carefully  entered,  will 
be  found  very  useful  for  this  purpose,  and  more  especially  with  reference  to  the  inferred 
extension  of  glaciers  down  the  valley  of  the  Rhone  to  the  Jura. 


EXTENSION    OF    ALPINE    GLACIERS. 


269 


the  snow-line  being  supposed  gradual,  the  glaciers  would  advance  as 
gradually,  and  the  blocks  derived  from  the  present  interior  portions  of 
the  Alps  would  be  moved  onwards  in  front.*  Let,  in  the  following  sec- 

*  Regarding  the  extension  of  Alpine  glaciers  from  increased  cold,  continued  through 
a  certain  amount  of  geological  time,  the  slopes  over  which  they  may  be  inferred  to  have 
passed  require  attention,  due  allowance  being  made  for  the  effects  which  would  arise 
from  the  supposed  greatly  increased  volume  of  many  glaciers.  As  connected  with  this 
subject,  M.  Elie  de  Beaumont  has  given  (Note  sur  les  pentes  de  la  limite  superieure  de 
la  zone  erratique,  &c.,  Annales  des  Sciences  Geologiques,  1842)  the  following  table  for 
the  upper  limit  of  the  erratic  block  zone  of  the  valley  of  the  Rhone,  &c. : — 


LOCALITIES. 

Distances. 

Differences 
m  the  Height 
of  the  two 
Localities. 

Inclination. 

Grimsel      1 

Metres. 

Metres. 

25,000 

487 

1°     6'    57" 

Brieff                                                   1 

10,000 

293 

1        2      56 

Brieff                                                  ) 

Martigny                                           J 

80,000 

70 

0      3       1 

Great  St  Bernard                   .       ") 

Plan-y-beuf    ...                     .  / 

15,000 

731 

2    47     24 

Plan-y-beuf    .     .                     •     •  \ 

18,000 

319 

1       0    55 

Martigny    .     .                           .     .  1 

Monthey     .     .                                .  j 

18,000 

293 

0    55    57 

Montigny   .     .                     ...  1 

Alimisse      ....           .     .     .  J 

44,000 

425 

0    33     12 

Mimisse      ....           .     .     .  "j 

Geneva  .               J 

49,000 

585 

0    41       2 

Martigny   ") 

Playau  .     .           J 

44,000 

228 

0     17     48 

Martigny    ~| 

Chasseron  f 

92,000 

400 

0     14    55 

Plavau  .                                         .  1 

Chasseron  j 

49,000 

172 

0     12      4 

Plan-y-beuf    *l 

110,000 

719 

0    22    28 

Great  St.  Bernard   ^ 

125,000 

1,450 

0     39    52 

Martigny    j" 

121,000 

850 

0    24      9 

Grimsel                                              S 

165,000 

1,078 

0    22    27 

Grimsel      .                                      \ 

Chasseron  .                                      j 

213,000 

1,250 

0    23     10 

Playau  ...                                  f 

140,000 

591 

0     14       3 

Neve  of  the  Ober  Aer   .     .     .     .  ^ 
Grimsel      ...                            L 

13  500 

624 

2     38    45 

Level  of  the  Roches  Moutonnees  J 
Grimsel      S 

29,000 

1,037 

2      2    52 

M.  Elie  de  Beaumont  remarks  that  he  does  not  know  in  the  Alps  any  glacier  which 
moves  through  any  considerable  extent,  such  as  a  league,  with  a  slope  much  less 
than  3°. 


270  TRANSPORTAL    OF    ERRATIC    BLOCKS 

tion,  (fig.  100)  a,  #,  be  the  level  of  perpetual  snow,  in  a  range  of  moun- 
tains amid  which  glaciers  are  formed,  d,  the  extension  of  one  of  these 

Fig.  100. 


ETT 


glaciers  under  any  given,  yet  needful,  conditions;  c  and/,  mountains, 
just  beneath  the  line  of  perpetual  snow.  If  now  the  conditions  so 
change  that  g,  h  becomes  the  perpetual  snow-line,  those  for  the  produc- 
tion of  glaciers  continuing,  the  supply  of  the  original  glacier  will  take 
place  at  a  lower  level,  while  the  ice  which  only  extended  to  (Z,  would  be 
forced  onward,  on  the  same  principle  as  the  ordinary,  however  tempo- 
rary, increase  of  a  glacier  may  be  effected.  With  it  any  collection  of 
blocks,  thrust  forward  in  the  usual  manner  to  &,  would  be  moved 
onward,  with  the  ice,  to  Z,  and  possibly  to  m,  the  proper  conditions 
prevailing.  With  such  increase  a  collateral  glacier  might  come  in  from 
a  valley  0,  between  n  and  e,  perhaps  the  extension  of  a  small  glacier 
previously  formed  at  jo,  or  altogether  new ;  and  thus  blocks  and  glaciers 
may  descend  against  the  extension  of  the  main  glacier  to  m.  The  face 
of  the  Alps,  as  regards  snow  and  ice,  would  be  most  materially  changed 
by  a  descent  of  the  snow-line,  so  as  to  be  of  about  the  same  altitude  as 
that  of  Chiloe,  and  a  further  decrease  of  temperature  would  necessarily 
still  further  extend  the  glaciers.  The  observer  is  thus  required  to 
weigh  well  the  consequences  of  a  diminished  general  temperature  in  the 
northern  regions,  not  only  as  regards  the  establishment  of  snows  and 
ice  upon,  and  around  portions  of  lands  now  free  from  them,  except 
during  winter,  but  also  the  extension  of  pre-existing  glaciers  at  the 
same  period. 

Assuming  a  depression  of  this  kind,  the  observer  has  to  take  into 
consideration  the  rise  of  the  sea  bottom  to  the  present  European  levels 
of  sea  and  land,  accompanied  by  an  elevation  of  general  temperature  to 
that  now  found.  As  the  land  rose  beaches  would  be  left  in  various 
situations,  showing  the  different  alterations  of  the  relative  levels  of  sea 
and  land.  Should  considerable  pauses  in  the  elevation  of  the  land  have 
taken  place,  these  would  be  marked  by  lines  of  cliff,  where  the  rocks 
could  be  sufficiently  worn  by  the  breakers.  The  production  of  coast 
ice  would  gradually  become  less,  so  that  its  formation  would  cease  in 
the  southern  lands,  and  the  glaciers  generally  would  decrease,  leaving 
their  lines  of  moraines,  and  many  angular  blocks  of  rock,  perched  on 
the  sides  of  mountains,  as  in  the  following  sketch  (a,  b,  fig.  101),  at 
altitudes  corresponding  with  the  volumes  of  their  transporting  glaciers 


BY    GLACIERS    AND    COAST -ICE.  271 

at  the  periods  of  their  chief  extension  down  valleys,  where  only  a  rem- 
nant of  such  glaciers  may  be  now  left  at  their  higher  extremities,  or 
even,  as  in  the  British  Islands,  no  portion  of  one  may  remain. 


Fig.  101. 


The  land  continuing  to  rise,  not  only  would  the  previous  sea  bottom, 
with  its  varied  accumulations  (in  some  of  which  the  remains  of  animal 
life  would  be  entombed,  often  in  regular  beds  of  sand,  silt,  and  mud), 
be  brought  within  the  destructive  influence  of  the  breakers,  as  above 
noticed  (p.  263),  but  rivers  also  would  begin  to  flow  amid  the  old  sea 
bottom.  According  to  circumstances,  such  rivers  would  present  varied 
characters,  and  some  would  carry  forward  ice-borne  detritus  to  the  sea, 
or  leave  it  on  their  courses,  as  it  might  happen,  until  only  certain  of 
them,  those  now  possessing  the  needful  conditions,  so  transported  mineral 
substances. 

From  the  interest  which  has  been  excited  respecting  the  transportal 
of  erratic  blocks,  many  of  great  volume,  by  means  of  ice,  a  mass  of  in- 
formation has  been  collected,  rendering  the  submergence  of  a  large 
portion  of  Northern  Europe,  Asia,  and  America,  accompanied  by  a  con- 
siderable depression  of  temperature,  extremely  probable.  The  effects 
of  floating  ice  have  for  a  long  time  engaged  attention.  Professor  Wrede, 
of  Berlin,  would  appear  to  have  been  among  the  first  to  account  for  the 
erratic  blocks  on  the  south  of  the  Baltic,  by  means  of  floating  ice,  there 
having  subsequently  been  a  change  of  level  in  that  region,  by  which 
the  sea  bottom  became  dry  land.*  Sir  James  Hall  also  long  since  re- 

*  Geognostical  Researches  relative  to  the  countries  on  the  Baltic,  and  particularly  to 
the  Low  Lands  at  the  Mouth  of  the  Oder,  with  Observations  on  the  gradual  Change  of 
the  Level  of  the  Sea  in  the  Northern  Hemisphere,  and  its  physical  causes,  as  quoted  by 
De  Luc,  Geological  Travels,  1810.  Professor  Wrede  supposed  a  slow  change  in  the 
centre  of  gravity  of  the  earth,  so  that  the  waters  retreated  from  the  northern  hemi- 
sphere, leaving  the  sea  bottom  dry,  with  the  ice-borne  blocks  of  rock  upon  it.  He  cal- 
culated the  ice  needed  to  float  an  erratic  block,  estimated  to  weigh  490,000  Ibs.,  occur- 
ring at  the  mouth  of  the  Oder. 


272  EVIDENCE    OF    GLACIERS    FORMERLY 

ferred  to  floating  ice,  combined  with  earthquake  waves,  as  a  means  of 
transporting  erratic  blocks  ;*  and  its  aid,  under  various  conditions,  has 
been  sought  in  explanation  of  the  transportal  of  large  and  often  angular 
blocks  of  rock  from  their  parent  masses  to  considerable  distances. 
Though  Prof.  Playfair  long  since  (1802)  pointed  out  glaciers  as  having 
been  the  means  of  carrying  erratic  blocks,f  even  (in  1806)  inferring 
that  those  on  the  Jura  may  have  been  transported  by  the  extension  of 
ancient  Alpine  glaciers  to  that  range  of  mountains,  the  subject  engaged 
no  great  attention  for  some  time.  M.  Venetz  appears  to  have  been  the 
first  who,  having  had  occasion  to  study  glacier  movements,  subsequently 
(1821)  took  the  same  view  ;J  one  adopted  afterwards  (1835)  by  M.  de 
Charpentier,§  and  further  extended  (in  1837)  by  M.  Agassiz.||  The 
subject  then  attracted  more  general  interest,  especially  from  the  writings 
of  M.  de  Charpentierlf  and  M.  Agassiz,**  and  the  consideration  of  the 
effects  produced  by  existing  glaciers  and  floating  ice,  with  the  proba- 
bility of  a  colder  state  than  at  present  of  the  northern  portions  of 
Europe,  Asia,  and  America,  at  a  comparatively  recent  time,  now  form 
one  of  the  usual  objects  of  geological  investigation. 

Sir  Charles  Lyell  long  since  called  attention  to  the  distribution  of 
blocks  and  minor  fragments  of  rock  over  the  sea  bottom  by  means  of 
icebergs,  and  to  the  manner  in  which  such  detritus  would  be  found 
scattered  over  various  levels,  if  this  sea  bottom  were  upraised  and  formed 
dry  land. ft  Subsequently  (in  1840)  after  noticing  the  action  of  drift 
ice,  charged  with  mud,  and  blocks  of  rocks,  he  pointed  out  the  manner 
in  which  the  floating  ice  may,  by  grounding  upon  coasts  or  banks,  so 
squeeze  the  upper  layers  of  mud,  sand,  and  gravel,  that  contorted 
masses  of  these  layers  may  repose  upon  undisturbed  and  horizontal  beds 

*  "  On  the  Revolutions  of  the  Earth's  Surface"  (1812),  Transactions  of  the  Royal 
Society  of  Edinburgh,  vol.  vii.  p.  157.  After  noticing  the  removal  of  a  block  of  rock 
four  or  five  feet  in  diameter,  being  a  boundary  mark  between  two  estates  on  the  shore  of 
the  Murray  Frith,  by  the  tide,  while  encased  in  ice,  for  90  yards,  and  also  the  magni- 
tude and  effects  of  earthquakes,  he  asks,  respecting  the  erratic  blocks  of  Northern 
Europe,  if  both  combined  would  not  produce  the  effects  required,  "  the  natural  place 
of  these  blocks  being  covered  perfectly  with  ice,  in  the  state  best  calculated  for  fulfil- 
ling the  office  here  assigned  it,"  p.  157.  He  inferred  that  in  the  Alps  similar  waves, 
assuming  the  fitting  conditions,  would  wash  off  portions  of  glaciers  with  their  load  of 
blocks. 

f  Playfair,  "Illustrations  of  the  Huttonian  Theory,"  §  349. 

j  Venetz,  "  Bibliotheque  Universelle  de  Geneve,"  torn,  xxi.,  p.  77,  and  "  Denkschriftcn 
der  Schweizerischen  Gesellschaft ;"  1  Band,  Zurich,  1833. 

$  De  Charpentier,  Notice  sur  le  cause  probable  du  Transport  des  Blocs  Erratiques 
de  la  Suisse,  "  Annales  des  Mines,"  3me  Series,  torn,  viii.,  1835. 

||  Agassiz,  "  Address  before  the  Helvetic  Society  of  Natural  Sciences,  at  Neuchatel," 
1837. 

.fl  "Essai  sur  les  Glaciers  et  sur  le  Terrain  Erratique  du  Bassin  du  Rhone,"  Lau- 
sanne, 1841. 

**  "Etudes  sur  les  Glaciers,"  1840. 

ff  «  Principles  of  Geology,"  1832. 


IN    GREAT    BRITAIN    AND    IRELAND.  273 

beneath.*  It  was,  however,  in  consequence  of  a  visit  to  this  country 
by  M.  Agassiz,  in  1840,  and  upon  the  extension  of  his  views  respecting 
glaciers  to  the  British  Islands, f  that  the  former  existence  of  glaciers  in 
them  has  attracted  attention.  Numerous  facts  have  since  been  adduced 
in  support  of  this  opinion  by  Dr.  Buckland,  Sir  Charles  Lyell,  Pro- 
fessor James  Forbes,  Mr.  Darwin,  and  others'. J  The  amount  of  sub- 

*  In  a  communication  on  the  Boulder  Formation  or  Drift,  and  associated  fresh-water 
deposits,  composing  the  mud  cliffs  of  Eastern  Norfolk,  "Proceedings  of  the  Geological 
Society  of  London"  (January,  1840),  vol.  iii.,  wherein  the  contortions  observed  on  that 
coast  are  thus  explained. 

f  In  the  "Proceedings  of  the  Geological  Society  of  London,"  vol.  iii.  p.  328  (1840), 
M.  Agassiz  has  given  a  summary  respecting  his  views  of  the  former  existence  of  glaciers 
in  the  British  Islands.  Ben  Nevis,  in  the  north  of  Scotland,  and  the  Grampians  in 
Southern  Scotland,  are  considered  by  him  as  the  great  centres  of  dispersion  of  erratic 
blocks  by  glacier  ice  in  that  part  of  Great  Britain.  He  pointed  out  the  mountains  of 
Northumberland,  Westmoreland,  Cumberland,  and  Wales,  as  well  as  those  of  Ayrshire, 
Antrim,  Wicklow,  and  the  West  of  Ireland,  as  also  centres  of  dispersion,  "  each  district 
having  its  peculiar  debris,  traceable  in  many  instances  to  the  parent  rock,  at  the  head 
of  the  valleys.  Hence,"  observes  M.  Agassiz,  "it  is  plain  the  cause  of  the  transport 
must  be  sought  for  in  the  centre  of  the  mountain  ranges,  and  not  from  a  point  without 
the  district."  The  Swedish  blocks  on  the  coast  of  England  do  not,  he  conceives,  con- 
tradict this  position,  as  he  adopts  the  opinion  that  they  may  have  been  transported  by 
floating  ice,  p.  329.  He  considered  that  the  best  example  of  glacier  striated  rocks  in 
Scotland  is  to  be  seen  at  Ballahulish. 

J  Dr.  Buckland  ("Proceedings  of  the  Geological  Society  of  London,"  vol.  iii.  p.  332, 
1840),  in  his  paper  "  On  the  Evidences  of  Glaciers  in  Scotland  and  the  North  of  Eng- 
land," points  out  localities  which  he  infers  show  the  remains  of  moraines  near  Dum- 
fries, in  Aberdeenshire,  in  Forfarshire,  at  Taymouth,  Glen  Cofield,  and  near  Callender, 
with  evidences  of  ancient  glaciers  on  Schiehallion,  in  and  near  Strath  Earn,  and  near 
Comrie  ;  and  of  glacial  action  at  Stirling  and  Edinburgh.  He  also  mentions  moraines 
in  Northumberland,  the  evidence  of  ancient  glaciers  in  Cumberland  and  Westmoreland, 
and  the  dispersion  of  Shap  Fell  granite  by  ice. 

In  his  address  to  the  Geological  Society  of  London,  as  its  President,  in  February, 
1841,  Dr.  Buckland  gave  a  condensed  statement  of  the  progress  of  investigations  on 
this  subject  during  the  preceding  year,  one  in  which  the  "  Glacial  Theory,"  was  so 
much  considered. 

Dr.  Buckland  subsequently,  in  his  memoir  on  the  Glacia-Diluvial  Phenomena  in 
Snowdonia,  and  the  adjacent  parts  of  North  Wales  (December,  1841),  "Proceedings  of 
the  Geological  Society,"  vol.  iii.  p.  579,  described  the  rounded  and  polished  surfaces, 
often  accompanied  by  grooves  and  scratches,  attributed  to  glacier  action,  in  the  valleys 
of  Conway,  of  the  Llugwy,  of  the  Ogwyn,  of  the  Sciant,  and  of  Llanberis,  of  Gwyrfain 
or  Forrhyd,  of  the  Nautel  or  Lyfni,  and  of  the  Gwynant. 

Sir  Charles  Lyell,  in  his  paper  "On  the  Geological  Evidence  of  the  former  existence 
of  Glaciers  in  Forfarshire,"  stated  that,  though  for  several  years  he  had  attributed  the 
transportal  of  erratic  blocks,  and  the  curvature  and  contortions  of  the  incoherent  strata 
of  gravel  and  clay,  resting  upon  the  unstratified  till,  to  drifting  ice,  he  had  found  diffi- 
culty in  thus  accounting  for  certain  other  facts  connected  with  the  subject,  until  Pro- 
fessor Agassiz  extended  his  glacial  theory  to  Scotland.  After  a  description  of  various 
minor  districts,  Sir  Charles  Lyell  observes,  "that  it  is  in  South  Georgia,  Kerguelen's 
Land,  and  Sandwich  Land,  we  must  look  for  the  nearest  approach  to  the  state  of  things 
which  must  have  existed  in  Scotland  during  the  glacial  epoch." 

Professor  James  Forbes,  in  his  "Notes  on  the  Topography  and  Geology  of  the 

18 


274          ERRATIC    BLOCKS    AND    SHINGLES    RAISED    BY 

mergence  at  this  period  has  been  variously  estimated.  Mr.  Darwin 
infers,  from  a  large  greenstone  boulder  on  Ashley  Heath,  Staffordshire, 
at  803  feet  above  the  sea,  and  apparently  derived  from  Wales,  a  con- 
siderable depression  of  England  beneath  the  sea,  and  that  Scotland, 
from  other  data,  must  have  been  submerged  1,300  feet.*  Looking  at 
the  heights  to  which  gravels  extend  in  Wales,  often  apparently  the 

Cuchullen  Hills,  in  Skye,  and  the  traces  of  ancient  glaciers  which  they  present,"  (Edin- 
burgh New  Philosophical  Journal,  1846,  vol.  xl.  p.  76),  points  out  groovings  and 
scratchings  upon  polished  rocks  of  a  marked  kind.  He  observes,  respecting  the  valley 
of  Coruisk,  that  "the  surfaces  of  hypersthene,  thus  planed  or  evened,  present  systems 
of  grooves  exactly  similar  to  those  so  much  insisted  on  in  the  action  of  glaciers  on  sub- 
jacent rocks,  and  as  evidence  of  glaciers  in  parts  of  the  Alps  and  Jura,  where  they  are 
now  wanting.  These  grooves  or  striae  are  as  well  marked,  as  continuous,  and  as 
strictly  parallel  to  what  I  have  elsewhere  shown  to  be  the  necessary  course  of  a 
tenacious  mass  of  ice  urged  by  gravity  down  a  valley,  as  anywhere  in  the  Alps.  They 
occur  in  high  vertical  cliffs,  as  near  the  Pissevache ;  they  rise  against  opposing  promon- 
tories, as  in  the  Valley  of  Hasli;  they  make  deep  channels  or  flutings  in  the  trough  of 
the  valley,  as  at  Pont  Pelissier,  near  Chamouni ;  and  as  at  Fee,  in  the  Valley  of  Saas. 
At  the  same  time  these  appearances  have  a  superior  limit,  above  which  the  craggy 
angular  forms  are  almost  exclusively  seen,  where  the  phenomena  of  wearing  and 
grooving  entirely  disappear.  In  short,"  adds  Professor  Forbes,  "it  would  be  quite 
impossible  to  find  in  the  Alps,  or  elsewhere,  these  phenomena  (except  only  the  high 
polish  which  the  rocks  here  do  not  admit  of)  in  greater  perfection  than  in  the  Valley 
of  Coruisk."  Other  evidence  of  the  like  kind  is  also  adduced. 

Mr.  Darwin,  in  his  "Notes  on  the  effects  produced  by  the  ancient  Glaciers  of  Caer- 
narvonshire, and  on  the  Boulders  transported  by  floating  Ice,"  (Philosophical  Magazine, 
1842,  vol.  xxi.  p.  180,)  after  mentioning  the  labours  of  Dr.  Buckland,  on  the  same 
county,  and  that  Mr.  Trimmer  had  first  noticed  (Proceedings  of  the  Geological  Society, 
vol.  i.  p.  332,  1831)  the  scoring  and  scratching  of  rocks  in  North  Wales,  adduces 
additional  evidence  of  glacial  action  in  that  district.  He  observes  that,  "within  the 
central  valleys  of  Snowdonia,  the  boulders  appear  to  belong  entirely  to  the  rocks  of  the 
country.  May  we  not  conjecture,"  he  continues,  "that  the  icebergs,  grating  over 
the  surface,  and  being  lifted  up  and  down  with  the  tides,  shattered  and  pounded  the 
soft  slate  rocks,  in  the  same  manner  as  they  seem  to  have  contorted  the  sedi- 
mentary beds  of  the  east  coast  of  England  (as  shown  by  Mr.  Lyell),  and  of  Tierra 
delFuego?"  ....  "  The  drifting  to  and  fro  and  grinding  of  numerous  icebergs  during 
long  periods  near  successive  uprising  coast  lines,  the  bottom  being  often  stirred  up, 
and  fragments  of  rocks  dropped  on  it,  will  account  for  the  sloping  planes  of  unstrati- 
fied  till,  occasionally  associated  with  beds  of  sand  and  gravel,  which  fringe  to  the 
west  and  north  the  great  Caernarvonshire  mountains."  Mr.  Darwin  further  remarks 
(p.  186),  as  not  "probable,  from  the  low  level  of  the  chalk  formation  in  Great  Britain, 
that  rounded  chalk  flints  could  often  have  fallen  on  the  surface  of  glaciers,  even  in  the 
coldest  times.  I  infer,  therefore,"  he  continues,  "that  such  pebbles  were  probably 
inclosed  by  the  freezing  of  the  water  on  the  ancient  sea-coasts.  We  have,  however, 
the  clearest  proofs  of  the  existence  of  glaciers  in  this  country,  and  it  appears  that, 
when  the  land  stood  at  a  lower  level,  some  of  the  glaciers,  as  in  Nant  Francon,  reached 
the  sea,  where  icebergs  charged  with  fragments  would  occasionally  be  found.  By  this 
means  we  may  suppose  the  great  angular  blocks  of  Welsh  rocks,  scattered  over  the 
central  counties  of  England,  were  transported."  The  deposits  of  this  date  in  Ireland 
have  occupied  the  attention  of  several  geologists,  among  whom  may  be  mentioned  Mr. 
Weaver,  Mr.  Griffith,  Colonel  Portlock,  Mr.  Trimmer,  Professor  Oldham,  Mr.  Bryce, 
Dr.  Lloyd,  Mr.  Hamilton,  and  Dr.  Scouler. 

*  Philosophical  Magazine,  1842,  vol.  xxi.  p.  186. 


COAST-ICE    DURING    SUBMERGENCE    OF    LAND.  275 

remains  of  masses  of  coast  shingles  and  sand,  a  like,  if  not  a  greater 
depression  beneath  the  present  sea  level  would  be  there'  required.  In 
Ireland,  we  find  large  blocks  of  granite  sometimes  perched  on  the 
heights,  amid  grooves  and  furrows  on  the.  surface  of  the  rocks  beneath, 
at  altitudes  of  1000  feet  and  more.  In  some  cases,  we  almost  seem  to 
have  before  us  a  portion  of  the  very  blocks  which  scratched  and  scored 
the  subjacent  rock-surfaces.* 

Erratic  blocks,  occasionally  of  considerable  magnitude,  are  found, 
in  some  localities,  at  various  elevations  above  rocks  of  their  kind,  and 
from  which  they  are  considered  to  have  been  detached.  Although  it 
is  obvious  that  each  fragment  so  detached  has  deprived  the  mass  of 
rock  whence  it  has  been  derived,  of  so  much  of  its  volume,  and  perhaps 
also  of  its  height,  as  regards  elevation  above  the  sea  level,  and  conse- 
quently that  if  multitudes  have  been  thus  detached,  previous  heights, 
composed  of  such  rocks,  may  have  been  much  reduced  by  the  loss  thus 
sustained,  there  are  instances  where  it  would  not  appear  a  sufficient 
explanation  to  infer  that  a  transport  of  erratic  blocks  had  been  effected 
by  ice  in  such  a  manner,  that  while  higher  portions  of  the  parent  rock 
floated  away  at  the  required  levels,  the  remaining  lower  portions  were 
denuded,  in  the  usual  manner,  as  the  land  emerged.  To  account  for 
such  instances,  Mr.  Darwin  considers  that  we  should  regard  the  probable 
effects  of  submerging  land,  where  coast  ice  could  be  formed,  upon 
blocks  of  rock  which  may  have  been  ice-transported  to  its  shores.  He 
points  out  that  erratic  blocks  and  other  portions  of  the  beaches  of  such 
shores  might  gradually  be  raised  as  the  land  became  submerged,  so 
that  finally  coast  detritus,  including  the  blocks  of  rocks  ice-transported 
from  various  distances,  would  be  elevated  to  heights  above  that  at 
which  it  was  accumulated  or  stranded.  Blocks,  with  other  coast  frag- 
ments and  shingle,  would  thus,  when  the  land  again  emerged  from 
beneath  the  sea,  be  found  raised  above  the  level  at  which  the  remains 
of  their  parent  rocks  are  now  found.f 

*  Although  in  several  parts  of  Ireland  the  facts  relating  to  the  transport  of  erratic 
blocks  can  be  well  studied,  and  the  altitudes  at  which  they  and  the  smoothing  and 
scratching  of  surface  rocks  are  found  well  observed,  there  are  few  places  where  the 
latter  can  be  seen  in  greater  perfection  than  the  beautiful  neighbourhood  of  Glengariff, 
county  Cork.  The  scoring  and  rounding  of  the  sides  and  bottom  of  the  valley  from 
the  lower  part  of  the  demesne  of  Glengariff  to  Bantry  Bay  is  particularly  worthy  of 
attentive  study. 

f  Darwin,  "On  the  Transportal  of  Erratic  Boulders  from  a  Lower  to  a  Higher 
Level." — Journal  of  the  Geological  Society,  1849,  vol.  v.  Mr.  Darwin  remarks  that 
the  fragments  of  rock,  "from  being  repeatedly  caught  in  the  ice  and  stranded  with 
violence,  and  from  being  every  summer  exposed  to  common  littoral  action,  will  gene- 
rally be  much  worn ;  and  from  being  driven  over  rocky  shoals,  probably  often  scored. 
From  the  ice  not  being  thick,  they  will,  if  not  drifted  out  to  sea,  be  landed  in  shallow 
places,  and  from  the  packing  of  the  ice,  be  sometimes  driven  high  up  the  beach,  or 
even  left  perched  on  ledges  of  rock." 


276  ERRATIC    BLOCKS     OF    THE    ALPS. 

Respecting  the  erratic  blocks  of  the  Alps,  and  of  the  adjoining 
countries,  a  large  mass  of  information  has  been  collected.*  The  main 
fact  of  the  blocks  and  associated  minor  detritus  having  been  trans- 
ported from  the  higher  Alpine  mountains  outwards  on  both  sides  the 
main  ranges,  showing  that  the  cause  of  their  dispersion  had  been  in  the 
Alps  themselves,  forms  the  base  of  the  chief  modern  hypotheses  con- 
nected with  the  subject,  whether  the  sudden  melting  of  snows  and 
glaciers  by  the  heat  and  vapours  accompanying  the  last  elevation  ex- 
perienced in  these  mountains,f  the  former  great  extension  of  Alpine 
glaciers,  or  the  latter  combined  with  a  considerable  submergence  of 
land,  so  that  the  sea  entered  many  of  the  valleys  of  the  Alps,  coast  ice 
being  possibly  also  produced. 

Yon  Buch,  De  Luc,  Escher,  Elie  de  Beaumont,  a*nd  other  geologists, 
long  since  pointed  out  that,  from  the  mode  of  occurrence  of  the  Alpine 
erratic  blocks,  the  great  valleys  of  the  Alps  existed  prior  to  their  dis- 
persion, and  much  observation  has  been  directed  to  the  sources  whence 
particular  kinds  of  blocks  have  been  derived.J  The  magnitude  of  the 
blocks  on  both  sides  of  the  Alps,  in  connexion  with  the  distances  they 

*  A  valuable  summary  of  the  labours  of  geologists  on  this  subject  will  be  found  in 
the  "Histoire  des  Progres  de  la  Geologic,  de  1834  a  1845,"  torn.  ii.  chap.  5,  by  the 
Vicomte  d'Archiac.  Appended  to  it  is  a  list  of  the  publications,  which  may  advan- 
tageously be  consulted. 

f  As  regards  the  transportal  of  blocks  of  rock  by  the  sudden  melting  of  snow  from 
the  escape  of  gases  rising  through  fissures  during  the  elevation  of  mountain  chains,  the 
observer  will  find  the  subject  carefully  treated  in  the  "Note  relative  a  1'une  des  causes 
prdsumables  des  phe'nome'nes  erratiques,"  by  Elie  de  Beaumont  (Bulletin  de  la  Soci6t6 
Ge"ologique  de  France,  t.  iv.  p.  1334, 1847).  On  the  supposed  heat  of  the  gases  re- 
quired for  the  melting  of  the  snow,  M.  Elie  de  Beaumont  remarks,  after  noticing  many 
circumstances  bearing  on  the  subject,  that  "it  is  unnecessary  to  attribute  to  the  gaseous 
current,  considered  to  have  been  disengaged  from  fissures  in  the  ground,  a  temperature 
higher  than  that  needed  to  overcome  the  atmospheric  pressure.  Little  would  be  gained 

by  giving  this  current  a  very  high  temperature." "The  hypothesis  which 

admits  the  erratic  thaw  to  have  been  produced  by  vapours  of  moderate  temperature, 
appears  to  me,"  he  continues,  "  also  that  according  to  which  nature  would  have  worked 
with  the  minimum  loss  of  heat." 

J  With  reference  to  the  mode  of  distribution  of  the  erratic  blocks  in  the  basin  of  the 
Rhone,  as  also  to  the  kinds  of  rocks  so  distributed,  M.  Guyot  has  remarked  (Bulletin 
de  la  Soc.  des  Sciences  de  Neuchatel,  1846,  Archives  de  Geneve,  Sept.,  1847):— 

1.  That  a  kind  of  rock  which  is  abundant  in  one  part  of  the  basin,  is  rare,  or  absent, 
in  another. 

2.  That  the  blocks  of  different  kinds,  commencing  with  the  locality  of  their  origin, 
form  parallel  series,  preserved  in  the  plain ;  blocks  of  the  right  side  of  the  valley 
keeping  to  the  right,  of  the  left  side  to  the  left,  while  those  of  the  centre  preserve 
their  central  position. 

3.  That  groups  composed  of  a  single  kind  of  rock,  to  the  exclusion  of  others,  are 
here  and  there  found  in  the  midst  of  various  rocks. 

These  views  M.  Guyot  considers  as  borne  out  by  numerous  facts,  and  he  infers  that 
the  blocks  have  been  distributed  by  glaciers  in  the  manner  in  which  similar  blocks 
now  are  by  the  moraines  of  actual  Alpine  glaciers.  He  states  that  similar  facts  are 
observable  in  the  valleys  of  the  Rheuss  and  Rhine. 


ERRATIC    BLOCKS    OF     THE    ALPS.  277 

must  have  travelled  from  their  parent  rocks,  has  also  long  engaged 
attention.  The  Pierre  d  Bot,  above  Neuchatel,  and  represented  be- 
neath (fig.  102),*  affords  a  good  example  of  an  erratic  block,  perched 
on  the  side  of  the  Jura,  far  distant  from  its  source.  ,  This  granite  mass 

Fig.  102. 


is  estimated  as  containing  about  40,000  cubic  feet,  and  considered  to 
have  been  transported  22  leagues  from  the  crest  of  the  Follaterres,  on 
the  north  of  Martigny.f  The  blocks  on  the  Jura  have  always  attracted 
much  attention,  from  the  circumstance  that  they  must  have  been  trans- 
ported over  the  great  valley  of  Switzerland,  intervening  between  that 
range  and  the  Alps.  The  blocks  on  the  Chasseron  are  estimated  as 
rising  to  the  height  of  about  3600  feet.J  On  the  southern  side  of  the 
Alps  striking  masses  of  erratic  blocks  are  to  be  seen  in  the  vicinity  of 
the  Lakes  of  Como  and  Lecco.  They  will  be  found  high  up  the  northern 
side  of  Monte  San  Primo,  a  mountain  well  separated  from  the  high 
Alps  by  the  intervening  Lake  of  Como.  The  foil  owing  (fig.  103)  is  a 
section  of  this  mountain,  showing  the  maniier  in  which  the  erratic 
blocks  rest  upon  it. 

Fig.  103. 


d  I  ddl 

P,  Monte  San  Primo ;  B,  bluff  point  of  Bellaggio,  rising  out  of  the 

*  Taken  from  a  view  in  the  "  Travels  in  the  Alps  of  Savoy,  &c.,"  by  Prof.  James 
Forbes,  2d  edition. 

f  M.  d'Archiac  remarks  (Histoire  des  Progres  de  la  Geologic,  t.  ii.  p.  249),  that 
granite  and  gneiss  generally  form  the  blocks  of  the  largest  size.  "A  block  of  granite, 
on  the  calcareous  mountain  near  Orsieres,  contains  more  than  100,000  cubic  feet. 
Above  Monthey,  many  blocks  derived  from  the  Val  de  Ferret,  and  which  have  thus 
travelled  a  distance  not  less  than  11  leagues,  contain  from  8,000  to  50,000  and  60,000 
cubic  feet."  .  .  .  "The  blocks  of  talcose  granite  of  Steinhof,  near  Seeberg,  one  of 
which  measures  61,000  cubic  feet,  has  travelled  about  60  leagues." 

Considering  the  40,000  cubic  feet  supposed  to  be  contained  in  the  Pierre  d  Bot,  as 
French  measure,  it  would  weigh  about  3,000  tons. 

J  Necker,  Etudes  Geologiques  dans  les  Alps,  vol.  i.     Paris,  1841. 


278  ERRATIC    BLOCKS    OB1    NORTHERN    EUROPE 

Lake  of  ComcyC ;  a  a  a  a,  blocks  of  granite,  gneiss,  &c.,  scattered  over 
the  surface  of  the  limestone  rocks,  II 1 1,  and  the  dolomite,  d  d  d.  V, 
the  Commune  di  Villa,  where  a  previously  existing  depression  has  been 
nearly  filled  with  transported  blocks  and  minor  detritus.  On  the  north 
side  of  the  Alpi  di  Pravolta,  V,  the  block  represented  beneath  (Fig. 
104),  is  seen,  one  however,  not  so  remarkable  for  size,  as  for  showing 
the  little  attrition  it  could  have  suffered  during  its  transport  from  the 
higher  Alps  to  its  present  position. 

Fig.  104. 


-:~ 


A  large  amount  of  information  has  been  obtained  respecting  the  dis- 
tribution of  erratic  blocks  in  Northern  Europe,  and  the  sources  in  Scan- 
dinavia whence  they  have  been  detached.*  The  area  over  which  they 
have  been  so  distributed  has  been  shown  in  a  map  by  Sir  Roderick 
Murchison,  M.  de  Verneuil,  and  Count  Keyserling,f  the  boundary  line 
exhibiting  the  southern  and  eastern  limits  of  the  erratic  blocks  extend- 
ing from  Prussia  to  Voroneje,  in  Russia,  and  thence  northwards  to  the 
Gulf  of  Tcheskaia,  on  the  North  Sea.  It  is  remarked  that  from  the 
German  Ocean  and  Hamburg  on  the  west,  to  the  "White  Sea  on  the 
east,  an  area  of  2000  miles  long,  varying  in  width  from  400  to  800 
miles  (which  may,  perhaps,  be  roughly  estimated  at  about  1,200,000 
square  miles),  is  more  or  less  covered  by  loose  detritus,  amid  which 
there  are  blocks  of  great  size,  the  whole  derived  from  the  Scandinavian 
mountains. 

"While  regarding  the  kind  and  extent  of  country  thus  more  or  less 

*  The  observer  would  do  veil  to  consult  the  Rapport  sur  un  Mdmoire  de  M.  Durocher, 
intituld  "  Observations  sur  le  Phe*nomene  Diluvien  dans  le  Nord  de  1'Europe,"  by  M. 
Elie  de  Beaumont  (Comptes  Rendus,  torn.  xiv.  p.  78,  1842),  wherein  an  excllent  sum- 
mary and  general  view  of  the  subject,  including  the  marking  of  subjacent  rocks,  up  to 
the  date  of  the  observations,  will  be  found.  He  should  likewise  consult  the  "  Geology 
of  Russia  in  Europe,  and  the  Ural  Mountains,"  1845,  by  Sir  Roderick  Murchison,  M. 
de  Verneuil,  and  Count  Keyserling;  chapter  xx.,  Scandinavian  Drift  and  Erratic  Blocks 
in  Russia;  and  chapter  xxi.,  Drift  and  Erratic  Blocks  of  Scandinavia,  and  Abrasion 
and  Striation  of  Rocks;  and  also  the  "  Ilistoire  des  Progres  de  la  Gdologie  de  1834  a 
1845,"  torn.  ii.  premidre  partie,  Terrain  Quaternaire  ou  Diluvien.  Formation  erratique 
du  Nord  de  1'Europe.  Paris,  1848.  Notwithstanding  the  title,  this  valuable  work 
contains  information  up  to  the  date  of  publication.  A  most  excellent  and  impartial 
summary  of  the  labours  relating  to  this  subject,  with  original  observations,  will  be  found 
in  this  "History." 

f  "Geology  of  Russia  in  Europe  and  the  Ural  Mountains,"  1845. 


DERIVED    FROM    SCANDINAVIA.  279 

covered  with  erratic  blocks  and  the  position  which  the  Scandinavian 
mountains  would  occupy  relatively  to  a  large  submerged  area,  the  opi- 
nion that  glaciers,  icebergs  (detached  from  them),  and  coast  ice,  may 
have  been  the  chief  means  of  dispersing  the  blocks  and  other  detritus 
from  a  large  isolated  region,  as  that  of  Scandinavia  would  then  be,  ap- 
pears far  from  improbable.  Careful  examinations  of  the  Scandinavian 
region  itself,  shows  that  the  whole  land  has  been  elevated  above  the 
present  level  of  the  adjoining  seas  in  comparatively  recent  geological 
times,  and  there  has  been  found  a  scoring  of  subjacent  rocks  and  dis- 
persion of  blocks  outwards  from  it,  according  with  this  view.* 

In  the  region  occupied  by  these  erratic  blocks,  ridges  of  them  and 
other  detrital  matter  have  been  observed  to  run  in  lines,  often  for  con- 
siderable distances.  These  are  commonly  known  as  skdrs,  or  osars.^ 
Count  Rasoumouski  would  appear  (in  1819)  to  have  been  among  the  first 
to  remark  upon  those  in  Russia  and  Germany,  observing  that  they 
usually  occurred  in  lines  having  a  direction  from  N.E.  to  S.W.  M. 
Brongniart  pointed  out  (in  1828),  that  those  of  Sweden,  though  some- 
times inosculating,  took  a  general  direction  from  north  to  south.  J  Much 
discussion  has  arisen  respecting  the  origin  of  these  lines  of  accumula- 
tion. Upon  the  supposition  that  lines  of  blocks  may  have  been  accu- 
mulated by  glaciers,  and  the  drift  of  iceberg  and  coast  ice  in  particular 
directions,  and  that  upon  the  uprise  o,f  such  lines  of  deposits,  breaker 
action  would  be  brought  to  bear  upon  them  for  a  time,  we  should  expect 
very  complicated  evidence. 

In  Northern  America  erratic  blocks  are  found  to  occupy  a  large  area, 
some  being  strewed  as  far  south  as  40°  N.  latitude.  Here,  as  in  northern 

*  M.  Daubree  states  (Comptes  Rendus,  vol.  xvi.  1843),  that  the  traces  of  transport  of 
detritus  and  of  friction,  diverge  from  the  high  regions,  precisely  as  in  the  Alps.  This 
was  observed  up  to  an  elevation  of  3800  feet  (English).  M.  de  Bohtlingk  (Poggendorff's 
Annalen,  1841),  states  that  Scandinavian  blocks  have  been  transported  from  the  coast 
of  Kemi  into  the  Bay  of  Onega,  and  from  Russian  Lapland  into  the  Icy  Sea,  that  is,  in 
northerly,  northwesterly,  and  northeasterly  directions,  as  quoted  also  in  the  "Geology 
of  Russia,"  vol.  i.  p.  528. 

f  It  is  worthy  of  remark  that  similar  accumulations  of  this  date,  in  Ireland,  are 
known  as  Escars. 

I  "  Annales  des  Sciences  Naturelles,"  1828.  M.  d'Archiac  observes  ("Histoire  des 
Progres  de  la  Geologic,"  1848,  torn.  ii.  p.  36),  that  "  the  form  of  the  osars,  their  dis- 
position, and  their  parallelism  with  the  furrows  and  scratches  of  erosion,  naturally  lead 
to  the  idea  of  a  current  which  has  swept  the  southern  part  of  Sweden  from  N.N.E.  to 
S.S.W.  M.  Durocher  has  found,  with  M.  Sefstrom,  that  the  osars  were  heaped  up  on 
the  southern  side  of  the  mountains,  which,  in  that  direction,  opposed  their  course.  The 
osars  in  Finland,  though  less  marked,  have  a  direction  from  N.  25°  W.  to  S.  25°  E., 
one,  which,  with  the  preceding,  represents  the  radii  of  the  semicircle  in  which  the  great 
erratic  block  deposit  of  Central  Europe  occurs." 

In  the  "Geology  of  Russia  in  Europe  and  the  Ural  Mountains,"  will  be  found  the 
views  of  its  authors  respecting  sk'ars  or  osars.  A  figure  is  given  of  an  iceberg  aground, 
and  the  consequences  of  its  melting  stated,  lines  of  angular  and  rounded  blocks  being 
strewed,  as  the  ice  dissolved,  by  a  current  acting  constantly  in  one  direction. 


280  ERRATIC    BLOCKS    OF    NORTH    AMERICA. 

Europe,  the  general  drift  of  detritus  appears  to  be  from  the  northward 
to  the  southward,  and  blocks  perched  at  various  altitudes,  scored  and 
scratched  surfaces  of  subjacent  rocks,  and  osars  or  lines  of  accumulation,* 
occur  in  the  same  manner.  Such  similar  effects  point  to  similar  causes, 
and  hence  the  explanations  offered  have  been  of  a  similar  general  cha- 
racter.f  A  large  amount  of  information  has  also  been  collected  respect- 
ing the  occurrence  of  these  blocks,  and  of  the  polishing  and  scoring  of 
subjacent  rocks.J  It  is  stated  that  the  divergence  of  any  blocks,  such, 
for  example,  as  those  of  the  Alps,  is  not  observed  in  the  United  States. 
Professor  Henry  Rogers  points  out  that  the  scorings  do  not  radiate 
from  the  high  grounds,  but  that  amid  the  mountains  of  New  England, 
and  in  the  great  plains  of  the  west,  and  in  Pennsylvania,  Vermont,  and 
Massachusetts,  they  preserve  a  southeast  direction  at  all  their  elevations  ; 
the  lower  parts  of  the  great  valleys  being  alone  excepted.  In  the  moun- 
tainous portions  of  the  region,  the  heights  and  flanks  exposed  to  the 
north  and  northwest,  are  the  most  polished  and  scored.  Blocks  of  large 
size  have  been  found  in  New  England,  New  York,  and  Pennsylvania, 
from  1000  to  1500  feet  above  the  sea. 

Erratic  blocks  are  also  found  in  South  America.  Mr.  Darwin  dis- 
covered them  up  the  Santa  Cruz  River,  Patagonia,  in  about  50°  10'  S. 
latitude,  and  about  67  miles  from  the  nearest  Cordillera.  Nearer  the 

*  An  interesting  account  of  two  remarkable  trains  of  angular  erratic  blocks  in  Berk- 
shire, Massachusetts,  is  given  by  Professors  Henry  and  William  Rogers,  in  the  "  Boston 
Journal  of  Natural  History,"  June,  1846.  These  two  trains,  one  extending  for  20  miles, 
both  previously  noticed  by  Dr.  Reid  and  Professor  Hitchcock,  were  traced  to  their 
{sources.  The  blocks  are  generally  large,  the  smaller  being  several  feet  in  diameter. 
One  weighs  about  2000  tons.  The  blocks  gradually  decrease  in  size  to  the  S.E.,  those 
which  have  travelled  farthest  being  the  most  worn.  They  are  stated  not  to  mingle  with 
the  general  drift  beneath  them,  the  boulders  and  pebbles  in  which  bear  "  the  traces  of 
a  long-continued  and  violent  rubbing."  "  Other  long  and  narrow  lines  of  huge  erratic 
fragments  are  seen  elsewhere  in  Berkshire,  and  abound,  we  think,  in  nearly  all  the 
mountainous  districts  of  New  England.  One  such  train,  originating  apparently  in  the 
Lennox  ridge,  about  two  miles  on  the  south  of  Pittsfield,  crosses  the  Housatonic  Valley, 
southeasterly,  as  far  at  least  as  the  foot  of  the  broad  chain  of  hills  in  Washington.  Some 
very  extensive  ones  are  to  be  seen  on  the  western  side  of  the  White  Mountains." 

f  These  will  be  found  in  the  works  and  memoirs  of  Hitchcock,  Mather,  Emmons,  Hall, 
Rogers,  Hubbart,  Redfield,  Jackson,  Christy,  Ch.  Martins,  and  other  geologists. 

J  We  are  indebted  to  Dr.  Bigsby  for  an  early  notice  of  the  erratic  blocks  of  North 
America. — (Trans.  Geol.  Soc.,  London,  vol.  i.,  second  series.) 

In  1833,  Professor  Hitchcock  (Report  on  the  Geology  of  Massachusetts,  Art.  Dilu- 
vium) adduced  abundant  evidence  of  the  northern  origin  of  these  blocks  in  the  districts 
described  by  him.  The  like  was  also  done  at  an  early  date  for  other  portions  of  North 
America,  by  Messrs.  Lapham,  Jackson,  Alger,  and  others.  The  observer  will  find  an 
able  summary  of  the  facts  known  in  1846,  on  this  subject,  in  Professor  Hitchcock's 
Address  to  a  meeting  of  the  Association  of  American  Geologists  in  that  year.  Professor 
Henry  Rogers  also  treated  in  a  general  manner  of  the  American  erratic  blocks  in  his 
Address  to  the  same  scientific  body  in  1844,  (American  Journal  of  Science,  vol.  xlvii.) 
Another  general  summary,  up  to  1848,  is  given  by  the  Vicomte  d'Archiac  (Histoire  des 
Prog  res  de  la  G6ologie,  torn,  ii.,  chap.  9,  Terrain  Quaternaire  de  TAmdrique  du  Nord). 


ERRATIC    BLOCKS     OF    SOUTH    AMERICA.  281 

mountains  (at  55  miles)  they  became  "extraordinarily  numerous."  One 
square  block  of  chloritic  schist  measured  5  yards  on  each  side,  and 
projected  5  feet  above  the  ground ;  another,  more  rounded,  measured 
60  feet  in  circumference.  "  There  were  innumerable  other  fragments 
from  2  to  4  feet  square."*  The  great  plain  on  which  they  stood  was 
1400  feet  above  the  sea,  sloping  gradually  to  sea  clifis,  of  about  800 
feet  in  height.  Other  boulders  were  found  upon  a  plain,  above  another, 
elevated  440  feet,  through  which  the  same  river  flows,  and  at  800  feet 
above  the  sea.  In  the  valley  of  the  Santa  Cruz,  and  at  30  or  40  miles 
from  the  Cordillera  (the  highest  parts  in  this  latitude  rise  to  about  6400 
feet),  blocks  of  granite,  sienite,  and  conglomerate,  not  found  in  the 
more  elevated  plains,  were  detected.  Mr.  Darwin  infers  that  these 
are  not  the  wreck  of  those  observed  on  the  higher  plain,  but  that  they 
have  been  subsequently  transported  from  the  Cordillera.  He  had  not 
opportunities  of  observing  other  erratic  blocks  in  Patagonia,  but  refers 
to  the  great  fragments  of  rocks  noticed  by  Captain  King  on  the  surface 
of  Cape  Gregory,  a  headland,  about  800  feet  high,  on  the  northern 
shore  of  the  Strait  of  Magellan.  Mr.  Darwin  also  describes  rock 
fragments  of  various  dimensions  and  kinds  in  Tierra  del  Fuego  and  the 
Strait  of  Magellan,  amid  stratified  and  unstratified  accumulations  of  a 
similar  general  character  to  those  of  this  geological  date  in  Europe. f 
Many  of  the  erratic  blocks  are  large,  one  at  St.  Sebastian's  Bay,  east 
coast  of  Tierra  del  Fuego,  was  47  feet  in  circumference,  and  projected 
5  feet  from  the  sand  beach.  The  general  drift  of  these  deposits  is 
considered  to  be  from  the  westward,  the  manner  in  which  the  trans- 
ported fragments  of  rock  would  be  carried  by  a  current  similar  to  that 
which  sweeps  against  the  present  land.  On  the  north  of  Cape  Virgins, 
.close  outside  the  Strait  of  Magellan,  the  imbedded  fragments  are  con- 
sidered to  have  been  transported  120  geographical  miles  or  more  from  the 
west  and  southwest.  On  the  northern  and  eastern  coasts  of  the  Island 
of  Chiloe,  extending  from  43°  26'  to  41°  46'  S.  latitude,  Mr.  Darwin 
detected  an  abundance  of  granite  and  sienite  boulders,  from  the  beach 

*  Darwin,  "  On  the  Distribution  of  Erratic  Boulders,  and  on  the  Contemporaneous 
Unstratified  Deposits  of  South  America." — Geol.  Trans.,  second  series,  vol.  vi.  p.  415. 

f  At  Elizabeth  Island,  Straits  of  Magellan,  there  occurs  "fine-grained,  earthy  or 
argillaceous  sandstone,  in  very  thin,  horizontal,  and  sometimes  inclined  laminae,  and 
often  associated  with  curved  layers  of  gravel.  On  the  borders,  however,  of  the  eastern 
parts  of  the  Strait  of  Magellan,  this  fine-grained  formation  often  passes  into,  and 
alternates  with  great  unstratified  beds,  either  of  an  earthy  consistence  and  whitish 
colour,  or  of  a  dark  colour  and  of  a  consistence  like  hardened  coarse-grained  mud,  with 
the  particles  not  separated  according  to  their  size.  These  beds  contain  angular 
and  rounded  fragments  of  various  kinds  of  rock,  together  with  great  boulders." — Geol. 
Trans.,  second  series,  vol.  vi.  p.  418.  Variations  of  these  accumulations  are  noticed 
as  occurring  in  other  places,  and  two  sections  of  contorted  and  confused  beds  at  Gre- 
gory Bay  are  given,  and  Mr.  Darwin  infers  that  this  disturbance  may  have  been  pro- 
duced by  grounded  icebergs. 


282       MOLLUSC    REMAINS    IN    SUPERFICIAL    DETRITUS. 

to  a  height  of  200  feet  on  the  land.  He  infers  that  these  boulders  have 
travelled  more  than  40  miles  from  the  Cordillera  on  the  east.* 

Upon  the  supposition  of  the  submergence  of  a  large  portion  of  the 
present  dry  land  of  Northern  Europe,  Asia,  and  America,  beneath  seas 
upon  which  ice  was  formed,  and  into  which  glaciers  protruded  in  lower 
latitudes  than  at  present,  we  should  expect  to  discover  in  the  marine 
deposits  of  these  regions  and  of  the  period,  now  upraised  into  the  atmo- 
sphere, evidences  of  the  marine  animal  life  of  the  time  having  corre- 
sponded with  the  low  temperature  to  which  it  was  then  exposed.  This 
evidence  is  considered  to  have  been  found. 

As  regards  the  British  Islands,  Mr.  Trimmer  pointed  out  in  1831, 
that  amid  the  detrital  accumulations  referred  to  this  date,  and  at  a 
considerable  height  above  the  sea  (since  ascertained  to  be  1392  feet), 
upon  Moel  Trefan  (one  of  the  hills  on  the  outskirts  of  the  chief  Caernar- 
vonshire mountains),  fragments  of  Buccinum,  Venus,  Natica,  and  Turbo 
of  existing  species  were  found.  He  also  stated  that  on  the  flanks  of 
the  Snowdonian  mountains,  and  between  them  and  the  adjoining  sea,  in 
the  Menai  Straits,  there  were  large  accumulations  of  boulders  and 
fragments  derived  from  a  distance  (among  them  chalk  flints),  mingled 
with  others  of  a  local  kind.  Mr.  Trimmer  subsequently  (1838),  pub- 
lished a  more  general  statement  on  the  same  subject,  noticing  various 
localities  where  he  and  others  had  found  shells  of  a  similar  character 
in  deposits  referring  to  this  date.f 

Commenting  on  the  facts  observed  by  Mr.  Trimmer  on  Moel  Trefan, 
Sir  Roderick  Murchison  (in  1832)  inferred  from  the  previous  discovery 
of  shells  of  existing  species  in  the  Lancashire  gravels  and  sands  by  Mr. 
Gilbertson,  one  which  he  was  enabled  to  confirm  from  actual  observa- 
tion, and  from  finding  similar  accumulations  over  a  large  tract  of 
country,  that  the  materials  of  the  ancient  shore 'of  Lancashire  and  of 
the  estuary  of  the  Kibble,  were  deposited  during  a  long-protracted 
period,  and  "  were  elevated  and  laid  dry  after  the  creation  of  many  of 

*  "  The  larger  boulders  were  quite  angular."  ..."  One  mass  of  granite  at  Chacao 
was  a  rectangular  oblong,  measuring  15  feet  by  11  feet,  and  9  feet  high.  Another,  on 
the  north  shore  of  Lemuy  islet,  was  pentagonal,  quite  angular,  and  11  feet  on  each 
side;  it  projected  about  12  feet  above  the  sand,  with  one  point  16  feet  high:  this 
fragment  of  rock  almost  equals  the  larger  blocks  on  the  Jura." — Geol.  Trans.,  second 
series,  vol.  vi.  p.  425. 

f  The  first  communication  was  made  to  the  Geological  Society  of  London  (Proceed- 
ings of  that  Society,  vol.  i.) ;  the  second  to  the  Geological  Society  of  Dublin,  in  a  me- 
moir, in  two  parts,  entitled,  "On  the  Diluvial  or  Northern  Drift  on  the  Eastern  and 
Western  side  of  the  Cambrian  Chain,  and  its  connexion  with  a  similar  Deposit  on  the 
Eastern  side  of  Ireland,  at  Bray,  Howth,  and  Glenismaule." — (Journal  of  the  Geolo- 
gical Society  of  Dublin.)  Mr.  Trimmer  mentions  that,  prior  to  his  discovery  of  the 
shells  on  Moel  Trefan,  Mr.  Gilbertson  had  found  shells  of  existing  species  in  gravel 
and  sand  near  Preston,  Lancashire,  and  that  Mr.  Underwood  had  observed  furrows  and 
scratches  on  the  surface  of  rocks  laid  bare  among  the  Snowdonian  mountains,  whca 
the  great  road  from  Bangor  to  Shrewsbury  was  in  progress. 


MOLLUSC     REMAINS    IN    SUPERFICIAL    DETRITUS.       283 

the  existing  species  of  molluscs."*  Numerous  facts  of  the  like  kind 
were  noticed  by  different  observers,!  hut  the  inference  as  to  a  tempera- 
ture less  at  that  geological  time  than  at  present,  as  shown  by  the 
remains  of  molluscs,  does  not  appear  to  have  taken  a  distinct  form 
until  Mr.  Smith,  of  Jordan  Hill,  published  his  views  on  the  subject  in 
1839. J  He  discovered  shells  in  places  where  their  animals  had  lived 
and  died,  in  the  counties  of  Lanark,  Renfrew,  and  Dumbarton,  and 
hence  inferred  their  entombment  by  depression,  a  half-tide  deposit 
being  converted  into  one  in  a  deeper  sea.  From  these  and  other 
researches,  Mr.  Smith  obtained  a  mass  of  evidence  which  led  him  to 
conclude  from  the  remains  of  the  molluscs  discovered  in  deposits  of  this 
date  in  different  localities,  that  the  climate  of  the  British  Islands  had 
then  been  colder  than  it  now  is,  more  especially  as  Arctic  molluscs, 
not  now  found  round  the  British  coasts,  were  obtained  from  these  accu- 
mulations^ 

*  Address,  as  President,  to  the  Geological  Society  of  London,  February,  1832. — Pro- 
ceedings of  that  Society,  vol.  i.  p.  366. 

f  Among  the  observations  of  the  time,  and  as  important  for  the  locality  noticed, 
should  be  mentioned  those  of  Sir  Philip  Egerton,  "On  a  bed  of  gravel  containing 
Marine  Shells  of  recent  Species,  at  Wellington,  Cheshire"  (Proceedings  of  the  Geolo- 
gical Society,  vol.  ii.  p.  189,  April,  1835).  Sir  Philip  notices  the  remains  of  Turritella 
terebra,  Cardium  edule,  and  Murex  arcnaceus,  and  infers  that  there  had  been  an  altera- 
tion of  70  feet  in  the  level  of  land  and  sea,  as  regards  the  locality,  since  the  deposit 
was  formed.  In  1837,  Mr.  Strickland  ("On  the  Nature  and  Origin  of  the  various 
kinds  of  transported  Gravel  occurring  in  England,"  read  at  the  British  Association  in 
that  year)  took  a  general  view  of  the  stratified  and  unstratified  character  of  these 
deposits,  and  divided  them  into  1.  Marine  drift,  formed  when  the  central  portions  of 
England  were  under  the  sea ;  and,  2.  Fluviatile  drift,  when  they  were  above  its  level, 
forming  dry  land,  the  first  composed  of  (a)  erratic  gravel,  without  chalk  flints  ;  (bj 
erratic  gravel,  with  chalk  flints  ;  and  (c)  local,  or  non-erratic  gravel. 

J  "On  the  late  changes  of  the  Relative  Levels  of  the  Land  and  Sea  in  the  British 
Islands,"  (Memoirs  of  the  Wernerian  Natural  History  Society,  Edinburgh,  vol.  viii.  p. 
49,  &c.)  In  this  memoir  Mr.  Smith  most  carefully  cites  all  those  who  had  previously 
discovered  facts  relating  to  the  subject,  giving  an  account  of  these  facts. 

g  Alluding  to  the  researches  of  M.  Deshayes,  to  whom  the  unknown  shells  discovered 
were  transmitted,  and  who  stated  that  those  still  found  recent,  but  not  in  the  British 
seas,  occur  in  northern  latitudes,  Mr.  Smith  remarks  that  this  view  confirmed  that 
which  he  had  previously  entertained  from  finding  many  of  the  shells  common  with 
those  obtained  by  Sir  Charles  Lyell,  at  Uddevalla,  in  Sweden,  and  figured  by  him 
(Phil.  Trans.  1835)  ;  from  having  been  informed  by  the  same  geologist  that  the 
Fusus  Peruvianus  still  inhabited  the  Arctic  seas  ;  and  from  Mr.  Gray  (of  the  British 
Museum)  having,  from  a  cursory  examination  of  the  shells  discovered,  remarked  that 
they  had  all  the  appearance  of  Arctic  shells.  Mr.  Smith  adds,  "  In  the  Clyde-raised 
deposits,  shells  common  to  Britain  and  the  northern  parts  of  Europe  occur  in  much 
greater  abundance  than  they  do  at  present.  The  Pecten  islandicus,  which  has  probably 
entirely  disappeared,  and  the  Cyprina  islandica,  which,  if  found  recent  in  the  Clyde, 
is  extremely  rare,  are  amongst  the  most  common  of  the  fossil  species."  Most  valuable 
catalogues  are  appended  to  the  memoir  of  Mr.  Smith,  consisting  of  lists  of  recent  shells 
in  the  basin  of  the  Clyde  and  north  coast  of  Ireland  (including  land  and  fresh-water 
shells)  ;  of  shells  from  the  newer  Pliocene  deposits  of  the  British  Islands  (also  including 
land  and  fresh-water  shells)  ;  and  of  recent  species  (then  new)  from  the  Frith  of  Clyde. 


284         EVIDENCE    OF    A    COLDER    CLIMATE    IN    BRITAIN, 

Professor  Edward  Forbes,  in  1846,  availing  himself  of  the  informa- 
tion then  existing,  and  of  his  own  researches  on  the  same  subject, 
pointed  out  that  the  total  number  of  species  of  molluscs  discovered  in 
the  deposits  of  the  British  area  and  referred  to  this  geological  time, 
was  about  124,  all,  with  a  few  exceptions  now  existing  in  the  seas 
around  the  British  Islands,  and  yet  indicating  by  their  mode  of  assem- 
blage a  colder  state  of  the  area  than  at  present.*  While  carefully 
noticing  the  error  which  might  arise  from  neglecting  the  occurrence  of 
species  at  different  depths  in  the  sea,  he  observes,  that  among  those 
found  in  these  deposits,  and  in  situations  where  they  must  have  lived 
and  died,  there  are  shells,  such  as  the  Littorince,  the  Purpura,  the 
Patella,  and  the  Lacunce,  "genera  and  species  definitely  indicating, 
not  merely  shallow  water,  but  in  the  first  three  instances,  a  coast 
line."t 

*  Professor  E.  Forbes,  "  On  the  Connexion  between  the  Distribution  of  the  existing 
Fauna  and  Flora  of  the  British  Isles,  and  the  Geological  Changes  which  have  affected 
their  Area  during  the  Period  of  the  Northern  Drift,"  (Memoirs  of  the  Geological  Survey 
of  Great  Britain,  vol.  i.  p.  367,  &c.)  The  Professor  observes,  that,  "as  a  whole,  this 
fauna  is  very  unprolific,  both  as  to  species  and  individuals,  when  compared  with  the 
preceding  molluscan  fauna  of  the  red  and  coralline  crags,  or  that  now  inhabiting  our 
seas  and  shores.  This  comparative  deficiency  depends  not  on  an  imperfect  state  of  our 
knowledge  of  the  fossils  in  the  glacial  formations :  on  that  point  we  now  have  ample 
evidence ;  but  on  some  difference  in  the  climatal  conditions  prevailing  when  those  beds 
were  deposited.  Such  a  deficiency  in  species  and  individuals  of  the  testaceous  forms 
of  mollusca,  indicates  to  the  marine  zoologist,  the  probability  of  a  state  of  climate 
colder  than  that  prevailing  in  the  same  area  at  present.  Thus  the  existing  fauna  of 
the  Arctic  seas  include  a  much  smaller  number  of  testaceous  molluscs  than  those  of 
Mid-European  seas,  and  the  number  of  testacea  in  the  latter  is  much  less  than  in  South- 
European  and  Mediterranean  regions.  It  is  not  the  latitude,  but  the  temperature  which 
determines  these  differences."  "  That  the  climate,"  he  subsequently  observes,  "  under 
which  the  glacial  animals  lived,  was  colder,  is  borne  out  by  an  examination  of  the  spe- 
cies themselves.  We  find  the  entire  assemblage  made  up,  1st,  of  species  (25)  now  living 
throughout  the  Celtic  region  in  common  with  the  northern  seas,  and  scarcely  ranging 
south  of  the  British  Isles ;  2d,  of  species  (24)  which  range  far  south  into  the  Lusitanis 
and  Mediterranean  regions,  but  which  are  most  prolific  in  the  Celtic  and  northern  seas  ; 
3d,  of  species  (13)  still  existing  in  the  British  seas,  but  confined  to  the  northern  poi 
tion  of  them,  and  most  increasing  in  abundance  of  individuals  as  they  approach  towards 
the  Arctic  circle  ;  4th,  of  species  (16)  now  known  living  only  in  European  seas,  north 
Britain,  or  in  the  seas  of  Greenland  and  Boreal  America ;  5th,  of  species  (6)  not  noi 
known  existing,  and  unknown  fossil  in  previous  deposits.  Two  other  species,  froi 
southern  deposits  in  Ireland,  were,  one  the  same  as  one  (Turritella  incrassata)  still  exh 
ing  in  the  South-European,  though  not  in  the  British  seas,  and  the  other  (Tornate 
pyramidata)  extinct,  but  found  fossil  in  the  crag."  Professor  E.  Forbes  remarks,  that 
it  is  "  of  consequence  to  note  the  fact  that  the  species  most  abundant  and  generally 
diffused  in  the  drift  are  essentially  northern  forms,  such  as  Astarte  elliptica,  compress 
and  borealiSj  Cyprina  communis,  Leda  rostrata,  and  minuta,  Tellina  calcarea,  Modiola 
garis,  Fusus  bamfius,  and  scalar  if  or  mis,  Littorince  and  Lacunce,  Natica  clausa  and  Bnccini 
undatum ;  and  even  Saxicava  rugosa  and  Turritella  terebra,  though  widely  distributed, 
much  more  characteristic  of  north  European  than  of  southern  seas." 

f  "  Memoirs  of  the  Geological  Survey  of  Great  Britain,"  vol.  i.  p.  370.     The 
fessor  adds,  "a  most  important  fact,  too,  is  that  among  the  species  of  Litlorina, 


FROM    MOLLUSC    REMAINS    AND    EXISTING    FLORA.       285 

Taking  a  general  view  of  the  flora  of  the  British  Islands,  and  of  the 
probable  sources  whence  its  parts  have  been  derived,  Professor  Edward 
Forbes  has  inferred  that  a  portion  was  obtained  from  northern  regions 
when  the  higher  parts  of  these  islands  were  alone  above  the  sea,  at  a 
time  corresponding  with  that  when  the  marine  molluscs  living  in  the 
seas  around  them  were  of  the  character  above  noticed,  and  when  the 
climate  was  colder  than  it  now  is,  the  evidence  of  the  land  flora  thus 
corroborating  that  afforded  by  the  remains  of  the  marine  molluscs. 
Under  such  conditions  he  infers  that  "  plants  of  a  subarctic  character 
would  flourish  to  the  water's  edge."  The  whole  area  being  subsequently 
upraised,  in  the  manner  above  noticed,  the  previous  islands  would  be- 
come mountain  heights,  and  the  plants,  uplifted  with  .them,  not  being 
deprived  of  the  climatal  conditions  fitted  for  them,  continued  to  flourish 
and  be  distributed  as  we  now  find  them.* 

As  confirming  his  views  respecting  the  effect  of  great  cold  at  this 
period  upon  the  marine  molluscs  in  the  seas  around  the  British  Islands, 
Professor  E.  Forbes  found,  while  dredging,  that  there  were  depressions 
off  the  coasts  in  which  molluscs  of  Arctic  character  still  remained,  as  if 
imprisoned  in  cavities  during  the  general  rise  of  the  sea  bottom,  so  that 
while  their  germs  still  found  the  needful  conditions  for  their  develop- 
ment in  such  depressions,  when  they  passed  beyond  them,  they  perished. 

Quitting  the  minor  area  of  the  British  Islands,  and  extending  our 
views  to  the  great  region  ranging  from  Scandinavia  eastward  along 
Northern  Asia  to  Behring's  Straits,  we  should,  in  the  higher  latitudes, 
expect  no  great  aid,  as  regards  evidences  of  a  colder  climate  having 
more  prevailed  at  that  geological  time  than  at  present,  from  the  remains 

genus,  all  the  forms  of  which  live  only  at  water-mark,  or  between  tides,  is  the  Littorina 
expansa,  one  of  the  forms  now  extinct  in  the  British,  but  still  surviving  in  the  Arctic 
seas." 

*  "  Memoirs  of  the  Geological  Survey,"  vol.  i.  Professor  E.  Forbes  divides  the  general 
flora  into  five  parts,  "four  of  which  are  restricted  to  definite  provinces,  whilst  the  fifth, 
besides  exclusively  claiming  a  great  part  of  the  area,  overspreads  and  commingles  with 
all  the  others."  "With  regard  to  his  general  view,  the  Professor  takes,  as  his  main  posi- 
tion, that  "  the  specific  identity,  to  any  extent,  of  the  flora  and  fauna  of  one  area  with 
those  of  another,  depends  on  both  areas  forming,  or  having  formed,  part  of  the  same 
specific  centre,  or  on  their  having  derived  their  animal  and  vegetable  population  by 
transmission,  through  migration,  over  continuous  or  closely  contiguous  land,  aided,  in 
the  case  of  Alpine  floras,  by  transportation  on  floating  masses  of  ice."  As  respects  the 
vegetation  to  which  reference  is  made  in  the  text,  Professor  E.  Forbes  observes,  "  The 
summits  of  ouji  British  Alps  have  always  yielded  to  the  botanist  a  rich  harvest  of  plants 
which  he  could  not  meet  with  elsewhere  among  these  islands.  The  species  of  these 
mountain  plants  are  most  numerous  on  the  Scotch  mountains — comparatively  few  on 
more  southern  ridges,  such  as  those  of  Cumberland  and  Wales.  But  the  species  found 
on  the  latter  are  all,  with  a  single  exception  (Lloydia  serotina),  inhabitants  also  of  the 
Highlands  of  Scotland ;  whilst  the  Alpine  plants  of  the  Scotch  mountains  are  all,  in 
like  manner,  identical  with  the  plants  of  more  northern  ranges,  as  the  Scandinavian 
Alps,  where,  however,  there  are  species  associated  with  them  which  have  not  appeared 
in  our  country." 


286  EXTINCT    FROZEN    ELEPHANT    OF    SIBERIA. 

of  marine  molluscs  entombed  amid  detritus,*  or  from  the  existing  flora 
there  found.  Under  the  hypothesis  of  a  depression  of  land,  accom- 
panied by  increased  cold,  it  is  not  difficult  to  conceive  that  the  marine 
fauna  and  terrestrial  flora  of  the  region  became  adjusted  to  the  condi- 
tions obtaining  at  the  different  times,  the  one  accommodating  itself  to  the 
new  shores,  the  other  creeping  to  the  proper  grounds,  as  the  sea  bottom 
changed  and  the  general  temperature  became  lowered  or  elevated.  The 
discovery,  however,  of  large  animals  entire  in  ice,  or  frozen  mud  or 
sand,  with  their  flesh  and  hair  preserved,  in  high  northern  latitudes, 
and  of  kinds  not  now  existing  there,  has  been  considered  as  affording 
somewhat  of  the  evidence  required. 

It  is  now  about  half  a  century  since  that  the  body  of  an  elephant,  of 
a  species  not  now  living,  but  the  remains  of  which  are  widely  dispersed 
amid  the  later  geological  accumulations  of  the  northern  portions  of  the 
northern  hemisphere, — its  flesh  so  fresh  that  bears  and  wolves  devoured 
it, — was  found  frozen  in  70°  N.  latitude,  near  the  embouchure  of  the 
Lena  in  Siberia.f  The  body  of  a  rhinoceros  also,  of  a  species  now 
extinct,  whose  hard  remains  are  also  discovered  in  somewhat  similar 
positions,  had  been  obtained  in  the  state  of  a  mummy  by  Pallas  thirty 
years  previously,  in  latitude  64°  N.,  from  the  banks  of  the  Wiljue, 
which  falls  into  the  Lena,  the  carcase  smelling  like  putrid  flesh,  the 
hair  still  partly  on  the  body.  These  discoveries  long  since  led  to  specu- 
lations respecting  a  change  of  climate  in  Siberia,  one  suddenly  destroy- 
ing the  animals  mentioned  by  cold,  so  that  their  carcases  were  pre- 

*  The  well-known  mass  of  shells  at  Uddevalla,  in  Sweden  raised  to  the  height  of  216 
feet  above  the  level  of  the  sea,  and  beneath  part  of  which  M.  Alexandre  Brongniart 
long  since  found  Balani  still  adhering  to  the  supporting  gneiss  rocks  on  which  they 
grew  (Tableau  des  Terrains  que  compose  1'Ecorce  du  Globe,  p.  89),  is  described  as 
composed  of  species  still  existing  in  the  neighbouring  seas.  A  list  of  these  shells  was 
given  by  M.  Hisinger,  "  Esquisse  d'un  Tableau  des  Petrifications  de  la  Svede,"  ed.  2me, 
Stockholm,  1831.  Professor  E.  Forbes  has  pointed  out  that  this  accumulation  of  shells 
was  noticed  by  Linnsous  in  1747,  and  that  the  species  discovered  by  him  are  now  known 
as  Balanus  scoticus,  Saxicava  rugosa  or  sulcala,  Mya  arenaria,  Littorina  liltorca,  Mytilus 
eduli*,  Fusus  scalariformis,  Pecten  islandicus,  Fusus  antiquus,  and  Balanus  sulcatus.  In  1806 
the  Uddevalla  shells,  and  others  of  existing  species,  raised  above  the  present  level  of 
the  sea  in  Norway,  were  observed  by  Von  Buch.  They  were  also  described  by  Sir 
Charles  Lyell,  in  his  account  of  the  rise  of  land  in  Sweden,  "Philosophical  Transac- 
tions," 1835. 

f  Mr.  Adams,  who  carefully  preserved  what  remained  of  this  animal,  relates  that  it 
was  first  observed  as  a  shapeless  mass  by  Schumakof,  a  Tungusian  chie£  and  owner  of 
the  peninsula  of  Tamset,  in  1799;  that  this  ice-covered  mass  fell  upon  the  sand  in  1803, 
and  that,  in  the  next  year,  the  chief  cut  off  the  tusks,  the  fossil  ivory,  if  it  may  from 
its  comparative  freshness  be  so  termed,  found  in  these  regions,  being  an  article  of  com- 
merce. Mr.  Adams,  visiting  the  spot  two  years  afterwards,  obtained  the  skeleton,  still 
in  part  covered  by  the  fleshy  remains,  with  portions  of  its  hair,  which,  together  with 
the  tusks,  subsequently  purchased,  is  now  preserved  in  the  Museum  at  St.  Petersburg; 
and  a  description  is  given  of  it  in  the  "  Memoirs  of  the  Imperial  Academy  of  Sciences," 
vol.  v.,  of  which  a  translation  was  published,  with  a  figure,  in  London,  in  1819. 


EXTINCT    FROZEN    ELEPHANT    OF    SIBERIA.  287 

served.  Professor  Play  fair  (in  1822)  would  appear  to  have  been  the 
first  to  infer  that  the  elephants  and  rhinoceroses  of  Siberia,  now  extinct, 
may  have  been  fitted  for  a  cold  climate,  though  the  elephants  of  the 
present  day  inhabit  regions  of  a  higher  temperature,  and  that  "  they 
may  have  migrated  with  the  seasons,  and  by  that  means  have  avoided 
the  rigorous  winters  of  the  high  latitudes."*  He  also  considered  that 
they  might  have  lived  farther  to  the  south  than  the  localities  where 
their  remains  are  now  found,  and  "  among  the  valleys  between  the  great 
ranges  of  mountains  that  bound  Siberia  on  that  side."  Sir  Charles 
Lyell,  in  1835,  took  a  similar  but  more  extended  view  of  the  subject. f 
Adverting  to  the  mode  of  occurrence  of  the  abundant  remains  of  ele- 
phants in  the  deposits  of  Siberia, — an  abundance  so  great  that  a  trade 
in  their  tusks  for  ivory  has  long  been  established,! — to  the  deposits 
themselves  in  which  they  are  discovered  having  been  formed  beneath 
the  sea,  since  they  contain  the  remains  of  marine  shells  ;  and  to  a  slow 
upheaval  of  the  borders  of  the  Icy  Sea,  as  is  now  taking  place,  he  con- 
sidered that  a  considerable  change  in  the  physical  geography  of  the 
whole  region  had  been  effected,  a  great  increase  of  land  northwards 
being  the  result  of  a  long-continued  and  slow  uprise  of  land  and  sea 
bottom.  He  inferred  a  general  decrease  of  temperature,  so  that  the 
elephants  and  rhinoceroses,  though  they  may  have  been  fitted  to  live  in 
colder  regions  than  any  of  the  kinds  now  existing,  gradually  perished. 

Sir  Roderick  Murchison  and  his  colleagues,  in  the  examination  of  the 
geology  of  Russia  and  the  Ural  Mountains,  adopted  similar  general 
views,  inferring  that  the  Ural,  Altai,  and  neighbouring  regions  of 
Siberia,  were  above  the  sea  when  these  great  mammals  existed,  and 
that  they  lived  in  herds  adjacent  to  lakes  and  estuaries, §  into  and  down 
which  their  remains  were  swept.  It  would  appear,  especially  by  the 
researches  of  M.  Middendorf,  that  the  shells  found  with  these  remains 
are  of  kinds  now  existing  in  the  seas  of  the  region,  so  that  the  molluscs 
of  that  time  and  the  neighbouring  seas  have  not  been  exposed  to  condi- 
tions effecting  their  destruction.  M.  Middendorf  also  mentions,  that  in 
1843,  the  carcase  of  an  elephant  was  found  in  the  Tas,  between  the 
Oby  and  Yenesei,  in  about  latitude  66°  30'  N.,  "  with  some  parts  of 
the  flesh  in  so  perfect  a  state,  that  the  bulb  of  the  eye  is  now  preserved 
in  the  Museum  of  Moscow. "||  Sir  Roderick  Murchison,  M.  de  Verneuil, 

*  Playfair's  "  Illustrations  of  the  Huttonian  Theory,"  Edinburgh,  1822. 

f  "Principles  of  Geology,"  4th  edition,  1835. 

$  This  fossil  ivory  is  still  imported  from  Russia  into  Liverpool,  where  it  finds  "a 
ready  sale  to  comb-makers  and  other  workers  in  ivory." — Owen,  "History  of  British 
Fossil  Mammals,"  p.  249. 

I  "  Geology  of  Russia  in  Europe  and  the  Ural  Mountains,"  vol.  i.  p.  500. 

||  The  discoveries  of  M.  Middendorf,  of  1843,  were  communicated  to  Sir  Charles  Lyell 
in  1846  (Principles  of  Geology,  7th  edition,  1847).  "  Another  carcase,  together  with 
another  individual  of  the  same  species,  was  met  with  in  the  same  year  (1843),  in  latitude 


288  EXTINCT    ELEPHANTS    AND    RHINOCEROSES 

and  Count  Keyserling  also  remark,  when  describing  the  range  and 
boundaries  of  the  erratic  blocks  of  Russia,  that  the  area  of  the  districts 
of  Perm,  Viatka,  and  Orenburg,  was  probably  "  above  the  waters  and 
inhabited  by  mammoths"*  at  this  period. 

With  regard  to  the  probable  habits  and  food  of  the  elephant  (Elepha* 
primigenim),  and  the  rhinoceros  (R.  tichorhinus),  the  researches  of 
Professor  Owen  have  shown,  f  that  on  physiological  grounds  the  Elephas 
primigenius  "  would  have  found  the  requisite  means  of  subsistence  at 
the  present  day,  and  at  all  seasons  in  the  sixtieth  parallel  of  latitude," 
so  that  by  adopting,  with  Prof.  Playfair  and  Sir  Charles  Lyell,  the  in- 
ference that  this  animal  migrated  northwards  during  the  warmer  parts 
of  the  year,  as  many  northern  mammals  now  do,  the  mammoth,  as  that 
kind  of  extinct  elephant  has  been  termed,  would  have  lived  easily  on 
the  land  considered  to  have  been  above  water  at  this  period.  The  Pro- 
fessor adds,  "  in  making  such  excursions  during  the  heat  of  that  brief 

75°  15'  N.,  near  the  river  Taimyr,  with  the  flesh  decayed.  It  was  embedded  in  strata 
of  clay  and  sand,  with  erratic  blocks,  at  about  15  feet  above  the  level  of  the  sea.  In 
the  same  deposit,  M.  Middendorf  discovered  the  trunk  of  a  larch  tree  (Pinus  larix),  the 
same  wood  as  that  now  carried  down  in  abundance  by  the  Taimyr  to  the  Arctic  Sea. 
There  were  also  associated  fossil  shells  of  living  northern  species,  and  which  are  more- 
over characteristic  of  the  drift,  or  glacial  deposits  of  Europe.  Among  these  Nucula 
pygmcea,  Tellina  calcarea,  Mya  truncata,  and  Saxacava  rugosa,  were  conspicuous." — Lyell's 
Principles,  7th  edition,  p.  83. 

*  Alluding  to  their  map,  it  is  further  observed  that  this  probably  happened  "  when 
the  erratic  blocks  were  transported  over  the  adjacent  northwestern  line  marked  in  the 
map,  as  the  extreme  boundary  of  the  granitic  erratics,  which  were,  we  believe,  stranded 
on  or  near  the  shelving  shore  of  this  ancient  land." — Geology  of  Russia,  vol.  i.  p.  522. 

•f-  "  History  of  British  Fossil  Mammals  and  Birds,"  1846.  To  the  previous  inference 
that  the  elephant,  from  its  warm,  woolly,  and  hairy  coat,  was  an  animal  fitted  to  live 
in  a  cold  climate,  (the  skin  of  the  carcase  from  the  Lena,  and  the  ground  on  which  it 
fell,  affording  many  pounds  weight  of  reddish  wool  and  coarse  long  black  hairs,)  Pro- 
fessor Owen  showed  that  its  teeth  especially  were  adapted  for  the  apparently  cold 
climate  in  which  its  remains  have  been  so  abundantly  detected.  "  The  molar  teeth  of 
elephants  possess,"  observes  the  Professor,  "  a  highly-complicated,  and  a  very  peculiar 
structure,  and  there  are  no  other  quadrupeds  that  derive  so  great  a  proportion  of  their 
food  from  the  woody  fibre  of  the  branches  of  trees.  Many  mammals  browse  the  leaves; 
some  small  rodents  gnaw  the  bark ;  the  elephants  alone  tear  down  and  crunch  the 
branches,  the  vertical  enamel-plates  of  their  huge  grinders  enabling  them  to  pound  the 
tough  vegetable  tissue  and  fit  it  for  deglutition.  No  doubt  the  foliage  is  the  more 
temptiug,  as  it  is  the  most  succulent  part  of  the  boughs  devoured ;  but  the  relation  of 
the  complex  molars  to  the  comminution  of  the  coarser  vegetable  substance  is  unmis- 
takable. Now,  if  we  find  in  an  extinct  elephant  the  same  peculiar  principle  of  con- 
struction in  the  molar  teeth,  but  with  augmented  complexity,  arising  from  a  greater 
number  of  triturating  plates,  and  a  greater  proportion  of  the  dense  enamel,  the  in- 
ference is  plain  that  the  ligneous  fibre  must  have  entered  in  a  larger  proportion  into 
the  food  of  such  extinct  species.  Forests  of  hardy  trees  and  shrubs  still  grow  upon  the 
frozen  soil  of  Siberia,  and  skirt  the  banks  of  the  Lena  as  far  north  as  latitude  00°.  In 
Europe  arboreal  vegetation  extends  ten  degrees  nearer  the  pole ;  and  the  dental  orga- 
nization of  the  mammoth  proves  that  it  might  have  derived  subsistence  from  the  leafless 
branches  of  trees,  in  regions  covered  during  a  part  of  the  year  with  snow." — p.  267. 


OF    NORTHERN    EUROPE    AND    ASIA.  289 

season  (the  northern  summer),  the  mammoths  would  be  arrested  in  their 
northern  progress  by  a  condition  to  which  the  reindeer  and  musk-ox 
are  not  subject,  viz.,  the  limits  of  arboreal  vegetation,  which,  however, 
as  represented  by  the  diminutive  shrubs  of  Polar  lands,  would  allow 
them  to  reach  the  seventieth  degree  of  latitude.  With  regard  to  the 
habits  and  food  of  the  two-horned  rhinoceros,*  found  frozen  in  Siberia, 
the  inferences  do  not  appear  so  clear  as  for  the  mammoth.  From  the 
greater  amount  of  hair  found  on  the  extinct  and  frozen  rhinoceros, 
noticed  by  Pallas,  than  upon  existing  rhinoceroses,  he  seems  to  have 
concluded  that  it  might  have  lived  in  the  temperate  regions  of  Asia. 
Professor  Owen  remarks  that,  "  although  the  molar  teeth  of  the  Rhino- 
ceros tichorJiinus  present  a  specific  modification  of  structure,  it  is  not 
such  as  to  support  the  inference  that  it  could  have  better  dispensed  with 
succulent  vegetable  food  than  its  existing  congeners ;  and  we  must  sup- 
pose, therefore,  that  the  well-clothed  individuals  who  might  extend  their 
wanderings  northwards  during  a  brief  but  hot  Siberian  summer,  would 
be  compelled  to  migrate  southward  to  obtain  their  subsistence  during 
winter."f 

Considering  the  general  evidence  thus  adduced  as  to  the  climate  of 
Northern  Europe  at  this  geological  time,  we  have  to  suppose  a  con- 
siderable depression  of  a  large  area  beneath  the  level  of  the  Atlantic ; 
an  increase  of  cold,  causing  glaciers  to  descend  into  the  sea  in  Scandi- 
navia, and  even  perhaps  in  the  British  Islands ;  a  great  increase,  if  not 
extension  into  the  sea,  of  the  glaciers  of  the  Alps,  icebergs  and  coast- 
ice  distributing  masses  and  minor  fragments  of  rocks  over  a  considerable 
European  area,  as  also  the  shingles  of  beaches,  sand,  and  mud,  accom- 
panied by  the  transported  remains  of  terrestrial  and  marine  creatures, 
and  a  movement  of  land  plants,  with  terrestrial  and  marine  animals,  in 
accordance  with  the  low  temperature  then  existing.  The  amount  of 
land  rising  above  the  sea,  prior  to  the  inferred  depression,  is  uncertain. 
It  may  have  been  more  or  less  than  that  which  we  now  find,  though 
deposits  of  varied  thickness  were  accumulated  at  this  time,  and  now 
constitute  a  part  of  the  dry  land  of  Europe,  and  probably  also  a  portion 
of  the  bottom  of  the  adjoining  seas. 

Respecting  the  great  mammals,  the  carcases  of  which  have  been  so 
well  preserved  in  Siberia,  and  admitting,  with  Professor  Owen,  their 
perfect  fitness  to  have  lived  in  a  climate  such  as  that  at  present  found 
in  Northern  Europe  and  Asia,  up  to  a  high  latitude,  we  have  to  con- 
sider that  at  the  time  of  greater  cold,  their  food  being  adjusted  to  it, 
their  range,  even  in  the  summer  season,  would  be  more  limited  north- 

*  The  horns  of  this  rhinoceros  have  been  ascertained  to  have  been  of  large  size. 
One  of  the  horns  of  an  individual,  probably  the  front  or  nasal  horn,  in  the  Museum  at 
Moscow,  measures,  according  to  Professor  Owen,  nearly  three  feet  in  length. 

f  "  History  of  British  Fossil  Mammals  and  Birds,"  1846,  p.  353. 

19 


290  EXTINCTION    OF    GREAT    NORTHERN     MAMMALS. 

ward,  not  only  by  any  coasts  which  might  then  be  thrown  back  by  the 
depression  beneath  the  sea  level,  but  also  by  the  supposed  decreased 
temperature.  The  great  rivers,  flowing  northward,  would,  as  Humboldt, 
Sir  Charles  Lyell,  and  Sir  Roderick  Murchison  have  pointed  out,  be 
then  under  similar  conditions  as  at  present,  their  embouchures  exposed 
to  lower  temperatures  than  their  courses  in  more  temperate  regions, 
such  courses,  though  somewhat  shorter,  being  still  liable,  as  now,  to  be 
blocked  up  by  ice  at  their  mouths.  In  such  a  state  of  things  there  is 
little  difficulty  in  inferring  that  the  elephants  and  rhinoceroses  lived,  as 
they  are  supposed  to  have  done,  in  a  climate  of  low  temperature,  and 
that  their  remains  were  buried  in  the  detritus  accumulated  in  lakes  and 
at  the  embouchures  of  the  northern  rivers  of  the  time,  numerous  car- 
cases washed  out  to  sea  and  preserved  amid  ice,  or  frozen  mud  and  sand, 
among  deposits  containing  the  remains  of  marine  molluscs,  such  as  are 
now  living  in  the  adjoining  Arctic  Sea. 

The  cause  of  the  extinction  of  the  great  mammals  mentioned  requires 
much  consideration,  and  a  careful  observation  of  the  facts  connected 
with  the  entombment  and  preservation  of  their  remains.  Humboldt 
has  remarked  that  the  low  temperature  at  present  experienced  across 
Poland  and  Russia  to  the  Ural  Mountains,  "is  to  be  sought  in  the  form 
of  the  continent  being  gradually  less  intersected,  and  becoming  more 
compact  and  extended, — in  the  increasing  distance  from  the  sea, — and 
in  the  feebler  influence  of  westerly  winds.  Beyond  the  Ural,  westerly 
winds  blowing  over  wide  expanses  of  land,  covered  during  several 
months  with  ice  and  snow,  become  cold  land  winds.  It  is  to  such  cir- 
cumstances of  configuration  and  of  atmospheric  currents  that  the  cold 
of  Western  Siberia  is  due."*  By  the  immersion  of  the  present  dry 
land  to  the  extent  supposed,  f  unaccompanied  by  the  general  decrease 
of  temperature  inferred  in  Northern  Europe,  there  might,  no  doubt,  be 
reason  to  expect  that  such  northern  portions  of  European  and  Asiatic 
Russia  as  were  above  water  would  have  a  higher  temperature  than  at 
present ;  but  how  far  this  would  be  met  by  such  a  decrease  of  the  pre- 
sent temperature  of  Scandinavia,  the  British  Isles,  and  a  portion  of 
Central  Europe,  that  glaciers  descended  to  the  then  sea  level,  it  is  more 
difficult  to  infer.  Because  icebergs  may  have  floated  from  Scandinavia, 
and  have  become  stranded  on  the  shores  of  the  districts  of  Perm,  Viatka, 
and  Orenberg,  and  thence  along  the  line  pointed  out  by  Sir  Roderick 
Murchison,  M.  de  Verneuil,  and  Count  Keyserling,  to  the  westward,  it  is 
not  a  necessary  inference  that  the  temperature  of  those  regions,  making 
every  allowance  for  the  influence  of  multitudes  of  icebergs  at  certain 

*  Cosmos,  7th  edit.  (Sabine's  Translation),  vol.  i.  p.  323. 

f  The  observer  would  do  well  to  refer  to  the  map  given  by  the  authors  of  the  Geology 
of  Russia  in  Europe,  and  the  Ural,  for  the  area  bounding  the  occurrence  of  erratic 
blocks. 


RANGE    OF    EXTINCT    NORTHERN    ELEPHANT.  291 

seasons,  had  been  very  low,  more  than  that  the  temperature  of  New- 
foundland should  be  that  of  Greenland  and  Baffin's  Bay,  whence  the 
icebergs  stranded  near  it  are  derived.  Even  supposing  that  as  the  land 
rose,  the  temperature  of  Siberia  became  such  as  we  now  find  it,  it  does 
not  seem  to  follow,  judging  from  the  researches  and  reasoning  of  Pro- 
fessor Owen,  that  the  mammoths  necessarily  perished  from  cold  or  the 
want  of  food.*  Assuming  that  the  great  cold  was  unfavourable  to 
their  continuance  in  Siberia,  that  the  country  towards  the  mountains 
on  the  south  was  equally  so  to  their  habits,  and  that  thus  they  may 
have  been  there  extirpated,  the  same  reasoning  does  not  seem  to  apply 
so  well  to  the  districts  on  the  west  of  the  Ural. 

It  is  now  well  known  that  the  mammoths  must  once  have  existed 
widely  spread  over  the  northern  portions  of  Europe,  Asia,  and  America ; 
whence  the  needful  inference,  on  the  hypothesis  that  they  all  proceeded 
from  a  common  stock,  or  centre,  that  they  spread  themselves  over  con- 
tinuous portions  of  land,  dry  for  the  time,  however  now  separated  they 
may  be  by  seas.  Their  remains  are  not  uncommon  in  Great  Britain, 
though  less  so  apparently  in  Ireland,  and  Professor  Owen  has  pointed 
out  the  connexion  of  these  islands  with  Europe  when  these  and  other 
contemporary  animals  passed  into  them.f  The  depth  of  Bearing' s 

*  On  this  subject  Professor  Owen  remarks,  that  "with  regard  to  the  geographical 
range  of  the  Elcphas  primigenius  into  temperate  latitudes,  the  distribution  of  its  fossil 
remains  teaches  that  it  reached  the  fortieth  degree  north  of  the  equator.  History,  in 
like  manner,  records  that  the  reindeer  had  formerly  a  more  extensive  distribution  in 
the  temperate  latitudes  of  Europe  than  it  now  enjoys.  The  hairy  covering  of  the  mam- 
moth concurs,  however,  with  the  localities  of  its  most  abundant  remains,  in  showing 
that,  like  the  reindeer,  the  northern  extreme  of  the  temperate  zone  was  its  metropolis. 
Attempts  have  been  made  to  account  for  the  extinction  of  the  race  of  northern  elephants 
by  alterations  in  the  climate  of  their  hemisphere,  or  by  violent  geological  catastrophes, 
and  the  like  extraneous  causes.  When  we  seek  to  apply  the  same  hypothesis  to  explain 
the  apparently  contemporaneous  extinction  of  the  gigantic  leaf-eating  megatheria  of 
South  America,  the  geological  phenomena  of  that  continent  appear  to  negative 
the  occurrence  of  such  destructive  changes.  Our  comparatively  brief  experience  of 
the  progress  and  duration  of  species  within  the  historical  period,  is  surely  insufficient 
to  justify,  in  every  case  of  extinction,  the  verdict  of  violent  death.  With  regard  to 
many  of  the  larger  mammalia,  especially  those  which  have  passed  away  from  the 
American  and  Australian  continents,  the  absence  of  sufficient  signs  of  extrinsic  extir- 
pating change  or  convulsion,  makes  it  almost  as  reasonable  to  speculate  with  Brocchi, 
on  the  possibility  that  species,  like  individuals,  may  have  had  the  cause  of  their  death 
inherent  in  their  original  constitution,  independently  of  changes  in  the  external  world, 
and  that  the  term  of  their  existence,  or  the  period  of  exhaustion  of  the  prolific  force, 
may  have  been  ordained  from  the  commencement  of  each  species." — History  of  British 
Fossil  Mammals  and  Birds,  p.  269. 

f  "History  of  British  Fossil  Mammals  and  Birds,"  1846,  Introduction,  p.  xxxvi. 
"If,"  Professor  Owen  observes,  "we  regard  Great  Britain  in  connexion  with  the  rest 
of  Europe,  and  if  we  extend  our  view  of  the  geographical  distribution  of  extinct  mam- 
mals beyond  the  limits  of  technical  geography, — and  it  needs  but  a  glance  at  the  map 
to  detect  the  artificial  character  of  the  line  which  divides  Europe  from  Asia, — we  shall 
there  find  u  close  and  interesting  correspondence  between  the  extinct  Europrco-Asiatic 


292      ELEPHANT  REMAINS  OF  ESCHSCHOLTZ  BAY. 

Straits  is  comparatively  trifling,  varying  from  132  to  192  feet,  so  that 
we  feel  little  surprise  in  finding  at  Eschscholtz  Bay,  in  about  66°  20'  N. 
on  the  North  American  shores,  inside  the  Straits,  the  remains  of  the 
Elephas  primigenius,  associated  with  the  hones  of  the  urus,  deer,  horse, 
and  musk-ox,  in  a  cliff  about  90  feet  high,  extending  about  2J  miles  in 
length.  These  remains  were  first  noticed  by  Dr.  Eschscholtz,  (during 
Kotzebue's  voyage,)  in  1816,  and  the  bones  were  supposed  to  be  em- 
bedded in  ice ;  but  the  observations  of  Captain  Beechey's  party,  in 
1826,  showed  that  the  ice  was  merely  superficial,  arising  from  the 
freezing  of  water  descending  over  the  face  of  the  cliff,  and  that  the  re- 
mains of  these  mammals  were  really  embedded  in  a  deposit  of  clay  and 
fine  quartzose  and  micaceous  sand.  A  smell,  as  of  heated  bones,  was 
observed  where  the  animal  remains  abounded.* 

This  facing  of  ice  having  been  thus  deceptive,  Dr.  Buckland  was  led 
to  inferf  that  there  also  might  have  been  some  error  respecting  the 
elephant  of  the  Lena  having  really  been  encased  in  ice,  and  not  in 
mud,  the  face  of  which  was  covered  by  ice,  as  at  Eschscholtz  Bay. 
Correct  observations  respecting  the  mode  of  occurrence  of  the  animals 
preserved  in  a  comparatively  fresh  state,  with  their  fleshy  portions  in 
part  or  wholly  remaining,  are  somewhat  important,  inasmuch  as,  if 
found  in  ice,  we  have  to  infer  either  that  such  ice  had  always  remained 
unthawed  in  the  atmosphere,  (at  least  so  far  as  the  portions  enveloping 
the  animals  are  concerned,)  from  the  time  when  these  mammals  were 
encased  in  it  to  the  present  time,  or  that  it  became  depressed  beneath 
detrital  accumulations  of  the  period,  and  also  remained  unthawed,  until 
the  whole  being  elevated  again  into  the  atmosphere,  it  became,  with  the 
accumulations  among  which  it  had  been  buried,  exposed  to  the  climatal 
and  denuding  conditions  of  the  present  day.  Though  there  would  be 
difficulty  in  submerging  ice,  from  its  specific  gravity,  beneath  water, 
and  especially  sea-water,  unless  sufficiently  well  loaded  with  detritus  to 
render  this  of  the  proper  kind,  it  may  readily  happen  that,  in  very  cold 
climates,  coast-ice  may  be  anchored,  so  to  speak,  in  such  a  manner  by 
penetrating  amid  shingles,  sand,  or  mud  beneath,  that  it  could  be 
covered  over  in  part,  or  in  thickness,  according  to  variations  in  seasons, 
by  detrital  matter,  so  as  to  be  in  the  condition  to  descend,  thus  covered 

Mammalian  Fauna  of  the  pliocene  period  and  that  of  the  present  day.  The  very  fact 
of  the  pliocene  fossil  mammalia  of  England  being  almost  as  rich  in  generic  and  specific 
forms  as  those  of  Europe,  leads,  as  already  stated,  to  the  inference  that  the  intersect- 
ing branch  of  the  ocean  which  now  divides  this  island  from  the  continent  did  not  then 
exist  as  a  barrier  to  the  migration  of  the  mastodons,  mammoths,  rhinoceroses,  hippo- 
potamuses, bisons,  oxen,  horses,  tigers,  hyaenas,  bears,  &c.,  which  have  left  such 
abundant  traces  of  their  former  existence  in  the  superficial  deposits  and  caves  of  Great 
Britain." 

*  "Beechey's  Voyage  to  the  Pacific  and  Behring's  Straits."  The  bones  were  exa- 
mined, and  the  animals  to  which  they  belonged  were  determined  by  Dr.  Buckland. 

t  Ibid. 


ICE-BEDS    BENEATH    DETRITAL    DEPOSITS.  293 

over,  to  those  depths  where  it  could  remain  unthawed,  with  any  animals 
entombed  in  it.  Indeed,  certain  facts  noticed  by  travellers  and  voyagers 
in  the  Arctic  regions  would  lead  us  to  infer  that  this  might  be  the  case, 
and  accounts  are  given  of  beds  of  actual  ice  being  found  beneath  detrital 
deposits  in  those  regions.*  Descended  to  a  proper  depth  beneath  the 
surface,  but  not  sufficient  to  bring  it  within  the  influence  of  the  heat 
found  to  exist  beneath  certain  depths  in  different  parts  of  the  globe,  ice 
might  remain  there,  only  to  be  thawed  by  a  great  increase  in  the  tempe- 
rature of  the  general  climate,  or  by  being  again  elevated,  with  a  sufficient 
denudation  of  protecting  detritus,  so  that  the  heat  of  the  atmosphere  in 
summer  would  dissolve  it,  and  disclose  any  animal  remains  which  may 
have  been  therein  preserved.  At  the  same  time,  mud  and  silt,  into  which 
the  bodies  of  such  animals  as  the  elephants  and  rhinoceroses,  above 
noticed,  may  have  been  borne  during  floods,  could  readily  have  become 
frozen,  and  covered  with  other  detritus,  and  thus  descending,  have  re- 
tained, from  what  we  learn  of  the  depth  to  which  the  frozen  ground 
extends  in  Siberia — a  depth  apparently  very  different  from  that  found 
in  North  America,  in  the  same  latitudes — the  remains  of  the  animals 
in  as  fresh  a  state  as  when  first  embedded  in  them,  to  a  level,  beneath 
that  of  the  sea,  of  400  feet,  if  the  cold  approached  that  now  experienced 
in  Northern  Siberia,  f 

*  M.  Middendorf  informed  Sir  Charles  Lyell,  that  in  1843  "he  had  bored  in  Siberia 
to  the  depth  of  70  feet,  and,  after  passing  through  much  frozen  soil  mixed  with  ice,  had 
come  down  upon  a  solid  mass  of  pure  transparent  ice,  the  thickness  of  which,  after 
penetrating  two  or  three  yards,  they  did  not  ascertain." — Principles  of  Geology,  7th 
edition,  p.  86. 

f  The  depth  to  which  frozen  mud  and  sand  could  descend  in  these  regions,  without 
being  thawed  by  the  influence  of  terrestrial  heat  beneath,  would  appear  from  the  infor- 
mation of  M.  Helmersen  (Observations  on  a  Pit  sunk  at  Jakoutsk,  Ann.  des  Mines  de 
Eussie,  vol.  v.,  1838),  to  be  between  300  and  400  feet.  On  the  25th  April,  1837,  the 
temperature  of  the  bottom,  378  (English)  feet  deep,  was  31-1°,  the  strata  on  the  sides 
of  the  pit  at  75  feet  being  21-2°  Fahr.  The  accumulations  passed  through,  were  com- 
posed of  clay,  sand,  and  lignite,  mixed  with  ice. 

Some  experiments  made  by  M.  Middendorf,  as  reported  to  the  Academy  of  Sciences 
of  St.  Petersburg  in  1844,  showed  that,  in  a  shaft  and  the  galleries  of  some  works 
near  the  Lena,  and  at  a  depth  of  384  (English)  feet,  the  frozen  crust  was  still  not 
passed  through,  though  a  marked  gradual  increase  of  temperature  was  observed  in  the 
descent.  "While,  in  one  series  of  experiments,  a  thermometer,  in  the  ground,  7  feet 
from  the  surface,  gave  on  the  25th  March,  — 1°  Fahr.,  the  temperature  gradually 
advanced  beneath  to  26-6°  Fahr.  According  to  M.  Erman  (Proceedings  of  the  Academy 
of  Sciences  at  St.  Petersburg,  1838),  the  depth  of  ground  thawed  in  September,  1838, 
in  Northern  Siberia,  was  4  feet  8  inches  in  woody  tracts,  and  6  feet  8  inches  in  the 
marshy  situations. 

From  Sir  John  Richardson  having  found  the  depth  of  the  frozen  ground  not  to  exceed 
26  feet  at  Fort  Simpson,  on  the  Mackenzie,  a  station  in  the  same  latitude  as  Jakoutsk 
(62°  N.),  M.  d'Archiac  has  inferred  (Histoire  des  Progres  de  la  Geologic,  vol.  i.  p.  88), 
that  the  cold  must  be  far  more  intense  in  Northern  Asia  than  in  North  America,  at 
these  high  latitudes.  Under  this  view,  the  bodies  of  animals  could  now  be  preserved 
in  Northern  Siberia,  by  descending  and  ascending  land,  which  could  not  be  so  preserved 
in  North  America. 


294  OSSIFEROUS    CAVBKNS    AND    BRECCIA. 

Ossiferom  Caverns  and  Osseous  Breccia. — While  on  the  subject  of 
the  bodies  of  elephants  and  rhinoceroses  found  thus  well  preserved  in 
Siberia, — and  nowhere,  as  has  often  been  remarked,  are  the  remains  of 
the  Elephas  primigenius  more  abundant  than  in  the  lowlands,  adjoining 
the  icy  sea  of  Northern  Asia,* — it  may  be  desirable  to  consider  the 
remains  of  the  same  kinds  of  elephant  and  rhinoceros,  with  those  of 
contemporary  mammals,  found  embedded  amid  accumulations  in  caves 
and  clefts  of  rock.  The  connexion  of  the  British  Islands  with  the  con- 
tinent of  Europe  and  Asia  has  been  above  noticed  (p.  291),  as  needed 
for  the  migration  of  the  Elephas  primigenius  and  Rhinoceros  tichorhinus 
into  the  former,  the  remains  of  these  mammals  so  occurring  as  to  leave 
no  room  for  doubting,  that  the  animals  themselves  here  found  the  con- 
ditions fitted  for  their  existence  and  increase.!  The  observer  has 

*  Dr.  Mantell  states  (Wonders  of  Geology,  vol.  i.  p.  148,  6th  edition,  1848),  that,  a 
company  of  merchants  having  been  formed  in  1844,  to  collect  fossil  ivory  in  Siberia, 
sixteen  thousand  pounds  of  jaws  and  tusks  of  mammoths  were  obtained  during  the 
year,  and  these  were  sold  at  St.  Petersburg,  under  the  denomination  of  Siberian  ivory, 
at  prices  from  30  to  100  per  cent,  above  those-  of  recent  elephantine  ivory. 

From  the  researches  of  M.  HedenstrOm,  multitudes  of  the  remains  of  elephants,  rhi- 
noceroses, oxen,  and  other  mammalia  occur  in  the  frozen  ground  between  the  Lena 
and  the  Kolima,  and  he  mentions  that  one  of  the  islands  of  New  Siberia,  or  the  Liakhor 
Islands,  in  the  Arctic  Ocean,  off  the  coast  of  Siberia,  between  the  embouchures  of  the 
Lena  and  Indigirka,  is  composed  of  little  else  than  a  mass  of  mammoth  bones,  which 
has  been  worked  for  many  years  by  the  traders  for  the  fossil  ivory  it  yields. 

This  statement  is  confirmed  by  those  of  other  travellers.  The  high  preservation  of 
fossil  ivory  is  not  confined  to  Siberia.  Mr.  Bald  mentions  (Wernerian  Transactions, 
vol.  iv.)  that  tusks  found  between  Edinburgh  and  Selkirk  were  made  into  chessmen. 

f  Respecting  the  mammals  existing  at  this  time  in  the  area  of  the  British  Islands, 
Professor  Owen  remarks  (History  of  British  Fossil  Mammals — Introduction),  after 
noticing  the  probable  disappearance  of  the  mastodon  from  it,  that  "gigantic  elephants 
of  nearly  twice  the  bulk  of  the  largest  individuals  that  now  exist  in  Ceylon  and  Africa, 
roamed  here  in  herds,  if  we  may  judge  from  the  abundance  of  their  remains.  Two- 
horned  rhinoceroses,  of  at  least  two  species,  forced  their  way  through  the  ancient 
forests,  or  wallowed  in  the  swamps.  The  lakes  and  rivers  were  tenanted  by  hippopo- 
tamuses as  bulky  and  with  as  formidable  tusks  as  those  of  Africa.  Three  kinds  of  wild 
oxen,  two  of  which  were  of  colossal  size  and  strength,  and  one  of  these  maned  and 
villous  like  the  bonassus,  found  subsistence  in  the  plains.  Deer,  as  gigantic  in  propor- 
tion to  existing  species,  were  the  contemporaries  of  the  old  Uri  and  Bisontcs,  and  may 
have  disputed  with  them  the  pasturage  of  that  ancient  land ;  one  of  these  extinct  deer 
is  well-known  under  the  name  of  the  *  Irish  Elk,'  from  the  enormous  expanse  of  its 
broad-palmed  antlers  [the  Professor  states  elsewhere,  Hist.  Brit.  Foss.  Mammals,  p. 
407,  that  the  remains  of  this  animal  have  been  found  in  the  ossiferous  cavern  of  Kent's 
Hole,  Devon]  ;  another  had  horns  more  like  that  of  the  wapiti,  but  surpassed  that  great 
Canadian  deer  in  bulk  :  a  third  extinct  species  more  resembled  the  Indian  hippelaphus ; 
and  with  these  were  associated  the  red  deer,  the  reindeer,  the  roebuck,  and  the  goat. 
A  wild  horse,  a  wild  ass  or  quagga,  and  the  wild  boar,  entered  also  into  the  series  of 
British  pliocene  hoofed  mammalia. 

"  The  carnivora,  organized  to  enjoy  a  life  of  rapine  at  the  expense  of  the  vegetable- 
feeders,  to  restrain  their  undue  increase,  and  abridge  the  pangs  of  the  maimed  and 
sickly,  were  duly  adjusted  in  numbers,  size,  and  ferocity  to  the  fell  task  assigned  to 
them  in  the  organic  economy  of  the  pre-Adamitic  world.  Besides  a  British  tiger  of 


CONNEXION  OF  ENGLAND  WITH  THE  CONTINENT.   295 

carefully  to  consider  the  evidence  afforded  as  to  the  precise  geological 
period  when  these  great  mammals  thus  prospered  upon  lands  now 
divided  from  the  continent  by  sea,  which  it  would  appear  scarcely  pro- 
bable they  safely  crossed,  either  by  will  or  accident.  The  geological 
time  when  the  needful  connexion  was  formed  between  the  British  Islands 
and  the  continent  of  Europe,  so  that  these  and  other  contemporary 
mammals  freely  roamed  from  the  one  part  of  a  general  area  to  the 
other,  becomes,  therefore,  a  matter  of  no  slight  interest. 

The  observer  has  to  bear  in  mind  that,  during  any  modified  distribu- 
tion of  land  and  sea  formerly  existing,  by  which  deposits  were  accumu- 
lated, and  the  carcases  of  animals  were  floated  out  to  sea,  or  swept  into 
fresh-water  lakes,  so  that  their  harder  parts  became  embedded  in  calca- 
reous matter,  mud,  silt,  or  gravel,  the  lighter  portions  of  the  accumula- 
tion, amid  which  they  were  entombed,  would,  as  now  in  the  German 
Ocean  and  some  other  parts  of  the  sea  adjacent  to  the  British  Islands, 
be  liable  to  be  washed  off,  either  at  the  proper  depths  beneath  the  sur- 
face of  the  sea  by  the  action  of  the  wind-waves,  or  on  the  shores  by  the 
breakers,  when  changes  of  level  of  the  sea  and  land  so  took  place  that 
this  action  could  be  experienced.  Tusks,  teeth,  and  the  bones  of  the 
ElepTias  primigenius  have  thus  been  fished  up  by  the  trawlers  and 
dredgers  on  the  southeast  of  England,  and  in  a  state  sometimes  show- 
ing little  marks  of  attrition,  bearing  more  the  appearance  of  having 
been  merely  relieved,  by  the  wave  action,  of  the  mud,  silt,  or  sand 

larger  size,  and  with  proportionally  larger  paws  than  that  of  Bengal,  there  existed  a 
stranger  feline  animal  (Machairodus)  of  equal  size,  which,  from  the  great  length  and 
sharpness  of  its  sabre-shaped  canines,  was  probably  the  most  ferocious  and  destructive 
of  its  peculiarly  carnivorous  family.  Of  the  smaller  felines,  we  recognise  the  remains 
of  a  leopard,  or  large  lynx,  and  of  a  wild  cat. 

"  Troops  of  hyaenas,  larger  than  the  fierce  crocuta  of  South  Africa,  which  they  most 
resembled,  crunched  the  bones  of  the  carcases  relinquished  by  the  nobler  beasts  of 
prey ;  and,  doubtless,  often  themselves  waged  the  war  of  destruction  on  the  feebler 
quadrupeds.  A  savage  bear,  surpassing  in  size  the  Ursus  ferox  of  the  Rocky  Moun- 
tains, found  its  hiding-place,  like  the  hyama,  in  many  of  the  existing  limestone  caverns 
of  England.  With  the  Ursus  spelazus  was  associated  another  bear,  more  like  the  common 
European  species,  but  larger  than  the  present  individuals  of  the  Ursus  Arctos.  Wolves 
and  foxes,  the  badger,  the  otter,  the  foumart,  and  the  stoat,  complete  the  category  of 
the  pliocene  carnivora  of  Britain. 

"Bats,  moles,  and  shrews  were  then,  as  now,  the  forms  that  preyed  upon  the  insect 
•world  in  this  island.  Good  evidence  of  a  fossil  hedgehog  has  not  yet  been  obtained ; 
but  the  remains  of  an  extinct  insectivore  of  equal  size,  and  with  closer  affinities  to  the 
mole-tribe,  have  been  discovered  in  a  pliocene  formation  in  Norfolk.  Two  kinds  of 
beaver,  hares  and  rabbits,  water-voles,  and  field-voles,  rats  and  mice,  richly  represented 
the  Rodent  order.  The  greater  beaver  (Trogontherium)  and  the  tailless  hare  (Lagomys] 
were  the  only  sub-generic  forms,  perhaps  the  only  species,  of  the  pliocene  Glircs  that 
have  not  been  recognised  as  existing  in  Britain  within  the  historic  period.  The  newer 
tertiary  seas  were  tenanted  by  cetacea,  either  generically  or  specifically  identical  with 
those  that  are  now  taken  or  cast  upon  our  shores." 


296  CONDITIONS    FOR    THE    PRESERVATION    OF 

which  once  enveloped  them.*  Supposing  the  elephants  and  rhinoceroses, 
with  other  contemporary  animals,  the  remains  of  which  are  found  with 
those  of  these  mammals,  to  have  been  spread  over  the  land  prior  to  the 
great  depression,  accompanied  by  increased  cold,  as  above  noticed,  and 
that  they  gradually  retreated  before  the  advance  of  the  sea,  diminishing 
the  amount  of  low  ground,  the  original  connexion  between  the  British 
Islands  and  the  land  of  the  continent  may  have  more  resembled  that 
shown  as  the  boundary  of  the  600  feet  depth  (Figs.  65  and  102),  than 
that  which  we  now  find.  In  such  a  state  of  this  part  of  Europe  there 
would  be  an  ample  area  of  continuous  dry  land  for  the  range  of  the 
elephants,  rhinoceroses,  and  their  contemporary,  but  the  now  extinct 
species  of  hippopotamus,  oxen,  deer,  tiger,  leopard,  hysena,  bear,  and 
other  mammals.  Accumulations  of  bones  could  readily,  as  the  land 
became  depressed,  be  washed  out  of  any  lacustrine  or  fluviatile  accumu- 
lations amid  which  they  might  have  been  embedded,  and  be  mingled 
with  marine  remains  of  the  gradually  encroaching  seas,  sometimes  being 
worn  and  re-embedded  in  gravel,  at  others  less  mutilated,  or  even 

*  Professor  Owen,  in  his  "  History  of  British  Fossil  Mammals,"  mentions  (p.  246), 
that  "  most  of  the  largest  and  best-preserved  tusks  of  the  British  mammoth,  have  been 
dredged  up  from  submarine  drift  near  the  coasts.  In  1827,  an  enormous  tusk  was 
landed  at  Ramsgate  ;  although  the  hollow  implanted  base  was  wanting,  it  still  measured 
9  feet  in  length,  and  its  greatest  diameter  was  8  inches;  the  outer  crust  was  decom- 
posed into  thin  layers,  and  the  interior  portion  had  been  reduced  to  a  soft  substance 
resembling  putty.  A  tusk,  likewise  much  decayed,  which  was  dredged  up  off  Dunge- 
ness,  measured  11  feet  in  length;  and  yielded  some  pieces  of  ivory  fit  for  manufacture. 
Captain  By  am  Martin,  who  has  recorded  this  and  other  discoveries  of  remains  of  the 
mammoth  in  the  British  Channel  (Geological  Transactions,  second  series,  vol.  vi.  p. 
1G1),  procured  a  section  of  ivory  near  the  alveolar  cavity  of  the  Dungeness  tusk,  of  an 
oval  form,  measuring  19  inches  in  circumference.  A  tusk  dredged  up  from  the  Goodwin 
Sands,  which  measured  6  feet  6  inches  in  length,  probably  belonged  to  a  female  mam- 
moth." .  .  .  "  This  tusk  was  sent  to  a  cutler  at  Canterbury,  by  whom  it  was  sawed 
into  five  sections,  but  the  interior  was  found  to  be  fossilized  and  unfit  for  use."  .... 
"  The  tusks  of  the  extinct  elephant,  which  have  reposed  for  thousands  of  years  in  the 
bed  of  the  ocean  which  washes  the  shore  of  Britain,  are  not  always  so  altered  by  time 
and  the  action  of  surrounding  influences,  as  to  be  unfit  for  the  purposes  to  which  recent 
ivory  is  applied."  Mr.  Charlesworth,  after  mentioning  that  a  large  lower  jaw  of  a 
i.i.uuinoth,  of  which  he  gives  a  figure  (Magazine  of  Natural  History,  new  series,  vol.  Hi. 
p.  348,  1839),  had  been  dredged  up  off  the  Dogger  Bank,  in  1837,  and  quoting  Mr. 
Woodward  (Geology  of  Norfolk),  as  stating  that  more  than  2000  elephants'  teeth  had 
been  dredged  up  off  Hasbro',  on  the  Norfolk  coast,  in  13  years,  relates  that  a  mam- 
moth's tusk,  dredged  up  by  some  Yarmouth  fishermen  off  Scarborough,  about  1830,  was 
so  slightly  altered  in  character,  that  it  was  sawn  up  into  as  many  pieces  as  there  were 
men  in  the  boat,  each  claiming  his  share  of  the  ivory.  One  portion  was  preserved  in 
the  collection  of  Mr.  Fitch,  of  Norwich.  A  large  humerus  was,  in  1837,  trawled  up  in 
midchannel  between  Dover  and  Calais,  in  120  feet  water.  A  large  femur  was  also 
found  while  trawling,  about  half-way  between  Yarmouth  and  Holland  in  150  feet  wntor, 
and  the  lower  jaw  of  a  young  animal  was  dredged  up  off  the  Dogger  Bank.  Other 
instances  of  elephant  remains,  brought  up  from  the  sea-bottom  off  the  English  coasts, 
are  also  known.  A  tusk  of  the  Hippopotamus  major  was  dredged  up  from  the  oyster-bed 
at  Happisburgh. 


MAMMOTH    REMAINS    IN    EUROPE.  297 

uninjured,  amid  more  tranquilly  formed  deposits.  Occasionally  some, 
or  portions,  of  the  original  lacustrine  or  fluviatile  deposits,  containing 
remains  of  these  animals,  may  never  have  been  disturbed  to  any  great 
extent,  so  that  the  deposits  and  the  included  bones  became  covered  by 
the  marine  accumulations  of  the  time.* 

Upon  the  hypothesis,  that  these  animals  could  have  spread  under 
such  conditions,  and  prior  to  the  submergence  previously  noticed,  a 
time  would  come  when  the  depression  of  the  old  land  would  be  such, 
that,  as  regards  the  British  Islands,  no  sufficient  or  fitting  dry  land 
would  be  found  for  them,  supposing  that  the  diminished  temperature 
did  not  destroy  them.  While  assuming  that  such  may  have  been  the 
conditions  in  this  particular  case,  it  by  no  means  follows,  with  submerg- 
ing dry  land  over  a  large  portion  of  Europe,  that  abundant  space  was 
not  left,  even  in  Northern  Asia,  for  the  existence  and  increase  of  the 
JElephas  primigenius  and  the  Rhinoceros  tichorhinus.  The  land  may 
not  have  experienced  a  contemporaneous  depression,  or  if  so,  not  one 
cutting  off  all  the  needful  feeding-grounds  for  the  support  of  these  mam- 

*  Professor  Owen  (Hist.  Brit.  Fossil  Mammals,  p.  347),  quotes  a  notice  in  a  Cam- 
bridge paper  of  26th  February,  1845,  in  which  mention  is  made  of  high  tides  having 
much  uncovered  the  lignite  beds  at  the  base  of  the  cliffs  near  Cromer,  Norfolk,  and  that 
among  the  fossil  remains  of  that  bed,  the  lower  jaw  of  a  rhinoceros,  with  seven  molar 
teeth  in  good  preservation,  together  with  the  molars  of  the  elephant,  hippopotamus, 
and  beaver,  were  discovered.  The  jaw  was  examined  by  Professor  Owen,  and  ascer- 
tained to  have  belonged  to  a  young  Rhinoceros  tichorhinus. 

Mr.  Strickland  pointed  out,  in  1834  (Account  of  Land  and  Fresh-water  Shells  found 
associated  with  the  Bones  of  Land  Quadrupeds  beneath  diluvial  gravel,  at  Cropthorn, 
Worcestershire,  Proceedings  Geol.  Soc.,  vol.  ii.  p.  Ill),  that  "a  layer  of  fine  sand, 
containing  23  species  of  land  and  fresh-water  shells,  with  fragments,  more  or  less 
rolled,  of  bones  of  the  hippopotamus,  bos,  cervus,  ursus,  and  canis,"  reposes  on  the  lias 
clay  of  that  district.  Professor  Owen  adds  the  mammoth  and  urus  to  this  catalogue 
(Hist.  Brit.  Fossil  Mammals,  p.  258).  "  The  sand  passes  upwards  gradually  into 
gravel,  which  extends  to  the  surface,  and  differs  in  no  respect  from  the  other  gravel  of 
the  neighbourhood,  being  composed  principally  of  pebbles  of  brown  quartz,  but  occa- 
sionally containing  chalk  flints,  and  fragments  of  lias  ammonites  and  gryphites.  The 
bones,  though  most  abundant  in  the  sand,  are  interspersed  also  in  the  gravel ;  but  the 
shells  are  confined  to  the  sand."  Two  of  the  species  of  shells  were  considered  to  be 
extinct.  From  the  fluviatile  habits  of  some  of  these  molluscs,  Mr.  Strickland  inferred, 
that  the  deposit  occupies  the  site  of  an  ancient  river  bed.  He  at  the  same  time  pointed 
out  "  the  greater  change  which  has  taken  place  in  the  mammifers  of  this  island  than 
in  the  molluscs,  since  the  era  when  the  gravel  was  accumulated  ;  and  the  little  varia- 
tion which  the  climate  appears  to  have  undergone  since  the  same  epoch."  He  also 
adverted  to  similar  deposits,  previously  known  at  North  Cliflf,  Yorkshire,  Market 
Weighton,  and  at  Copford,  near  Colchester. 

The  section  given  by  Sir  Roderick  Murchison,  M.  de  Verneuil,  and  Count  Keyser- 
ling  (Geology  of  Russia  in  Europe,  and  of  the  Urals,  vol.  i.  p.  502),  would  appear  to 
show,  that  as  respects  a  part  of  Russia,  and  beneath  a  covering  of  "  clay  drift,  con- 
taining numerous  bones  and  teeth  of  the  mammoth,  50  feet  thick,"  there  was  a  "band 
of  finely  laminated  sand,  full  of  shells,  specifically  identical  with  those  which  inhabit 
the  adjacent  river  Don."  The  latter  reposes  upon  a  tertiary  limestone. 


298  OSSIFEROUS    CAVE    OF    KIRKDALE. 

mals.  Thus,  in  several  parts  of  Europe,  -when  the  sea-bottom  emerged, 
— the  former  land,  variously  modified  during  its  submergence,  coated 
more  or  less  with  the  detritus  drifted  over  and  thrown  down  upon  it,  and 
embedding  the  remains  of  such  animals  as  perished  during  the  submerg- 
ence, there  might  be  many  sources  whence  the  elephants,  rhinoceroses, 
and  other  contemporary  animals  could  spread  over  the  new  land  as  the 
fitting  conditions  obtained.  It  is  not  difficult  to  conceive  that  these 
mammals  may  thus  have  revisited  the  area  of  the  British  Islands,  again 
connected  with  the  main  land,  so  that  their  remains  may  be  found  in 
lacustrine  and  fluviatile  deposits  above  the  marine  accumulations  formed 
during  the  interval  of  depression.*  As  there  is  evidence  in  Western 
Europe  of  oscillations,  as  regards  the  relative  level  of  sea  and  land,  in 
the  more  recent  geological  time,  requiring  much  attention  on  the  part 
of  the  observer,  he  will  have  carefully  to  consider  their  influence  on  the 
spread  of  mammals,  such  as  those  under  consideration.  Assuming, 
however,  only  one  submergence  sufficient  to  disconnect  the  British 
Islands,  followed  by  an  elevation  restoring  the  connexion,  it  would  be 
inferred  that  lacustrine  and  fluviatile  accumulations  would  be  the  highest 
amid  which  we  should  expect  to  discover  the  remains  of  the  Ulephas 
primiyenim  and  his  contemporary  mammals,  partly  extinct,  partly  now 
existing. 

Amid  any  changes  arising  from  the  depression  and  elevation  of  land 
and  adjacent  sea  bottoms,  should  animals  have  lived  in  caves,  carrying 
in  their  prey,  if  they  had  been  carnivorous,  or  have  fallen  into  fissures 
in  the  manner  previously  mentioned  (p.  137),  their  remains,  so  pre- 
served, would  appear  the  most  safe  from  rearrangement  by  waves,  tidal 
streams,  or  ocean  currents.  Though  the  bones  of  extinct  bears  and 
other  animals  found  in  caves  had  previously  attracted  much  attention, 
it  was  from  the  discovery  of  the  remains  of  mammals  in  a  cavern  at 
Kirkdale,  in  Yorkshire,  in  1821,  and  from  the  descriptions  of  all  the 
circumstances  attending  the  mode  of  occurrence  of  these  remains,  and 
of  the  condition  of  the  cavern  itself,  subsequently  given  by  Dr.  Buck- 
land,  who  visited  the  spot  a  few  months  only  after  the  discovery,  that 
ossiferous  caves  attained  a  new  interest.  This  cave  was  found  by  cut- 
ting back  a  quarry,  as  many  others  have  also  been.  Its  greatest  length 
was  found  to  be  245  feet,  and  its  height  generally  so  inconsiderable, 
that  in  two  or  three  situations  only  could  a  man  stand  upright.  The 
following  (Fig.  105)  is  the  section  of  it,  as  given  by  Dr.  Buckland  ;f — 
a,  a,  a,  a,  horizontal  beds  of  limestone,  in  which  the  cave  occurs ; 

*  Localities  are  mentioned  where,  in  the  British  Islands,  bones  of  these  and  of  con- 
temporary mammals  have  been  found  entombed  in  fluviatile  or  lacustrine  deposits, 
supposed  to  be  above  the  accumulations  referred  to  the  period  when  erratic  blocks 
and  other  ice-transported  detritus  were  strewed  over  the  sea  bottom  in  this  part  of 
Europe. 

f  Reliquire  Diluvianoo,  1823. 


OSSIFEROUS    CAVE.  OF    KIRKDALE.  299 

stalagmite  incrusting  some  of  the  bones,  and  formed  before  the  mud  was 
introduced ;  c,  bed  of  mud  containing  the  bones  ;  d,  stalagmite  formed 
since  the  introduction  of  the  mud,  and  spreading  over  its  surface ;  e, 


Fig.  105. 


insulated  stalagmite  on  the  mud ;  /,  /,  stalactites  depending  from  the 
roof.  "  The  surface  of  the  sediment  when  the  cave  was  first  opened 
was  nearly  smooth  and  level,  except  in  those  parts  where  its  regularity 
had  been  broken  by  the  accumulations  of  stalagmite,  or  ruffled  by  the 
dripping  of  water ;  its  substance  was  an  argillaceous  and  slightly  mica- 
ceous loam,  composed  of  such  minute  particles  as  could  easily  be  sus- 
pended in  muddy  water,  and  mixed  with  much  calcareous  matter,  that 
seems  to  have  been  derived  in  part  from  the  dripping  of  the  roof,  and  in 
part  from  comminuted  bones."53  The  remains  of  the  hyaena,  tiger,  bear, 
wolf,  fox,  weasel,  elephant,  rhinoceros,  hippopotamus,  horse,  ox,  three 
species  of  deer,  and  some  other  animals,  were  found  to  be  so  strewed 
over  the  bottom  of  the  cave  when  the  mud  was  removed,  the  proportion 
of  hyaena  teeth  over  those  of  other  animals  was  so  great,  and  the  bones 
of  other  anifhals  were  so  broken  and  gnawed,  that  Dr.  Buckland  consi- 
dered the  Kirkdale  Cave  to  have  been  the  den  of  the  extinct  hyaenas,  the 
remains  of  which  were  found  in  it,  during  a  succession  of  years ;  that 
they  brought  in,  as  prey,  the  animals  the  bones  and  teeth  of  which  are 
now  mingled  with  their  own,  and  that  these  conditions  were  suddenly 
changed  by  the  irruption  of  muddy  water  into  the  cave,  burying  all  the 
remains  of  the  animals  in  an  envelope  of  mud,  including  the  faeces  of 
the  hyaenas,  which  occurred  in  the  Kirkdale  Cave,  precisely  as  such  now 
do  in  the  dens  of  existing  hyaenas.  Many  bones  were  found  to  be 
rubbed  smooth  and  polished  on  one  side,  in  this  respect  differing  from 
the  other  side ;  a  fact  showing,  Dr.  Buckland  infers,  that  one  side  had 
been  exposed  to  the  walking  and  rubbing  of  the  hyaenas. 

There  would  thus  appear  to  have  been  a  hole  or  cavern  at  first  raised 
above  common  detrital  accumulations,  and  freely  communicating  with 
the  atmosphere,  when  the  stalagmite  b  was  formed,  then  a  change  by 
which  water  containing  fine  mineral  detritus  was  introduced,  the  latter 
subsiding  from  the  water,  which  may  have  completely  filled  the  whole 
of  the  cavern,  and,  thirdly,  a  time  when  the  cave  was  out  of  the  reach 

*  Reliquiaj  Diluvianae,  1823. 


300      INTRODUCTION    OF    MUD    INTO    OSSIFEROUS    CAVES. 

of  water,  again  freely  communicating  with  the  atmosphere,  so  that  sta- 
lagmites were  thrown  down  upon  the  even  floor  of  mud.  The  stalactites 
depending  from  the  top  may  have  been  partly  formed  during  both  pe- 
riods when  the  cavern  communicated  with  the  atmosphere.  Stalactites 
would  not  be  formed  if  the  cave  were  full  of  water,  the  solution  of  the 
bicarbonate  of  lime,  even  supposing  such  to  have  passed  through  into 
the  cavern,  would  mingle  in  the  usual  way  with  the  general  volume  of 
the  water.  Even  assuming  deposits  from  such  a  solution,  it  would 
scarcely  take  the  forms  of  depending  stalactites,  those  which  so  mark 
an  accumulation  of  the  particles  of  carbonate  of  lime  by  the  loss  of  car- 
bonic acid  and  evaporation  of  the  water  in  the  air. 

As  regards  the  introduction  of  fine  sedimentary  matter  into  caves 
during  a  submergence  of  previously  dry  land  beneath  the  sea,  the  result- 
ing mud  not  containing  the  hard  parts  of  marine  animals,  much  would 
necessarily  depend  upon  the  circumstances  under  which  the  entrances, 
or  fissures  communicating  with  the  old  surface  of  dry  land,  were  placed. 
Should  the  entrances  be  blocked  up  by  beaches  or  shingles  drifted  over 
them  (independently  of  any  which  may  have  been  closed  by  the  accu- 
mulation of  fallen  fragments  before  submergence)  as  the  land  descended 
and  the  coast  conditions  changed,  the  shores  ranging  gradually  to  higher 
levels,  the  matter  of  fine  mud  could  be  water-borne  through  the  shingles 
or  fragments.  Such  muddy  water  once  in  the  cavern,  either  from  this 
source,  or  entering  amid  other  cracks  and  chinks,  the  resulting  mud 
would  settle  over  the  floor,  enveloping  all  within  its  reach  in  a  mass  of 
fine  sediment.  In  either  case,  any  germs  of  marine  aniiaals  secreting 
hard  parts,  and  entering  with  the  water,  would  scarcely  be  properly 
developed  in  such  a  situation. 

Ossiferous  caverns  being  merely  those  amid  caves  in  general,  which, 
from  fitting  circumstances,  mammals  have  made  their  dens,  or  into 
which  they  have  fallen  or  been  drifted,  all  the  sinuosities  and  irregula- 
rities of  such  cavities,  both  as  regards  horizontal  and  vertical  range, 
have  to  be  expected  in  them.  They  are  found  to  be  variously  filled  in 
different  localities,  so  that  it  becomes  difficult  to  point  out  any  particular 
arrangement  of  parts  common  to  the  whole.  At  the  same  time,  the  fol- 
lowing longitudinal  section  (Fig.  106)  may  afford  somewhat  of  a  general 
view  of  many  which  have  been  discovered.  In  it  I,  /,  Z,  represent  the 
section  of  a  limestone  hill  (these  caverns  being,  like  caves  in  general, 
most  common  in  limestone  rocks),  in  which  there  is  a  cavern,  J,  £>,  com- 
municating with  a  valley,  v,  by  an  entrance,  a.  A  floor  of  stalagmite, 
c?,  c?,  covers  bones  and  fine  sediment  accumulated  in  the  cavities,  <?,  c. 
A  column  of  stalactite  and  stalagmite  is  represented  between  the  two 
chief  chambers  of  the  cave,  and  which  may,  or  may  not  have  blocked 
up  the  passage  from  one  to  the  other.  Any  circumstances  having  re- 
moved a  covering  of  the  entrance,  a,  or  the  latter  being  even  constantly 


CONDITIONS    FOE-    STALACTITE    AND    STALAGMITE.        301 

open  and  well  known,  an  observer,  if  not  informed  respecting  ossiferous 
caverns,  might  easily  enter  such  a  cave  and  remark  nothing  more  than 


Fig.  106. 


the  chambers,  the  stalactites  depending  from  the  roof  or  covering  the 
walls,  and  a  floor  partly  rock,  partly  formed  of  stalagmite  ;  and  even, 
if  the  passage  between  the  chambers  be  closed  by  stalactite  and  stalag- 
mite, return  from  the  outer  cave  without  being  aware  of  the  chamber 
beyond  it. 

It  will  be,  at  once,  apparent,  seeing  that  the  bones  in  ossiferous 
caves  may  either  have  been  chiefly  collected  by  predaceous  animals ; 
have  fallen  into  them  from  openings  in  the  ground  above ;  have  been 
drifted  into  them,  or  be  the  remains  of  mammals  which  have  entered 
and  died  in  the  caves,  that  great  attention  should  be  paid  to  the  mode 
in  which  the  bones  may  be  accumulated,  and  to  their  whole,  fractured, 
gnawed,  or  other  state.  Very  careful  and  complete  sections  require  to 
be  made  of  the  ossiferous  accumulations,  and  these  should  not  be  con- 
fined to  one  portion  of  a  cavern ;  for  during  a  long  lapse  of  time,  an 
open  cave  may  have  been  variously  tenanted  or  strewed  with  bones.  If 
an  observer  be  in  search  of  evidence  of  ossiferous  caves  having  been  the 
dens  of  predaceous  animals,  not  only  the  marks  of  their  teeth  upon  the 
remains  of  such  bones  as  may  not  have  been  consumed  are  valuable,  but 
also  the  mode  of  occurrence  of  faecal  remains,  and  the  rubbing  and 
polishing  of  portions  of  the  walls,  especially  in  the  narrower  passages, 
are  important. 

With  respect  to  stalactitic  and  stalagmitic  incrustations,  they  may 
tave  happened  at  all  times  when  a  cavern  was  above  the  sea  or  water- 
Irainage  of  the  time,  so  that  the  atmosphere  entered  it,  and  bicarbonate 
)f  lime  percolated  in  solution  through  the  containing  rock  into  the  cave. 

lus  bones,  as  in  the  Kirkdale  cave,  may  have  been  embedded  in  this 
calcareous  substance,  as  well  prior  to  the  introduction  of  any  fine  sedi- 
ment by  means  of  water,  as  afterwards.  It  is  the  repose  of  stalag- 
mite upon  an  even  flooring  of  the  sedimentary  matter  enveloping  the 
bones,  which  shows  an  alteration  of  conditions,  one  from  a  state  of 
things  when  stalagmite  could  not  be  accumulated  on  the  bottom  of  the 
cave,  to  that  which  permitted  it. 


302     CEKTAIN  OSSIFEROUS  CAVES  INFERRED  TO 

As  the  remains  of  mammals  of  existing  kinds,  such  as  the  red  deer,* 
of  the  roebuck,f  badger,{  polecat,§  stoat,||  wolf,lf  fox,**  water-vole, 
field-vole,  bank-vole,  hare  and  rabbit, ff  have  been  discovered  in  caves 
mingled  with  those  which  are  extinct,  and  as  the  remains  of  man  have 
been  detected  in  similar  caverns,  it  becomes  needful  most  carefully  to 
study  the  circumstances  under  which  all  these  remains  may  occur ; 
so  that  while,  on  the  one  hand,  we  do  not  neglect  the  kind  of  evidence 
which  might  thus  show  the  contemporaneous  existence  of  mammals 
now  partly  extinct,  and  partly  living,JJ  and  also  of  man  with  the  same 
kinds  of  animals,  on  the  other,  the  accidents  which  may  have  brought 
such  apparently  contemporaneous  mixtures  together,  may  be  duly  re- 
garded. Thus,  had  not  Dr.  Buckland  employed  the  needful  caution, 
human  remains  (those  of  a  woman)  in  Paviland  Cave,  Glamorganshire, 
might  have  been  regarded  as  proving  the  contemporaneous  existence  of 
man  and  of  the  Elephas  primigenius.  Rhinoceros  tichorhinus,  and 
Hycena  spelcea.  In  this  case,  the  cave  had  evidently  been  employed  as 
a  place  of  sepulture  by  some  of  the  early  inhabitants  of  that  part  of 
Wales,  and  the  ground  containing  the  remains  of  the  extinct  animals 
moved. §§ 

*  In  Kirkdale  Cavern,  Yorkshire,  and  Kent's  Hole,  Torquay ;  Buckland,  "  Reliquiae 
Diluvianae,"  and  Owen,  "  Hist.  Brit.  Foss.  Mammals." 

f  Fissure  in  limestone,  with  the  remains  of  Rhinoceros  tichorhinus,  Caldy  Island,  Pem- 
brokeshire ;  Owen,  "  Hist.  British  Foss.  Mammals,"  p.  488.  Dr.  Buckland  mentions 
an  antler,  "  approaching  that  of  the  roe,"  in  the  Paviland  Cave. 

t  Kent's  Hole,  Torquay;  Owen,  "Hist.  Brit.  Foss.  Mammals,"  p.  110. 

g  Belgian  Cave,  Dr.  Schmerling.  Berry  Head,  Devon;  Owen,  "Hist.  Brit.  Foss. 
Mammals,"  p.  113. 

||  Kirkdale  Cave;  Buckland,  "Reliquiae  Diluvianoe."  Kent's  Hole,  Torquay;  Owen, 
"  Hist.  Brit.  Foss.  Mammals." 

][  Kirkdale  Cave ;  Paviland  Cave  ;  Oreston,  Plymouth  ;  Kent's  Hole,  Torquay.  Buck- 
land,  "  Reliquino  Diluvianse  ;"  Owen,  "  Hist.  Brit.  Foss.  Mammals." 

**  Kent's  Hole,  Torquay;  Oreston,  Plymouth.  Owen,  "Hist.  Brit.  Foss.  Mammals." 

ff  Buckland,  "  Reliquiae  Diluviance ;"  Owen,  "Hist.  Brit.  Foss.  Mammals." 

it  The  following  list  of  animals,  the  remains  of  which  have  been  found  in  the  caves 
of  the  British  Islands,  is  given  by  Professor  Owen,  in  his  "History  of  British  Fossil 
Mammals:" — Vespertilio  noctula,  Rhinolophus ferrum-eguinum,  Ursus priscus  and  spelceus ; 
Meles  taxus,  Putorius  vulgaris  and  ermineus  ;  Lutra  milgaris  (from  Durdham  Down,  Bristol, 
on  the  authority  of  Mr.  E.  T.  Higgins) ;  Canis  lupus  and  vulpcs ;  Ilycena  spelcea,  Felis 
spelcea  and  catus ;  Machairodus  latideus,  Mus  musculus,  Arvicola  amphibia,  agrcstis,  and 
pratensis;  Lepus  timidus,  and  cuniculus  ;  Lagomys  spelceus,  Elephas  primigcnius,  Rhinoceros 
tichorhinus,  Equus  fossilis  (caballus?)  and  plicidens  ;  Asinus  fossilis,  Hippopotamus  major, 
Sus  scrofa,  Megaceros  Hibernicus,  Strongyloceros  spelceus,  Cervus  Elaphus,  Tdrandus,  Ca- 
preolus,  and  Bucklandi;  Bison  priscus,  and  minor,  and  Bos  primigenius. 

§§  The  cave  in  which  these  remains  were  discovered  is  one  of  two  on  the  coast  between 
Oxwich  Bay  and  the  Worm's  Head,  part  of  the  district  known  as  Gower,  on  the  west 
of  Swansea,  and  formed,  in  great  part,  by  carboniferous  or  mountain  limestone.  It  is 
known  as  the  Goat's  Hole,  and  is  accessible  only  at  low  water,  except  across  the  face 
of  a  nearly  precipitous  cliff,  rising  to  the  height  of  about  100  feet  above  the  sea.  The 
floor  at  the  mouth  of  the  cave,  is  about  30  to  40  feet  above  high-water  mark,  so  that, 
during  heavy  on-shore  gales,  the  spray  of  the  breakers  dashes  into  it.  Beneath  a 


HAVE    BEEN    DENS    OF^EXTINCT    CARNIVORA.  303 

In  many  instances  of  the  mixed  remains  of  extinct  and  existing 
species  of  mammals,  independently  of  the  condition  and  mode  of  occur- 
rence of  the  remains  themselves,  the  probable  habits*  of  the  animals 
may  offer  the  observer  much  assistance.  In  this  manner,  certain  caves 
have  been  inferred  to  have  been  the  dens  of  extinct  bears  and  hyaenas, 
in  the  latter  case,  faecal  remains,  considered  to  be  of  a  very  characte- 
ristic kind,  marking  the  continued  residence  of  these  bone-consuming 
animals,  and  a  quiet  entombment  of  such  bodies  with  ordinary  osseous 
remains.  One  kind  of  animal,  such  as  the  cavern  bear,  may  have 
occupied  a  cave  at  one  time,  while  hyaenas  may  have  tenanted  it  at 
another,  and  both  may  have  been  preceded  or  replaced  by  the  cave 
tiger,  and  its  contemporary  great  feline,  the  Macliairodus.^  During 

shallow  covering,  Dr.  Buckland  discovered  the  "nearly  entire  left  side  of  a  female 
skeleton."  He  adds  ("  Reliquiae  Diluvianse,"  p.  88),  "  Close  to  that  part  of  the  thigh- 
bone where  the  pocket  is  usually  worn,  I  found  laid  together,  and  surrounded  also  by 
ruddle,  about  two  handfuls  of  small  shells  of  the  Nerita  littoralis,  in  a  state  of  complete 
decay,  and  falling  to  dust  on  the  slightest  pressure.  At  another  part  of  the  skeleton,  viz., 
in  contact  with  the  ribs,  I  found  40  or  50  fragments  of  small  ivory  rods,  nearly  cylindri- 
cal, and  varying  in  diameter  from  a  quarter  to  three-quarters  of  an  inch,  and  from 
one  to  four  inches  in  length.  Their  external  surface  was  smooth  in  a  few  which  were 
least  decayed,  but  the  greater  number  had  undergone  the  same  degree  of  decomposition 
with  the  large  fragments  of  tusk  before  mentioned."  Fragments  of  ivory  rings  were 
also  discovered,  supposed,  when  complete,  to  have  been  four  or  five  inches  in  diameter. 
Portions  of  elephants'  tusks  were  obtained,  one  nearly  two  feet  long ;  and  Dr.  Buck-- 
land inferred  that  the  rods  and  the  rings  had  been  made  of  the  fossil  ivory,  the  search 
for  which  had  caused  the  marked  disturbance  of  the  ossiferous  ground  observed,  the 
ivory  being  then  in  a  sufficiently  hard  and  tough  state  to  be  so  worked.  Charcoal  and 
pieces  of  more  recent  bones  of  oxen,  sheep,  and  pigs,  "apparently  the  remains  of 
food,"  showed  the  cave  had  been  used  by  man.  The  toe-bone  of  a  wolf  was  shaped, 
and  it  was  inferred  that  it  had  been  probably  employed  as  a  skewer.  As  regards  the 
date  when  this  cave  may  have  been  thus  worked  for  its  ivory,  and  the  woman  buried, 
Dr.  Buckland  calls  attention  to  the  remains  of  a  Roman  camp  on  the  hill  immediately 
above  the  cave.  Amid  the  disturbed  ossiferous  ground  there  were  not  only  recent 
bones,  but  also  the  remains  of  edible  molluscs,  Buccinum  undatum,  Littorina  litioria,  L. 
neritoidcs,  Patella  vulgata,  and  Trochus  crassus. 

*  No  doubt  much  caution  will  be  required  as  to  any  inferences  drawn  from  the 
habits  of  existing  animals  of  a  particular  genus  ;  as,  for  instance,  if  the  hare  were  an 
extinct  mammal,  and  the  rabbit  only  found  living,  it  would  be  a  serious  error  to  infer, 
from  the  habits  of  the  latter,  that  the  former  always  lived  in  burrows  which  it  dug  for 
itself.  At  the  same  time  it  may  not  be  unreasonable  to  suppose  that  animals,  such  as 
elephants,  rhinoceroses,  deer,  and  oxen,  did  not  make  caves  their  habitations,  even 
when  entrances  into  them  were  sufficiently  large  and  easy,  though  they  may  have 
occasionally  found  their  way  into  them,  as  we  have  often  seen  oxen  do  in  England,  for 
shelter  from"  very  heavy  rains  or  great  heats. 

f  Mr.  Austen,  when  noticing  Kent's  Hole  and  other  ossiferous  caves  of  Devonshire, 
("Geology  of  the  Southeast  of  Devonshire,"  Geological  Transactions,  2d  series,  vol.  vi. 
p.  445,)  calls  attention  to  the  habits  of  the  lion  and  panther,  which,  after  killing  their 
prey,  "  secure  it  in  their  jaws,  and  bear  its  weight  on  their  powerful  shoulders,  re- 
treating with  it  to  these  caves."  After  mentioning  the  great  size  of  the  animals  which 
the  African  lions  carry  off,  he  adds,  that  "with  respect  to  their  usual  abodes,  we  have 
the  authority  of  all  African  travellers  and  hunters,  that  chasms,  caves,  overhanging 


304  HUMAN    REMAINS    IN    OSSIFEROUS    CAVES. 

the  occupation  of  the  more  roomy  portions  of  a  cave  by  such  great 
mammals,  smaller  animals  could  have  lived  in  the  minor  holes  and  fis- 
sures, occasionally  feeding  upon  remnants  of  the  prey  brought  in  by 
the  larger  carnivora,  and  sometimes  falling  victims  themselves  to  the 
latter.  In  certain  caves,  bats  may  often  have  clustered  in  places  in 
the  higher  parts  of  the  chambers,  secure  from  the  bears,  hyaenas,  or 
felines,  their  remains,  from  time  to  time,  being  mingled  with  the  bones 
of  the  other  animals  beneath.  With  regard  to  several  mammals,  the 
remains  of  which  are  discovered  in  ossiferous  caves,  we  feel  certain  that 
not  only  would  their  bulk  have  prevented  them  from  passing  through 
the  only  communications,  which  can  either  be  seen  or  suspected,  between 
the  open  air  and  chambers  of  many  caves,  but  also  that  their  habits 
would  not  direct  them  to  such  retreats.  As  prey  to  carnivorous  mam- 
mals inhabiting  caves,  dragged  in  piecemeal  through  comparatively 
small  apertures,  when  their  bodies  were  dismembered,  there  appear  no 
difficulties  ;  indeed,  there  is  good  evidence  on  this  head.  It  has  been 
remarked,  that  the  teeth  of  the  extinct  elephant  found  in  caves,  show 
that  young  animals  of  this  kind  had  chiefly  been  brought  into  them. 
This,  however,  does  not  seem  to  have  been  the  case  with  respect  to  the 
Rhinoceros  tichorhinus,  since  the  remains  of  full-formed  individuals  of 
this  species  are,  in  some  cases  sufficiently  abundant  ;*  neither  does  it 
show  that  many  a  large  elephant  may  not  have  fallen  a  prey  to  the 
great  carnivora,  especially  the  feline,  its  bones  and  teeth  being  left 
elsewhere,  and  perhaps  in  a  great  measure  consumed  on  the  spot  by 
hyaenas. 

That  men  have  at  various  times  inhabited  caves,  and  used  them  as 
tombs,  is  well  known,  and  the  case  of  the  skeleton  of  the  woman  at  Pavi- 
land,  noticed  above,  is  sufficient  to  show  that  ossiferous  caverns  may 
have  been  thus  employed.f  If  man  had  been  a  contemporary  inhabitant 
of  the  regions  where  these  extinct  carnivora  roamed  in  search  of  their 
prey,  he  might,  as  well  as  other  creatures,  particularly  while  only  armed 

ledges  of  rocks,  and  similarly  protected  places,  are  their  haunts,  and  the  spots  to  which 
they  carry  their  prey." 

*  Having  examined  the  ossiferous  cave  of  Spritsail  Tor,  in  Gower,  Glamorganshire, 
shortly  after  its  discovery,  by  the  cutting  back  of  a  carboniferous  limestone  quarry, 
we  were  much  struck  by  the  narrowness  of  a  part  of  the  entrance,  where  predaceous 
animals,  apparently  hyienas  (//.  spclcea)  seem  to  have  been  stopped,  with  large  portions 
of  the  carcases  of  the  Rhinoceros  tichorhinus,  numbers  of  the  teeth  of  which,  among  the 
other  remains,  were  accumulated  close  outside  it. 

f  Sir  Philip  Egerton,  "On  the  Ossiferous  Caves  of  the  Hartz  and  Franconia"  (Pro- 
ceedings of  the  Geological  Society,  vol.  ii.  p.  94),  when  enumerating  the  osseous  remains 
which  rewarded  the  researches  of  himself  and  the  Earl  of  Enniskillen  in  the  caves  of 
Gailenruth,  Kiihloch,  Scharzfeld,  and  Baumanns  Hb'hle,  mentions  that  fragments  of 
rude  pottery  were  discovered  in  these  four  caves ;  "  old  coins  and  iron  household  imple- 
ments of  most  ancient  and  uncouth  forms  in  that  of  Rabenstein,"  and  recent  bones  of 
pigs,  birds,  dogs,  foxes,  and  ruminants,  in  every  cave  examined. 


HUMAN    REMAINS    IN    OSSIFEROUS    CAVES.  305 

as  he  was  likely  to  have  been  in  earlier  times,  have  occasionally  formed 
a  portion  of  such  prey.  While,  however,  these  extinct  great  bears, 
hyaenas,  or  felines  occupied  or  retreated  to  the  caves,  for  the  purpose 
of  shelter,  or  of  consuming  their  prey,  he  could  scarcely,  as  has  been 
remarked,  have  been  a  joint  inhabitant  of  such  places  with  them ;  so 
that  where  pieces  of  pottery  are  discovered,  which  appear  to  mark  the 
residence  of  man  in  the  caves,  we  merely  seem  to  have  evidence  that  he 
frequented  them  at  some  period,  perhaps  not  well  denned ;  unless,  in- 
deed, the  mode  of  occurrence  of  the  pottery  be  such  that  no  doubt  of  the 
relative  date  of  its  introduction  can  exist.*  With  flint  or  other  stone 
arrow-heads  and  knives,  such  as  have  been  discovered  in  Kent's  Hole, 
and  elsewhere,  there  would  be  more  difficulty,  if  other  evidence  was  not 
opposed  to  the  inference,  since  they  may  have  been  attached  to  man,  as 
weapons,  when  carried  off  as  prey,  and  therefore  would  freely  mingle 
with  the  general  mass  of  bones  in  a  cave  when  the  flesh  of  the  men  was 
eaten.  When  bones  of  men,  as  they  are  stated  to  have  been,  are  disco- 
vered really  mixed  amid  those  of  the  extinct  carnivora  and  other  animals 
found  in  ossiferous  caves, f  the  subject  is  one  of  no  slight  interest,  and 

*  The  description  of  the  cavern  of  Miallet,  near  Anduze,  department  of  the  Gard,  by 
M.  Tessier  (Bulletin  de  la  Socie'te'  Geologique  de  France,  torn,  ii.),  affords  a  useful 
illustration  of  the  manner  in  which  human  bones  may  occur  with  those  of  extinct 
mammals.  The  cavern  is  situated  30  yards  above  a  valley,  on  a  steep  slope,  and  in  a 
dolomitic  rock.  The  lowest  bed,  reposing  on  the  bottom  of  the  cavern,  is  composed  of  a 
dolomitic  sand,  irregularly  covered  with  thin  stalagmite,  and  here  and  there  by  an 
argillo-ferruginous  clay,  more  than  a  yard  ^thick.  This  bed  contains  the  abundant 
remains  of  bears.  Beneath  stalagmite  and  a  bed  of  clayey  sand,  from  8  to  16  inches 
thick,  human  remains  were  discovered  in  different  parts  of  the  cavern.  At  the  inmost 
end  they  were  decidedly  mixed  with  those  of  bears,  which  predominated;  but  at  the 
entrance  the  human  bones  prevailed.  On  the  ossiferous  clay,  and  beneath  a  very  rocky 
projection,  a  nearly  entire  human  skeleton  was  discovered,  and  close  to  it  a  lamp  and 
a  baked  clay  figurine ;  copper  bracelets  being  found  at  a  short  distance.  In  other  places 
were  the  remains  of  coarse  pottery,  worked  bones,  and  small  flint  tools,  exhibiting  a 
ruder  state  of  the  arts  than  the  preceding.  M.  Tessier  infers — 1.  An  epoch  when  the 
cavern  was  inhabited  by  bears.  2.  A  time  when  man,  little  advanced  in  civilization, 
inhabited,  and  probably  was  buried,  in  the  cave ;  and  3,  the  Roman  epoch,  shown  by 
the  remains  of  more  advanced  art.  As  regards  the  mixed  bones  of  man  and  the  bears, 
it  is  inferred  that  this  is  accidental,  as  men  and  bears  could  not  have  lived  together  in 
this  cavern. 

|  Dr.  Schmerling  (Ossemens  Fossiles  des  Cavernes  de  Li6ge)  mentions  human  bones 
as  decidedly  mixed  with  those  of  the  extinct  elephant,  rhinoceros,  bear,  and  other  mam- 
mals in  the  same  clay  and  breccia  in  caves  near  Li6ge.  From  the  mode  of  occurrence 
of  the  whole,  he  infers  that  the  human  as  well  as  the  other  bones  were  all  washed  into 
the  caves  together,  men  and  these  extinct  mammals  being  then  coexistent.  Instances 
of  the  mixed  bones  of  extinct  mammals  and  of  man,  in  the  south  of  France,  are  men- 
tioned by  M.  Marcel  de  Serres  (Geognosie  des  Terrains  Tertiaires),  M.  de  Cristol,  M. 
Tournal,  and  other  geologists,  who  supported  the  view  that  men  and  these  extinct  ani- 
mals had  been  contemporaneous,  a  view  opposed  by  M.  Desnoyers  (Bulletin  de  la 
Socie'te  Geologique  de  France,  torn,  ii.),  who  points  out  that  the  pottery  and  weapons 
discovered  in  the  ossiferous  caves  correspond  with  those  of  the  early  inhabitants  of 
England,  Germany,  and  Gaul ;  and  that  while  in  the  monuments  of  the  latter  similar 

20 


306  COMPLICATED    ACCUMULATIONS    IN 

requires  at  least  very  careful  investigation,  without  prejudgment  of  any 
kind.* 

Ossiferous  caverns  may  offer  greater  complication  than  those  previ- 
ously noticed,  in  which  the  apertures  or  mouths  opening  to  the  air  are 
considered  to  have  been  more  or  less  lateral,  presenting  ready  ingress 
and  egress  to  mammals,  no  great  clefts  or  fissures  communicating  with 
any  surface  of  ground  above.  A  cavern  of  the  kind  represented,  in 
longitudinal  section,  beneath  (fig.  107),  may  have  been  of  a  mixed  kind, 
partly  composed  of  a  portion  <?,  rising  upwards,  as  in  many  which  are 
not  ossiferous  is  also  seen,  and  partly  having  a  more  horizontal  range, 
0,  a.  If  the  upright  cleft  did  not  reach  the  surface  at  the  time,  in  a 


manner  to  permit  animals  falling  through  it  to  the  cave  beneath,  frag- 
ments only  of  the  rock  in  which  the  whole  is  situated  so  doing  (and  it 
should  be  remembered,  that  in  numerous  caverns  the  fall  of  rocks  from 
various  parts  of  the  roofs  and  sides  may  have  happened  at  all  times), 
the  osseous  remains  of  animals  en-tombed  would  belong  to  those  which 
may  have  entered,  lived  in,  or  been  dragged  into  the  chambers,  including 
birds  and  bats  finding  their  way  down  the  upright  clefts,  supposing  the 
cave  to  have  been  the  den  of  predaceous  mammals  with  the  needful 
habits.  If  the  cleft  were  sufficiently  wide  for  animals  to  fall  through, 
as  mammals  now  do  similar  fissures,  there  might  be  two  modes  of  accu- 
mulating the  remains  of  the  same,  or  nearly  the  same  creatures ;  one 
resulting  from  the  occupation  of  the  cave  by  predaceous  animals,  and 
any  others  able  to  live  in  the  same  place  with  them ;  the  other,  by  the 
fall  of  animals  through  the  fissure,  sometimes  bringing  down  with  them 
fragments  of  rocks,  and  so  wholly  or  partly  burying  their  carcases 
beneath  such  fragments. 

If  we  assume  a  submergence  of  such  a  cavern,  much,  as  to  the  results, 
would  depend  on  the  rapidity  or  slowness  of  the  submergence.  Sup- 
artificial  objects  occur,  no  remains  of  the  extinct  mammals  are  discovered,  though  those 
of  species  now  inhabiting  Europe  are  detected. 

*  Professor  Owen  has  pointed  out  (Hist.  Brit.  Fossil  Mammals,  p.  97)  that  "  of  no 
other  quadruped  than  the  bear  is  the  femur  more  likely  to  be  mistaken  by  the  unprac- 
tised anatomist  for  that  of  the  human  subject,  especially  the  femur  of  the  gigantic 
extinct  species  commonly  found  in  caves."  Figures  and  descriptions  are  added  in  con- 
firmation of  this  statement. 


SOME    OSSIFEROUS    CAVERNS.  307 

posing  the  latter,  and  that  the  mouth  of  the  cave  was  closed,  either 
prior  to  it  or  during  its  progress,  fragments  of  rock,  such  as  we  often 
see  thickly  strewed  (the  effects  of  atmospheric  influences  and  the  action 
of  gravity  combined)  over  limestone  hill  and  mountain  sides,  descending 
readily  over  it,  the  common  earth  (usually  the  cementing  matter  of  such 
fragments  on  hillsides)  would  be  removed  by  the  wash  of  the  sea,  and 
muddy  water,  in  part,  perhaps,  thus  derived,  enter  the  cave,  in  the 
manner  previously  noticed,  enveloping  with  fine  sediment  the  bones  in 
the  interior,  a,  g.  The  sediment  rising  only  according  to  the  amount 
of  matter  introduced,  it  might  so  happen,  that  an  even  floor  did  not  sur- 
mount the  level  </,  mud  alone  completely  intermingling  with  fragments 
of  rocks  or  bones  in  the  lower  part  of  the  mass  h.  Submergence  slowly 
continuing,  and  the  fissure,  c,  still  open,  animals  could,  as  before,  fall 
through,  until  finally  the  whole  hill  was  beneath  the  water.  Much  com- 
plication might  arise  in  such  a  case,  and  more  especially  if  the  upper 
part  of  a  fissure  had  never  been  closed  over  by  detritus  even  to  its  emer- 
gence, or  that  it  had  not  been  covered  by  water  at  all,  so  that  it  was 
always  open  to  catch  unwary  animals,  or  those  hunted  by  predaceous 
mammals,  during  a  time  when  the  quadrupeds  of  the  country  may  have 
been  changed  or  much  modified.  Perpendicular  fissures  in  caves  are 
sometimes  so  filled  with  fragments  of  rock,  sand,  clay,  and  earth,  as  to 
show  the  necessity  of  great  caution,  when  inferring  that  the  osseous 
remains  of  many  caverns  had  been  derived  through  the  lateral  mouths 
alone.  The  study  of  the  mode  of  occurrence  of  many  caverns  now  open 
to  the  surface,  shows  us  that  in  cases  of  total  submergence,  not  only 
may  they  be  filled  from  above  by  fragments  of  rock  and  animals  pre- 
viously falling  into  them,  and  with  the  settlement  of  mud,  sand,  frag- 
ments of  rock,  and  even  pebbles,  but  also  by  the  carcases  of  animals 
then  swept  in. 

In  examining  ossiferous  caverns,  it  is  needful  that  an  observer  very 
carefully  studies  the  kind  of  foreign  detrital  matter  introduced  into 
them,  either  occurring  amid  the  bones  and  fragments  of  the  rock  in 
which  the  cave  is  formed,  and  constituting  layers  or  beds,  or  which 
may  be  strewed  about.  Let  us  suppose  that  in  a  valley,  v,  of  which 
the  following  sketch  is  a  section  (fig.  108),  two  ossiferous  caverns,  a  and 
bj  occur  on  the  side  of  the  hill,  c,  a  river,  r,  being  of  sufficient  size  to 
bring  down  mud,  sand,  and  gravel,  especially  during  floods.  The  lower 
cavern,  b,  would  from  this  cause  be  exposed  to  deposits,  enveloping  the 
bones  of  mammals  which  there  occurred,  floods  from  time  to  time  sur- 
prising and  killing  animals  suddenly  caught  by  them  in  it.  This  would 
not  be  the  case  with  the  higher  cavern  out  of  the  reach  of  such  fluviatile 
action  and  deposits.  If  the  surface  of  the  land  had  been  disposed  much 
as  we  now  find  it,  anterior  to  a  submergence  beneath  water  (a  suppo- 
sition by  no  means  necessary),  both  these  caverns  may  have  had  detritus 


308      DEPOSITS    IN    SUBTERRANEAN    RIVER    CHANNELS. 

introduced  into  them,  as  previously  noticed,  whatever  additions  may 
have  been  made  to  the  lower  cave,  6,  by  bones  or  detritus  from  the 
action  of  the  river,  r.  As  pebbles  of  fair  size  afford  evidence  which 

Fig.  108. 


finer  sediment  may  not,  it  is  always  important  to  collect  and  very  care- 
fully examine  any  found  in  ossiferous  caves,  as  from  them  some  con- 
clusion may  be  formed  as  to  the  direction  whence  moving  water  may 
have  carried  them,  either  from  their  parent  rocks,  or  from  any  gravel 
or  shingle  accumulation  where,  for  a  time,  they  may  have  been 
stationary.* 

Much  and  very  proper  stress  has  been  laid  upon  the  accumulation  of 
bones  with  mud,  sand,  gravel,  and  fragments  of  rock  in  those  subter- 
ranean and  cavernous  channels  through  which  streams  and  rivers  so 
often  pass  in  limestone  districts.  Into  these,  animals  surprised  by 
floods  are  often  carried,  and  from  them  are  seldom  known  to  emerge, 
the  passages  being  commonly  so  complicated,  that  even  inferring  suffi- 
cient space  for  the  bodies  to  pass  through,  the  intricacies  and  vertical 
arrangements  of  the  channel  are  such  that  the  osseous  remains  of  the 
animals,  whatever  may  become  of  the  flesh,  whether  eaten  or  decom- 
posed, remain  and  accumulate  in  these  cavernous  passages.  In  some 
tropical  and  limestone  countries,  as  for  instance  in  Jamaica,  it  is  very 
instructive  to  watch  the  effects  of  a  sudden  flood  hurrying  forward  a 
mass  of  turbid  water,  and,  occasionally,  various  creatures  into  great 

*  As  regards  the  contents  of  the  ossiferous  cave  of  Kent's  Hole,  often  mentioned 
above,  Dr.  Buckland  informed  me  that  Mr.  M'Enery  found  rounded  portions  of  granite 
and  greenstone  beneath  the  stalagmitic  crust,  as  also  fragments  of  sandstone  and  slate, 
some  of  them  rolled.  The  cave  itself  is  in  limestone,  the  sandstone,  slate,  and  green- 
stone rocks  associated  with  it  in  the  district,  but  granite  does  not  occur  nearer  than 
Dartmoor,  13  miles  distant.  According  also  to  Colonel  Mudge  (Proceedings  of  the 
Geological  Society,  vol.  ii.  p.  400),  the  pebbles  discovered  in  the  ossiferous  bed  at 
Yealm  Bridge  Cave,  six  miles  from  Plymouth  (five  distinct  deposits  being  noticed,  the 
highest  only  containing  bones),  "are  apparently  derived  from  the  confines  of  Dartmoor, 
and  differ  from  those  contained  in  the  bed  of  the  Yealm."  The  remains  found  in  this 
bed,  34  feet  thick,  were  those  of  the  elephant,  rhinoceros,  horse,  ox,  hyaena,  sheep, 
dog,  wolf,  fox,  bear,  hare,  water-rat,  and  a  bird  of  considerable  size.  Many  of  the 
bones  were  "splintered,  chipped,  and  gnawed,"  and  coprolites  were  found  in  the 
ossiferous  bed.  Pebbles  are  found  in  several  ossiferous  caverns. 


DEPOSITS    IN    SUBTERRANEAN    RIVER    CHANNELS.       309 

sink-holes.*  In  more  temperate  climates,  a  sudden  flood  often  sur- 
prises animals,  occasionally  large,  in  low  grounds  near  the  entrances 
into  cavernous  channels,  and,  according  to  the  capacity  of  the  channel 
and  the  size  of  the  entrance  into  it,  will  depend  the  ready  disappear- 
ance of  the  animals  thus  swept  onwards.  Sometimes  the  volume  of 
water  is  so  great,  that  they  are  not  readily  engulfed,  whirling  about  at 
the  entrance,  then  beneath  the  level  of  the  water  ponded  back,  until 
the  flood  somewhat  subsiding,  the  bodies  of  the  animals  enter  and  be- 
come lost  in  the  caverns. 

Even  under  the  somewhat  simple  conditions  of  such  cavernous  chan- 
nels, as  shown  in  the  section  beneath  (fig.  109),  it  will  be  obvious  that 


not  only  detrital  matter  and  fluviatile  molluscs,  but  also  terrestrial 
mammals  may  be  introduced  into  a  cavern  5,  <?,  d,  and  the  finer  sedi- 
ment, held  in  mechanical  suspension,  alone  emerge,  supposing  the 
channel  to  be  sufficiently  short  and  the  water  be  kept  in  the  proper 
agitation  throughout.  Under  ordinary  conditions,  a  large  amount  of 
the  elongated  cavern  would  be  beneath  the  level  at  which  the  water 
emerged  at  d,  so  that  the  heavier  sediment  would  settle  at  the  bottom 
of  the  inequalities,  such  as  /  and  g.  The  bodies  of  animals  would 
scarcely  be  forced  through  even  so  comparatively  ample  a  passage  as 
that  above  represented,  the  general  form  of  the  channel,  and  especially 
the  depending  portions  of  the  roof,  c,  c,  c,  opposing  obstacles  to  their 
transport  outwards  to  d.  Should  the  impediments  to  the  passage  of  the 
water  gradually  accumulate  (and  among  these  large  falls  of  fragments 
from  the  roof  would  be  important),  an  outlet  of  this  kind  may  be  even 
completely  stopped.  If  we  suppose  a  submergence  of  the  land,  such  a 
channel  might  also  be  completely  filled  with  detritus,  so  that  upon  a 
subsequent  emergence,  the  drainage  formerly  effected  through  the  pas- 
sage, 5,  d,  being  blocked  up,  it  passed  elsewhere,  and  the  former  out- 

*  With  the  various  land  molluscs  caught  by  heavy,  and  often  sudden  tropical  rains, 
and  swept  into  these  sink-holes,  land,  hermit,  or  soldier  crabs  are  in  certain  localities 
also  carried  in,  sometimes  bearing  marine  univalve  shells  which  they  have  brought  with 
them,  occasionally  many  miles,  during  their  migrations  to  and  from  the  sea-coast.  We 
have  seen  these  crustaceans  at  12  to  14  miles  from  the  sea  in  the  limestone  districts, 
and  can  confirm  the  statement  of  Mr.  R.  C.  Taylor  (Notes  on  the  Geology  of  Cuba, 
Philosophical  Magazine,  1837),  respecting  their  habits  as  noticed  by  him  in  similar  dis- 
tricts of  Cuba.  Marine  shells  may  thus  readily  be  included  in  the  stalagmites  of  the 
caverns,  often  of  large  size,  common  in  the  white  limestone  portions  of  Jamaica. 


310  OSSIFEROUS    CAVES    WITHOUT    STALAGMITE. 

let,  dj  might  form  the  entrance  into  an  ossiferous  cavern  on  the  lower 
side  of  a  hill. 

Many  caverns  convey  out  waters  which  have  accumulated  amid  the 
rocks  of  which  they  form  a  part,  especially  in  limestone  districts,  not 
forming  a  continuous  subterranean  channel  for  a  river,  entering  at  a 
higher  level.  These  streams  sometimes  choke  up  parts  of  the  cave,  so 
that  they  cannot  be  passed  during  a  rise  of  water,  though  communi- 
cating between  chambers  still  above  the  level  of  that  water.  Such  sub- 
terranean streams  occasionally  transport  sedimentary  matter,  and  leave 
it  in  situations  whence  it  is  not  easily  detached,  and  where  it  may  cover 
up  the  osseous  remains  of  animals,  or  the  works  of  men,  even  the  bones 
of  the  latter  also.  This  would  appear  to  have  been  the  case  as  respects 
the  mode  of  occurrence  of  the  human  remains  observed  by  Dr.  Buck- 
land,  in  one  of  the  branch  chambers  at  Wokey  Hole,  in  the  Mendip 
Hills,  near  Wells.  Human  teeth  and  fragments  of  bones  were  "dis- 
persed through  reddish  mud  and  clay,  and  some  of  them  united  with  it 
by  stalagmite  into  a  firm  osseous  breccia."*  Among  the  loose  bones 
he  found  "a  small  piece  of  a  coarse  sepulchral  urn."  The  mud  and 
clay  seemed  clearly  to  have,  been  derived  from  the  adjacent  subterranean 
river,  which,  in  its  overflowing,  reached  this  chamber. 

Ossiferous  caverns  are  sometimes  entirely  destitute  of  stalagmite, 
forming  a  level  crust  over  a  floor,  or  even  any  deposits  or  incrustations 
of  the  kind.  The  ossiferous  mass  found  in  Banwell  Cave,  Mendip  Hills, 
was  composed  of  little  else  than  fragments  of  the  limestone  in  which 
the  cave  occurs,  mingled  with  the  bones  of  the  cavern  bear  and  other 
extinct  mammals.  Similar  caves  have  been  found  elsewhere,  the  bones 
and  fragments  of  rock  only  requiring,  as  M.  Therria  long  since  re- 
marked, a  cementing  substance,  such  as  carbonate  of  lime,  indurated 
clay,  or  other  mineral  matter,  to  form  those  accumulations  known  as 
osseous  breccia*.}  As  caverns  which  may  have  been  the  dens  of  pre- 
daceous  mammals,  occasionally  present  clefts  and  fissures  filled  in  this 
manner,  it  is  important  to  ascertain,  when  such  are  exposed  to  view  by 
the  cutting  back  of  quarries,  whether  they  are  merely  clefts  and  fissures, 
such  as  represented  beneath  (fig.  110),  and  which  have  probably  never 
formed  a  portion  of  a  cavern,  properly  so  called,  or  are  parts  of  an 
ossiferous  cave,  which  further  researches  may  expose. 

In  this  section  (fig.  110),  a,  6,  and  c,  represent  fissures  filled  with 
ossiferous  breccia,  an  offset  at  /,  giving  a  horizontal  character  to  part 

*  "Reliquioo  Diluviante,"  p.  165. 

f  "Mdm.  de  la  Socie'te'  d'Histoire  Naturello  de  Strasbourg,"  vol.  i.,  whorem  M. 
Therria  describes  the  Grotte  de  Fouvent,  in  which,  according  to  Cuvier,  the  remains  of 
the  elephant,  rhinoceros,  hyoona,  cave  bear,  horse,  ox,  and  a  large  feline  animal,  were 
found.  These  remains  were  considered  to  have  entered  through  a  cleft  in  the  rock, 
laid  open  by  quarrying  back  a  limestone.  The  cave  was  completely  filled  by  bones,  a 
yellow  marl,  and  angular  fragments  of  the  limestone  and  rocks  of  the  vicinity. 


OSSEOUS    BRECCIA    IN    VARIOUS    COUNTRIES.  311 

of  one  of  them.  In  limestone  districts,  and  in  such  countries,  clefts 
containing  osseous  breccias  are  the  most  common ;  a  reddish  and  cal- 
careous cement  is  not  unfrequent,  though  not  constant,  the  hardness 


and  consolidation  of  the  general  accumulation  being  very  variable. 
The  red  colour  and  substance  usually  arises  from  the  decomposition  of 
limestones,  in  or  near  which  the  fissures  occur,  as  has  long  since  (1834) 
been  remarked  by  M.  de  Cristol.*  The  carbonate  of  lime  being  wholly, 
or  in  great  part  removed  in  solution  (the  needful  carbonic  acid  being 
present),  the  remaining  portions  of  the  limestone,  comprising  any  car- 
bonate of  lime  which  may  have  been  left,  alumina,  silica,  or  other  sub- 
stances, including  iron,  become  coloured  by  the  peroxidation  of  the 
latter,  as  may  be  frequently  observed  in  the  soil  of  limestone  districts, 
particularly  among  the  carboniferous  limestone  countries  of  the  British 
Islands  and  Belgium.  These  fissures,  when  clearly  unconnected  with 
caves  (more  or  less  horizontal  in  parts),  are  inferred  to  have  been  filled 
by  the  falling  in  of  animals,  f 

Osseous  breccias  are  found,  as  might  be  expected,  in  different  coun- 
tries ;  their  contents  variable,  and  pointing  to  differences  in  the  time, 
though  always  at  comparatively  recent  geological  periods,  when  they 
were  accumulated ;  indeed,  such  could  scarcely  but  have  happened  with 
these  ossiferous  accumulations,  whether  found  in  caverns  or  in  fissures, 
since  we  have  reason  to  infer  that  the  bones  of  animals  are  now  being 
gathered  together  in  similar  situations  in  different  parts  of  the  world.  J 

*  Observations  Generales  sur  les  Breches  Osseuses,  Montpellier,  1834. 

f  With  respect  to  the  falling  in  of  animals  into  fissures,  Dr.  Buckland,  directing 
attention  .to  this  subject  in  1823  (Reliquiae  Diluvianse,  pp.  56  and  78),  mentions  that 
animals  now  fall  into  a  fissure  in  Duncombe  Park,  Yorkshire,  as  it  "lies  like  a  pitfall 
across  the  path  of  animals  which  pass  that  way."  This  fissure  was  found  to  contain 
the  skeletons  of  dogs,  sheep,  deer,  goats,  and  hogs,  "each  on  the  spot  on  which  it 
actually  perished."  It  is  remarked,  that  if  a  body  of  water  entered  this  fissure,  the 
bones  and  the  fragments  of  the  limestone  in  which  it  occurs  would  be  all  washed  to  the 
bottom.  Dr.  Buckland  also  referred  to  the  loss  of  cattle  down  fissures,  and  into  caves, 
experienced  by  the  farmers  in  the  limestone  districts  of  Derbyshire,  Monmouthshire, 
and  Glamorganshire. 

J  Ossiferous  caverns  and  fissures  are  found  in  various  parts  of  Europe.     They  have 

/  been  discovered  in  England,  Spain,  France,  Italy,  Sardinia,  Dalmatia,  Croatia,  Car- 

niola,  Styria,  Austria,  Hungary,  Poland,  and  Germany.    In  the  latter,  bone  caves  have 

long  been  well  known,  and  Cuvier  pointed  out,  in  1812,  that  they  extended  over  200 

leagues  (Ossemens  Fossiles,  Ire  Ed.)    In  1823  Dr.  Buckland  took  a  general  view  of  the 


312  OSSEOUS    BRECCIA     IN    VAKIOUS     COUNTRIES. 

It  is  only  as  regards  the  possible  or  probable  connexion  with  the  in- 
ferred interval  of  increased  cold,  at  a  particular  time  in  the  northern 
hemisphere,  that  ossiferous  caves  and  breccias  are  here  noticed.  Under 
the  hypothesis  of  this  increase  of  cold  being  accompanied  by  the  sub- 
mergence of  a  large  portion  of  Europe,  affecting  the  area  above  men- 
tioned, such  submergence  being  gradual,  perhaps  with  oscillations, 
unequal  in  different  portions  of  the  general  area,  and  followed  by  a  rise 
of  the  same  area,  also  perhaps  with  oscillations,*  and  with  very  con- 
subject  (Reliquiae  Diluvianse)  as  far  as  it  was  then  known.  In  his  History  of  British 
Fossil  Mammals  and  Birds,  Professor  Owen  brought  it  up,  with  much  new  information, 
to  1846,  more  especially  as  regards  the  osseous  remains  of  this  kind  discovered  in  the 
British  Islands;  and,  in  1848,  the  Vicomte  d'Archiac  (Histoire  des  Progres  de  la 
Geologic,  vol.  ii.,  Ire  Partie)  published  abstract  statements  of  the  knowledge  obtained 
from  1834  to  that  date  respecting  ossiferous  caves  and  fissures,  and  of  their  connexion 
with  the  superficial  deposits  of  the  more  recent  geological  accumulations  in  various 
parts  of  the  world.  Australia  has  furnished  its  ossiferous  caves  and  breccias,  the  re- 
mains of  the  animals  detected  in  them  being  chiefly  of  the  marsupial  character,  one  so 
strongly  marking  the  mammalia  of  that  land  in  the  present  day.  Part  of  the  species 
of  mammals,  the  remains  of  which  are  thus  obtained,  are  extinct,  while  others  still  live 
in  Australia. 

*  As  regards  oscillations,  when  the  caves  were  situated  at  a  small  elevation  above  a 
tideway  in  an  estuary,  or  at  such  a  distance  up  a  river,  tidal  at  the  lower  end,  that  a 
change  in  the  height  of  the  tides  would  alter  the  previous  level  of  the  river,  there  could 
be  oscillations  at  one  time  permitting  a  cave  to  be  inhabited  by  predaceous  mammals, 
at  others  so  filling  it  with  water  that  they  retreated  from  it.  Where  there  are  alterna- 
tions of  stalagmitic  floors,  covering  even  surfaces  with  bone  accumulations,  as  is  stated 
to  have  been  the  case  at  Chockier,  on  the  banks  of  the  Meuse,  about  two  leagues  from 
Lie'ge,  it  is  always  desirable  to  consider  the  extent  to  which  the  presence  or  absence  of 
sufficient  water  in  the  lower  parts  of  caverns  may  have  produced  such  alternations, 
the  roof  and  sides  always  furnishing  the  needful  carbonate  of  lime,  at  one  time  form- 
ing the  stalagmitic  crusts,  at  another  being  too  much  dispersed  in  the  water  to  afford 
a  deposit. 

Though  the  osseous  breccia  beneath  the^  Castle  Hill  at  Nice,  of  which  the  following 
(fig.  Ill)  is  a  section  (made  in  1827),  may  not  be  immediately  connected  with  the 
northern  movement  of  land  noticed  in  the  text,  it  may  yet  assist  the  observer,  as  show- 
ing the  kind  of  evidence  which  may  occasionally  present  itself.     The  face  of  the 
quarry,   q,   had  been  cut  back   beyond   the   fissure,   the 
- 111<  sides  of  which  were  bored  at  I,  I,  I,  by  the  common  Lif/m- 

domus,  now  inhabiting  that  part  of  the  Mediterranean,  so 
that  it  was  once  an  open  fissure,  beneath  the  level  of  the 
sea.  This  fissure,  up  to  the  lip  of  the  cavity  on  that  side, 
c,  then  became  filled  with  rolled  pebbles,  chiefly  trans- 
ported from  a  distance,  and  afterwards  cemented  by  cal- 
careous matter.  Above  this  was  the  osseous  brecci 
rising  up  to  the  top  of  the  fissure  on  the  side  a,  but 
whether  this  was  accumulated,  like  most  osseous  breccias, 
on  dry  land,  is  not  so  clear,  marine  as  well  as  terrestrial 
shells  being  mingled  with  it.  Osseous  breccias  are  found 
in  the  same  vicinity,  up  to  the  height  of  at  least  500  feet 
above  the  level  of  the  Mediterranean,  and  some  breccias, 
not  ossiferous,  but  otherwise  similar,  solely  contain  marine 

remains,  so  that  perhaps  these  fissures  may  have  been  partly  filled  on  dry  land,  and 
partly  in  the  sea.  At  Cagliari,  Sardinia,  the  remains  of  a  Mytilus  are  found  mixed 
with  osseous  breccia  at  150  feet  above  the  sea. 


RETREAT    AND    ADVANCE    OF    EXTINCT    MAMMALS.         313 

siderable  modifications  of  its  surface,  there  are  apparently  conditions 
for  much  movement  amid  the  terrestrial  animals  of  this  portion  of  the 
northern  hemisphere.  They  would  be  sometimes  isolated  and  destroyed, 
as,  by  continued  depression,  the  sea  passed  over  their  feeding-grounds ; 
at  others,  they  would  retreat  to  regions  where  they  could,  for  a  time, 
establish  themselves  and  increase,  some  species  being  better  able  to 
preserve  themselves  than  others.  Upon  a  rise  of  the  sea  bottom,  and 
the  consequent  formation  of  new  lands,  migrations  would  be  effected, 
according  to  the  relative  levels  of  these  lands,  as  regards  the  sea,  and 
as  passages  for  the  movement  of  certain  animals  would  sometimes  pre- 
sent themselves  more  favourably  in  one  direction  than  in  another.* 
Evidence  of  the  accumulation  of  the  osseous  portions  of  elephants, 
rhinoceroses,  and  other  animals  of  several  of  the  same  species,  the  re- 
mains of  which  occur  in  accumulations  beneath  those  formed  at  the  cold 
or  "glacial"  time,  are  considered  to  have  been  detected  also  above 
them,  together  with  the  remains  of  some  mammals  not  previously  in- 
habiting the  area  of  the  British  Islands,  and  adjacent  portions  of  the 
continent  of  Europe.  This  subject  offers  a  fertile  field  for  the  labours 
of  an  observer.  Though  much  may  have  been  accomplished,  much  re- 
mains to  be  done,  and  it  will  require  his  especial  care  to  see,  that  amid 
the  new  lakes  and  river  channels  formed,  when  the  ground  took  that 
general  configuration  which  we  now  find,  a  rearrangement  of  bones, 
washed  out  of  the  older  deposits  containing  remains  of  the  Elephas 
primigenius.  Rhinoceros  tichorhinus,  and  their  contemporary  mammals, 
and  carried  into  the  newer  lacustrine  and  fluviatile  beds,  may  not  occa- 
sionally be  such  as  to  mingle  the  osseous  remains  of  the  species  of  one 
time  with  those  of  another. 

As  to  ossiferous  caves,  several  which  may  have  been  closed  at  their 
mouths  during  a  time  of  submergence,  may  have  been  reopened  by  the 
subsequent  removal  of  the  detrital  matter  then  accumulated,  so  that 
animals  of  the  later  time  and  of  suitable  habits  again  entered  or  dragged 
their  prey  into  them ;  other  caverns  being  laid  open  for  the  first  time 

*  Mr.  John  Morris,  when  noticing  the  occurrence  of  mammalian  remains  at  Brent- 
ford (Athenaeum,  Pro.  Geol.  Society,  5  Dec.  1849),  points  out  as  important  "that  it  is 
generally  along  those  valleys  where  the  present  drainage  of  the  country  is  effected  that 
we  find  the  most  extensive  deposits  of  mammalian  remains  and  recent  shells,  and  con- 
sequently that  very  little  alteration  can  have  taken  place  in  the  physical  configuration 
of  the  country  since  their  deposition."  The  remains  discovered  at  Brentford,  and 
giving  rise  to  these  observations,  were  those  of  the  elephant,  rhinoceros,  hippopotamus, 
auroch,  short-horned  ox,  red  deer,  rein  deer,  and  great  cave  tiger  or  lion.  A  few 
shells  of  recent  fresh-water  species  were  found  at  the  same  time.  As  regards  the  ex- 
istence of  land  and  fresh-water  molluscs,  of  the  kinds  still  inhabiting  Britain,  Mr. 
Searles  Wood,  in  his  remarks  "On  the  Age  of  the  Upper  Tertiaries  in  England" 
(Athenamm,  Geol.  Society,  5  Dec.  1849),  infers,  from  a  list  of  the  mammals  at  different 
geological  periods,  "that  a  race  of  animals  has  arisen  and  departed  whilst  the  land 
and  fresh-water  mollusca  have  lived  on  unaltered,"  and  also  that  "fresh-water  mollusca 
have  a  greater  specific  longevity  than  marine." 


314 


INEQUALITIES    COVERED    BY    GRAVEL. 


for  the  entrance  or  fall  of  mammals,  from  the  removal  of  the  rock  or 
other  deposits  over  or  against  them,  by  the  ordinary  marine  causes  of 
denudation,  during  a  depression  and  subsequent  upheaval  of  the  land. 
Many  an  equality  is  covered  over  by  gravels,  concealing  former  inequa- 
lities, amid  which  there  may  be  caves  and  fissures,  ossiferous  or  not, 
according  to  circumstances.  The  accompanying  section  (Fig.  112)  is 

Fig.  112. 


one  of  a  quarry  wherein  limestone  5,  5,  presenting  a  very  irregular  out- 
line, is  covered  over  by  gravels  #,  a,  giving  a  general  rounded  outline 
to  the  surface.  The  quarry  is  situated  at  Waddon  Barton,  near  Chud- 
leigh,  Devon,  and  the  limestone  is  of  the  kind  (Devonian)  wherein  several 
caverns  and  fissures  of  the  district  are  found  (Kent's  Hole,  Yealm  Bridge, 
Plymouth,  and  elsewhere),  partly  ossiferous  and  partly  without  bones. 
Amid  such  varied  modifications  of  surface  as  would  follow  submergence 
beneath,  or  emergence  from  seas,  at  one  time  perhaps  bounding  the 
area  of  the  British  Islands  and  adjacent  portions  of  the  Continent,  as 
represented  (figs.  65  and  99)  by  a  line  of  depth,  now  no  more  than 
600  feet  beneath  the  surface  of  the  Atlantic ;  at  another  cutting  exist- 
ing highlands  at  about  1000  or  1300  feet  above  that  level,  and  finally 
producing  the  present  distribution  of  land  and  water  in  "Western  Europe, 
it  could  scarcely  happen  but  that  caves  and  fissures  were  placed  under 
many  modifications  of  condition.  Not  only  may  they  have  been  closed 
at  one  time,  and  open  at  another,  never  completely  blocked  up,  or  pre- 
viously laid  open,  as  above  noticed,*  but  they  may  also  be  cut  back  in 

*  Mining  operations  in  limestone  districts,  such,  for  instance,  as  that  of  Derbyshire, 
afford  numerous  instances  of  the  irregular  distribution  of  caverns,  so  that  new  surfaces 
of  land  being  produced,  changes  of  this  kind  would  follow.  The  Speedwell  Mine  in  that 
county  is  a  good  example  of  a  lofty  cave,  cut  into  while  driving  a  mining  tunnel,  this 
cavern  evidently  communicating  with  the  great  cave  of  the  Peak  at  Castleton,  since 
the  rubbish  from  the  one  gets  drifted  into  the  other  by  the  water  passing  through  a 
series  of  subterranean  channels.  It  was  in  1822,  while  working  the  Dream  lead-mine, 
near  Wirksworth,  in  the  same  district,  that  a  cavernous  termination  to  a  fissure,  com- 
municating with  the  surface,  was  discovered ;  one  which  was  found  by  Dr.  Buckland  to  con- 


MODE    OF    OCCURRENCE    OF    MASTODON    REMAINS.         315 

such  a  manner  with  the  adjacent  rocks,  that  though  they  contain  the 
osseous  remains  of  earlier  times,  they  are  now  apparently  unfit,  or  at 
least  most  inconveniently  situated,  for  the  retreat  or  dens  of  predaceous 
mammals,  or  for  trap-falls  to  them  and  the  animals  on  which  they  lived.* 
With  regard  to  the  migration  of  the  great  mammals  of  the  northern 
hemisphere  immediately  before,  during,  and  after  the  time  when  the 
cold  is  inferred  to  have  been  such  as  above  noticed,  and  when,  by  means 
of  ice,  huge  masses  of  rock  and  other  detritus  were  transported,  and 
thrown  down  on  sea  bottoms,  parts  of  which,  upraised,  now  constitute 
a  large  portion  of  the  dry  land  of  Northern  Europe,  Asia,  and  America, 
it  becomes  interesting  for  the  observer  to  consider  the  mode  of  occur- 
rence of  the  remains  of  the  mastodon,  a  genus  of  great  proboscidian 
mammals,  approximating  to,  and  of  about  the  bulk  and  general  form  of 
the  elephant.  Those  discovered  in  England  have  not  been  numerous, 
and  have  hitherto  only  been  obtained  from  accumulations  in  Norfolk,f 
formed  anterior  to  those,  in  the  British  Islands,  in  which  are  found  the 
remains  of  the  Elephas  primigenius,  the  Rhinoceros  tichorhinus,  and 

tain  among  other  osseous  remains,  those  of  a  Rhinoceros  tichorhinus  so  placed  as  to  leave 
little  doubt  that  they  constituted  the  skeleton  of  an  animal  which  had  fallen  from  above 
through  the  fissure. — See  Reliquise  Diluvianse,  p.  61-67,  and  Plate  X. 

*  Dr.  Buckland,  in  1823  (Reliquiae  Diluvianse,  p.  95),  describing  the  Paviland  Cave, 
occurring  in  the  face  of  a  limestone  cliff  near  Swansea,  remarks  on  this  kind  of  denu- 
dation, observing  that  these  caves  are  analogous  to  those  "in  the  equally  vertical  and 
not  less  lofty  cliffs  that  flank  the  inland  valleys  of  the  Avon  at  Clifton  (Bristol),  of  the 
Weissent  River  at  Muggendorf,  of  the  Bode  River  at  Rubeland  in  the  Hartz,  and  of  the 
Mur  at  Peckaw,  near  Gratz,  in  Styria;"  all  these  being  the  truncated  portions  of  ossi- 
ferous  caverns  cut  back  by  denuding  influences. 

f  The  "Crag,"  as  these  deposits  are  usually  termed,  is  an  accumulation  of  gravel, 
sand,  and  clay,  with  often  an  abundance  of  shells,  extending  over  parts  of  Norfolk, 
Suffolk,  and  Essex.  It,  and  deposits  above  it,  have  been  described  by  Mr.  Taylor 
(Geology  of  East  Norfolk,  1827),  Mr.  Woodward  (Geology  of  Norfolk,  1833),  Mr.  Charles- 
worth  (London  and  Edin.  Phil.  Magazine,  1835;  British  Association,  1836,  &c.),  Sir 
Charles  Lyell  (Mag.  Nat.  Hist.,  new.series,  vol.  iii.,  1839;  London  and  Edin.  Phil.  Mag., 
1840),  Mr.  Searles  Wood  (Catalogue  of  Craig  Shells,  Mag.  Nat.  Hist.  1840-42),  Mr. 
Trimmer  (Geology  of  Norfolk,  Journal  of  the  Agricultural  Society,  vol.  vii.),  and  others. 
The  lower  part  of  these  deposits  is  known  as  the  Coralline  Crag,  from  containing  nume- 
rous fossil  corals,  and  400  species  of  shells  are  stated  to  be  found  in  it.  Upon  this  reposes 
the  Red  or  Norfolk  Crag,  in  which  300  species  of  shells  have  been  found,  about  half  of  the 
latter  occurring  also  in  the  coralline  crag.  Above  these  are  beds  known  as  the  Mammilife- 
rous,  or  Fluvio-marine  Crag,  containing  fresh-water  accumulations.  In  connexion  with 
the  latter,  and  stated  to  be  rooted  upon  it,  there  are  the  remains  of  a  forest  of  fir-trees. 
Mr.  Trimmer  also  notices  a  marine  deposit  between  the  fresh-water  beds  and  the  suc- 
ceeding mass  of  boulder  clay,  the  parts  of  which  are  so  strangely  contorted  and  twisted, 
the  effects,  it  has  been  inferred,  of  the  action  of  grounded  icebergs  and  coast  ice  on  a 
sea  bottom  or  coast.  Though  there  have  been  doubts  expressed  as  to  the  beds  to  which 
some  of  the  mammalian  remains  should  be  referred,  it  seems  agreed  that  those  of  the 
Mastodon  angustideus  occur  in  the  fluvio-marine  or  fresh-water  accumulations,  which  are 
also  remarkable  for  containing  many  existing  shells.  Dr.  Mantell  mentions  (Wonders 
of  Geology,  6th  edit.,  1848,  vol.  i.,  p.  224),  thirteen  teeth  of  the  mastodon  as  having 
been  obtained  from  the  latter. 


316      OCCURRENCE    OF    THE    REMAINS    OP    THE    MAMMOTH 

other  mammals  of  that  time.     As  far  as  can  be  inferred  from  negative 
evidence,  the  Mastodon  angustideus,  the  species  which  inhabited  the 
British  area  and  parts  of  Europe,*  had  passed  away,  at  least  in  the 
former,  before  the  mammoth  appeared.     Wherever  this  elephant  may 
have  retreated  during  the  supposed  greater  cold  in  the  higher  latitudes 
of  the  northern  hemisphere,  it  passed,  in  its  subsequent  migration,  into 
North  America,  apparently  roaming  amid  the  same  districts   with  a 
gigantic  mastodon  (M.  giganteus),  if  the  inference  be  correct,  that  the 
dispersion  of  the  erratic  blocks  and  associated  detritus  of  that  region 
was  contemporaneous  with  that  over  northern  Europe.     At  all  events, 
the  surface  on  which  both  these  mammals  fed,  appears  certainly  to  have 
been  that  which  resulted  from  the  dispersion  of  such  accumulations  in 
North  America,  both  animals  sometimes  lost  in  boggy  ground,  as  many 
an  animal  now  is  at  the  present  day,  and  there  perishing,  their  bones, 
after  the  decay  of  the  flesh,  preserved  in  a  certain  amount  of  original 
arrangement.     If  it  should  eventually  be  found  that  the  remains  of  the 
mammoth  do  not  occur  in  lower  deposits  of  North  America,  that  the 
North  American  is  certainly  the  same  elephant  with  the  ElepTias  primi- 
genius,  and  the  erratic  blocks  and  associated  drift  of  both  regions  are 
really  contemporaneous,  there  will  have  been  evidence  of  a  remarkable 
migration  of  the  mammoth  from  the  west  to  the  east,  after  an  interval 
of  increased  cold  in  the  northern  regions,  and  a  submergence  of  them 
beneath  the  sea.     On  the  east  the  mammoths  would  have  become  asso- 
ciated with  a  species  of  a  huge  proboscidian  which  had  disappeared,  as 
a  genus,  from  Western  Europe,  prior  to  their  existence  there,  but  which 
still  continued  to  flourish  on  the  continent  of  America.     The  remains  of 
the  mastodon  are  stated  to  be  found  amid  the  superficial  deposits  of 
that  continent  as  far  as  latitude  66°  N.,  thus  bringing  them  within  the 
climates  apparently  not  unfavourable  to  the  mammoth,  though,  as  Pro- 
fessor Owen  has  remarked,  "  the  metropolis  of  the  Mastodon  giganteus 
in  the  United  States,  like  that  of  the  Mastodon  angustideus  in  Europe, 
lies  in  a  more  temperate  zone,  and  we  have  no  evidence  that  any  species 
was  specially  adapted,  like  the  mammoth,  for  braving  the  rigours  of  an 
Arctic  winter,  "f 

The  observer  will  readily  perceive  that  much  requiring  great  care  is 

*  The  remains  of  the  Mastodon  angustideus  have  been  discovered  in  France,  Germany, 
and  Italy. 

f  "  Hist,  of  British  Fossil  Mammals,"  p.  297. 

Respecting  the  remains  of  the  Mastodon  giganteus,  Bigbone  Lick,  in  Northern  Kentucky, 
and  about  seven  miles  up  a  tributary  of  the  Ohio,  has  long  been  celebrated  for  them, 
and  they  have  also  been  discovered  in  several  other  localities.  The  "  Lick"  is  so  called 
from  the  saline  springs  which  various  animals  frequent.  Even  the  contents  of  the 
stomach  of  the  Mastodon  giganteus  have  been  discovered,  containing  crushed  branches 
and  leaves,  grass,  and  a  reed  now  well  known  in  Virginia.  A  summary  of  the  know- 
ledge respecting  the  mode  of  occurrence  of  the  American  mastodons  will  be  found  in 
Sir  Charles  Lyell's  Travels  in  North  America.  In  his  Taper  (Proceedings  of  the  Geol. 
Society,  vol.  iv.  p.  36,  1843,)  on  the  Geological  Position  of  the  Mastodon  giganteum,  and 


RELATIVELY  TO  THOSE  OF  THE  MASTODON.      317 

needed  in  investigations  of  this  kind,  and  that,  when  endeavouring  to 
trace  the  paths  by  which  such  animals  may  have  migrated,  and  to  ascer- 
tain the  localities  from  whence,  after  retreating,  they  may  again  have, 
in  part,  been  dispersed,  districts  over  which,  during  the  lapse  of  the 
supposed  geological  time,  no  seas  have  passed,  are  of  no  slight  value. 
Hence,  among  other  objects  of  geological  interest,  the  region  of  extinct 
volcanoes  in  Central  France  is  important,  inasmuch  as  it  seems  to  have 
constituted  dry  land  during  a  range  of  time  when  several  animals  which 
once  lived  on  its  surface  became  extinct,  among  them  the  mammoth  and 
Rhinoceros  tichorhinus.  Amid  the  various  notices  of  the  remains  of 
mammals  found  in  situations  giving  them  geological  date,  may  be  men- 
tioned that  of  M.  Pomel,  wherein  he  describes  an  ossiferous  fissure  in  a 
lava  current  (near  Orbieres,  on  the  south  of  Clermont),  which  had  issued 
from  Gravenoire.  It  was  filled  with  volcanic  sand,  pulverulent  carbonate 
of  lime,  and  bones  which  are  stated  to  be  the  same  as  those  of  Coudes 
and  other  contemporaneous  accumulations,  containing  the  remains  of 
the  elephant,  Rhinoceros  tichorhinus,  horse,  ox,  &c.*  Land  shells,  of 
species  now  existing  in  the  district,  are  mentioned  by  M.  Pomel  as 
associated  with  these  ossiferous  deposits,  so  that  in  this  region  also,  as 
in  others  of  Europe  and  North  America,  great  mammals  have  become 
extinct,  while  land  and  fresh-water  molluscs,  living  with  them,  have  con- 
tinued to  exist  up  to  the  present  time. 

Volcanoes  and  their  Products. — Distributed  over  various  portions  of 
the  earth's  surface,  as  well  in  high  southern  and  northern  latitudes,  as 
in  temperate  and  tropical  regions ;  at  points  in  the  ocean  far  distant 
from  main  masses  of  dry  land,  as  well  as  upon  the  latter  themselves, 
free  communications  are  effected  between  the  interior  of  our  planet  and 
its  atmospheric  covering,  through  which  molten  rock,  cinders,  and  ashes 
are  ejected.  That  great  heat,  if  not  the  primary,  is  at  least  a  chief 
secondary  cause  by  which  these  mineral  substances  are  thus  upheaved, 
is  rendered  evident  by  the  high  temperature  of  the  bodies  thrown  out. 
The  molten  rock  flows  as  a  viscous  fluid,  and  retains  its  high  temperature 
for  a  long  succession  of  years ;  and  mineral  substances  are  volatilized, 

associated  Fossil  Remains  of  Bigbone  Lick,  Kentucky,  and  other  localities  in  the  United 
States  and  Canada,  he  pointed  out  that  "on  both  sides  of  the  Appalachian  Chain,  the 
fossil  shells,  whether  land  or  fresh-water,  accompanying  the  bones  of  the  mastodons, 
agree  with  species  of  mollusca  now  inhabiting  the  same  regions."  He  also  concluded 
that  "the  extinct  quadrupeds  before  alluded  to  in  the  United  States  (mastodon,  ele- 
phant, mylodon,  megatherium,  andmegalonix),  lived  after  the  deposition  of  the  northern 
drift ;  and  consequently  the  coldness  of  climate,  which  probably  coincided  in  date  with 
the  transportal  of  the  drift,  was  not,  as  some  pretend,  the  cause  of  their  extinction." 

*  Bull,  de  la  Soc.  de  France,  torn.  xiv.  1842-3.  A  very  instructive  lecture  was  given 
by  Sir  Charles  Lyell,  at  the  Royal  Institution  of  Great  Britain,  on  this  region,  in  1847, 
an  account  of  which  appeared  in  the  Athenaeum  of  the  time.  He  especially  called  atten- 
tion to  changes  which  its  mammals  had  undergone,  as  shown  by  the  osseous  remains 
preserved  in  the  alluviums  associated  with  volcanic  accumulations,  "no  flood  or  return 
of  the  ocean  having  disturbed  the  surface." 


318  VOLCANOES    AND    THEIR    PRODUCTS. 

which,  we  learn  from  our  laboratories  and  furnaces,  are  only  raised  to 
that  state  by  great  heat.  At  the  same  time  that  these  mineral  bodies  are 
ejected,  vapours  and  gases,  of  a  certain  marked  character,  are  expelled; 
so  that  by  carefully  combining  the  mode  of  occurrence  of  the  various 
products,  with  the  composition  of  the  substances  themselves,  an  observer, 
by  the  aid  of  sound  chemistry  and  physics,  may  hope  so  to  direct  his 
inquiries,  as  to  obtain  a  fair  insight  into  the  causes  and  effects  of  vol- 
canic action. 

As  regards  altitude  above  the  level  of  the  sea,  a  somewhat  fallacious 
mode  of  measurement,  inasmuch,  as  far  as  volcanic  products  are  con- 
cerned, they  may  be,  and  ^  are  accumulated  upon  rocks  of  a  different 
kind  at  various  heights  above  that  level,  doubtless  also  forming  the 
basis  of  many  volcanoes  beneath  it  on  the  floor  of  the  ocean,  the  highest 
known  volcanoes  constitute  such  an  insignificant  fraction  of  the  earth's 
radius,  that  when  phenomena  common  to  numerous  points  on  the  earth's 
surface  are  under  consideration,  variations  in  height  do  not  appear  to 
offer  any  great  aid  in  ascertaining  the  causes  of  volcanic  action,  though 
certain  of  its  effects  may  thereby  be  somewhat  modified,  especially  when 
volcanoes  rise  into  the  regions  of  perpetual  snow.  Cotopaxi,  the  cone  of 
which  rises,  in  the  Andes,  12  leagues  S.S.E.  from  Quito,  to  the  height 
of  somewhat  more  than  19,000  feet  above  the  sea,  forms  but  an  insigni- 
ficant part  of  3963  miles,  the  radius  of  the  earth,  not  constituting  so 
much  as  33  miles  of  that  radius,  or  about  yy^th  of  it.* 

With  respect  to  the  kind  of  openings  through  which  the  gaseous  and 
mineral  substances  are  vomited  forth,  there  has  existed  much  difference 
of  opinion.  While  some  geologists  infer  that  the  rocks  through  which 
the  volcanic  forces  found  vent  had  been  so  acted  upon  that  they  were 
upraised  in  a  dome-like  manner,  the  gaseous  products  bursting  through 
the  higher  part,  driving  the  lighter  substances  into  the  atmosphere,  if 
the  dome  were  elevated  into  it,  and  raising  the  viscous  molten  rock,  so 
that  it  flowed  out  of  the  orifice ;  others  consider  that  there  has  been  a 
simple  fissure  or  aperture  in  the  prior-formed  rocks  through  which  the 
volcanic  products  were  propelled,  the  solid  substances  accumulating 
round  the  vent,  so  that  a  deceptive  dome-like  appearance  is  presented. 

The  following  sections  (figs.  113  and  114)  may  assist  in  showing  the 
differences  between  the  "  craters  of  elevation,"  first  brought  under  notice 
by  M.  Von  Buch,  and  so  ably  illustrated  by  M.  Elie  de  Beaumont  and 
other  geologists,  and  the  "  craters  of  eruption,"  as  they  have  been 
termed.  Fig.  113  represents  a  portion  of  deposits  more  or  less  hori- 
zontally arranged,  fractured  and  upraised  in  a  conical  or  dome-shaped 

*  Humboldt  (Kosmos)  refers  to  the  relative  height  of  volcanoes  as  probably  of  conse- 
quence if  we  should  assume  their  seat  of  action  at  an  equal  depth  beneath  the  general 
surface  of  the  earth.  He  refers  to  eruptions  being  commonly  more  rare  from  lofty  than 
from  low  volcanoes,  enumerating  the  following: — Stromboli,  2318  feet  (English) ;  Gua- 
camayo  (Province  of  Quiros),  where  there  are  almost  daily  detonations ;  Vesuvius,  3876 
feet;  Etna,  10,870  feet;  Peak  of  Teneriffe,  12,175  feet;  and  Cotopaxi,  19,070  feet. 


CRATERS    OF    ELEVATION    AND    OF    ERUPTION. 


319 


mass,  a  portion  of  them,  g  a  c  b  h,  being  divided  and  rent  at  c,  so  that 
volcanic  forces,  pressing  through,  find  vent.  For  the  sake  of  illustra- 
tion, the  rocks  broken  are  assumed  to  be  accumulated  in  beds.  This  is 
by  no  means  essential,  the  mass  disrupted  may  have  been  composed  of 
certain  crystalline  rocks,  such  as  granite,  to  be  hereafter  noticed,  bear- 
ing no  marks  of  stratiform  arrangement.  If  now  ashes  and  cinders  be 

Fig.  113. 


thrown  out  of  this  vent,  and  accumulate  in  more  or  less  conical  layers, 
one  outside  the  other,  until  at  g  and  h  the  original  and  upheaved  beds 
are  concealed,  and  a  crater  presents  itself  at  v,  through  which  similar 
substances  continue  to  be  thrown,  it  may  be  very  difficult  to  distinguish 
such  an  arrangement  of  parts  from  those  eifected  by  the  propulsion  of 
similar  substances  through  a  simple  longitudinal  crack,  as  represented 
in  fig.  114.  In  this  section,  a  series  of  beds,  a  b  (for  more  contrast  re- 
Fig.  114. 


presented  as  upraised  in  a  mass,  and  as  all  sloping  or  dipping  in  one 
direction),  is  traversed  by  a  crack,  which,  though  it  divides  the  beds, 
has  not  been  accompanied  by  upheaval  or  depression  of  one  side  or  the 
other.  Through  this  vent,  c,  cinders  and  ashes  are  supposed  to  have 
accumulated  in  conical  layers,  as  before,  the  apex  crowned  by  the 
crater  v. 

It  will  be  obvious  that  in  both  cases,  if  the  volcanic  accumulations 
had  been  subaerial,  even  with  the  addition  of  the  flow  of  lava  currents, 
and  of  cracks  amid  the  ashes  and  cinders,  filled  with  molten  rock, 
(which  have  been  excluded  from  the  sections  to  render  them  more 


320  FOSSILIFEROUS     VOLCANIC    ASHES    AND 

simple,)  much  difficulty  would  arise  from  the  general  similarity  in  the 
arrangement  of  the  volcanic  products  exposed  to  sight,  unless  denuda- 
tion from  atmospheric  influences,  or  the  sinking  or  blowing  off  of  a 
large  part  of  the  volcano,  had  afforded  a  better  insight  into  the  general 
structure  of  the  mass,  so  that,  as  shown  by  fig.  113,  portions  of  sub- 
jacent and  tilted  beds  of  dissimilar  rocks  could  be  seen,  as  at  g  and  h, 
or  of  similar  volcanic  accumulations,  as  in  fig.  114. 

Evidence  of  a  better  kind  would  be  expected,  should  the  ashes, 
cinders,  and  molten  matter  have  been  accumulated  both  beneath  and 
above  a  sea  level,  the  action  of  the  breakers  denuding  the  general  mass, 
so  that  more  illustrative  sections  would  be  afforded.  Thus,  if  upraised 
above  the  sea  level,  the  original  dome  or  cone-shaped  rocks,  a,  b  (fig. 
113),  though  covered,  for  a  time,  by  a  mass  of  matter,  g  v  7i,  the  result  of  a 
high  state  of  activity  in  the  volcano,  may  finally  become  visible,  and 
afford  the  information  sought.  In  the  same  manner,  evidence  of 
another  kind  may  be  obtained,  as  regards  the  accumulation  from  simple 
volcanic  eruption,  by  marine  denudation,  as  shown  in  fig.  114.  In 
both  sections  it  is  supposed,  that  volcanic  action  not  ceasing,  conical 
accumulations  may  continue  to  be  formed  inside  a  crateriform  cavity, 
more  or  less  occupied  by  water,  cliffs  all  round  facing  an  active  volcanic 
vent,  as  at/,  fig.  113. 

Under  even  these  favourable  circumstances,  the  observer  should  em- 
ploy great  caution.  The  facts  presented  to  him  may  require  no  little 
comparison  and  classification,  for  in  such  localities,  more  especially,  he 
has  to  consider  how  far  the  relative  levels  of  the  sea  and  land  may  have 
remained  the  same  since  the  various  accumulations  before  him  have 
been  effected.  Let  it  be  supposed,  for  illustration,  that  he  detects 
organic  remains  in  beds  surrounding  the  interior  basin  of  water,  in 
which  the  volcanic  island  still  vomits  forth  various  gases  and  products. 
Should  the  deposits  g  and  h  (fig.  113),  be  of  the  more  recent  geological 
times,  commonly  marked  by  the  presence  of  the  remains  of  molluscs, 
not  much,  if  at  all,  differing  from  those  still  existing  in  the  vicinity, 
and  should  the  mineral  composition  of  the  including  beds  not  be 
decisive  on  the  point,  the  subject  may  not  be  so  clear,  unless  the  angle 
to  which  the  deposits  are  upraised,  be  such  as  to  preclude  the  idea  that 
they  were  in  that  manner  accumulated.  By  reference  to  the  section 
(fig.  114),  it  will  be  seen  that  if  the  line  d  e,  representing  the  present 
level  of  the  sea,  be  raised,  and,  consequently,  the  whole  mass  of  rocks, 
including  the  supporting  deposits,  a  c  b,  relatively  depressed,  that  the 
layers  now  above  the  sea,  being  then  below  it,  molluscs  may  have  lived 
upon  and  amid  these  layers  while  they  successively  constituted  the  sea 
bottom,  as  upon  any  other  sea  bottoms,  and  as  many  molluscs  must 
now  do  around  volcanic  islands.  There  is  no  difficulty  in  considering 
that  during  a  long  lapse  of  time,  breaker  action  aided  in  the  re-arrange- 
ment of  many  substances,  including  animal  remains,  on  the  subaqueous 


CINDERS    RAISED    ABOVE    THE    SEA    LEVEL.  321 

slopes  of  volcanoes,  the  angle  of  the  beds  varying  according  to  obvious 
conditions.  Any  change  in  the  relative  levels  of  the  sea  and  land, 
which  the  observer,  as  he  pursues  his  researches,  will  find  to  have  been 
so  frequent,  and  often  so  considerable,  that  should  raise  the  mass  (fig. 
114),  so  that  d  e  be  the  line  of  sea  level,  would  expose  the  edges  of 
these  fossiliferous  beds  facing  the  interior.  And  it  should  be  borne  in 
mind,  that  in  many  localities  calcareous  beds,  and  even  limestone,  may 
become  mingled  with  such  deposits  during  their  submarine  accumula- 
tion. * 

When  studying  the  fractures  and  contortions  of  rocks,  as  well  on 
the  small  as  the  large  scale,  an  observer  will  have  frequent  occasion  to 
remark,  as  will  be  more  particularly  shown  hereafter,  the  mixture  of 
flexures  and  fissures,  and  the  extension  of  the  one  into  the  other.  The 
subjoined  example  (fig.  115)  of  the  termination  of  a  fracture  or  a 
flexure,  occurring  amid  the  slightly  inclined  beds  of  lias  near  Lyme 
Regis,  Dorset,  may  aid  in  illustrating  a  point  of  much  interest  connected 

Fig.  115. 


with  the  present  subject,  namely,  that  in  the  more  marked  instances 
adduced  of  "  craters  of  elevation,"  a  considerable  break  or  outlet  is 
often  found  on  one  side.  The  plan  (fig.  115)  shows  an  alternation  of 
the  thin-bedded  limestone  of  the  lias  of  Dorsetshire  with  shale,  the 
whole  broken  through  by  a  crack,  a  6,  the  continuation  of  one  where 
there  is  dislocation  producing  movement  on  the  sides,  and  which  termi- 
nates in  a  boss  at  5,  with  somewhat  diverging  small  cracks.  The  interior 
is  composed  of  limestone,  round  which  shale,  covering  it,  is  exposed 
by  the  pear-shaped  protrusion,  outside  which  is  another  limestone  bed, 
c  c  c,  dipping  outwards  from  the  central  portion  6,  the  whole  taking  a 
more  horizontal  character  towards  a,  where,  for  a  certain  length,  the 
plane  surface  is  merely  broken  by  a  fissure.  With  proper  forces  and 
resistances  employed,  a  like  disposition  of  parts  could  be  obtained  on 
the  large  scale. 

If,  as  on  the  subjoined  plan  (fig.  116),  such  a  state  of  things  has 
been  brought  about  on  the  large  scale,  and  volcanic  forces  have  been 
enabled  to  find  vent  at  different  points,  there  may  be  good  evidence  of 
a  crater  of  elevation,  and  of  other  volcanoes  presenting  no  such  evi- 
dence, all  situated  on  a  great  line  of  fracture  ending  in  a  dome-like 
flexure,  with,  perhaps,  a  common  communication  between  them.  At 

21 


322  DIFFERENT    CRATERS    ON    THE    SAME    FISSURE. 

d  a  c,  the  beds  broken  through  would  dip,  with  radiating  cracks,  around 
a  gorge  opening  in  the  direction  of  the  main  fissure  towards  5,  while 
surrounding  the  volcanic  vents,  e  and  /,  the  strata  may  be  horizontal. 
Under  such  circumstances,  the  volcanic  accumulations  being  continued, 

Fig.  116. 


so  that  they  may  be  intermingled,  if  the  whole  be  regarded  with 
reference  to  depression  beneath  the  sea,  or  elevation  above  its  level, 
the  observer  will  perceive  that  numerous  complications  would  arise, 
requiring  no  slight  care  properly  to  appreciate. 

As  there  is  every  reason  to  infer  that  volcanic  substances  have  been, 
and  are  ejected  at  various  depths  beneath  the  sea  level,  as  well  as  above 
it,  the  modifications  of  the  products  arising  under  the  former  conditions 
have  to  be  properly  estimated,  more  particularly  when  we  have  to  asso- 
ciate such  modifications  with  changes  in  the  relative  levels  of  sea  and 
land,  so  that  accumulations  formed  at  various  depths  beneath  water 
may  be  mingled  with  those  gathered  together  in  the  atmosphere.  That 
subaqueous  would  gradually  approximate  to  subaerial  deposits,  as  the 
accumulations  round  volcanic  vents  rose  from  different  depths  in  the 
sea  above  its  level,  will  readily  be  understood.  When  eruptions  pierce 
through  the  sea  level,  ashes,  cinders,  and  stones  are  gathered  round  a 
crater,  and  vapours  and  gases  are  evolved,  as  happened  off  St.  Michael's, 
Azores,  in  1811  (p.  116),  and  in  the  Mediterranean,  between  Pantel- 
laria  and  the  coast  of  Sicily  in  1831  (p.  80).  At  such  times  the  vol- 
canic forces  so  accumulate  mineral  substances  around  the  vent,  and  so, 
for  the  time,  overpower  the  action  of  the  sea,  that  it  is  not  until  these 
forces  have  been  expended,  or  greatly  abated,  that  the  breakers  can 
abrade  the  land,  and,  supposing  no  subsidence,  or  falling  in  of  the  mass 
of  volcanic  matter  thus  raised,  and  the  latter  sufficiently  incoherent, 
level  off  the  accumulations  to  the  depths  to  which  waves  can  mechani- 
cally act. 

Fully  to  appreciate  the  modification  which  may  arise  in  volcanic 
action  at  various  depths  in  water,  productive  of  effects  which  can  only 
be  inferred,  very  careful  study  of  the  gases  and  vapours  evolved,  of  the 
chemical  composition  and  mineralogical  character,  and  of  the  mode  of 
occurrence  of  the  solid  substances  thrown  out  from  subaerial  volcanoes, 
is  needed.  With  regard  to  the  vapours  and  gases  evolved,  the  chief 
appear  to  be  aqueous  vapour  or  steam,  sulphurous  acid,  sulphuretted 
hydrogen,  hydrochloric  acid,  and  carbonic  acid.  Steam  is  a  very  com- 


VOLCANIC    VAPOURS    AND    GASES.  323 

mon  product,  and,  as  Dr.  Daubeny  has  remarked,  is  sometimes  emitted 
for  ages  from  volcanic  fissures.*  Hydrochloric  acid  is  also  common  in 
various  parts  of  the  world.  Sulphurous  acid  has  been  inferred  to  pre- 
dominate "  chiefly  in  volcanoes  having  a  certain  degree  of  activity ;  whilst 
sulphuretted  hydrogen  has  been  most  frequently  perceived  amongst 
those  in  a  dormant  condition. "f  Carbonic  acid  is  observed  at  the  close 
of  eruptions,  or  in  extinct  volcanoes,  and  is  stated  to  be  emitted  more 
from  the  bases  and  neighbourhood  of  volcanoes,  than  from  their  craters.  J 
Besides  these  gaseous  products,  which  can  be  collected  when  volcanic 
vents  can  be  approached  sufficiently  near  for  the  purpose,  it  is  now  con- 
sidered that  there  is  an  inflammable  gas  occasionally  evolved  from  some 
craters  and  volcanic  fissures,  which  gives  the  flame  often  mentioned, 
but  at  one  time  much  doubted.  Of  what  kind  this  gas  may  really  be, 
appears  as  yet  uncertain,  and  may  long  remain  so,  inasmuch,  as  it 
seems  chiefly  evolved  under  conditions,  such  as  violent  eruptions,  unfa- 
vourable to  examination.  Flame  observed  by  Professor  Pilla  to  be 
emitted  from  the  crater  of  Vesuvius,  in  June,  1833,  was  of  a  violet 
red  colour,  and  the  gas  producing  it  inflamed  only  when  in  contact  with 
the  air.§  As  Dr.  Daubeny  observes,  hydrogen  and  its  compounds  not 
inflaming  when  steam  or  hydrochloric  acid  is  mingled  with  them  in 
certain  proportions,  and  both  these  being  abundantly  evolved  in  most 
eruptions,  an  inflammable  gas  might  escape  into  the  air  thus  mixed, 
without  being  inflamed.  Hence,  though  this  gas  may  be  often  present 

*  "Description  of  Active  and  Extinct  Volcanoes,"  2d  edit,  p.  607;  1848.  There 
would  appear  to  be  a  constant  emission  of  steam  from  Tongariro,  New  Zealand,  a  vol- 
canic mountain  rising  to  about  6200  feet  above  the  sea.  From  time  to  time  hot  water 
and  mud  are  ejected,  and  pour  down  the  mountainside,  "  coupled  with  ejections  of 
steam  and  black  smoke,  with  a  noise  like  that  of  a  steam  engine,  but  no  lava  or  scoriae." 
Ib.  p.  429. 

f  Daubeny,  "Volcanoes,"  2d  edit.,  p.  608.  As  regards  the  discharge  of  sulphurous 
acid  and  sulphuretted  hydrogen,  the  one  more  in  some  places  than  in  others,  Dr.  Dau- 
beny remarks,  that  the  presence  of  the  one  does  not  prove  the  entire  absence  of  the 
other,  since  these  two  gases  when  they  meet  decompose  each  other,  forming  water  and 
depositing  sulphur;  and  "  that  merely  the  portion  of  either  which  exceeds  the  quantity 
necessary  for  their  mutual  decomposition  will  escape  from  the  orifice;  so  that  the  gas 
which  actually  appears  indicates  only  the  predominance  of  the  one,  and  not  the  entire 
absence  of  the  other." 

|  Daubeny,  "Volcanoes,"  2d  edit.,  p.  612. 

$  Edinburgh  New  Philosophical  Journal,  1843.  From  observations  made  by  him  in 
the  crater  of  Vesuvius  in  1883  and  1834,  Professor  Pella  concluded  that  flames  never 
appear  at  Vesuvius  but  when  the  volcanic  action  is  energetic,  and  is  accompanied  with 
a  development  of  gaseous  substances  in  a  state  of  great  tension  ;  that  they  do  not  appear 
when  the  action  is  feeble  ;  that  their  appearance  always  accompanies  explosions  from 
the  principal  mouth,  where,  however,  they  cannot  be  observed  except  under  favourable 
circumstances  ;  that  they  likewise  show  themselves  in  the  small  cones  in  action,  which 
are  formed  in  the  interior  of  the  crater,  or  at  the  foot  of  the  volcano  ;  and  that,  finally, 
they  are  not  visible  except  in  the  openings  which  are  directly  in  communication  with 
the  volcanic  fire,  and  never  on  the  moving  lavas,  which  are  at  a  distance  from  their 
sources. 


324  VOLCANIC    SUBLIMATIONS. 

during  violent  eruptions,  it  may  not  always  be  so  under  conditions  for 
supporting  flame. 

As  regards  the  sublimations  from  volcanoes,  we  should  anticipate  that 
they  would  be  varied,  seeing  that  the  conditions  under  which  volcanic 
forces  and  products  may  find  vent  could  scarcely  but  be  variable  also. 
Among  the  most  common  is  chloride  of  sodium,  or  common  salt,  one 
which  is  important  from  being  found  connected  with  volcanic  action  in 
such  different  parts  of  the  earth's  surface.  Specular  iron  ore  is  often 
found  sublimed  in  chinks  and  cavities,  as  is  also  muriate  of  ammo- 
nia in  certain  volcanoes.  Respecting  sulphur,  it  has  been  inferred  to  be 
derived  "either  from  the  mutual  decomposition  of  sulphurous  and 
sulphuretted  hydrogen  gases,  or  from  the  catalytic  action  exerted  upon 
the  latter  gas  by  porous  bodies,  assisted  by  a  certain  temperature."* 
The  sublimations  of  the  sulphurets  of  iron  and  copper,  chloride  of  iron, 
oxide  of  copper,  muriate  and  sulphate  of  potass,  selenium,  and  others, 
though  apparently  accidental,  have  been  shown  by  M.  Elie  de  Beau- 
montf  to  have  an  important  bearing  upon  the  filling  of  mineral  veins, 
as  will  be  hereafter  stated. 

The  ashes,  cinders,  and  molten  rock  ejected,  may  often  be  considered 
as  little  else  than  modifications  of  the  same  substance,  at  one  time  kept 
in  a  state  of  fusion,  vapours  and  gases  piercing  through  it,  at  another 
driven  off  by  these  vapours  and  gases  in  portions  of  different  volume, 
more  or  less  impregnated  with  them,  so  as  to  be  rendered  cellular ; 
these  portions  finally  so  triturated  and  worn  into  fine  grains  and  powder, 
that  while  part  may  fall  with  the  cinders  in  a  conical  form  around  the 
volcanic  vent,  another  portion  may  be  so  light  as  to  be  borne  great 
distances  by  the  winds,  as  from  St.  Vincent's,  in  the  West  Indies,  above 
the  trade-winds,  far  eastward  over  the  Atlantic. 

The  rock  in  fusion,  while  occasionally,  but  somewhat  rarely,  uplifted 
in  a  volcanic  vent  to,  or  so  near  the  lip  of  the  crater,  as  to  flow  over 
the  outside  in  a  viscous  stream,  more  frequently  breaks  through  different 
portions  of  the  side ;  a  result  which  would  be  anticipated  from  the  pres- 
sure of  a  substance  of  the  kind,  and  from  rents  formed  in  the  sides  of 
a  volcano  during  violent  eruptions.  After  ejection,  its  solidification  will 
necessarily  depend  upon  the  conditions  to  which  it  is  exposed,  the  volume 
of  the  molten  mass  thrown  out  being  duly  regarded.  Like  all  other 
mineral  bodiea  of  the  like  kind,  if  rapidly  cooled,  lavas  form  glasses, 

*  Daubeny,  "Active  and  Extinct  Volcanoes,"  2d  edit.,  p.  615.  After  quoting  M. 
Dumas  (Annales  de  Che'mie,  Dec.,  1846),  as  having  shown  that  "where  sulphuretted 
hydrogen,  at  a  temperature  above  100°  Fahrenheit,  and  still  better  when  near  190°, 
comes  into  contact  with  certain  porous  bodies,  a  catalytic  action,  as  it  is  called,  is  set 
up,  by  which  water,  sulphuric  acid,  and  sulphur  are  produced,"  Dr.  Daubeny  points 
out  that  the  vast  deposits  of  sulphur,  associated  with  the  sulphates  of  lime  and  strontia 
of  Western  Sicily,  may  have  been  thus  produced. 

f  Sur  les  Emanations  Volcaniques  et  Me"talliferes. — Bull,  de  la  Soc.  Ge*ol.  de  France, 
2d  serie,  t.  iv.,  p.  1249. 


MOLTEN    VOLCANIC    PRODUCTS.  325 

commonly  known  as  obsidians,  when  associated  with  volcanic  products ; 
if  slowly  cooled,  and  in  sufficient  volume,  crystallizing,  as  is  easily  illus- 
trated by  experiment.*  The  heat  of  lava  currents  would  appear  to 
vary, — a  circumstance  to  be  expected,  as,  whatever  may  have  been  the 
temperature  of  the  molten  mass  when  in  the  volcano,  that  of  its  exclu- 
sion would  depend  upon  the  cooling  influences  to  which  it  may  have 
been  exposed  before  it  flowed  outside  the  volcano,  and  could  be  exa- 
mined. It  has  been  inferred  that  the  temperature  at  which  lava  will 
continue  to  flow  is  sufficient  to  melt  silver,  lead  being  rendered  fluid  in 
about  four  minutes.  Whatever  the  .requisite  heat  may  be,f  lava  is 
found  to  retain  it  for  a  long  series  of  years. 

Being  a  bad  conductor  of  heat,  as  rocks  in  general  are,  lava,  when 
subjected  to  the  comparatively  low  temperature  to  which  it  is  exposed 
after  ejection,  soon  covers  itself  with  a  coating  of  solidified  matter.  This 
is  necessarily  broken  as  the  flow  of  the  viscous  mass  continues  beneath 
it,  and  it  will  be  more  or  less  scoriaceous,  according,  as  in  cooling,  it 
retains  any  cellular  texture  from  the  passage  or  dissemination  of  vapours 
and  gases  through  it.  Hence  the  surface  of  lava  currents  is  often 
broken  and  rugged,  as  is  represented  in  the  accompanying  view  of  one 
at  Vesuvius  (fig.  117)4  Under  the  conditions  usually  obtaining  during 
the  flow  of  lava,  the  viscous  current,  at  a  moderate  distance  from  the 
place  of  its  actual  discharge,  may  be  considered  as  moving  in  a  kind  of 

*  So  far  back  as  1804,  the  experiments  of  Mr.  Gregory  Watt  (Observations  on  Basalt, 
and  on  the  Transitions  from  the  Vitreous  to  the  Stony  Texture  which  occurs  in  the 
Refrigeration  of  Melted  Basalt,  Phil.  Trans.,  1804),  proved,  as  respects  basalt  (that  of 
Rowley  Hill,  near  Dudley),  when  a  mass  of  it  weighing  seven  hundred  weight  was 
melted  and  slowly  cooled  in  an  irregular  figure,  that  according  to  the  rate  of  cooling  of 
the  various  parts,  was  the  structure,  one  passing  from  the  vitreous  to  the  stony.  The 
silicates  forming  common  glass  may,  as  is  well  known,  by  slow  cooling  be  made  to  pass 
into  a  stony  state.  We  have  made  many  hundreds  of  experiments  upon  the  melting 
and  recrystallization  of  igneous  rocks,  even  succeeding  in  the  reduction  of  certain  gra- 
nites into  a  glass,  and  again  rendering  this  glass  stony.  The  varied  chemical  composi- 
tion of  the  substances  which  may  be  reduced  to  the  vitreous  state  is  quite  sufficient  to 
show  that  obsidian  is  a  mere  rock-glass,  which  can  be  formed  under  the  requisite  con- 
dition of  comparatively  rapid  cooling  from  very  different  compounds.  We  have  reduced 
portions  of  some  stratified  rocks  to  this  state.  This  is  by  no  means  difficult  to  accom- 
plish when  a  moderate  amount  of  lime  is  present,  so  that  silicate  of  lime  may  be  pro- 
duced and  act  as  a  flux,  as  in  the  ordinary  smelting  of  the  argillaceous  iron  ores  of  the 
coal  measures.  By  a  little  management,  slates  and  shales,  with  the  requisite  dissemi- 
nation of  carbonate  of  lime,  may  be  converted  into  excellent  pumice,  intumescence 
being  produced  in  the  melted  viscous  substance  by  the  carbonic  acid.  The  experiment 
requires,  however,  to  be  carefully  watched ;  for  if  the  crucible  be  not  removed  in  time, 
the  carbonic  acid  escapes,  and  the  vitreous  substance  alone  remains,  which  may  readily, 
if  thought  desirable,  be,  by  slow  cooling,  rendered  stony.  To  produce  crystallization 
by  very  slow  cooling  requires  great  care,  and,  for  the  most  part,  a  somewhat  large 
portion  of  rock. 

f  In  our  experiments,  ordinary  greenstone,  when  pounded  fine,  and  placed  in  a  cru- 
cible, usually  melted  at  about  the  heat  required  for  melting  copper :  experiments,  how- 
ever, on  so  small  a  scale  may  be  very  deceptive. 

J  Taken  from  Abich's  Views  of  Vesuvius  and  Etna. 


326  FLOW    OF    LAVA    STREAMS. 

pipe,  this  breaking  from  time  to  time,  as  the  molten  rock  in  the  interior 
tends  to  drag  the  parts  becoming  solid  with  it.  In  this  manner  the 
pipe  will  even  convey  the  lava  current  up  rising  ground,  should  the  re- 
sistance of  its  sides  be  equal  to  the  pressure  exerted  upon  them.  As  a 
high  angle  of  descent  would  be  unfavourable  to  the  proper  slow  cooling 
and  quiet  adjustment  of  particles  needed  for  crystallization,  MM.  Du- 
fre*noy  and  Elie  de  Beaumont  consider  that  beyond  a  moderate  angle 
lava  does  not  take  a  crystalline  texture.  That  the  external  character 
of  a  lava  current  should  conform  to  the  velocity  of  its  flow,  this  depend- 
ing, other  conditions  be  equal,  upon  the  amount  of  slope,  would  be  anti- 
cipated. The  observer  should,  however,  be  aware  that  when  crystalline 
minerals  may  be  found  in  lava,  it  does  not  always  follow  that  their  par- 
ticles have  separated  out  from  the  other  component  parts  of  the  mass, 

Fig.  117. 


after  the  whole  has  been  in  a  molten  state.  They  seem  to  have  been 
sometimes  formed  prior  to  the  outflow  of  the  lava.  Of  this  a  good  ex- 
ample is  inferred  to  have  occurred  at  Vesuvius  in  April,  1822,  when 
fine  crystals  of  leucite  were  included  in  a  lava  stream  which  issued  from 
the  base  of  a  small  cone  occupying  the  crater,  the  comparative  infusi- 
bility  of  the  leucite  crystals  preserving  them  entire  amid  the  melted 
rock.*  In  like  manner  should  the  lava  be  in  part  composed  of  a  re- 
melted  rock  containing  disseminated  minerals,  which  resisted  the  lieut 
to  which  the  whole  was  exposed,  such  minerals  might  upon  an  outflow 

*  Daubeny,  quoting  Professor  Scacchi,  of  Naples,  "  Volcanoes,"  2d  edit.,  p.  230. 


VAPOURS    AND    GASES    IN    MOLTEN    LAVA.  327 

accompany  the  lava  stream,  and  be  again  dispersed  amid  the  new  mass, 
otherwise,  perhaps,  not  crystalline.* 

It  would  scarcely  be  expected  that  a  molten  mass,  known  to  be  driven 
about  in  a  crater  by  vapours  and  gases,  could  either  overflow  the  lip  of 
that  crater,  or  burst  out  from  the  sides  of  a  volcano  without  having  some 
portions  of  these  vapours  and  gases  intermingled  with  it  ready  to  escape 
into  the  air.  This  it  would  accomplish  the  easier  as  the  lava  was  the 
more  fluid,  and  its  temperature  high,  the  vapours  and  gases  then  striving 
most  to  increase  their  volume.  In  proportion  as  the  molten  rock  cooled, 
and  the  expansive  power  of  the  vapours  and  gases  decreased,  cavities 
would  remain,  corresponding  in  size  to  the  equalization  of  the  resistance 
of  the  cooling  rock  on  the  one  hand,  and  the  expansive  power  of  the 
vapours  and  gases  on  the  other.  As  these  conditions  varied  so  would 
the  results,  and  thus  according  to  circumstances  the  hollows  formed 
would  differ  from  good-sized  caves,  lined  with  picturesque  stalactites  of 
lava,  to  small  vesicles.  Vapours  and  gases  sometimes  continue  to  escape 
for  a  long  time  through  the  chinks  and  cracks  of  cooling  lava. 

The  cavities  thus  produced  in  lavas  will  necessarily  take  different 
shapes,  according  to  varying  conditions.  Lava  poured  out  so  as  to  form 
a  broad  and  comparatively  deep  mass,  with  little  movement  of  import- 
ance after  its  outflow  from  a  volcano,  the  fluid  state  long  preserved, 
would  have  its  cavities,  large  and  small,  placed  under  different  circum- 
stances, from  a  stream  cooling  more  rapidly,  yet  still,  from  moving  on 
greater  slopes,  continuing  steadily  to  advance  for  a  long  distance.  In 
the  latter  case  the  hollows  and  vesicles  would  be  elongated  in  the  direc- 
tion of  the  flow,  spherical  cavities  pulled  out  into  almond-shaped  forms, 
and  irregular  hollows  still  exhibiting  a  stretching  in  the  line  of  move- 
ment. This  elongation  of  vesicles  may  be  so  continued  that,  as  in  the 
subjoined  section  (fig.  118),  they  may  become  completely  flattened,  the 

Fig.  118. 


tenacity  of  the  lava  being  of  a  proper  kind.     If  c  d  be  a  surface  on 
which  a  lava  stream  moves,  and  e  f  a  portion  where  its  viscosity  is  such 

*  In  regions  where  volcanoes  traverse  igneous  rocks  of  an  older  date,  remelting  por- 
tions of  them,  it  is  easy  to  conceive  occurrences  of  this  kind.  Should  a  felspathic  por- 
phyry, containing  crystals  of  quartz,  or  mica,  be  thus  remelted,  and  the  heat  be  only 
capable  of  fusing  the  felspathic  matter,  these  minerals  may  be  left  untouched.  In  ex- 
periments made  for  this  purpose,  we  have  often  found  this  view  borne  out,  and  the 
quartz  disseminated  through  many  slags,  as,  for  example,  in  many  of  the  first  copper 
slags  in  the  furnaces  at  Swansea,  affords  another  example  of  the  like  kind. 


328       LAVA    EXCRESCENCES    FROM    ESCAPE    OF    GASES. 

that  by  moving  in  the  direction  e  /,  spherical  hollows  take  almond-shaped 
forms,  the  lava  becoming  more  tenacious  towards  the  surface  c  .d,  these 
almond-shaped  vesicles  would  become  flatter  at  a  5,  so  as  finally  to  pre- 
sent, in  section,  mere  streaks  or  lines,  giving  a  lamina-ted  appearance  to 
that  portion  of  a  lava  current  when  cooled.  Upon  the  solidification  of 
the  portion  a  b,  the  movement  continuing,  and  the  upper  part  gradually 
taking  the  tenacity  previously  possessed  by  a  5,  the  like  appearance  of 
lamination  might  happen  there.  Thus,  as  the  upper  part  of  a  sheet  of 
lava  may,  as  regards  loss  of  fluidity,  and  the  friction  of  the  viscous  upon 
the  solid  outside  portion,  be  also  placed  in  a  somewhat  similar  condition 
as  the  lower  part,  a  laminated  character  may  more  or  less  be  given  to  a 
considerable  portion  of  a  stream  of  lava.  The  conditions  needed  no 
doubt  require  nice  adjustment,  but  they  are  such  as  would  appear  occa- 
sionally to  prevail. 

Mr.  Darwin,  describing  the  laminated  obsidian  beds  of  the  Island  of 
Ascension,  and  comparing  them  with  the  zoned  and  laminated  character 
of  obsidians  and  different  volcanic  rocks  of  other  localities,  mentions, 
with  another  cause  of  lamination,  the  stretching  and  flattening  of  vesicles 
by  the  flow  of  those  rocks  in  a  pasty  state.*  It  has  also  been  noticed 
by  Humboldt,  and  other  geologists,  and  is  often  to  be  seen  in  cabinet 
specimens. 

Sometimes  vapours  and  gases  escape  through  molten  lava,  either  for 
the  time  occupying  portions  of  craters,  or  flowing  as  streams,  producing 
the  most  fantastic  forms.  The  annexed  sketch  (fig.  119)  represents  a 

Fig.  119. 


somewhat  regular  accumulation  of  lava  from  this  cause.  It  was  seen 
by  Mr.  Dana,  in  the  crater  of  Kilauea,  in  Hawaii,  and  rose  as  a  whole, 
to  the  height  of  about  40  feet.  "  It  had  been  formed  over  a  small  vent, 
through  which  the  liquid  rock  was  tossed  out  in  driblets  and  small  jets. 
The  ejected  lava  falling  around,  gradually  raised  the  base ;  the  column 
above  was  then  built  up  from  successive  drops,  which  were  tossed  out, 

*  "Geological  Observations  on  the  Volcanic  Islands  visited  during  the  Voyage  of 
H.M.S.  Beagle,"  p.  62,  &c. 


ERUPTIONS    FROM    SMALL    VENTS. 


329 


and  fell  back  on  one  another ;  being  still  soft,  they  adhered  to  each 
other,  lengthening  a  little  at  the  same  time  while  cooling.* 

The  following  is  also  (fig.  120)  an  example  of  the  like  kind  observed 
by  Dr.  Abich,f  at  Vesuvius,  in  1834,  scoriaceous  lava  being  gradually 
built  up  into  a  hollow  column  by  the  additions  of  portions  of  pasty 


Fig.  120. 


matter  adhering  to  each  other  when  thrust  out  of  the  general  molten 
mass  by  a  current  of  vapour  or  gas.  In  a  similar  manner,  great  blisters 
are  sometimes  raised,  which  bursting  on  one  side,  parts,  sufficiently 
hard,  remain,  and  any  molten  lava  inside  flowing  out,  singular  cavities 
are  left.  Indeed,  the  varieties  of  hollows  left  by  the  consolidation  of 
lava,  and  arising  either  from  the  intermixture  of  vapours  and  gases,  or 
from  the  flow  of  the  fluid  rock,  partially  or  wholly,  out  of  inequalities 
in  lava  streams,  or  their  tubular  cases,  would  appear  to  be  endless. 
The  observer  may  derive  much  instruction  from  studying  the  erup- 

*  "  Geology  of  the  United  States  Exploring  Expedition,"  1838-42,  p.  177.  Mr.  Dana 
mentions  other  similar  examples,  some  on  a  miniature  scale,  about  Mauna  Loa.  The 
figure  of  a  man  has  been  added  to  the  original  sketch  by  Mr.  Dana,  in  order  to  give  a 
general  idea  of  the  height  of  the  volcanic  projection. 

f  "  Geologischer  Erscheinungen  beobachtet  am  Vesuv  und  Aetna,"  Berlin,  1837. 
The  height  of  the  excrescence  represented  is  only  eight  feet. 


330  VOLCANIC    CONES. 

tions  from  small  vents,  either  in  the  craters  of  volcanoes,  when  such 
can  be  approached,  or  on  their  sides,  where  they  are  also  sometimes 
found,  not  only  as  respects  vapours  and  gases,  but  also  the  discharge 
and  mode  of  accumulation  of  fluid  and  viscous  lava,  cinders,  and  ashes. 
In  some  vents  the  molten  rock  is  not  much  intermingled  with  the 
vapours  and  gases,  at  others  it  becomes  frothy  by  intimate  admixture 
with  them ;  the  mineral  matter  occupying  much  the  less  portion  of  the 
compound.  Occasionally  the  uplifting  of  the  mass  merely  raises  the 
lava,  so  that  it  falls  over  the  accumulations  around  the  vent,  not  un- 
commonly more  or  less  conical ;  at  other  times  portions  of  the  molten 
mass  are  suddenly  caught  and  whirled  high  up  into  the  air,  acquiring  a 
spheroidal  form  by  their  motion.*  When  only  ejected  short  distances, 
they  fall  around,  squashing  into  irregular  and  rough  discs,  and  by  their 
multiplication  forming  a  coating,  which  may,  or  may  not,  be  inter- 
mingled with  scoriaceous  cinders,  now  and  then  discharged  in  showers. 
Small  lava  streams  sometimes  burst  from  these  conical  accumulations, 
the  resistance  of  the  sides  being  overcome,  and  cracks  being  formed, 
the  molten  matter  may  be  seen  to  rise  in  them.  Many  of  the  effects 
of  volcanic  action  on  the  large  scale  may  thus,  in  miniature,  be  con- 
veniently observed. 

Although  conical  accumulations  round  a  vent  mark  the  effects  of 
volcanic  action  from  it,  driving  out  ashes  and  cinders,  large  and  small, 
with  patches  of  frothy  molten  rock,  and  streams  of  fluid  and  viscous 
lava,  more  or  less  radiating  from  a  central  vent,  whether  raised  over 
the  lips  of  a  crater,  or  breaking  through  the  sides  of  a  volcano,  the 
whole  braced  together  by  more  or  less  vertical  bands  of  lava,  which 
have  entered  cracks,  effected  from  time  to  time  in  the  general  mass ; 
this  is  not  necessarily  the  case  with  all,  nor  with  all  parts  of  a  mountain 
of  which  one  or  more  of  these  conical  accumulations  may  form  a  part. 
As  respects  cones,  the  following  viewf  of  Cotopaxi  will  illustrate  the 

*  Kespecting  these  volcanic  bombs,  as  they  have  been  termed,  Mr.  Darwin,  remarking 
on  those  found  in  the  Island  of  Ascension  (Volcanic  Islands,  p.  36),  which  exhibit  a 
cellular  interior,  inside  a  shell  of  compact  lava,  observes,  that  "if  we  suppose  a  mass 
of  viscid,  scoriaceous  matter,  to  be  projected  with  a  rapid,  rotatory  motion  through  the 
air,  whilst  the  external  crust,  from  cooling,  became  solidified,  the  centrifugal  force,  by 
relieving  the  pressure  in  the  interior  parts  of  the  bomb,  would  allow  the  heated  vessels 
to  expand  their  cells ;  but  these  being  driven  by  the  same  force  against  the  already 
hardened  crust,  would  become,  the  nearer  they  were  to  this  part,  smaller  and  smaller, 
and  less  expanded,  until  they  became  packed  into  a  solid  concentric  shell." 

f  Taken  from  the  Voyage  de  Humboldt  et  Bonpland,  Atlas  Pittoresque,  PI.  X.,  Paris, 
1810.  Explosions  from  Cotopaxi  are  heard  at  great  distances.  In  1744  the  bellow- 
ings  from  the  mountain  were  heard  at  Honda,  200  common  leagues  distant.  Humboldt 
and  Bonpland  heard  them  day  and  night  at  Guayaquil,  62  leagues  distant  in  a  straight 
line.  They  were  like  repeated  discharges  of  a  battery.  During  the  eruption  of  April, 
1768,  the  quantity  of  cinders  vomited  from  the  crater  was  so  great,  that  in  the  towns 
of  Hambato  and  Tacunda  night  was  prolonged  to  three  o'clock  on  the  5th,  and  the  in- 
habitants were  obliged  to  go  about  with  lanterns.  The  eruption  of  1803  was  preceded 


I 

COTOPAXI. 

production  of  one  of  great  size,  its  beautifully  regular  shape*  showing 
how  well  adjusted  the  volcanic  forces,  and  the  substances  acted  on,  must 


Fig.  121. 


have  been  for  its  formation.  As  to  its  volume,  that  of  course  affords 
no  measure  of  the  time  which  the  cone  may  have  taken  for  its  produc- 
tion, but  it  shows  the  great  mass  of  volcanic  matter  which  seems  thus 
heaped  by  successive  coatings  into  this  shape. f  The  manner  in  which 
such  a  mountain  may  be  braced  together  by  lava  currents  and  dykes  we 
know  not.  Certainly  the  general  form  would  lead  us  to  infer  a  great 
amount  of  ashes  and  cinders,  including  among  the  latter  large  ejected 
masses  of  viscous,  scoriaceous,  and  frothy  (pumicy)  lava,  forced  through 
a  vent  keeping  in  one  place  during  the  accumulation. 

Mauna  Loa  and  Mauna  Kea,  in  Hawaii,  also  lofty  volcanic  moun- 
tains, the  former  considered  to  be  13,760  feet,  and  the  latter  13,950 
feet  above  the  sea,|  appear  to  afford  much  modification  in  structure  from 
that  found  at  Cotopaxi,  one  also  marked  by  their  outlines,  as  shown  by 

by  the  sudden  melting  of  the  snow  on  the  volcano.  For  20  years  previously  neither 
vapour  nor  smoke  had  issued  from  it,  when,  in  a  single  night,  the  cone  became  so  much 
heated,  that,  the  snow  being  melted,  it  appeared  black  from  the  scoriae  alone. 

*  Humboldt  (Kosmos)  points  to  the  form  of  Cotopaxi  as  at  once  the  most  regular 
and  most  picturesque  of  any  volcanic  cone  which  he  had  ever  seen. 

f  According  to  Humboldt  (Kosmos),  Cotopaxi  rises  to  the  height  of  19,070  (English) 
feet  above  the  sea. 

J  According  to  Dana,  "  Geology  of  the  United  States  Exploring  Expedition," 
1838-42. 


332  VOLCANOES     OP    HAWAII. 

the  accompanying  sketch  of  Hawaii  (fig.  122),  taken  from  the  east- 
ward.* Maps  and  descriptions  show  that  Hawaii  (which,  as  Mr.  Dana 
remarks,  is  one  of  a  group  about  400  miles  in  length,  ranging  from 
N.W.  to  S.E.,  the  islands  composing  it  being  merely  the  higher  points 
of  mountains  rising  above  the  sea)  is  a  mass  of  volcanic 
Fig.  122.  matter,  with  three  principal  elevations,  Loa,  Kea,  and  Hua- 
lalai.f  The  remarkable  crater  in  activity  is  that  of  Kilauea, 
on  the  flank  of  Loa,  and  distant  about  20  milesj  from  its 
summit. 

Ellis§  described  the  crater  as  situated  on  a  lofty  elevated 
plain,  bounded  by  precipices,  apparently  sunk  from  200  to  400 
feet  below  its  original  level.  "  The  surface  of  this  plain  was 
uneven,  and  strewed  over  with  loose  stones  and  volcanic  rock, 
and  in  the  centre  was  the  great  crater."  .  .  .  .  "  Immediately 
before  us  yawned  an  immense  gulf,  in  the  form  of  a  crescent, 
about  two  miles  in  length,  from  N.E.  to  S.W.,  nearly  a  mile 
,5  in  width,  and  apparently  800  feet  deep.  The  bottom  was 
*  covered  with  lava,  and  the  southwest  and  northern  parts  of 
§  it  were  one  vast  flood  of  burning  matter,  in  a  state  of  terrific 
ebullition,  rolling  to  and  fro  its  <  fiery  surge'  and  flaming 
billows.  Fifty-one  conical  islands,  of  varied  form  and  size, 
containing  so  many  craters,  rose  either  round  the  edge,  or 
from  the  surface  of  the  burning  lake ;  22  constantly  emitted 
columns  of  gray  smoke,  or  pyramids  of  brilliant  flame ;  and 
several  of  these  at  the  same  time  vomited  from  their  ignited 
mouths  streams  of  lava,  which  rolled  in  blazing  torrents  down 
their  black  indented  sides  into  the  boiling  mass  below."  .  .  . 
"  The  sides  of  the  gulf  before  us,  though  composed  of  different 
strata  of  ancient  lava,  were  perpendicular  for  about  400  feet, 
jj  and  rose  from  a  wide  horizontal  ledge  of  solid  black  lava  of 

*  Ibid.  p.  159. 

f  Mr.  Dana  remarks  (Geology  U.  S.  Exploring  Expedition,  p.  158),  "Be- 
sides the  three  lofty  summits  there  are  great  numbers  of  craters  in  all  con- 
ditions scattered  over  the  slopes,  some  overgrown  with  forests,  while  about 
others  streams  of  lava,  now  hard  and  black,  may  be  traced  along  their  route 
for  miles.  Areas,  hundreds  of  square  miles  in  extent,  are  covered  with  the 
refrigerated  lava  flood,  over  which  the  twistings  and  contortions  of  the 
sluggish  stream  as  it  flowed  onward  are  everywhere  apparent ;  other  parts 
are  desolate  areas  of  ragged  scoriae.  But  a  few  months  before  our  visit 
(1840)  a  surface  of  15  square  miles  had  been  deluged  with  lava,  which  came 
by  an  under-ground  route  from  Lua  Pele  (Kilauea)." 

J  Mr.  Dana  gives  the  distance  as  19-8  miles,  and  the  height  of  Kilauea 
as  8970  feet  above  the  sea,  quoting  Mr.  Douglas  (Journal  of  the  Geo- 
graphical Society,  vol.  iv.),  as  estimating  it  from  barometrical  measure- 
ments at  3845-9— 3873-7,  and  Strzelecki  at  4101  feet. 

$  "  Tour  in  Hawaii."     London,  1826. 


CRATER    OF    KILAUEA,    HAWAII. 


333 


irregular  breadth ;  but  extending  completely  round,  beneath  this  ledge, 
the  sides  sloped  gradually  towards  the  burning  lake,  which  was,  as 
nearly  as  we  could  judge,  300  or  400  feet  lower.  It  was  evident  that 
the  large  crater  had  been  recently  filled  with  liquid  lava  up  to  this 
black  ledge." 

The  descriptions  of  this  crater  given  by  other  observers,*  corresponds 
generally  with  that  of  Mr.  Ellis,  due  allowance  being  made  for  modifi- 
cations, such  as  might  be  expected  in  a  volcanic  vent  of  any  kind.  The 
following  is  an  eye- sketch  plan  (fig.  123)  of  Kilauea,  made  during  the 

Fig.  123. 


visit  of  the  United  States  Exploring  Expedition,  under  Captain  Wilkes, 
to  Hawaii.  It  well  exhibits  the  cliffs  surrounding  the  cavity,  seven 
miles  and  a  half  in  circuit,  as  also  the  great  ledge  above  mentioned. 
Combined  with  the  following  section  given  by  Mr.  Dana,f  it  strongly 
suggests  the  idea  of  an  extensive  area  of  molten  rock,  rising  and  falling 
according  to  the  uplifting  force  of  the  time,  this  somewhat  suddenly 


Fig.  124. 


changing,  as  is  not  unfrequent  in  volcanic  action,  so  that,  in  some 
states,  vertical  walls  would  be  formed  from  the  lowering  of  the  fused 
mass,  while  at  others  this  might  again  fill  the  cavity,  and  even  overflow. 
In  the  above  section  (fig.  124),  which  is  taken  across  the  shortest 
diameter  (scale  equal  for  height  and  distance),  m  m'  is  the  whole 
breadth  of  the  crater  in  that  line,  o  n,  o'  n'  the  black  ledge,  p  p1  the 
bottom  of  the  lower  pit,  n  p,  ri  p'  the  walls  of  the  lower  pit,  342  feet 

*  Mr.  Douglas,  "  Journal  of  the  Geographical  Society,"  vol.  iv. ;  Captain  Kelly,  "  Ame- 
rican Journal  of  Science,"  vol.  xl.  ;  Count  Strzelecki,  "  New  South  Wales  and  Van 
Diemen's  Land,"  and  others. 

f  "  Geology  of  the  United  States  Exploring  Expedition,"  p.  174. 


334  CRATER    OF    MAUNA    LOA,    HAWAII. 

in  height,  and  m  0,  m'  o'  the  walls  above  the  black  ledge,  650  feet  in 
height.  Mr.  Dana  describes  the  beds,  exposed  by  the  cliffs,  as  nearly 
horizontal,  and  the  crater  as  being,  at  the  time  of  his  visit  (November, 
1840),  somewhat  in  a  tranquil  state;*  one,  however,  still  variable. 
During  subsequent  examinations  by  the  United  States  Exploring  Expe- 
dition, in  December,  1840,  and  January,  1841,  the  lava  was  observed 
both  to  rise  and  fall  in  a  marked  manner,  independently  of  minor 
oscillations.  On  one  occasion  Dr.  'Judd  had  but  just  time  to  escape 
from  a  sudden  uprise  and  overflow  of  one  of  the  molten  pools,  which 
discharged  a  mass  of  liquid  lava,  not  only  over  the  spot  where  he  was 
standing  immediately  prior  to  this  upburst,  but  also  over  a  mile  in 
width  and  a  mile  and  a  half  in  length.  The  volume  of  lava  then  ejected 
was  afterwards  estimated  by  Captain  Wilkes  at  200,000,000  cubic  feet. 
The  next  morning  (January  17,  1841)  the  molten  lava  of  the  chief  lake 
was  ascertained  to  have  subsided  about  100  feet. 

Proceeding  from  Kilauea  to  Mokua-weo-weo,  the  crater  on  the  summit 
of  Loa,  over  a  slope  described  as  one,  on  the  average,  of  only  6°,  a 

*  The  descriptions  given  of  the  arrangement  of  the  beds,  and  of  other  facts  connected 
with  this  crater,  have  an  important,  theoretical  bearing.  "These  bluff  sides  of  the 
pit,"  he  observes,  "consist  of  naked  rock  in  successive  layers;  and  in  the  distance 
they  look  like  cliffs  of  stratified  limestone.  The  layers  vary  from  a  few  inches  to  30 
feet  in  thickness,  and  are  very  nearly  horizontal.  They  are  much  fissured  and  broken, 
and  some  have  a  decidedly  columnar  structure.  Open  spaces  or  caverns  and  rugged 
cavities  often  separate  the  adjacent  layers,  adding  thus  to  the  broken  character  of  the 
surface,  and  at  the  same  time  giving  greater  distinctness  to  the  stratification.  The 
black  ledge  varies  in  width  from  1000  to  3000  feet.  With  such  dimensions,  it  is  no 
unimportant  feature  in  the  crater.  The  lower  pit  is  surrounded  by  vertical  walls, 
which  have  the  same  distinctly  stratified  character  as  those  above,  and  are  similar  in 
other  features.  More  numerous  fissures  intersect  them,  indicative  of  the  unstable 
basis  on  which  they  rest."  .  .  .  The  southwest  extremity  formed  a  partly  isolated 
basin,  of  an  oval  form,  and  contained  a  large  boiling  lake.  "  The  rest  of  the  bottom 
of  the  pit,  at  the  time  visited  by  the  author,  was  a  field  of  hardened  lava,  excepting 
two  small  boiling  pools,  one  on  the  western  side,  the  other  near  the  eastern."  p.  174. 

Describing  the  day  scene,  Mr.  Dana  states,  that  the  "  incessant  motion  in  the  blood- 
red  pools  was  like  that  of  a  cauldron  in  constant  ebullition.  The  lava  in  each  boiled 
with  such  activity,  as  to  cause  a  rapid  play  of  jets  over  its  surface.  One  pool,  the 
largest  of  the  three  then  in  action,  was  afterwards  ascertained  by  survey  to  measure 
1500  feet  in  one  diameter,  and  1000  in  the  other,  and  this  whole  area  was  boiling,  as 
seemed  from  above,  with  nearly  the  mobility  of  water." "On  descending  after- 
wards to  the  black  ledge,  at  the  verge  of  the  lower  pit,  a  half-smothered  gurgling 
sound  was  all  that  could  be  heard  from  the  pools  of  lava.  Occasionally  there  was  a 
report  like  that  of  musketry,  which  died  away,  and  left  the  same  murmuring  sound, 
the  stifled  mutterings  of  a  boiling  fluid."  p.  171. 

"  The  dense  white  vapours  rose  gracefully  from  many  parts  of  the  black  lava  plain, 
and  the  pools  boiled  on  without  any  unnecessary  agitation.  The  jets  playing  over  the 
boiling  surface  darted  to  a  height  of  10  or  12  yards,  and  fell  again  into  the  pools,  or 
upon  its  sides.  At  times,  the  ebullition  was  more  active,  the  cauldrons  boiled  over, 
and  glowing  streams  flowed  away  to  distant  parts  of  the  crater ;  and  then  they  settled 
down  again,  and  boiled  as  before,  with  the  usual  grum  murmur.  Thus  simple  and 
quiet  was  the  action  of  Loa  Pele."  p.  176. 


CRATER    OF    MAUNA    LOA,    HAWAII. 


335 


volcanic  vent  is  found  of  much  the  same  general  character  as  that  of 
the  former.     The  annexed   sketch  (fig.   125)  is  a  reduction  of  that 


Fig.  125. 


given  by  Captain  Wilkes.*  The  deepest  part  of  the  crater  is  nearly- 
circular,  and  about  8000  feet  in  diameter.  The  walls  are  described  as 
nearly  vertical,  stratified  like  those  of  Kilauea,  784  feet  high  on  the 
west  side,  470  on  the  east.f  An  eruption  of  this  crater  occurred  in 
1843,  so  that  Mauna  Loa  may  be  considered  as  still  active.  It  has 
been  remarked  by  Mr.  Dana,  as  an  interesting  fact,  that  this  outbreak 
did  not  affect  Kilauea,  though  a  great  lateral  crater  on  the  same  vol- 
canic dome,  10,000  feet  lower  down  its  side.J  The  mass  of  lava  seems 

*  "Narrative  of  the  United  States  Exploring  Expedition,"  vol.  vi. 

f  Dana,  "Geology  of  Exploring  Expedition,"  p.  206. 

J  Mr.  Dana  quotes  from  the  "  Missionary  Herald,"  vol.  xxxix.  p.  381,  and  vol.  xl. 
p.  44,  an  account  of  this  eruption,  in  order  to  render  it  more  publicly  known  to  sci- 
entific persons.  For  the  like  reason  we  insert  a  portion  of  it  here,  not  only  as  it  is 
in  itself  geologically  important,  but  also  as  it  is  stated  that  only  a  somewhat  limited 
number  of  Mr.  Dana's  valuable  work  has  been  printed.  The  Rev.  T.  Coan  states  that 
"  On  the  morning  of  January  10  (1843),  before  day,  we  discovered  a  small  beacon-fire  near 
the  summit  of  Mauna  Loa.  This  was  soon  found  to  be  a  new  eruption  on  the  north- 
eastern slope  of  the  mountain,  at  an  elevation  of  near  13,000  feet.  Subsequently  the 
lava  appeared  to  burst  out  at  different  points  lower  down  the  mountain,  from  whence 
it  flowed  off  in  the  direction  of  Mauna  Kea,  filling  the  valley  between  the  mountains 
with  a  sea  of  fire.  Here  the  stream  divided,  one  part  flowing  towards  Waimea,  north- 
ward, and  the  other  eastward  towards  Hilo.  Still  another  great  stream  flowed  along 
the  base  of  Mauna  Loa  to  Hualalai  in  Kona.  For  about  four  weeks  this  scene  con- 
tinued without  much  abatement.  At  the  present  time,  after  six  weeks,  the  action  is 
much  diminished,  though  it  is  still  somewhat  vehement  at  one  or  two  points  along  the 
line  of  eruption."  Mr.  Coan  ascended  the  mountain,  passing  fields  of  scoriaceous  and 
smoother  lavas,  and  regions  at  times  still  steaming  and  hot.  "  Soon,"  he  continues, 
"we  came  to  an  opening  in  the  superincumbent  stratum,  of  20  yards  long  and  10  wide, 


336  ERUPTION    OF    ASHES    FROM    KILAUEA. 

to  have  burst  out  of  cracks  around  the  summit  of  the  mountain,  and  in 
one  instance  a  subterranean  channel  for  a  portion  of  the  molten  rock 
was  observed. 

From  all  accounts  respecting  the  mineral  volcanic  products  in 
Hawaii,  the  ejection  of  cinders  and  ashes  would  appear  to  be  compara- 
tively rare.  They  are,  however,  occasionally  thrown  out  in  quantities 
relatively  too  small  to  produce  much  influence  in  the  arrangements  of 
the  other  and  common  volcanic  products  which  have  accumulated  in  a 
molten  state.  It  is  stated  that,  during  an  eruption  of  Kilauea  in  1789, 
ashes  and  cinders  were  abundantly  thrown  out,  darkening  the  air,  and 
destroying  some  men  forming  part  of  an  army  then  on  its  march ;  and 
Mr.  Dana  mentions  that  near  Kilauea,  "  a  few  miles  south  and  south- 
east, great  quantities  of  pumice-like  scoria,  with  stones  and  sand,  are 
believed  to  have  been  thrown  out  at  this  time."* 

An  uplifting  of  liquid  lava  in  the  craters,  and  a  rending  of  the  solid 
rocks  around  them,  or  further  down  on  the  flanks  of -the  great  volcanic 
mounds,  through  which  the  molten  rock  is  discharged,  would  appear 

through  which  we  looked,  and  at  the  depth  of  50  feet  we  saw  a  vast  tunnel,  or  sub- 
terranean canal,  lined  with  smooth  vitrified  matters,  and  forming  the  channel  of  a  river 
of  fire,  which  swept  down  the  steep  side  of  the  mountain  with  amazing  velocity.  As  we 
passed  up  the  mountain  we  found  several  similar  openings  into  this  canal,  through 
which  we  cast  stones ;  these,  instead  of  sinking  into  the  viscid  mass,  were  borne  along 
instantly  out  of  our  sight.  Mounds,  ridges,  and  cones  were  also  thrown  up  along  the 
line  of  the  lava  stream,  from  the  latter  of  which  steam,  gases,  and  hot  stones  were 
ejected.  At  three- o'clock  we  reached  the  verge  of  the  great  crater,  where  the  eruption 
first  took  place,  near  the  highest  point  of  the  mountain.  Here  we  found  two  immense 
craters  close  to  each  other,  of  vast  depth,  and  in  terrific  action." 

To  queries  transmitted  by  Mr.  Dana,  Mr.  Coan  replied  as  follows :  "  The  angle  of 
descent  down  which  the  lava  flowed  from  the  summit  to  the  northern  base  of  Mauna 
Loa  is  6° ;  but  there  are  many  places  on  the  side  of  the  mountain  where  the  inclination 
is  10°,  15°,  or  25°,  and  even  down  these  local  declivities  of  half  a  mile  to  two  miles  in 
extent,  the  lava  flowed  in  a  continuous  stream.  This  was  the  fact,  not  only  during 
the  flow  of  several  weeks  on  the  surface,  but  also  in  that  wonderful  flow  in  the  sub- 
terranean duct,  described  in  the  '  Missionary  Herald.'  There  was  no  insurmountable 
barrier  in  the  way  of  the  flow  from  the  summit  of  Mauna  Loa  to  the  base  of  Mauna 
Kea,  a  distance  of  25  or  30  miles.  The  stream  sometimes  struck  mounds  or  hillocks, 
which  changed  its  course  for  a  little  space,  or  around  which  it  flowed  in  two  channels, 
reuniting  on  the  lower  side  of  the  obstacle,  and  thus  surrounding  and  leaving  it  an 
island  in  the  fiery  stream.  Ravines,  caves,  valleys,  and  depressions  were  filled  up  by 
the  lava  as  it  passed  down  the  slope  of  the  mountain,  and  between  the  two  mountains. 
In  conclusion,  I  may  remark  that  the  stream  was  continuous  for  more  than  25  miles, 
with  an  average  breadth  of  1J  miles,  and  flowed  down  a  declivity  varying  from  1°  to 
25°."— Dana,  "  Geology  of  the  United  States  Exploring  Expedition,"  p.  210. 

*  Mr.  Dana  ("  Geology  of  the  United  States  Exploring  Expedition,"  p.  181).  quotes 
from  a  "  History  of  the  Sandwich  Islands,"  published  by  the  Rev.  J.  Dibble,  at  Lahai- 
naluna  (Island  of  Maui),  in  1843,  an  account  from  the  lips  of  those  who  were  in  the 
body  of  men  thus  partly  destroyed  by  the  eruption.  A  large  volume  of  cinders  and 
sand  is  noticed  as  thrown  to  a  great  height,  and  as  falling  in  a  destructive  shower  for 
many  miles  around.  Some  of  the  men  appeared  to  have  been  killed  by  this  shower  of 
cinders  and  ashes,  and  others  to  have  perished  from  an  emanation  of  heated  vapour  or 
gas. 


GREAT    FLUIDITY    OF    THE    KILAUEA    LAVA.  337 

the  characteristic  action  of  the  Hawaiian  volcanoes.  Mr.  Dana  has 
well  stated  this  mode  of  eruption,  which  he  terms  the  quiet  mode. 
Alluding  to  Kilauea,  he  remarks,  "  The  boiling  pools  of  the  lower  pit 
have  gradually  filled  this  (the  lower)  part  of  the  crater  with  their  over- 
flowings, each  stream  cooling,  and  then,  in  a  few  hours  or  days,  fol- 
lowed by  another  and  another  overflow  in  different  parts  of  the  vast 
area,  till  the  rising  bottom  became  as  high  as  the  black  ledge."  .... 
"  The  black  ledge  is  finally  flooded,  and  the  accumulation  reaches  the 
maximum  which  the  sides  of  the  mountain  can  bear."  The  pressure 
increases,  and  passages  are  broken  out  for  the  molten  rock.  "  In  some 
cases,  on  the  side  of  the  island  where  the  escape  takes  place,  the  first 
indication  of  the  eruption  is  the  approach  of  the  flowing  lava.  We 
would  not  imply  that  the  land  is  proof  against  earthquakes,  for  slight 
shocks  not  unfrequently  happen,  and  they  have  been  of  considerable 
force  during  an  eruption.  But  earthquakes  are  no  necessary  attendants 
on  an  outbreak  at  Kilauea.  It  is  a  simple  bursting  or  rupture  of  the 
mountain  from  pressure,  and  the  disruptive  force  of  vapours,  in  conse- 
quence of  which  the  mountain,  thus  tapped,  discharges  itself."* 

The  mode  of  fissuring  seems  to  have  been  well  observed  in  the 
eruption  from  Kilauea,  in  June,  1840.  The  fissures  are  noticed  as  at 
first  small.  Those  through  which  the  molten  lava  poured  formed  series 
at  intervals.  Through  the  last  twelve  miles  there  were  several  rents, 
two  or  three  in  some  places  running  nearly  parallel.  The  mass  of  lava 
derived  from  these  several  fissures  reached  the  sea,  on  coming  into  con- 
tact with  which  it  became  shivered  like  melted  glass  cast  into  water. 
Into  the  sea  it  continued  to  flow  for  three  weeks,  and  the  waters  were 
so  much  heated  that  the  shores  were  strewed  with  dead  fish  for  the 
distance  of  twenty  miles.  The  depth  of  the  lava  is  considered  to  have 
averaged  10  or  12  feet,  though  in  some  places  only  6  feet  thick.  The 
area  covered  by  it  was  estimated  at  about  fifteen  square  miles.  The 
lower  pit,  of  Kilauea,  calculated  to  have  held  15,400,000,000  cubic  feet 
of  molten  matter,  was  emptied  by  the  outflow  of  the  lava  through  the 
fissures. f  The  settling  down  of  the  lava  in  Kilauea,  would  appear 
always  to  accompany  these  eruptions. 

The  lavas  of  Hawaii  seem  to  have  been  usually  very  fluid,  judging 
from  the  mode  in  which  they  occur.  That  they  are  so  now  in  Kilauea 
seems  generally  admitted.  The  production  of  the  capillary  volcanic 
glass,  known  at  Hawaii  as  Peles  Hair£  is  an  interesting  example  of 
this  fluidity.  Mr.  Dana,  who  witnessed  its  formation  at  one  of  the  pools 

*  "  Geology  of  the  United  States  Exploring  Expedition,"  p.  195. 

f  Mr.  Dana  estimates  that  this  gives  the  best  measure  of  the  amount  of  lava  poured 
out  during  this  eruption.  As  measured  by  the  amount  of  matter  observed  on  the 
surface,  a  much  less  quantity  was  erupted,  estimated  in  this  way  at  5,000,000,000 
cubic  feet. 

%  Pele  is  the  reputed  principal  goddess  of  the  volcano. 

22 


338  EFFECTS    OF    VERY    LIQUID    LAVA    ON    TREES. 

of  melted  lava,  states  that  "  it  covered  thickly  the  surface  to  leeward, 
and  lay  like  mown  grass,  its  threads  being  parallel,  and  pointing  away 
from  the  pool.  On  watching  the  operation  a  moment  it  was  apparent 
that  it  proceeded  from  the  jets  of  liquid  lava  thrown  up  by  the  process 
of  boiling.  The  currents  of  air,  blowing  across  these  jets,  bore  off  small 
points,  and  drew  out  a  glassy  fibre,  such  as  is  produced  in  the  common 
mode  of  working  glass.  The  delicate  fibre  floated  on  till  the  heavier 
end  brought  it  down,  and  then  the  wind  carried  over  the  lighter  capil- 
lary extremity.  Each  fibre  was  usually  ballasted  with  the  small  knob 
which  was  borne  off  from  the  lava-jet  by  the  winds."* 

In  the  flow  of  the  lava  outburst  from  Kilauea,  in  June,  1840,  the  molten 
rock,  as  it  passed  amid  forests,  not  only  enclosed  the  stems  of  indivi- 
dual trees,  leaving  cylindrical  holes  from  the  total  or  partial  destruction 
of  the  wood,  but  sometimes  also  adhered  to  the  branches,  descending 
from  them  in  the  form  of  stalactites.  In  these  latter  cases  the  heat  is 
described  as  having  been  barely  sufficient  to  scorch  the  bark,  though 
the  branches  were  clasped  by  the  molten  rock.  Should  the  branch 
have  contained  much  fluid  matter,  we  can  suppose  that,  the  heat  and 
fluidity  of  the  lava  being  great,  vapour  from  the  bark  may  have  pre- 
vented actual  contact  with  it  for  a  time  sufficient  for  the  passage  of  the 
lava  stream  at  a  height  at  which  the  branches  could  be  entangled  in  it.f 
The  lava  descending  suddenly  from  this  height,  by  the  lowering  of  the 
general  level  of  the  fluid  stream  as  it  passed  onwards,  and  as  the  stalac- 
titic  form  of  the  depending  portions  of  it  would  appear  to  show,  equally 
sudden  exposure  to  the  atmosphere  would  preserve,  by  quickly  cooling, 
the  adhering  and  depending  portions,  so  that  little  heat  acted  on  the 
branches.!  The  case  would  be  different  where  the  heated  lava  con- 

*  "  Geology  of  the  United  States  Exploring  Expedition,"  p.  179. 

f  The  summary  given  by  Mr.  Dana  of  the  effects  of  this  flow  of  lava  amid  the  forest 
ground,  is  highly  interesting  in  many  respects.  "  The  islets  of  forest  trees,"  he  states, 
"  in  the  midst  of  the  stream  were  from  one  to  fifty  acres  in  extent,  and  the  trees  still 
stood,  and  were  sometimes  living.  Captain  Wilkes  describes  a  copse  of  bamboo  which 
the  lava  had  divided  and  surrounded ;  yet  many  of  the  stems  were  alive,  and  a  part 
of  the  foliage  remained  uninjured  ('  Narrative  of  Exploring  Expedition,'  vol.  iv.  p. 
184).  Near  the  lower  part  of  the  flood  the  forests  were  destroyed  for  a  breadth  of 
half  a  mile  on  either  side,  and  were  loaded  with  the  volcanic  sand  ;  but  in  the  upper 
parts  Dr.  Pickering  found  the  line  of  the  dead  trees  only  20  feet  wide.  The  lava  some- 
times flowed  around  the  stumps  of  trees,  and  as  the  tree  was  gradually  consumed,  it 
left  a  deep  cylindrical  hole,  sometimes  2  feet  in  diameter,  either  empty  or  filled  with 
charcoal.  (Mr.  Dana  refers  here  to  similar  facts  observed  by  M.  Bory  de  St.  Vincent 
at  the  Isle  Bourbon,  '  Voyage  aux  Isles  d'Afrique,'  1804.)  Towards  the  margin  of 
the  stream  these  stump-holes  were  innumerable,  and  in  many  instances  the  fallen  top 
lay  near  by,  dead  but  not  burnt.  Dr.  Pickering  also  states  that  some  epiphytic  plants 
upon  these  fallen  trees  had  begun  again  to  sprout."  The  fact  is  then  mentioned  of  the 
lava  depending  in  stalactitic  forms  from  the  branches  of  the  trees,  and  "  although  so 
fluid  when  thrown  off  from  the  stream  as  to  clasp  the  branch,  the  heat  had  barely 
scorched  the  bark." — "  Geology  of  the  United  States  Exploring  Expedition,"  p.  191. 

I  The  results  have  been  long  known  at  the  manufactories  of  crown-glass,  attendant 


ERUPTIONS    OF    VESUVIUS.  339 

tinued  to  surround  the  lower  parts  of  the  trees.  Whatever  may  have 
been  the  moisture  preventing  immediate  contact,  as  the  cooling  pro- 
ceeded, a  time  would  come  for  the  scorching,  if  not  actual  contact,  of 
the  included  stems. 

Cotopaxi  and  the  volcanoes  of  Hawaii,  though  thus  useful  in  showing 
how  modified  the  results  of  volcanic  action  may  be,  and  pointing  to  dif- 
ferences in  that  action  of  no  slight  importance  to  the  observer  seeking 
for  facts  to  guide  him  to  the  knowledge  of  its  probable  cause,  have  yet 
been  so  recently  known  to  us,  that  when  studying  the  changes  which 
may  have  taken  place  in  volcanic  vents,  he  must  look  to  volcanic  lands 
of  which  there  may  be  records  extending  back  a  few  centuries,  at  least, 
for  the  requisite  data.  Fortunately  for  this  inquiry  the  volcanoes  of 
Italy  have  engaged  attention  for  many  centuries.  Vesuvius  offers  an 
excellent  instance  of  a  volcanic  vent  which,  after  remaining  long  dor- 
mant, somewhat  suddenly  became  active,  nearly  1800  years  ago,  and 
has  more  or  less  continued,  with  intervals  of  various  lengths,  in  that 
state  ever  since.  After  a  repose,  not  known  to  have  been  interrupted 
during  a  long  period,*  suddenly,  on  the  24th  August,  79,  after  earth- 
quakes of  several  days'  duration,  cinders  and  ashes  were  furiously  driven 
out,  partly,  no  doubt,  a  portion  of  the  old  volcanic  accumulations. 
Their  abundance  was  so  great  that  three  cities,  Stabise,  Pompeii,  and 
Herculaneum,  were  overwhelmed  by  them  (p.  143).  We  may  assume 
that  lava  currents  were  also  vomited  forth  out  of  the  volcano  at  this 
eruption,  one,  apparently,  of  the  greatest  of  Vesuvius  on  record.  There 
then  seems  to  have  been  a  state  of  repose,  or  at  least  of  only  minor 
movements  insufficient  to  create  attention,  for  134  years,  when  another 
eruption  occurred,  succeeded  by  a  similar  interval  of  quiet  for  269 
years,  when  there  was  an  outburst  so  considerable  as  to  cover  a  portion 
of  Europe  with  ashes. f  There  were  then  intervals  between  the  erup- 

on  plunging  a  highly  heated  body  into  a  liquid,  and  which  have  of  late  attracted  much 
attention,  especially  from  the  experiments  and  reasoning  of  M.  Boutigny,  the  vapour 
or  steam  preventing  actual  contact  in  the  first  instance,  so  that  the  plunged  body  does 
not  acquire  the  temperature  that  might  at  first  be  expected.  In  those  establishments 
it  has  been,  from  time  immemorial,  the  practice  to  plunge  the  melted  and  very  highly 
heated  glass  in  some  of  the  first  processes,  after  removal  from  the  melting-pot,  into 
cold  water,  to  reduce  the  temperature.  This  does  not  fracture  the  glass,  the  steam 
produced  preventing  contact  between  the  highly  heated  glass  and  the  water.  In  after 
processes  with  the  same  piece  of  glass,  a  mere  drop  of  water  is  employed  to  sever  a 
large  attached  glass  stem,  the  heat  being  now  so  reduced  that  contact,  with  its  conse- 
quences, is  immediate.  It  is  not  a  little  interesting,  at  great  crown-glass  works,  to 
see  both  effects,  frequently  produced  at  the  same  time,  and  within  the  distance  of  a 
few  feet. 

*  A  very  excellent  condensation  of  our  information  respecting  the  ancient,  interme- 
diate, and  modern  states  of  Vesuvius,  will  be  found  in  "  Daubeny's  Description  of 
Active  and  Extinct  Volcanoes,"  2d  edition,  1848. 

|  When  reference  is  made  to  the  depth  of  cinders  and  ashes  now  found  covering 
Stabise,  Pompeii,  and  Herculaneum,  it  is  needful  to  recollect  that  a  portion  of  them 


340  ERUPTIONS    OF    ETNA. 

tions,  the  accounts  of  which  have  reached  us,  of  40,  173,  308,  43,*  13, 
89,  1,  167,  194,  131,  29,  22,  12,  3,  and  1  years,  bringing  them  down 
to  1698.  "From  that  time  to  the  present,"  observes  Dr.  Daubeny, 
respecting  Vesuvius,  "its  intervals  of  repose  have  been  less  lasting, 
though  its  throes  perhaps  have  diminished  in  violence  ;  for  the  longest 
pause  since  that  time  was  from  1737  to  1751,  and  no  less  than  eighteen 
distinct  eruptions  are  noticed  in  the  course  of  little  more  than  a  cen- 
tury, several  of  which  continued  with  intermission  for  the  space  of  four 
or  five  years."f 

Even  supposing  the  earlier  recorded  eruptions  of  Vesuvius  to  be  only 
approximations  to  the  real  number,  some  being  omitted  which  would 
now  not  fail  to  be  noticed,  the  irregularity  of  the  intervals  of  consider- 
able activity  would  still  be  so  far  marked  as  to  point  to  inconstancy  in 
the  final  conditions  upon  which  a  marked  eruption  depends.  At  the 
same  time,  also,  the  different  intensity  of  the  eruptions  themselves 
leads  to  the  same  inference.  Not  only  was  the  crater  of  Vesuvius  so 
tranquil,  prior  to  the  great  outburst  of  79,  that  it  was  clothed  with 
vegetation,  that  crater  occupying  the  depression  now  known  as  the 
Atrio  del  Cavallo  (the  present  Monte  Somma  forming  a  portion  of  its 
ancient  walls),  but  also  between  the  eruptions  of  1500  and  1631,  the 
crater  of  the  period  was  covered  with  herbage,  {  as  those  of  earlier  times 
may  have  been  between  other  long  intervals  of  repose  following  the 
great  eruption  of  79. 

Etna  also  becomes  valuable  for  the  length  of  time  during  which  its 
outbursts  have  been  noticed.  According  to  researches  respecting  the 
earlier  eruptions  of  this  volcano,§  the  year  480  B.C.,  or  thereabouts, 
would,  appear  that  to  which  any  marked  outburst  can  be  traced  during 
historic  times.  This  would  give  us  about  2330  years  for  a  record,  if 
not  of  all,  of  at  least  a  considerable  number  of  the  chief  eruptions  of 
this  volcano,  the  geological  records  of  the  activity  of  which  would 
appear  to  extend  far  beyond  this  comparatively  limited  time.  Taking 
the  early  historic  notices  for  the  value  they  may  possess,  including  that 

may  have  been  accumulated  during  eruptions  such  as  this,  and  at  other  subsequent 
times. 

*  A  great  eruption,  in  1036,  during  which  much  lava  was  poured  out,  as  is  stated, 
from  the  crater  as  well  as  from  the  sides. 

|  "Description  of  Volcanoes,"  p.  226. 

j  "  In  the  interval  between  the  eruption  of  1500  and  1631,  the  mountain  put  on  the 
appearance  of  an  extinct  volcano,  the  interior  of  the  crater,  according  to  Braccini, 
being,  in  1611,  covered  with  shrubs  and  rich  herbage,  the  plain  called  the  Atrio  del 
Cavallo  overgrown  with  timber  and  sheltering  wild  animals,  whilst  in  another  part 
there  were  three  pools,  two  of  hot  and  one  of  cold  water,  and  two  of  these  impregnated 
with  bitter  salts."— Daubeny,  "Description  of  Volcanoes,"  p.  235. 

\  A  table  of  the  dates  of  the  eruptions  of  Etna  and  Vesuvius,  taken  from  Von  Hoff's 
"  Qeschichte  der  Veranderungen  der  Erdoberflache,"  with  some  few  additions,  is  given 
by  Dr.  Daubeny,  in  his  "Description  of  Volcanoes,"  2d  edition,  p.  289. 


ERUPTIONS    FROM    THE     ICELANDIC    VOLCANOES.          341 

of  480  B.C.,  there  have  been  marked  eruptions  recorded  between  that 
date  and  the  commencement  of  the  Christian  era.  With  the  exception 
of  a  lapse  of  time  between  396  B.C.,  and  140  B.C.  (256  years),  the 
outbursts  noticed  occurred  at  intervals  of  53,  31,*  5,  10,  3,  66,  12,  and 
8  years.  They  thus  correspond  in  frequency  with  those  recorded 
between  A.D.  1284  and  the  present  time.f  From  A.D.  40,  or  there- 
abouts, to  1169,  the  eruptions  from  this  volcano  did  not,  apparently, 
receive  much  attention.  If  we  assume  that  this  lapse  of  time  had  not 
been  one  of  repose  more  than  those  which  preceded  and  followed  it, 
Etna  seems  to  have  been  a  somewhat  active  volcano  for  at  least  2330 
years. 

The  volcanoes  of  Iceland  have  also  been  known  as  more  or  less  in 
activity  during  a  long  lapse  of  historic  time.  Of  the  known  marked 
outbursts  of  Hecla  there  -  have  been  23,  including  that  of  1845,  since 
1004  or  1005.  These  have  varied  in  intensity  and  in  the  length  of  the 
intervals  of  repose  between  them.  The  eruption  of  1845  appears  to 
have  driven  out  a  vast  abundance  of  cinders  and  ashes,  the  latter 
carried  by  the  movements  of  the  atmosphere  to  great  distances.^  From 
Kattlagiau-jokull  there  have  been  several  eruptions  since  the  year  900. 
While  thus  these  volcanoes  have  vomited  forth  molten  rock,  cinders,  and 
ashes  at  intervals  for  845  and  950  years,  eruptions  from  other  vents  of 
the  same  great  volcanic  mass  of  Iceland,  such  as  Krabla,  of  which  there 
•were  four  outbursts  during  the  last  125  years,  have  also  taken  place. 
Another  great  volcano,  Skaptar-jokull,  previously  dormant,  as  far  as 
the  historic  records  of  that  land  extend,  suddenly  became  active  in 
1783.  During  this  eruption,  which  was  preceded  by  earthquakes  over 

*  Respecting  this  eruption  of  396  B.C.,  Dr.  Daubeny  mentions  ("  Description  of  Vol- 
canoes," p.  283),  that  the  stream  of  lava  which  then  stopped  the  march  of  the  Cartha- 
ginian army  against  Syracuse,  is  to  "be  seen  on  the  eastern  slope  of  the  mountain, 
near  Giarre,  extending  over  a  breadth  of  more  than  two  miles,  and  having  a  length  of 
24  from  the  summit  of  the  mountain  to  its  final  termination  in  the  sea.  The  spot  in 
question  is  called  the  Bosco  di  Aci ;  it  contains  many  large  trees,  and  has  a  partial 
coating  of  vegetable  mould,  and  it  is  seen  that  this  torrent  covered  lavas  of  an  older 
date  which  existed  on  the  spot." 

f  From  1284,  the  intervals  of  repose  have  been  in  years  45,  4,  75,  33,  1,  1,  and  82. 
Then  a  continuance  of  small  eruptions  for  58  years  (1566  to  1624),  after  which  the 
intervals  were  9,  11,  9,  15,  13,  6, 1,  5,  8,  21,  12, 12,  8,  4,  4,  3,  14,  1,  6,  5,  6,  1, 1,  2,  7, 
2,  8,  12,  1,  and  10  years  (in  December,  1842),  calculated  from  the  table  in  Daubeny's 
"Description  of  Volcanoes,"  p.  289-291. 

J  "  On  the  2d  of  September,  1845,  the  day  of  the  eruption  of  Hecla,  a  Danish  vessel, 
near  the  Orkney  Islands,  at  a  distance  of  115  Danish  miles  (about  500  English)  from 
the  volcano,  was  covered  with  ashes." — Daubeny,  "Volcanoes,"  2d  edition,  p.  307. 
According  to  Professor  Forchhammer  (Poggendorff's  Annalen,  vol.  Ixvi.,  1845),  the 
cinders  and  ashes,  so  abundantly  discharged,  were  ejected  from  three  vents  on  the 
southwest  slope  of  Hecla,  and  the  lava  from  a  fourth,  situated  a  little  distance  beneath 
them.  The  eruptions  continued  in  force  on  the  12th  of  the  following  month  (October), 
the  lava  still  flowing.  The  eruption  did  not  finally  cease,  though  there  were  intervals 
of  repose,  until  the  commencement  of  March,  1846. 


342  CONSTANT    ACTIVITY    OF    STROMBOLI. 

the  whole  of  Iceland,  and  the  ejection  of  volcanic  matter  in  the  adjacent 
sea,  considerable  masses  of  lava  were  thrown  out,  according  to  Sir 
George  Mackenzie,*  from  three  different  points,  about  eight  or  nine 
miles  from  each  other,  on  the  lower  flanks  of  the  mountain,  spreading 
in  some  places  to  the  breadth  of  many  miles.  Of  the  20  volcanic  vents, 
as  Dr.  Daubeny  has  pointed  out,  which  have  ejected  lava,  cinders,  or 
ashes  during  the  950  years  since  Iceland  was  colonized,  "  eleven  have 
had  but  one  eruption,  and  amongst  these  four  only  occurred  within  the 
last  century;  whilst  of  the  remaining  nine,  Myrdalls-jokull,  Skaptar- 
jbkull,  Sandfells-jokull,  Skeidarar-jokull,  Reikianes,  Hecla,  and  Krabla 
alone  would  appear  to  be  active  at  present ;  Trblladyngia  having  had 
no  eruption  since  1510 ;  Oroefa-jbkull  none  since  1362 ;  and  others 
having  been  for  a  nearly  equal  time  in  a  state  of  quiescence,  "f 

While  Vesuvius,  Etna,  and  volcanoes  in  Iceland  thus  afford  informa- 
tion as  to  alternate,  but  irregular,  intervals  of  repose  and  activity,! 
the  eruptions  themselves  differing  in  intensity,  the  two  former  during 
the  lapse  of  more  than  2000  years,  and  the  latter  approaching  towards 
a  period  of  1000,§  Stromboli,  a  volcanic  vent  rising  through  the  sea 

*  "  Travels  in  Iceland,"  2d  edition.  Noticing  this  eruption  from  Skaptar-jokull,  in 
1783,  Sir  George  Mackenzie  states,  that  in  January  of  that  year,  volcanic  eruptions, 
represented  as  accompanied  by  flame,  rose  through  the  sea,  about  30  miles  from  Cape 
Reikianes,  and  that  several  islands  were  observed,  as  if  upraised,  a  reef  of  rocks  now 
existing  where  these  appearances  occurred.  "  The  flames  lasted  several  months,  during 
which  vast  quantities  of  pumice  and  light  slags  were  washed  on  shore.  In  the  begin- 
ning of  June  earthquakes  shook  the  whole  of  Iceland ;  the  flames  in  the  sea  disappeared ; 
and  the  dreadful  eruption  commenced  from  the  Skaptar-jokull,  which  is  nearly  200 
miles  distant  from  the  spot  where  the  marine  eruption  took  place." 

The  eruption  of  1783,  is  stated  to  have  thrown  out  such  an  abundance  of  cinders  and 
ashes  that  the  whole  island  was  covered  by  them.  The  ashes  were  windborne  as  far 
as  Holland. 

f  Daubeny,  "Description  of  Active  and  Extinct  Volcanoes,"  2d  edition,  p.  306. 

J  Selecting  Hecla  from  the  table  given  by  Dr.  Daubeny  ("Volcanoes,"  p.  314),  and 
taken  from  Garlieb  (Island  rucksichlich  seiner  Vulcans,  &c.,  Freiberg,  1812),  with  ad- 
ditions, it  would  appear  that  its  marked  eruptions,  commencing  with  that  of  1004, 
have  occurred  at  intervals  of  25,  75,  9,  44,  47,  18,  72,  46,  34,  16,  46,  74,  44,  29,  36,  6, 
11,  57,  35,  26,  12,  6,  and  73  years,  the  last  terminating  with  the  eruption  of  1845. 
The  intervals  between  the  outbursts  of  Trolladyngia,  commencing  with  the  eruption  of 
1150,  were  38,  171,  116,  and  35  years.  For  340  years  (since  1510)  this  vent  has  been 
quiet.  While  Hecla  has  shown  the  most  constancy  in  position  amid  the  volcanic  vents 
of  Iceland,  active  at  various  intervals  for  the  last  1046  years,  and  while  single  erup- 
tions have  only  been  known  at  other  points,  certain  vents  have  shown  themselves  active 
during  the  lapse  of  the  same  time  for  a  few  years  only.  Thus  eruptions  are  recorded 
at  Reikianes  as  occurring  in  1222,  1223,  1226,  1237,  and  1240,  altogether  only  for  18 
years,  since  which  time  thqy  have  ceased.  At  Krabla,  also,  they  commenced  in  1724, 
were  repeated  in  1725,  1727,  1729,  and  in  1730,  after  which  none  have  occurred.  At 
Skeidarar-jokull  eruptions  began  in  1725,  were  repeated  in  1727  and  1728,  and  ter- 
minated with  one  in  1753.  The  outburst  of  Sandfells-jokull  in  1748  is  recorded  as 
continued,  probably  with  intervals  of  repose,  to  1752,  the  eruptions  being  mentioned 
as  annual  for  that  time. 

$  The  volcano  of  Eldborgarhraun,  in  Iceland,  is  inferred  to  have  had  an  eruption  in 
the  year  850. 


RECORDS    OF    VOLCANIC    ACTION.  343 

between  Naples  and  Sicily,  has  been  equally  marked,  for  more  than 
2000  years,  as  exhibiting  the  same  amount  of  activity.  "No  cessation," 
as  Dr.  Daubeny  remarks,  "has  ever  been  noticed  in  the  operations  of 
this  volcano,  which  is  described  by  writers  antecedent  to  the  Christian 
era  in  terms  which  would  be  well  adapted  to  its  present  appearance."* 
There  seems  a  constant  boiling  of  molten  matter  in  the  crater,  a  louder 
explosion  occurring  at  regular  intervals  with  an  escape  of  steam,  and 
the  throwing  out  of  blocks  of  lava  to  a  considerable  height,  f  From 
the  smaller  and  lower  of  three  apertures  within  the  crater,  "a  small 
stream  of  lava,  like  a  perennial  spring,  is  constantly  flowing.  "J 

Not  only  do  ancient  and  modern  records  thus  present  the  observer 
with  the  needful  information  respecting  both  intermittent  and  continued 
volcanic  action  for  2000  years  and  more,  and  with  the  ejection  of  lava, 
cinders,  and  ashes  from  vents  which  had  been  previously  dormant  as 
far  back  as  human  knowledge  and  tradition  extend,  but  also  regarding 
the  cessation  of  the  same  action  for  so  long  a  period,  that  the  volcanic 
vents  thus  circumstanced  form  a  kind  of  transition  from  active  volcanoes 
to  those  commonly  termed  "extinct."  The  last  stream  of  lava  which 
issued  from  Monte  Rotaro,  in  Ischia,  is  that  of  1302,  known  as  Arso. 
The  only  traces  of  volcanic  action  now  existing  in  this  island  are  its  hot 
springs.  Thus  no  eruptions  of  molten  rock,  cinders,  or  ashes  have 
taken  place  at  that  old  volcanic  vent  for  about  five  centuries  and  a  half. 
It  may  not  be  improbable,  frx)m  ancient  writings  and  modern  appear- 
ances, that  at  the  promontory  of  Methana  (formerly  Methone),  on  the 
coast  of  Greece,  volcanic  forces  were  in  activity,  and  had  not  finally 
ceased  in  the  time  of  Strabo,  though  since  then  that  volcanic  vent  has 
remained  quiescent.  §  Dr.  Daubeny  infers,  from  Livy  and  Julius  Ob- 
sequens,  that  the  volcanic  action  observable  in  the  Alban  Hills  (Central 
Italy)  may  have  continued  down  to  historic  times. || 

*  "Description  of  Volcanoes,"  2d  edition,  p.  247. 

f  Hoffmann,  "Poggendorff's  Annalen,"  1832. 

j  Daubeny,  "Description  of  Volcanoes,"  p.  247.  "It  flows  down  the  mountain," 
Dr.  Daubeny  states,  "in  the  direction  of  the  sea,  which,  however,  it  never  appears  to 
reach,  becoming  solid  before  it  arrives  at  that  point.  Some  portions,  however,  of  the 
congealed  mass  are  continually  detached,  and  roll  down  into  the  sea." 

$  Daubeny,  "Volcanoes,"  p.  328.  It  would  appear  that  at  that  time  the  volcano 
was  sometimes  so  hot  as  to  be  inaccessible,  and  to  be  visible  afar  off  at  night,  the  sea 
also  being  heated  near  it.  The  hills  of  the  peninsula,  according  to  Virlet  ("Expedition 
Scientifique  de  Moree,"  1839),  are  741  metres  (2431  English  feet)  above  the  sea,  and 
he  infers  that  among  the  igneous  rocks  of  different  dates  there  found,  the  last  volcanic 
action,  here  noticed,  occurred  on  the  western  part  of  the  peninsula,  where  the  trachyte 
presents  a  black  and  scoriaceous  aspect. 

||  He  observes  ("Volcanoes,"  p.  170)  that  "there  are  indeed  some  passages  in 
ancient  writers  which  might  lead  us  to  suppose  a  volcano  to  have  existed  among  these 
mountains  even  at  a  period  within  the  limits  of  authentic  history,  for  Livy  notices  a 
shower  of  stones,  which  continued  for  two  entire  days,  from  Mount  Albano,  during  the 
Second  Punic  War;  and  Julius  Obsequens,  in  his  work  'De  Prodigiis,'  remarks  that  in 
the  year  640,  A.  U.  C.,  the  hill  appeared  to  be  on  fire  during  the  night." 


344 

The  eruption  at  the  promontory  of  Methana  may,  it  would  appear, 
have  been  sudden,  a  considerable  mound  having  been  thrust  up,  or 
accumulated  in  a  short  time,  in  the  manner  of  Jorullo,*  which  rose 
above  the  Mexican  plain,  in  about  four  months,  to  the  height  of  1600 
feet,  or  the  still  more  rapid  production  of  the  Monte  Nuovo,  near 
Naples,  which,  in  about  two  days,  attained  an  altitude  of  440  feet,  with 
a  circumference  of  about  a  mile  and  .a  half.  These  sudden  outbursts 
are  important  as  regards  the  causes  of  volcanic  action,  more  especially 
when  no  appearance  of  a  previous  volcanic  vent  seems  to  have  presented 
itself.  It  would  appear  that  prior  to  June,  1759,  the  area  upon  which 
Jorullo  now  stands  was  covered  by  plantations  of  indigo  and  sugar, 
bounded  by  two  brooks,  the  Cuitimba  and  San  Pedro.  In  June,  sub- 
terranean noises,  accompanied  by  earthquakes,  commenced,  and  lasted 
fifty  to  sixty  days.  In  September  all  appeared  again  tranquil,  but  on 
the  28th  and  29th  of  that  month  the  subterranean  noises  were  repeated, 
and  according  to  Humboldt,  an  area  of  three  or  four  square  miles  rose 
up  like  a  bladder.  This  uprise  is  considered  to  be  marked  by  an  eleva- 
tion of  39  feet  around  the  edges  of  the  ground  thus  moved;  one  con- 
tinued to  the  height  of  524  feet  towards  the  centre  of  the  present 
volcanic  district.  The  subsequent  eruption  was  very  violent,  fragments 
of  rock  being  ejected  to  great  heights,  cinders  and  ashes  thrown  out  in 
abundance,  and  the  light  emitted  being  visible  at  considerable  distances. 
The  Cuitimba  and  San  Pedro  poured  themselves  into  the  new  volcanic 
vent.  "  Thousands  of  small  cones,  from  6  to  10  feet  in  height,  called 
by  the  natives  Hornitos  (ovens),  issued  forth  from  the  Malpays.  Each 
small  cone  is  a  fumerole,  from  which  a  thick  vapour  ascends  to  the 
height  of  from  22  to  32  feet.  In  many  of  them  a  subterranean  noise 
is  heard,  which  appears  to  announce  the  proximity  of  a  fluid  in  ebul- 
lition." •  Six  volcanic  masses,  varying  from  300  to  1600  feet  in  height, 
were  thrown  up  from  amid  these  cones,  out  of  a  chasm  having  a  N.N.E. 
and  S.S.W.  direction.  From  the  north  side  of  the  highest  (Jorullo)  a 
considerable  quantity  of  lava  was  ejected,  containing  fragments  of  other 
rocks.  The  great  eruptions  terminated  in  February,  1760. 

Respecting  Monte  Nuovo,  the  first  indications  of  its  production  were 
noticed  on  the  28th  of  September,  1538,  when,  according  to  an  eye-wit- 
ness, f  the  sea  bottom  near  Puzzuoli  became  dry  for  1300  yards,  and 
the  fish  left  upon  it  were  carried  away  in  wagons.  At  eight  o'clock 
next  morning  the  ground  is  reported  to  have  sunk,  where  the  volcanic 
orifice  afterwards  appeared,  about  13  feet.  At  noon  the  earth  began 
to  swell  up,  and  became  as  high  as  the  Monte  Rossi,  and  from  the  vent 
formed,  fire,  stones,  and  ashes  were  ejected,  so  that  finally  the  hill  took 

*  Daubeny,  "Description  of  Volcanoes,"  p.  327. 

f  Francesco  del  Nero.  A  letter  of  his  to  Nicola  del  Benino  of  Naples,  and  sent  to 
Rome  in  1538,  was  first  published  in  Leonhard's  "  Jahrbuch  fur  Geologic,"  184G,  and 
Daubeny  gives  a  translation  of  it,  "Description  of  Volcanoes,"  2d  edition,  p.  208. 


FALLING    IN    OF    PAPANDAYANG.  345 

the  form  now  seen.  For  70  miles  around  the  volcano  the  country  was 
covered  with  ashes,  killing  birds,  hares,  and  smaller  animals,  and  break- 
ing down  trees.  Monte  Nuovo  is  439  English  feet  high,  and  has  a 
crater  in  its  centre  420  feet  deep,  according  to  M.  Dufrenoy.  At  the 
bottom  there  is  a  cavern,  at  the  extremity  of  which  Professor  James 
Forbes  found  a  spring  issuing  with  a  temperature  of  182-5°. 

These  instances  of  the  sudden  production  of  volcanic  vents  on  dry 
land  (and  when  we  consider  the  chances  for  observing  and  recording 
them,  they  were  probably  far  more  numerous  within  the  last  1000  years) 
are  sufficient  to  show  the  observer  that  the  uprise  of  volcanoes  through 
the  sea  would  be  expected  amid  and  around  volcanic  islands  and  regions. 
In  the  atmosphere  they  retain  their  forms,  such  as  are  presented  at 
Jorullo  and  Monte  Nuovo ;  raised  through  the  level  of  the  sea,  the 
stability  of  such  portions  depends,  as  above  mentioned  (p.  95),  upon  the 
power  of  the  volcanic  mass  to  resist  the  action,  first,  of  the  breakers, 
and.  secondly,  of  the  wind-waves,  where  the  former  may  have  cut  it 
down  to  the  proper  depths.  The  volcanic  outbursts  of  this  kind  between 
Pantellaria  and  Sicily,  off  the  coast  of  Iceland,  and  among  the  Azores, 
have  been  already  noticed  (pp.  95  and  123).  To  these  may  be  added 
(as  showing  how  much  depends  on  the  opportunity  and  ability  to  have 
such  submarine  terminating  in  subaerial  eruptions  recorded,  and  the 
range  of  time  during  which  they  have  been  known),  the  mud,  smoke, 
and  flame  noticed  by  Strabo  as  rising  through  the  sea  amid  the  Lipari 
Islands,  and  the  flame  also  rising  there  above  its  level  during  the  Social 
War,  as  mentioned  by  Pliny.* 

Volcanic  accumulations  would  appear  sometimes  to  rest  upon  conside- 
rable hollows,  and  also  to  have  large  cavities  distributed  among  them, 
the  portions  covering  or  surrounding  which  being  either  unable  to  resist 
the  pressure  of  the  superincumbent  weight,  even  in  the  tranquil  periods 
of  a  volcano,  or  broken  through  during  eruptions,  the  volcanic  matter 
falls  in,  or  water  retained  amid  the  cavities  is  ejected.  Of  the  falling 
in  of  volcanic  accumulations,  depressions  sometimes  taking  the  place  of 
protrusions,  many  instances  are  given;  but  of  those  which  happen  to 
have  become  known,  the  disappearance  of  Papandayang,  a  volcano  of 
Java,  in  1772,  would  seem  to  be  most  remarkable.  Papandayang, 
formerly  one  of  the  largest  volcanoes  in  Java,  was  situated  on  the  south- 
western part  of  that  island.  After  a  short  but  violent  paroxysm,  and 
about  midnight,  between  the  llth  and  12th  of  August,  a  luminous  cloud 

*  Detailing  the  evidence  on  this  head,  Dr.  Daubeny  (Description  of  Volcanoes,  p.  253) 
asks  if  the  comparatively  recent  origin  of  the  Island  of  Lipari  itself  may  not  be  inferred 
from  its  present  fertility  as  compared  with  the  sterility  ascribed  to  it  by  Cicero.  He 
also  points  to  the  fresh  condition  of  the  craters  of  this  island,  as  observed  by  Hoffman, 
the  hot  springs  and  stufes  at  San  Calogero,  near  the  town  of  Lipari,  and  the  statement 
of  Strabo  that  this  island  emitted  a  fiercer  fire  than  Stromboli,  as  perhaps  showing  that 
an  active  volcano  may  have  existed  in  it  even  within  the  historical  period. 


346     PISH  LIVING  IN  CAVITIES  OF  VOLCANOES. 

enveloped  the  mountain.  The  inhabitants  of  the  sides  and  foot  of  the 
volcano  betook  themselves  to  flight,  "  but  before  they  could  all  save 
themselves,  the  whole  mass  began  to  give  way,  and  the  greatest  part  of 
it  actually  fell  in  and  disappeared  in  the  earth."  This  was  accompa- 
nied by  sounds  like  the  discharge  of  heavy  cannon,  and  an  abundance 
of  volcanic  substances  were  thrown  out  and  spread  around  the  adjoining 
country.  The  area  thus  swallowed  up  was  estimated  as  measuring 
fifteen  by  six  miles.  Forty  villages  are  stated  to  have  been  partly 
swallowed  up,  and  partly  destroyed  by  the  volcanic  substances  thrown 
out,  and  2957  inhabitants  perished.  Persons  sent  to  examine  the  locality 
found  the  heat  of  the  substances  surrounding  it,  and  piled  up  to  the 
height  of  three  feet,  so  great,  that  they  were  unable  to  approach  the 
spot  six  weeks  afterwards.* 

Cavities  amid  volcanic  accumulations  may  not  only  be  partially  or 
wholly  filled  by  water,  the  condensation  of  aqueous  vapours,  finding 
their  way  into  them,  or  derived  from  the  percolation  of  rain  or  melted 
snows  upon  the  exterior  of  a  volcano,  but  the  waters  in  them  may  be 
sometimes  of  a  temperature  and  kind,  permitting  the  existence  and  in- 
crease of  animal  life.  Humboldt  records,  that  "  when,  in  the  night  of 
the  19th  June,  1698,  the  summit  of  Carguairazo  (18,000  French  feet 
in  height,)f  fell  in,  leaving  two  immense  peaks  of  rock  as  the  sole  re- 
mains of  the  wall  of  the  crater,  masses  of  liquid  tufa,  and  of  argillaceous 
mud  (lodazales),  containing  dead  fish,  spread  themselves  over,  and  ren- 
dered sterile  a  space  of  nearly  two  square  German  miles.  The  putrid 
fevers,  which  seven  years  before  prevailed  in  the  mountain  town  of 
Ibarra,  north  of  Quito,  were  attributed  to  the  quantity  of  dead  fish 
ejected  in  like  manner  from  the  volcano  of  Imbaburu."J  The  fish 
here  noticed  (Pimdodus  cyclopum),  Humboldt  further  informs  us, 
" multiply  by  preference  in  the  obscurity  of  the  caverns;"  possibly, 
also,  there  may  be  something  in  the  temperature  of  the  waters.  He 
observes,  that  it  was  in  consequence  of  these  discharges  of  waters,  pent 
up  in  volcanic  cavities,  that  the  inhabitants  of  the  plains  of  Quito  be- 
came acquainted  with  these  little  fish,  called  by  them  Prenadilla. 

That  the  waters  of  such  hollows  and  cavities  are  not  always  thus  fitted 
for  the  existence  and  increase  of  animal  life  would  be  expected,  when 
the  observer  reflects  upon  the  varied  conditions  under  which  they  are 
likely  to  occur.  As  an  example  of  the  effects  produced  by  the  admix- 
ture of  gaseous  volcanic  emanations  with  the  waters  in  such  reservoirs, 
we  may  adduce  the  great  flow  of  acid  water  which  accompanied  an  erup- 
tion of  the  Javanese  volcano  of  Guntur,  or  Gounung  Guntur,  in  1800, 

*  Dr.  Horsfield,  as  quoted  by  Dr.  Daubeny,  "Description  of  Volcanoes,"  2d  edition, 
p.  406. 

f  19,200  English  feet. 

j  Kosmos,  7th  edition  (Sabine's  Translation),  p.  222.  This  fact  has  long  since  been 
mentioned  by  Humboldt  in  his  earlier  works. 


SUDDEN    MELTING     OF    SNOWS    ON    VOLCANOES.  347 

when  not  only  streams  of  lava  were  poured  out  (a  rare  circumstance,  it 
would  appear,  among  the  Javanese  volcanoes,  commonly  ejecting  little 
else  than  cinders  and  ashes),*  but  also  an  acid  torrent.  A  river  de- 
scending from  this  volcano  is  described  as  suddenly  swelling,  "  charged 
with  a  large  quantity  of  white,  acid,  sulphurous  mud."  On  the  8th  of 
October  of  that  year,  "  the  waters  came  pouring  down  into  the  valley, 
carrying  everything  before  them,  sweeping  away  the  carcases  of  men 
and  sundry  animals,  and  covering  the  face  of  the  country  with  a  thick 
coat  of  mud."  On  the  12th,  a  still  greater  "  deluge  of  mud"  came 
down  the  valley.  Such  sudden  increases  of  the  volume  of  water  would 
seem  to  point  to  its  discharge  from  extensive  cavities  where  it  was,  for 
the  time,  pent  up,  and  where  it  became  impregnated  with  sulphuric  acid, 
derived,  as  Dr.  Daubeny  points  out,  from  the  decomposition  of  sulphu- 
retted hydrogen  gas.f 

Without  uselessly  multiplying  examples  of  the  discharge  of  conside- 
rable volumes  of  water,  apparently  pent  up  in  the  hollows  of  volcanoes, 
it  may  be  mentioned  that,  in  1755,  a  volume  of  water  was  suddenly  dis- 
charged from  a  cavern  below  the  great  crater  of  Etna,  and  that,  dashing 
over  the  snows  and  side  of  the  mountain,  it  destroyed  and  carried  before 
it  a  large  amount  of  matter.  Torrents  of  water  are  stated  to  have  issued 
from  Vesuvius  during  the  great  eruption  of  1631,  but  whether  from  caverns 
amid  the  accumulations,  or  as  the  result  of  the  somewhat  sudden  conden- 
sation of  large  volumes  of  aqueous  vapour  discharged  from  the  crater,  is 
not  clear.  Be  this  as  it  may,  the  collection  of  waters  amid  volcanic  accu- 
mulations, would  appear  the  needful  consequence  of  the  existence  of 
such  cavities,  and  of  the  condensation  of  aqueous  vapour  in,  or  the  infil- 
tration of  rain  or  melted  snow  into  them.  These  outbursts  require  to 
be  carefully  distinguished  from  the  torrents  descending  the  sides  of  vol- 
canoes more  or  less  covered  by  snow,  either  in  the  higher  northern  and 
southern  latitudes,  or  rising  above  the  line  of  perpetual  snow  in  the 
temperate  or  tropical  regions.  The  suddenly-melted  snows  of  Cotopaxi 
(fig.  121)  pour  down  the  furrows  on  its  sides,  as  in  the  eruption  of  1803, 
when,  in  a  single  night,  the  snows  disappeared  from  the  cone,  and  the 
resulting  torrents  of  water  transported  cinders  and  ashes  into  the  Rio 
Napo  and  the  Rio  de  los  Alaques.J  Humboldt  refers  generally  to  the 

*  In  a  letter  to  Dr.  Daubeny  (Description  of  Volcanoes,  p.  409),  Mr.  Beete  Jukes, 
alluding  to  the  almost  entire  absence  of  hard  rock  on  the  surface  of  the  ground  in  the 
volcanic  districts  of  Java,  infers,  that  the  Javanese  volcanoes  "had  long  ceased  to  erupt 
lava,  and  have  for  ages  been  burying  the  previous  streams  under  piles  of  ashes  and 
powder." 

f  Daubeny  (Description  of  Volcanoes,  p.  408),  quoting  Boon  Mesch,  "  Dissertatio  de 
Incendiis  Montium  Javsc,"  1826,  who  obtained  his  information  from  Reinwardt,  the 
Dutch  traveller  in  Java. 

J  "Voyage  de  Humboldt  et  Bonpland,"  Atlas,  Art.  Catopaxi,  Paris,  1810. 


348   MINERALOGICAL  STRUCTURE  OF  VOLCANIC  ROCKS. 

high  volcanoes  of  the  Andes  as  thus,  by  the  sudden  melting  of  their 
snows  transporting  smoking  scoriae  among  the  lower  lands,  producing 
great  inundations.*  Similar  effects  necessarily  follow  similar  causes  in 
the  temperate  regions.  Probably,  however,  the  consequences  of  the 
sudden  melting  of  snow  and  ice  from  volcanic  action  are  nowhere  so 
great  as  in  the  higher  latitudes,  where  large  glaciers,  holding  or  sup- 
porting mineral  matter,  are  broken  up,  and  partly  melted  and  partly  in 
fragments  are  hurried  onwards  to  the  lower  levels.  The  accounts  given 
of  the  effects  thus  produced  in  Iceland  show,  that  the  torrents  so  caused 
and  intermingled  with  ice,  are  of  no  slight  geological  importance.  Al- 
though, under  ordinary  circumstances,  so  little  mineral  matter  appears 
capable  of  being  moved  on  Victoria  Land  (p.  256),  it  is  easy  to  conceive 
that,  during  considerable  eruptions  of  such  volcanoes  as  those  of  Mount 
Erebus  and  Mount  Terror,  great  heats  may  suddenly  melt  the  snows 
clothing  these  mountains,  producing  large  volumes  of  water,  which  may 
continue  liquid  for  a  time  sufficient  to  furrow  into,  and  carry  off  scoriae 
and  ashes,  usually  bound  together  by,  and,  to  a  certain  extent,  not  un- 
frequently  interstratified  with,  the  great  snow  covering  of  those  regions. 

The  observer  should  well  consider  the  mineralogical  structure  and 
chemical  composition  of  the  various  volcanic  products,  whether  these 
may  be  in  the  form  of  lava  streams,  of  molten  rock  which  has  risen  in, 
and  more  or  less  filled  fissures,  of  scoriaceous  substances  of  considerable 
bulk,  or  of  those  lighter  bodies  commonly  known  as  pumice,  cinders, 
and  ash.  Though  much  has  been  accomplished,  more  especially  of  late 
years,  respecting  this  knowledge,  the  discoveries  in  chemistry  greatly 
advancing  such  inquiries,  and  though  some  apparently  sound  general 
conclusions  have,  from  time  to  time,  been  formed,  it  will  be  evident, 
before  certain  of  these  can  be  fully  admitted,  however  they  may  be 
applicable  to  the  particular  localities  noticed,  that,  looking  at  the  dis- 
tribution of  volcanic  vents  over  the  surface  of  the  globe,  an  observer 
possesses  ample  opportunities,  by  careful  research  in  various  parts  of 
the  world,  of  still  further  advancing  our  knowledge  in  this  respect. 

Whether  the  solid  volcanic  rocks  are  crystalline,  stony,  or  vitreous, 
will,  as  we  have  seen  (p.  324),  often  in  a  great  measure  depend  upon 
the  conditions  as  to  cooling,  to  which  they  have  been  exposed,  all  other 
circumstances  being  the  same.t  Hence  the  chemical  composition  of 

*  Kosmos,  7th  English  edition  (Sabine),  p.  221. 

f  It  is  very  essential,  in  such  investigations,  to  bear  the  other  equality  of  conditions 
in  mind,  for  there  may  fre  circumstances  much  modifying  the  external  parts  of  lava 
currents.  Thus  M.  Dufre'noy  (Me"moires  pour  servir  a  une  Description  Gdologique  de 
la  France,  t.  iv.)  mentions  having  found  that  two-thirds  of  the  interior  of  a  lava  current 
near  Naples  were  formed  of  a  mineral  which  could  be  acted  upon  by  acids,  while  the 
surface  was  principally  composed  of  one  not  so  attackable.  In  like  manner  also,  as 
has  been  remarked  by  Mr.  Dana  (Geology  of  the  United  States  Exploring  Expedition, 
p.  203),  a  body  of  molten  and  very  liquid  lava  kept  long  boiling  or  simmering  in  a 


TRACHYTE    AND    DOLERITE.  349 

volcanic  rocks,  which  have  been  ejected  and  flowed  in  a  molten  state, 
may  often  be  the  same,  notwithstanding  the  different  states  of  mineral 
aspect.  If  the  adjustment  of  the  particles  composing  certain  crystalline 
minerals  has  been  prevented  by  the  absence  of  the  needful  conditions, 
such  as  by  a  sudden  refrigeration  of  the  mass,  these  particles  would 
remain  diffused. 

The  solid  volcanic  products  most  studied  and  known  to  us  have  been 
divided  into  rocks  named  trachyte  and  dolerite,  and  it  has  been  sup- 
posed that  the  former  often  preceded  the  latter  in  the  time  of  produc- 
tion. Minerals  of  the  felspar  family  constitute  essential  portions  of 
these  rocks,  entering  more  extensively  into  the  composition  of  trachyte 
than  into  that  of  dolerite.  Both  rocks  may  be  also  viewed  as  silicates, 
chiefly  of  alumina,  lime,  magnesia,  potash,  and  soda.  Trachytes  are 
indeed  considered  "  chemically  trisilicates,  with  or  without  an  excess  of 
silica."*  Trachyte  may,  however,  according  to  the  definitions  given, 
also  contain  free  silica  or  quartz,  and  the  separate  minerals  mica,  horn- 
blende, or  augite.  Dolerite  is  composed  of  the  felspar  known  as  labra- 
dorite  and  of  augite,  and  the  term  augite  rock  is  sometimes  given  to  this 
compound.  In  this  latter  rock  the  proportion  of  silica  is  diminished, 
and  that  of  lime  and  magnesia  increased.f  This  classification  of  the 
more  solid  volcanic  products  into  two  main  divisions,  however  convenient 
as  affording  facilities  for  investigation,  is  found  to  need  such  modifica- 
tion, that  an  intermediate  class  of  rocks,  termed  trachyte-dolerites,  has 
been  proposed  by  Dr.  Abich,  in  which  the  composition  partakes  of  the 
mineral  characteristics  of  both  trachyte  and  dolerite.  With  respect  to 
changes  in  chemical  composition,  Dr.  Daubeny  remarks,  that  "  the  gra- 
dual increase  of  soda  is  likewise  a  remarkable  circumstance,  modern 
lavas  appearing  to  contain  a  much  larger  quantity  of  it  than  the  vol- 
canic products  of  ancient  periods,  and  various  minerals  being  hence 
produced  in  which  this  alkali  is  predominant  (natrolite,  nepheline,  thom- 
sonite,  &c.)J 

It  is  highly  needful  that  the  observer  should  most  carefully  study  the 
mode  of  occurrence  of  these  rocks  in  volcanic  districts,  as  he  will  readily 

volcanic  vent,  like  Kilauea,  in  Hawaii,  may  have  certain  of  its  parts  separable,  the  more 
especially  as  the  temperature  may  increase  in  any  column  of  lava  in  proportion  to  the 
pressure  upon  its  parts. 

*  Daubeny,  "Description  of  Volcanoes,"  2d  edition,  p.  15. 

•}•  Respecting  the  diminution  of  silica,  Dr.  Daubeny  observes  (Description  of  Volcanoes, 
2d  edition,  p.  17),  that  it  is  "  indicated  by  the  substitution  of  labradorite  for  orthoclase, 
or,  in  other  words,  of  one  atom  of  silica  instead  of  three,  coupled  with  the  presence  of 
hornblende  or  augite,  in  both  which  minerals  the  silica  bears  a  still  smaller  proportion 
to  the  base  with  which  it  is  combined."  Rammelsberg  (Dictionary  of  Mineralogy, 
Berlin,  1841)  is  quoted  as  pointing  to  augite  as  R3  Sr2,  where  R  is  either  lime,  mag- 
nesia, protoxide  of  iron,  or  protoxide  of  manganese,  the  silica  being  sometimes  also 
replaced  by  alumina,  as  is  also  the  case  in  hornblende. 

J  "Description  of  Volcanoes,"  p.  19. 


350  SPECIFIC    GRAVITIES    OF    VOLCANIC    ROCKS. 

perceive  that  if  their  somewhat  general  sequence  be  from  the  trachytic 
to  the  doleritic  compounds,  an  important  change  had  been  effected  as 
to  the  conditions  under  which  the  earlier  and  later  substances  have  been 
ejected  from  volcanoes.  The  subject  requires  to  be  regarded  on  the  large 
scale,  and  due  weight  given  to  those  modifications  arising,  as  will  be 
further  noticed  hereafter,  from  the  admixture  of  matter  derived  from 
various  rocks,  amid  which  mineral  volcanic  products  may  have  had  to 
pass  before  they  were  finally  ejected. 

In  such  examinations  the  chemical  composition  of  the  rock,  more  espe- 
cially when  the  minerals  noticed  may  be  either  ill  developed,  or  their 
component  parts  have  been  unable  to  collect  together  in  definite  arrange- 
ments, is  evidently  of  importance.  The  rock-glasses,  or  obsidians,  may 
as  well  belong  to  one  class  as  the  other,  and  so,  also,  certain  stony  va- 
rieties, wherein  any  real  development  of  distinct  minerals  has  not  been 
effected.  Dr.  Abich  has  proposed  the  relative  specific  gravity  of  vol- 
canic rocks  as  affording  great  aid  in  ascertaining  the  amount  of  silica 
in  them,  a  view  in  which  Dr.  Daubeny  would  appear  to  concur,  remark- 
ing that  in  these  rocks  "  the  specific  gravity  of  the  mineral  is  inversely 
as  the  amount  of  silica,  and  directly  as  that  of  the  other  bases,  so  that 
a  near  approximation  may  also  be  obtained  to  their  chemical  composi- 
tion by  merely  ascertaining  their  weight."* 

When  assuming  chemical  composition  from  mineral  structure,  and 
that  the  substances  constituting  the  base  of  certain  definite  forms  are 
constant,  the  observer  has  not  only  to  distinguish  the  minerals  them- 
selves, but  also  to  give  due  weight  to  the  replacement  of  some  sub- 
stances by  others,  without  altering  the  form  of  the  mineral, f  and  to 

*  Ibid.  p.  13.     The  following  table  is  given  in  illustration  :— 

Specific  Gravity.        Silica  per  cent. 
Trachytic  porphyry,      ....         2-5783  69-46 

Trachyte, 2-6821  65-85 

Domite, 2-6334  65-50 

Andesite, 2-7032  64-45 

Trachyte-dolerite,          ....         2-7812  57-66 

Dolerite, 2-8613  53-09 

Clinkstone,  with  a  specific  gravity  of  2-5770,  and  containing  57-66  of  silica,  and 
glassy  andesite,  specific  gravity  2-5851,  with  silica  66-55,  not  harmonizing  with  this 
view,  it  is  remarked,  that  though  clinkstone  chemically  resembles  trachyte-dolerite,  it 
"has  a  different  mineral  composition,  for  it  appears  to  be  a  mixture  of  a  zeolitic  mine- 
ral with  glassy  felspar,"  and  that  "probably  the  same  may  apply  to  glassy  andesite." 
f  Before  engaging  in  investigations  of  this  kind,  the  observer  should  make  himself 
acquainted  with  the  bodies  termed  isomorphous,  or  those  which  replace  each  other  with- 
out causing  any  alterations  in  the  structure  of  minerals.  In  inquiries  into  the  chemical 
composition  of  rocks,  a  knowledge  of  these  substances  is  highly  important.  Thus,  for 
example,  magnesia,  lime,  protoxide  of  iron,  and  protoxide  of  manganese,  replace  each 
other  in  any  proportion.  As  M.  Dufre"noy  has  well  remarked  (Traite*  de  Mineralogie, 
torn.  i.  p.  19),  "  it  is  not  necessary,  in  order  to  present  the  same  composition,  that  mine- 
rals should  exactly  contain  the  same  weight  of  their  simple  constituent  substances ;  it 
is  sufficient  that  there  is  an  exact  relation  between  the  bases  and  the  acids  they  contain, 
or  between  their  isomorphous  substances." 


CHEMICAL    COMPOSITION    OF    VOLCANIC    ROCKS.          351 

the  amount  of  matter  of  different  kinds  which  may,  as  it  were,  be 
entangled  with  that  which  gives  the  form,  the  entangled  matter  being 
sometimes  more  considerable  than  might  at  first  be  supposed,  compelled, 
as  it  were,  by  that  considered  essential  to  the  mineral,  to  take  the 
arrangement  of  parts  belonging  to  it.* 

Carefully  searching  for  facts  illustrative  of  the  conditions  under 
which  the  mineral  matter  ejected  from  volcanoes  may  have  been  derived 
in  the  first  place,  or  modified  afterwards,  it  is  essential  to  apply  for  aid 
to  chemistry  as  well  as  mineralogy,  important  as  the  latter  may  be. 
The  passage  of  vapours  and  gases  through,  or  their  entanglement  in, 
lavas,  whether  solid,  somewhat  vesicular,  or  highly  cellular,  as  pumice, 
is  often  sufficient  to  produce  modifications  requiring  great  attention. 
Again,  after  cooling,  with  cavities  in  them  of  various  sizes,  containing 
matter  partly  gathered  together  out  of  the  mass  of  the  containing  rock, 
and  partly  from  extraneous  sources,  lavas  may  not  only  be  modified  in 
their  composition,  but  mineral  substances  may  be  formed  in  them  of  a 
different  character  from  those  which  would  have  separated  out  from  the 
original  fused  rock.  Again,  also,  lavas,  from  exposure  to  atmospheric 
influences,  may  have  lost  some  of  the  soluble  substances  originally 
entering  into  their  composition.  Thus  no  little  care  is  required  in  the 
selection  of  portions  of  a  volcanic  rock  which  shall  properly  represent 
its  original  condition,  as  regards  its  component  chemical  substances. 

As  the  felspathic  minerals  enter  so  largely  into  volcanic  rocks,  and 
indeed  constitute  a  considerable  part  of  igneous  rocks,  viewed  generally, 
the  annexed  table  (page  352)  of  their  chemical  composition  and  spe- 
cific gravities,  by  Dr.  Abich,f  may  be  found  useful. 

*  This  power  of  one  compound  to  compel  others  to  take  its  crystalline  form  is  of  no 
little  importance,  also,  in  estimating  the  chemical  composition  of  rocks.  These  admix- 
tures are  clearly  mechanical  in  some  instances,  as  for  example  in  the  well-known  crys- 
tallized sandstone,  as  it  is  sometimes  termed,  of  Fontainebleau,  where  grains  of  siliceous 
sand,  in  large  quantity,  are  entangled  in  carbonate  of  lime,  so  crystallized  as  to  include 
them  without  destroying  its  form.  Artificial  compounds  may  be  made,  in  which  large 
proportions  of  some  substances  maybe  mingled  with  others,  the  fundamental  crystalline 
form  of  the  former  remaining  uninjured ;  thus,  for  instance,  M.  Beudant  succeeded  in 
producing  crystals  of  the  form  of  sulphate  of  iron,  which  contained  85  per  cent,  of  sul- 
phate of  zinc,  the  remaining  15  per  cent,  only  being  the  proportion  of  the  substance 
giving  the  form  to  the  crystals  ("  Annales  des  Mines,"  1817,  t.  ii.  p.  10). 

•}•  "  Ueber  die  Natur  und  den  Zusammenhang  der  vulkanischen  Bildungen,"  Bruns- 
wick, 1841. 


352 


COMPOSITION    OF    THE    FELSPARS. 


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COMPOSITION    OF    CERTAIN    LAVAS    AND    PUMICES.      353 

From  the  same  author  has  also  been  compiled  the  following  table  of 
the  chemical  constituents  of  several  trachytes  and  other  volcanic 
rocks : — 


1 

i 

3 

4 

5 

6 

7 

8 

9 

10 

Silica      .     . 

73-46 

68-35 

67-09 

61-19 

61-03 

67-07 

57-76 

62-20 

53-88 

49-21 

Alumina.     . 

13-05 

13-92 

15-63 

17-18 

17-21 

13-19 

17-56 

20-80 

12-04 

15-76 

Oxide  of  iron 

1-49 

2-28 

4-59 

/  4-84 

4-74 

6-73 

4-30 

9-25 

11-84 

manganese 

trace 

5-46 

(0-17 

0-32 

0-82 

Lime       .     . 

0-45 

0-85 

2-25 

1-52 

1-43 

3-69 

5-46 

2-70 

8-83 

6-97 

Magnesia     . 

0-39 

2-20 

0-97 

0-23 

2-07 

3-46 

2-76 

1-40 

7-96 

6-01 

Potash    .     . 
Soda  .     .     . 

4-39 
6-28 

3-24 
4-29 

3-56 
5-07 

4-37 

7-98 

7-16 
4-64 

2-18 
4-90 

1-42 

6-82 

3-10 
5-20 

J4-76 

J4-37 
\6-06 

1.  Porphyritic  trachyte,  with  mica,  from  Ponza.  2.  Porphyritic  trachyte  from 
Monte  Guadia,  Lipari.  3.  Trachyte  from  the  Drachenfels.  4.  Lava  from  Monte 
Nuovo.  5.  Lava,  named  Arso,  Ischia.  7.  Trachyte-dolerite  from  the  Peak  of  Tene- 
riffe.  8.  Rocca  di  Gianaicolo,  Val  del  Bove,  Etna.  9.  Dolerite  of  Strombolino.  10. 
Lava  of  Vesuvius. 

The  annexed  table  has  been  constructed  from  the  analyses  of  the 
lavas  from  Vesuvius  and  Monte  Somma,  as  given  by  M.  Dufre'noy : — 


1 

3 

3 

4 

5 

Silica      .... 
Alumina      .     .     . 
Protoxide  of  iron  . 
Lime.          .     .     . 

53-10 
16-58 
9-96 
3-34 

50-55 
20-30 
8-60 
5-20 

49-10 

22-28 
7-32 
3-88 

50-98 
22-04 
8-39 
5-94 

48-02 
17-50 
7-70 
0-24 

Magnesia    .     .     . 
Soda  
Potash   .... 
Loss  

1-16 
9-46 
2-23 
4-17 

1-21 

8-42 
2-52 
3-20 

2-92 
9-04 
3-06 
2-40 

1-23 
8-12 
3-54 

9-84 
2-40 
12-74 
1-56 

Increase      .     .     . 

0-24 

1.  Lava  of  Palo.  2.  Lava  of  1834,  taken  immediately  below  the  Piano.  3.  Lava  of 
Ganatello.  4.  Lava  from  La  Scala.  5.  Monte  Somma,  mean  of  two  analyses. 

Comparing  the  composition  of  the  lavas  of  Vesuvius  with  those  of 
Monte  Somma,  M.  Dufre'noy  points  out,  that  while  the  latter  are 
almost  unattackable  by  acids,  those  of  the  former  are  in  a  great  mea- 
sure soluble  in  them,  in  about  the  proportion  of  4  : 1 ;  and  that  while 
the  lava  of  Monte  Somma  contains  a  large  proportion  of  potash,  in  that 
of  Vesuvius  soda  predominates.* 

*  Parallele  entre  les  diffe'rents  products  volcaniques  des  environs  de  Naples,  et  rap- 
port entre  leur  composition  et  les  phdnomenes  que  les  ont  produit ;  Me"moires  pour 
servir  a  une  Description  Geologique  de  la  France,  t.  iv.  p.  381,  (1838.)  M.  Dufre'noy 
adds,  that  this  difference  of  composition  is  also  apparent  in  the  minerals  common  to  the 
two  lavas,  the  augite  of  Monte  Somma  having  a  base  of  iron,  while  that  of  Vesuvius 
enters  among  the  calcareous  varieties,  such  as  sahlite. 

23 


354 


COMPOSITION     OF    CERTAIN    OBSIDIANS. 


Respecting  lava  replete  with  vesicles  or  cells  (pumice),  the  following 
analyses  are  taken  from  Dr.  Abich  :* 


l 

8 

3 

4 

5 

6 

7 

8 

9 

Silica     .... 
Silica  and  Titanic 
acid    .... 
Alumina      .     .     . 
Oxide  of  iron  .     . 

60-79 

1-46 
16-43 
4-26 
0-23 
0-62 
0-79 
11-25 
2-97 

61-08 

1-45 

17-34 
7-77 
0-62 
1-46 
4-02 
2-85 
1-82 

62-42 

0-74 
14-72 
6-84 
0-18 
6-25 
3-28 
4-74 
1-55 

62-29 

16-89 
4-15 
trace 
1-24 
0-50 
6-21 
3-98 

62-04 

16-55 
4-43 

1-31 
0-72 
639 
3-66 

68-11 

1-23 
8-21 
8-23 
trace 
0-14 
0-37 
8-32 
1-60 

69-79 

12-31 
4-66 

1-68 
0-68 
6-69 
2-02 

73-77 

10-83 
1-80 

1-21 
1-30 
4-29 
3-90 

73-70 

12-27 
2-31 

6-65 
0-29 
4-52 
4-73 

Lime       .... 
Magnesia    .     .     . 
Potash   .... 
Soda       .... 

1.  Pumice  from  Teneriffe.  2.  From  the  Island  of  Ferdinandea.  3.  From  the  vol- 
cano of  Arequipa,  Bolivia.  4.  From  the  Island  of  Ischia.  5.  From  the  Phlegrean 
Fields.  6.  From  the  Island  of  Pantellaria.  7.  From  the  Island  of  Santorino.  8. 
From  Llactacunga. 

According  to  Professor  B.  Silliman,  jun.,  the  modern  lava  and  vol- 
canic glass  of  Kilauea,  Hawaii,  not  only  contains  a  considerable  amount 
of  oxide  of  iron,  but  also  soda,  to  the  exclusion  of  potash,  all  the  con- 
stituent substances  varying  much  in  their  relative  proportions,  f 

*  "  Ueber  die  Natur  und  den  Zusammenhang  der  vulkanischen  Bildungen,"  Bruns- 
wick, 1841. 

f  Dana,  "Geology  of  the  United  States  Exploring  Expedition,"  p.  200,  whence  the 
following  analyses  are  extracted: — 


1 

a 

3 

4 

Silica  

39-74 
10-55 

51-93 
14-07 

50-67 

59-80 

Protoxide  of  iron  .     .     . 
Lime 

22-29 
2-74 

10-91 
6-20 

33-62 
3-66 

31-33 

2-40 

1-73 

1-13 

1-71- 

Soda   

21-62 

6-31 

10-52 

4-83 

1.  Dark-coloured  Pele's  Hair.  2.  Scoria.  3.  Compact  vitreous  lava.  4.  Compact 
stony  lava.  3  and  4  are  from  the  same  specimen,  the  former  constituting  the  exterior 
portion  of  the  latter. 

Mr.  Dana  also  gives  the  following  analysis  of  Pele's  Hair  by  Mr.  Peabody,  which 
agrees  with  the  above  as  to  the  large  proportion  of  protoxide  of  iron,  but  differs  from 
it  by  giving  potash: — 

Silica 50-00 

Protoxide  of  iron 28-72 

Lime 7-40 

Alumina 6-16 

Potash 6-00 

Soda    .  2-00 


COMPOSITION    OF    OLIVINE    AND    LEUCITE. 


355 


The  following  are  analyses  of  rock-glasses,  or  obsidians,  from  different 
parts  of  the  world,  showing  their  variable  composition: — 


1 

3 

3 

4 

5 

6 

7 

Silica 

60-52 

62-70 

74-05 

74-80 

84-00 

70-34 

69-46 

Alumina    
Oxide  of  iron  

19-05 
4-22 

16-98 
4-98 

12-97 
2-73 

12-40 
2-03 

4-64 
5-01 

8-63 
10-52 

2-60 
2-60 

0-33 

0-39 

0-1^ 

0-32 

Lime     
Magnesia 

0-59 
0-19 

1-77 

0-82 

0-28 

1-96 

0-90 

2-39 

4-56 
1-67 

7-54 

2-60 

Potash 

10-63 

6-09 

4-15 

6-40 

7-12 

Soda 

3-50 

4-35 

5-11 

3-55 

3-34 

5-08 

1.  From  Teneriffe  (Abicli).  2.  Island  of  Procida  (Abich).  3.  Lipari  (Abich).  4. 
Telkebanya  (Erdmann).  5.  Iceland  (Thomson).  6.  India  (Damour).  7.  Pasco  (Ber- 
thier). 

As  olivine  and  leucite  are  minerals  often  entering  largely  into  vol- 
canic rocks,  it  is  useful  that  the  observer,  while  estimating  the  chemical 
composition  of  those  in  which  they  may  occur,  should  bear  in  mind  that 
the  former  is  a  silicate  of  magnesia  and  protoxide  of  iron  [(Mg,  Fe)3  Si], 
and  the  latter  a  silicate  of  potash  and  alumina  (K3  Si2  +  3  Al  Si2).* 


*  The  following  analyses  may  aid  in  showing  the  similar  composition  of  olivine  from 
various  localities.     Several  others  might  be  added  of  the  same  kind: — 


1 

a 

3 

4 

5 

Silica 

40  09 

40-45 

41-54 

41-44 

40  12 

Magnesia       . 

50-49 

50-67 

50-04 

49-19 

44-55 

Protoxide  of  iron                   .     . 

8-17 

8-07 

8-66 

9.79 

15-32 

0-20* 

0-18* 

0-25 

0.1  q 

O.oq 

Alumina  . 

0-19 

0-19 

0-06 

0-16 

0-14 

1.  From  the  Vogelsberg,  Giessen  (Stromeyer),  contains  also  0-37  protoxide  of  nickel. 
2.  Kasalthoff,  Bohemia  (Stromeyer),  contains  also  0-33  protoxide  of  nickel.  3.  Isce- 
weise  (Walmstedt).  4.  Le  Puy,  Vivarais  (Walmstedt),  contains  also  0-21  of  lime. 
5.  Monte  Somma  (Walmstedt). 

As  respects  this  mineral,  it  is  highly  interesting  to  find  that  the  olivine  found  in  the 
meteoric  iron  of  Siberia  and  Otumba,  South  America,  should  possess  a  similar  compo- 
sition. 


1 

2 

Silica  

40-86 

38-25 

Magnesia  

47-35 

49-68 

Protoxide  of  iron  

11-72 

11-75 

O.JO 

0.1  1 

•11 

1.  From  Siberia  (Berzelius).     2.  From  Otumba  (Stromeyer). 

With  respect  to  leucite,  the  following  two  analyses,  the  first  from  Vesuvius,  by 


a  Peroxide  of  manganese. 


356 


CHIEF  SUBSTANCES  FORMING  VOLCANIC  ROCKS. 


He  should  also  recollect  that  augite  is  a  silicate  of  lime  and  magnesia* 
(Ca3  Si2  -f  Mg3  Si2),  labradorite,  a  silicate  of  alumina,  lime,  and  sodaf 
(R  Si  +  Al  Si),  orthoclase  (potash-felspar),  a  silicate  of  alumina  and 
potash!  (K  Si  +  Al  Si3),  albite  (soda-felspar),  a  silicate  of  soda  and 
alumina§  (Na  Si  -f  Al  Si3). 

The  chief  substances  entering  into  the  composition  of  volcanic  rocks 
are  the  silicates  of  alumina,  oxide  of  iron,  lime,  magnesia,  potash,  and 
soda,  the  fusibility  of  the  different  compounds  of  which,  constituting 
distinct  minerals,  varies,  the  rocks  into  which  augite,  or  that  into  which 
silicate  of  lime  enters  most  largely,  being  the  easiest  of  reduction  to 
the  fluid  state  by  heat.  As  labradorite  likewise  contains  a  considerable 
proportion  of  silicate  of  lime,  and  is  more  fusible  than  orthoclase  (the 
potash-felspar),  both  the  minerals  entering  into  the  composition  of 
dolerite,  render  it  much  more  fusible  than  trachyte,  chiefly  formed  of 
the  potash-felspars.  Silicate  of  lime  may  indeed  be  considered  as  a 
characteristic  substance  in  the  dolerites,  while  it  is  comparatively  rare 
in  the  trachytes,  that  is,  of  those  in  which  true  orthoclase  predominates.  || 
In  localities,  therefore,  where  trachytic  have  clearly  preceded  doleritic 
rocks,  the  more  fusible  have  succeeded  the  least  fusible  products, — a 
fact  of  no  little  theoretical  value. 

With  respect  to  the  diffusion  of  certain  minerals,  such  as  olivine  and 
leucite,  through  the  mass  of  a  volcanic  rock,  having  once  been  formed, 

Arfvedson,  and  the  second  from  Monte  Somma,  by  Awdejew,  will  serve  to  show  the 
proportion  of  the  constituent  parts: — 


1 

2 

Silica  

56-10 

56-05 

Alumina  .               

23-10 

23-03 

Potash      

21-15 

20-40 

Soda    

1-02 

Peroxide  of  iron    

0-95 

*  In  the  very  numerous  analyses  which  have  been  made  of  augite,  the  silica  varies 
from  47-05  (Arendal,  Gillenfelder  Maar  Eifel)  to  57-40  (Tjotten,  Norway),  the  lime 
from  17-76  (Tyrol)  to  25-60  (Achmatowsk),  and  the  magnesia  from  6-83  (Finland)  to 
18-22  (Vallde  de  Fassa).  There  is  usually  protoxide  of  iron  varying  from  4-31  (Tyrol) 
to  26-08  (Tunaberg,  Sweden),  as  also  alumina  from  0-14  (Dalecarlia)  to  6-67  (Gillen- 
felder Maar  Eifel). 

f  R  being  taken  as  $  lime  and  £  soda,  the  chemical  composition  of  labradorite  is 
considered  to  be  =  53-7  silica,  29-7  alumina,  12-1  lime,  and  4-5  soda.  There  are 
usually  also  small  portions  of  potass  varying  from  1-79  to  0-3. 

|  The  chemical  composition  of  orthoclase  is  inferred  to  be  65-4  silica,  18  alumina, 
and  16-6  potash,  a  little  soda  and  lime  being  included  in  the  latter. — Nicol,  "Manual 
of  Mineralogy,"  p.  119. 

$  Albite  is  considered  to  be  essentially  composed  of  69-3  silica,  19-1  alumina,  11-6 
soda,  part  of  the  last  often  replaced  by  lime  or  potass. — Nicol,  "Manual  of  Mine- 
ralogy," p.  124. 

||  In  those  compounds  referred  to  orthoclase,  in  which  soda  is  more  abundant  than 
potash,  it  may  be  much  doubted  how  far  they  really  deserve  the  name,  unless  it  be  in- 
ferred, with  Dr.  Abich,  that  soda  and  potash  are  both  isomorphous  and  dimorphous. 


DIFFERENT    FUSIBILITY    OF    VOLCANIC    MINERALS.      357 

that  is,  the  component  particles  of  the  silicates  of  magnesia  and  protoxide 
of  iron  of  the  one,  and  the  silicates  of  potash  and  alumina  of  the  other, 
having  been  placed  under  the  conditions  permitting  them  freely  to 
move  and  become  aggregated  in  the  definite  and  needful  manner,  these 
minerals  may  become  so  many  comparatively  infusible  bodies  amid  a 
more  fusible  mass.  Hence,  by  the  application  of  a  certain  amount  of 
heat,  the  containing  substance,  should  it,  for  example,  be  any  of  the 
doleritic  mixtures,  may  be  fused,  while  these  bodies  may  remain  un- 
melted,  retaining  their  forms  and  general  characters,  until  finally  acted 
upon  by  the  surrounding  molten  mass,  with  its  large  proportion  of 
silicate  of  lime,  forming  a  flux,  and  perhaps  by  a  more  elevated  tempe- 
rature. It  is  easy,  therefore,  to  conceive  that,  as  has  been  above  men- 
tioned, a  lava  stream  may  be  ejected  containing  leucites  and  olivines 
derived  from  the  remelting  of  a  previously  formed  volcanic  rock.  Judg- 
ing from  the  specific  gravity  of  dolerites,  when  cold  and  solid  (2-94 — 
2-96),  leucite  crystals  (spec.  grav.  2-4 — 2-5)  would  easily  be  upborne, 
rising  towards  the  top  of  the  rock  in  its  fluid  state,  ready  to  be  ejected 
in  a  lava  stream.  This  would  not  be  the  case  with  olivine,  the  specific 
gravity  of  which  (3-3 — 3-5)  is  greater  than  that  of  the  dolerites,  so  that 
if  the  latter,  containing  disseminated  olivine,  were  remelted,  this 
mineral,  from  its  little  fusibility  and  greater  weight,  would  have  a 
tendency  to  descend,  like  any  substance  mechanically  suspended  in  a 
fluid  lighter  than  itself.  As  to  augite,  disseminated  crystals  of  it 
would,  from  their  ready  fusibility,  be  soon  melted,  though  their  specific 
gravity  would  be  3-2 — 3'5. 

It  may  not  be  out  of  place  to  remark,  as  it  has  been  thought  that 
trachytic  may  have  been  formed  from  felspar-porphyritic  and  granitic 
rocks  of  much  older  date,  that  upon  the  heat  to  which  the  one  or  the 
other  would  be  exposed,  might  depend  the  melting  of  these  rocks  either 
partially  or  wholly.  However  silica,  if  mingled  with  some  other  sub- 
stances, may  be  readily  fusible,  when  once  separated,  as  quartz,  it  is 
highly  refractory,  even  if  surrounded  by  fusible  silicates,  as  may  be 
readily  tried  in  the  laboratory,  and  seen  daily  in  the  slags  in  many 
great  metallurgical  works.  The  felspathic  portions,  which,  in  some 
granitic  and  felspar-porphyritic  rocks,  contain  soda  as  well  as  potash, 
are  not  difficult  of  fusion,  as  may  easily  also  be  found  by  experiment. 
With  the  mica,  much  depends  upon  whether  it  is  a  potash,  lithia,  or 
magnesia  mica.  The  second  of  these  fuses  more  easily  than  the  first, 
and  both  more  readily  than  the  third,  which  we  have  found,  in  experi- 
ments, still  crystallized,  after  the  fusion  of  a  felspar-porphyry,  through 
the  base  or  paste  of  which  crystals  of  it  were  disseminated.  There 
appears  no  difficulty  in  conceiving  that,  upon  the  melting  of  a  granite, 
composed  of  orthoclase,  quartz,  and  magnesia-mica,  the  first,  after 
fusion,  may  again  crystallize  and  envelope  the  two  latter,  held  mechani- 
cally suspended  in  the  molten  fluid  during  the  fusion  of  the  felspathic 


358  POSITION    OF    MINERALS    IN    MOLTEN    ROCK. 

portion.  Even  supposing  some  of  the  quartz  to  have  been  fused  (being 
surrounded  by  a  substance  acting  as  a  flux),  upon  the  recrystallization 
of  the  orthoclase,  we  should  expect  that  the  extra  amount  of  silica,  not 
required  for  the  formation  of  that  mineral,  "would  be  excluded  as  quartz. 
As  to  the  position  of  any  unmelted  quartz  and  mica  of  a  granite,  the 
felspathic  portion  of  which  was  alone  fused,  if  the  latter  were  wholly 
composed  of  orthoclase  (sp.  grav.  2*53 — 2*58),  the  quartz  (sp.  grav. 
2*6)  might  have  no  great  tendency  to  descend  in  the  fluid  body.  The 
mica  would  more  readily  fall  down,  its  specific  gravity,  for  the  potash 
kind,  being  2-8 — 3*1,  and  for  the  magnesia  species,  that  which  is  some- 
what common  in  granites,  2-85 — 2-9.  In  some  felspar-porphyries,  mica 
or  quartz,  and  sometimes  both,  are,  with  felspar,  and  occasionally  other 
minerals,  well  crystallized,  so  that  supposing  the  descent  of  the  mica 
through  the  molten  mass,  and  the  quartz  more  mechanically  suspended 
in  it,  an  ejected  upper  portion  may  contain  the  quartz  crystals,  and  a 
subsequent  lava,  the  mica,  supposing  that  it  remained  still  unfused. 

The  attention  of  the  observer  is  called  to  this  mode  of  viewing  the 
subject,  so  that,  even  on  the  minor  scale,  while  certain  trachytic  rocks 
are  before  him,  he  may  duly  estimate  the  sinking  or  rising  of  certain 
minerals  in  a  fluid  mass  of  molten  rock,  the  higher  or  lower  parts  of 
which  may  be  poured  out  of  a  volcano,  as  its  sides  may  either  hold 
firm,  so  that  lava  overflows  the  crater,  or  be  fissured,  letting  off  the 
fluid  matter  at  a  lower  level.  Viewing  the  whole  height  of  a  volcano 
known  to  us  as  a  minor  fractional  part  of  the  depth  to  which  the  molten 
matter,  partially  from  time  to  time  thrown  out,  may  descend,  certain 
minerals  which  have  remained  unfused  upon  the  partial  melting  of  fel- 
spar-porphyritic  or  granite  rocks  (at  first  taking  their  relative  positions 
according  to  their  specific  gravities),  may  be  subsequently  melted,  their 
elements  mingling  with  the  general  mass,  to  be  afterwards  elevated  and 
ejected.  Thus  supposing  much  magnesia-mica  to  have  descended  in 
the  molten  fluid,  upon  the  partial  melting  of  the  granite  which  con- 
tained it,  the  magnesia,  upon  the  final  fusion  of  the  mica,  might  wholly, 
or  partially,  aid  in  the  production  of  olivine  in  subsequently  ejected 
lava.*  The  sinking  of  minerals  in  fluid  lava  long  since  engaged  the 
attention  of  Von  Buch,  who  found  felspar  crystals  more  abundant  in 
the  lower  than  in  the  higher  part  of  a  current  of  obsidian  at  Teneriffe, 
and  Mr.  Darwin  has  more  recently  directed  attention  to  it.f 

*  In  some  of  the  micas  the  magnesia  amounts  to  more  than  25  per  cent.  One  from 
Lake  Baikal,  analyzed  by  Rose,  gave  25-97  of  this  substance,  and  another  from  Sala 
afforded  Svanberg  25-39  per  cent. 

f  Von  Buch,  "  Description  des  Isles  Canaries;"  and  Darwin,  "  Geological  Observa- 
tions on  the  Volcanic  Islands  visited  during  the  Voyage  of  the  Beagle."  After  quoting 
the  labours  of  Von  Buch,  and  the  experiments  of  M.  de  Dr£e  (mentioned  by  him),  in 
which  crystals  of  felspar  in  melted  lava  were  found  to  have  a  tendency  to  descend  to 
the  bottom  of  the  crucible,  Mr.  Darwin  discusses  at  length  the  subject  of  the  relative 


FUSION  OF  ROCKS  BROKEN  IN  VOLCANIC  VENTS.   359 

Volcanoes  having  apparently  pierced  through  rocks  of  most  varied 
chemical  composition,  as  shown  by  the  fragments  of  them  so  often 
ejected,*  it  may  be  assumed  that  portions  of  such  rocks,  when  not 
thrown  out  as  fragments,  may  be  often  fused  in  the  interior  of  the  vol- 
cano, their  elementary  substances  mingling  with  the  general  molten 
mass.  While  such  fragments  are  sometimes  little  altered,  as  if,  after 
being  broken  off  suddenly  from  their  parent  rocks,  they  had  not  been 
exposed  to  a  heat  sufficient  to  effect  much  change  in  them,  others  appear 
to  have  been  acted 'upon  in  various  degrees,  producing  modification  in 
the  arrangement  of  their  component  particles,  and  even  the  addition  to, 
or  subtraction  of  some  of  the  latter  themselves. f 

By  breaking  through,  and  entangling  portions  of  limestones  and  dolo- 
mitic  rocks,  much  lime  and  magnesia  may  be  obtained  by  fusion,  useful 
in  affording  materials  for  the  production  of  the  silicates  of  lime  and 
magnesia  of  augite,  and  the  silicate  of  magnesia  of  olivine.  So,  also, 
with  other  accumulations  disrupted  and  partially  melted.  Indeed,  upon 
estimating  whence  the  mineral  matter  of  a  volcano  may  have  been  de- 
rived, it  becomes  not  only  desirable  to  consider  the  probable  composition 
of  any  igneous  rocks  which  may  have  been  remelted,  and  the  circum- 
stances attending  this  refusion,  but  also  the  aqueous  deposits  of  various 
kinds  which  may  have  become  more  or  less  exposed  to  fusion  during  the 
time  that  a  volcano  has  been  ejecting  mineral  matter,  either  as  molten 
rock,  cinders,  or  ashes. J 

•specific  gravities  of  minerals  in  fluid  lavas.  "In  a  body  of  liquified  rock,"  he  remarks, 
''left  for  some  time  •without'  any  violent  disturbance,  we  might  expect,  in  accordance 
with  the  above  facts  (alluding  to  those  above  noticed,  and  the  granulation  of  argentife- 
rous lead  in  Patterson's  process,  by  which  grains  or  imperfect  crystals  of  lead  descend 
to  the  bottom  of  the  fluid  mass),  that  if  one  of  the  constituent  minerals  became  aggre- 
gated into  crystals  or  granules,  or  had  been  enveloped  in  this  state  from  some  pre- 
viously existing  mass,  such  crystals  or  granules  would  rise  or  sink  according  to  their 
specific  gravity.  Now,  we  have  plain  evidence  of  crystals  being  embodied  in  many 
lavas,  while  the  paste  or  basis  has  continued  fluid.  I  need  only  refer,  as  instances,  to 
the  several  great  pseudo-porphyritic  streams  at  the  Galapagos  Islands,  and  to  the  tra- 
chytic  streams  in  many  parts  of  the  world,  in  which  we  find  crystals  of  felspar  bent 
and  broken  by  the  movement  of  the  surrounding  semi-fluid  matter." 

*  They  have  long  been  known  on  Vesuvius,  where  the  fragments  of  limestone,  on  the 
Monte  Somma  portion  of  that  volcano,  have  attracted  much  attention.  A  fragment  of 
fossiliferous  limestone  has  there  also  been  found.  Without  entering  generally  upon  the 
various  instances  of  the  ejected  fragments  of  rocks  from  volcanoes,  it  may  be  useful  to 
recall  the  attention  of  the  observer  to  those  of  limestone,  dolomite,  and  sandstone 
thrown  out  when  the  volcanic  island  rose  through  the  sea  between  Pantellaria  and 
Sicily,  in  1831  (p.  95),  as  showing  that  they  may  be  sought  for  in  such  cases. 

f  Dr.  Daubeny  notices  the  probable  conversion  of  the  ordinary  Alpine  limestone  of 
the  vicinity  of  Naples  into  granular  limestone  by  heat,  as  seen  in  the  fragments  of  the 
latter  limestone  found  at  the  Monte  Somma,  and  he  quotes  the  researches  of  Dr.  Fara- 
day, as  showing  that  carbonic  acid  cannot  be  expelled  from  limestone  unless  steam  be 
present. 

J  As  respects  the  volcanic  region  of  Naples,  and  the  fragments  of  rocks  which  have 
been  ejected  by  Vesuvius,  it  is  interesting  to  consider  the  modifications  of  igneous 


360 


LAMINATION  OF  LAVA  STREAMS. 


One  kind  of  lamination  observed  in  igneous  rocks  has  been  above 
noticed  (p.  328)  as  due  to  the  elongation  and  compression  of  vesicles, 
so  that  by  their  extreme  flattening  this  structure  is  produced.  In  the 
cases  of  minerals  ejected  in  an  unfused  state,  the  lava  current  in  which 
they  are  included  moving  onwards,  so  that  they  would  adjust  themselves 
according  to  their  forms  and  the  different  velocities  of  movement  pro- 
duced by  friction  against  the  supporting  rocks,  or  any  casing  of  more 
consolidated  portions  of  the  molten  stream,  we  might  expect  a  certain 
amount  of  arrangement  in  planes,  or  of  lamination  to  be  produced. 
Mixtures  of  substances  of  different  kinds  may  sometimes  also  be  so  jux- 
taposed before  ejection  that  when  flowing  as  a  lava  current  they  formed 
separate  layers,  the  thinner,  other  circumstances  being  the  same,  when 
the  more  elongated.*  Looking  also  to  the  spherical  bodies,  commonly 
formed  of  radiating  crystals  of  part  of  the  compound,  observed  when 
glasses  are  passing  into  the  stony  form  (examples  of  which  are  not 
unfrequently  produced  artificially),  we  should  anticipate,  under  the  cir- 
cumstances of  lava  passing  into  the  stony  from  its  fluid  condition,  and 
movement  still  prevailing  in  the  mass,  that  the  cooling  portions,  more 
especially  adjacent  to  the  ground  over  which  the  whole  was  passing, 
might  sometimes  have  their  parts  so  acted  upon  that  planes,  composed 
of  little  spherules,  might  be  formed :  even  alternations  of  them  produced 
as  successive  portions  of  the  fluid  lava  became  exposed  to  similar  condi- 

matter  which  might  arise  from  the  addition  of  lime  and  magnesia  to  any  fundamental 
igneous  product  derived  from  great  depths.  Dr.  Abich  (Ueber  die  Natur  und  den  Zu- 
sammenhang  des  vulkanischen  Bildungen,  Explanation  of  Plates,  p.  iv.),  gives  the  fol- 
lowing analysis  of  the  dolomites  and  limestones  of  that  vicinity : — 


1 

2 

3 

4 

5 

6 

r 

8 

9 

10 

Carbonate  of  lime,  .     . 
Carbonate  of  magnesia, 
Oxide  of  lime  and  alu- 
mina,      
Silica  and  bitumen, 

52-30 
46-97 

0 
0 

56-57 
43-43 

0 
0 

54-10 
39-00 

0-94 
5-25 

65-20 
34-79 

0 
0 

96-00 
2-30 

0 
0 

98-04 
1-96 

0 
0 

98-08 
1-78 

0 

0 

98-17 
1-48 

0 
0 

96-72 
1-69 

0-32 
1-00 

98-40 
1-51 

0 
0 

1.  From  Capri.  2.  Valle  di  Sambruo,  between  Minuri  and  Majuri.  3.  Minuri. 
4.  Between  Vico  and  Sorento.  5.  Valle  di  Sambruo.  6.  Monte  St.  Angelo,  Castella- 
mare.  7.  Punta  di  Lettere,  Castellamare.  8.  Capri.  9.  Vico.  10.  Capri. 

*  With  respect  also  to  the  lamination  of  igneous  rocks,  Mr.  Darwin  directs  attention 
to  the  probable  arrangement  of  parts  in  a  viscous  lava-flow  analogous  to  that  described 
by  Professor  James  Forbes  (p.  220),  as  effected  in  glaciers:  a  circumstance  to  be  re- 
garded so  far  as  the  similar  conditions  of  the  two  bodies,  glacier-ice  and  a  viscous  lava- 
stream,  may  extend.  Mr.  Darwin  (Volcanic  Islands,  p.  70),  when  describing  the  Island 
of  Ascension,  enters  largely  into  the  causes  of  lamination  in  volcanic  rocks,  seen  there 
and  in  many  other  parts  of  the  world.  Among  other  remarks,  he  concludes  "that,  if 
in  a  mass  of  cooling  volcanic  rock,  any  cause  produced  in  parallel  planes  a  number  of 
minute  fissures  or  zones  of  less  tension  (which,  from  the  pent-up  vapours,  would  often 
be  expanded  into  crenulated  air-cavities),  the  crystallization  of  the  constituent  parts, 
and  probably  the  formation  of  the  concretions,  would  be  superinduced  or  much  favoured 
in  such  places  ;  and  thus  a  laminated  structure  of  the  kind  we  are  consuk'ring  would 
be  generated." 


LAMINJE    OF    SPHERULES    IN    OBSIDIAN.  361 

tions.  Obsidian  is  but  the  vitreous  state  of  melted  rock,  and  all  the 
conditions  obtaining  when  artificial  glasses  are  passing  into  the  stony 
state,  such  as  those  producing  separate  crystals  of  certain  silicates,  and 
the  arrangement  into  spherules,  has  to  be  looked  for  as  well  in  the  one 
as  in  the  other,  the  modifications  depending  on  the  kind  and  abundance 
of  the  different  silicates,  with  due  regard  to  the  conditions  under  which 
the  general  mass  may  have  moved  or  remained  quiet.  The  obsidians, 
in  certain  volcanic  countries,  are  especially  advantageous  for  studies  of 
this  kind,  and  will  well  repay  the  attention  of  an  observer.*  He  will 
also  find  examples  of  lamination  in  volcanic  rocks  which  have  passed 
the  vitreous  state,  or  intermixture  with  that  state  in  cooling,  and  it  will 
be  desirable  that  such,  as  well  as  the  obsidians,  should  be  well  examined 
for  evidence  either  of  movement  while  consolidation  was  being  effected, 
or  for  the  simple  and  very  gradual  crystallization  of  parts  during  any 
long  period  during  which  the  whole  body  of  rock  may  have  taken  to 
cool.f  In  such  researches  the  observer  will  have  to  recollect,  that  the 

*  Dr.  Daubeny  points  out  (Description  of  Volcanoes,  p.  256),  with  respect  to  the  ob- 
sidian of  Lipari,  that  "  some  of  its  varieties  possess  a  remarkable  resemblance  to  certain 
products  obtained  by  Mr.  Gregory  Watt  (Philosophical  Transactions,  1804)  during  the 
ceoling  of  large  quantities  of  basalt,  an  incipient  crystallization  beginning  to  manifest 
itself  in  the  midst  of  the  vitreous  mass  in  the  appearance  of  white  or  lighter  coloured 
spots,  which  appear  to  be  made  up  of  points  radiating  from  a  common  centre.  In  many 
of  the  Lipari  obsidians,  however,  these  round  spots  are  composed  of  concentric  laminae, 
and  are  disposed  in  general  in  lines,  so  as  to  give  a  resemblance  of  stratification  to  the 
mass.  In  other  cases  the  whole  mass  is  made  up  of  globules  of  this  kind,  which  are 
hollow  internally,  and  are  sometimes  cemented  by  black  obsidian." 

Mr.  Darwin  gives  (Volcanic  Islands,  pp.  54 — 65),  an  interesting  account  of  laminated 
volcanic  beds  alternating  with  and  passing  into  obsidian  at  the  Island  of  Ascension.  After 
describing  these  beds  he  remarks,  that  "as  the  compact  varieties  are  quite  subordinate 
to  the  others,  the  whole  may  be  considered  as  laminated  or  striped.  The  laminae,  to 
sum  up  their  characteristics,  are  either  quite  straight,  or  slightly  tortuous,  or  convo- 
luted ;  they  are  all  parallel  to  each  other,  and  to  the  intercalating  strata  of  obsidian ; 
they  are  generally  of  extreme  thinness ;  they  consist  either  of  an  apparently  homoge- 
neous, compact  rock,  striped  with  different  shades  of  gray  and  brown  colours,  or  of  crys- 
talline felspathic  layers  in  a  more  or  less  perfect  state  of  purity,  and  of  different  thick- 
nesses, with  distinct  crystals  of  glassy  felspar  placed  lengthways,  or  of  very  thin  layers 
chiefly  composed  of  minute  crystals  of  quartz  and  augite,  or  composed  of  black  and  red 
specks  of  an  augitic  mineral  and  of  an  oxide  of  iron,  either  not  crystallized,  or  imper- 
fectly so."  Mr.  Darwin  also  mentions  the  occurrence  of  layers  of  globules  or  spherulites 
in  the  transition  of  one  class  of  beds  into  the  other,  one  kind  of  spherulites  white  or 
translucent,  the  other  dark  brown  or  opaque,  the  former  distinctly  radiated  from  a 
centre,  the  latter  more  obscurely  so.  While  remarking  on  the  spherulites  in  obsidians 
and  in  artificial  glasses,  Mr.  Darwin  calls  our  attention  to  the  observations  of  M.  Dar- 
tigues  (Journal  de  Physique,  t.  59,  pp.  10,  12,  1804),  on  the  difficulty  of  remelting 
spherulitic  and  devitrified  glasses  without  first  pounding  them  and  mixing  the  whole 
well  together,  the  separation  of  certain  parts  from  the  general  compound  in  the  sphe- 
rules or  crystals  rendering  this  necessary. 

•j-  In  all  such  researches  the  slow  cooling  of  a  lava  stream  has  to  be  well  considered. 
Dr.  Daubeny  mentions,  that  he  found  the  temperature  of  the  lava  stream,  ejected  from 
Vesuvius  in  August,  1834,  to  be  390°  Fahr.,  four  months  after  its  outflow,  the  thermo- 


362  COMPOSITION    OF    VOLCANIC    ASHES. 

top  of  a  lava  stream  is  so  far  differently  circumstanced  from  the  lower 
portion,  that,  while  the  former  is  exposed  to  the  atmosphere  and  all  its 
changes,  the  latter  rests  upon  a  bad  conductor  of  heat,  so  that  somewhat 
modified  effects  may  often  be  produced,  as  regards  the  arrangement  of 
the  component  substances,  in  the  one  part  and  the  other. 

With  regard  to  the  cinder  and  ash  accumulations  on  the  sides  of  vol- 
canoes, the  adjacent  country,  and  the  far- distant  regions  to  which  the 
latter  may  be  borne,  it  would  be  expected  that  their  chemical  composi- 
tion would  be  similar  to  the  lavas,  for  the  time,  of  their  respective  vol- 
canoes, should  any  be  thrown  out,  subject  to  such  modifications  as  their 
more  complete  exposure  to  the  vapours  and  gases  rushing  out  might 
occasion.  We  should  anticipate  that  during  the  eruptions  of  trachytic 
lavas  the  cinders  and  ashes  would  be  likewise  trachytic,  and  so  with 
the  other  kinds  of  volcanic  rocks.  Thus,  should  trachytic  have  pre- 
ceded doleritic  eruptions,  in  any  localities,  the  ashes  and  cinders  of  the 
one  would  have  preceded  the  other.*  Ashes  and  cinders  being  so  ex- 
posed, particularly  the  former,  to  be  intermingled  with,  and  surrounded 
by,  these  volcanic  vapours  and  gases,  much  would  depend,  as  to  any 
modification  or  change  in  the  original  mineral  substance,  upon  the  time 
during  which  this  action  might  last,  as  also  upon  the  kinds  of  vapours 
and  gases  to  which  the  ashes  or  cinders  may  be  exposed.  In  all  cases 
it  would  be  expected  that  where  the  cinders  and  ashes  were  the  most 
abundantly  and  speedily  accumulated,  as  upon  the  cone  or  sides  of  a 
volcano,  the  effects  arising  from  an  intermixture  of  the  acids  and 
vapours  with  the  ashes  and  cinders  would  be  the  most  considerable. 
For  instance,  where  hydrochloric  acid  is  much  mingled  with  the  ashes 
and  cinders,  the  whole  piled  around  a  crater  in  a  hot  moist  state,  such 
portions  as  were  soluble  in  that  acid  might  be  much  acted  upon.  The 
like  also  with  sulphurous  and  carbonic  acids. 

In  considering  the  original  composition  and  subsequent  modification 
which  any  mass  or  layers  of  volcanic  cinders  may  have  sustained,  it  is 
also  needful  for  the  observer  to  search  for  evidence  as  to  the  probability 
of  these  cinders  and  ashes  having  been  arranged,  as  now  found,  either 
in  the  air  or  beneath  water,  such  for  instance  as  is  afforded  by  the  oc- 

meter  placed  upon  the  lava,  after  the  scoriae  on  the  surface  had  been  removed.  Daniell's 
pyrometer  gave  similar  results  when  introduced  into  a  cavity  of  the  lava  (Description 
of  Volcanoes,  p.  229). 

*  M.  Dufr6noy  (Examen  chimique  et  microscopique  de  quelquescendres  volcaniqucs ; 
M^moires  pour  servir  a  une  Description  Ge"ologique  de  la  France,  t.  iv.)  considers  that 
volcanic  ashes  are  most  frequently  composed  of  distinct  minerals,  therein  differing  from 
the  powder  produced  by  the  trituration  of  rocks,  usually  formed  of  the  union  of  several 
minerals.  He  therefore  infers  that  volcanic  ash  "is  rather  the  result  of  a  confused 
crystallization,  produced  under  the  influence  of  brisk  agitation,  such  as  in  the  saltpetre 
prepared  for  the  manufacture  of  gunpowder,  than  the  product  of  trituration  of  lavas 
in  volcanic  vents,  though  the  ashes,  collectively,  do  not  the  less  represent  the  composi- 
tion of  the  lava." 


VOLCANIC    TUFF. 


363 


currence  of  shells  or  other  organic  remains  among  them,*  or  by  layers 
of  detritus  or  chemically  deposited  matter,  showing  a  subaqueous  accu- 
mulation. Ashes  and  cinders  descending  into  water,  and  afterwards 
arranged  by  it,  would  probably  be  well  washed,  so  that  little  change 
would  be  effected  afterwards  by  any  acids  adhering  to,  or  mingled  with 
them. 

The  term,  tuff  or  tufa,  is  not  uncommonly  given  to  the  ash  and  cinder 
accumulations  of  volcanic  regions.  Dr.  Abich  has  given  the  following 
analyses  of  the  tuff  of  the  Phlegrean  Fields,  Posilippo,  and  the  Island 
of  Yivara,  the  two  former  being  termed  trachytic  tuff,  the  last  basaltic 
tuff: 


1 

3 

3 

4 

5 

6 

7 

Silica  .... 

51-65 

52-80 

54-41 

54-57 

56-63 

45-50 

51-08 

Alumina  . 

15-08 

15-83 

15-40 

17-93 

15-33 

16-05 

13-71 

Oxide  of  Iron    . 

6-21 

7-57 

7-74 

5-49 

7-11 

11-69 

13-16 

Lime   .... 

5-43 

3-13 

3-17 

0-77 

1-74 

5-03 

7-09 

Magnesia      .     . 

1-18 

0-84 

1-50 

0-77 

1-36 

3-20 

4-72 

Patash      .     .     . 

6-19 

7-86 

7-54 

523 

6-54 

4-12 

2-94 

Soda   .... 

1-01 

2-90 

2-87 

6-40 

4-84 

2-28 

2-94 

1.  Yellow  tuff,  from  Nola.  2.  Yellow  tuff,  from  Posilippo.  3.  White  tuff,  from 
Posilippo.  4.  Tuff,  from  Epomoeo.  5.  From  the  crater  of  Monte  Nuovo.  6.  Yellow 
tuff,  from  the  Island  of  Vivara.  7.  Gray  tuff,  from  Vivara.-f- 

Looking  at  the  varied  manner  in  which  ashes  and  cinders  may  be 
accumulated,  either  wholly  in  the  atmosphere  or  beneath  water,  to  the 
substances  with  which  they  have  been  mingled  in  the  crater  of  a  vol- 
cano, and  which  may  more  or  less  coat  or  impregnate  them  afterwards, 

*  So  long  since  as  the  time  of  Sir  William  Hamilton,  shells  were  detected  in  the  tuff 
of  the  vicinity  of  Naples.  They  have  also  been  noticed  in  other  localities  in  that  vicinity, 
and  are  described  as  those  of  species  still  living. 

•j-  M.  Dufrenoy  (Memoires  pour  servir  a  une  Description  Geologique  de  la  France,  t. 
iv.  p.  384)  observes,  that  the  tuffs  of  Posilippo,  Pompeii,  and  Ischia  (the  two  former 
analyzed  by  M.  Berthier,  the  last  by  himself),  present  nearly  the  same  general  cha- 
racters, with  the  exception  of  that  of  Pompeii,  which  contains  nine  per  cent,  of  carbo- 
nate of  lime,  a  substance  which  he  infers  was  infiltrated,  adding  weight  to  the  opinion, 
that  the  entombment  of  Herculaneum  and  Pompeii  was  produced  by  an  alluvion  of  the 
tuff  forming  the  flanks  of  Monte  Somma,  water  having  greatly  aided  the  filling  up  of 
the  edifices  in  the  two  towns.  Remarking  on  the  trachytic  tuff  of  the  Phlegrean  Fields, 
Dr.  Daubeny  observes  (Description  of  Volcanoes,  p.  16)  that  the  analysis  of  it  proves 
that,  "like  pumice,  it  is  only  a  metamorphosed  condition  of  trachyte."  He  considers 
tuff,  pumice,  and  obsidian,  as  all  modifications  of  the  same  basis,  the  two  former  con- 
taining "water  chemically  combined,  namely — yellow  tuff,  three  atoms;  white  tuff,  two 
atoms;  pumice,  one."  "Now  lava,"  he  continues,  "  although  commonly  accompanied 
at  the  time  of  its  eruption  by  abundance  of  steam,  and  containing,  even  for  several 
months  afterwards,  entangled  with  it  a  large  quantity  of  this  and  other  volatile  matters, 
holds  no  water  in  chemical  combination,  so  that  the  fact  with  respect  to  tuff  and  pumice 
shows,  that  these  formations  may  have  been  placed  under  circumstances  of  another 
kind  than  those  of  molten  lavas." 


364  PALAGONITE    TUFF    OF    ICELAND. 

and  to  the  infiltrations  through  beds  and  masses  of  them  subsequently 
to  their  deposit,  either  adding  to,'  abstracting  from,  or  modifying  the 
arrangement  of  their  component  substances,  we  should  expect  that  at 
times  even  very  solid  rocks  may  be  produced,  at  first  sight  presenting 
little  of  the  aspect  of  an  accumulation  of  fine  powder  and  cinders.  Mr. 
Darwin  describes  a  tuff,  apparently  of  this  kind,  at  Chatham  Island 
(Galapagos  Archipelago),  one  evidently  formed  at  first  of  cinders  and 
ashes,  but  now  having  a  somewhat  resinous  appearance,  resembling 
some  pitchstones.  He  attributes  this  alteration  to  "  a  chemical  change 
on  small  particles  of  pale  and  dark-coloured  scoriaceous  rocks  ;  and  this 
change  could  be  distinctly  traced  in  different  stages,  round  the  edge  of 
even  the  same  particle."* 

In  Iceland,  a  tuff  apparently  also  in  a  changed  or  modified  condition 
from  that  of  its  original  accumulation,  and  named  palagonite-tuff,f 
would  seem  to  be  of  much  importance.  According  to  Professor  Bunsen 
(of  Marbourg),  the  palagonite-tuff  of  Iceland  has  a  density  of  2-43,  and 
contains  nearly  17  per  cent,  of  combined  water.  The  following  is  the 
composition  assigned  to  this  rock  by  him : — 

Silica 37-947 

Sesquioxide  of  iron 14-751 

Alumina 11-619 

Lime 8-442 

Magnesia 5-813 

Potash 0-659 

Soda 0-628 

Water 16-621 

Residue 4-108J 

*  Volcanic  Islands,  p.  99.  Mr.  Darwin  describes  this  tuff,  where  best  characterized, 
as  "of  a  yellowish-brown  colour,  translucent,  and  with  a  lustre  somewhat  resembling 
resin ;  it  is  brittle,  with  an  angular,  rough,  and  very  irregular  fracture,  sometimes, 
however,  being  slightly  granular,  and  even  obscurely  crystalline;  it  can  easily  be 
scratched  with  a  knife,  yet  some  points  are  hard  enough  just  to  mark  common  glass  ;  it 
fuses  with  ease  into  a  blackish-green  glass.  The  mass  contains  numerous  broken 
crystals  of  olivine  and  augite,  and  small  particles  of  black  and  brown  scoria :  it  is  often 
traversed  by  thin  seams  of  calcareous  matter.  It  generally  affects  a  nodular  or  concre- 
tionary structure.  In  a  hard  specimen,  this  substance  would  certainly  be  mistaken  for 
a  pale  and  peculiar  variety  of  pitchstone  ;  but  when  seen  in  mass,  its  stratification,  and 
the  numerous  layers  of  fragments  of  basalt,  both  angular  and  rounded,  at  once  render 
its  subaqueous  origin  evident." 

f  From  Palagonia,  in  Sicily,  where  a  similar  tuff  is  found. 

J  On  the  intimate  connexion  existing  between  the  pseudo-volcanic  phenomena  of 
Iceland : — A  Memoir,  translated  by  Dr.  G.  E.  Day,  Chemical  Reports  and  Memoirs, 
Works  of  the  Cavendish  Society,  1848.  From  the  chemical  composition  noticed,  Pro- 
fessor Bunsen  derives  the  formula — 


f  F'e    \  ... 

Si3+2    \    ...      f  Si+H. 
I  Al    J 


MODIFICATION    AND    CHANGE    EFFECTED    IN    TUFFS.      365 

It  will  be  obvious,  that  in  the  volcanic-tuff  accumulations  much  will 
depend,  as  respects  subsequent  modification  and  change,  upon  any 
foreign  matter  with  which  they  may  be  mixed,  so  that  when,  as  beneath 
water,  calcareous  matter  (often,  perhaps,  derived  through  animal  life), 
as  well  as  clay  or  other  fine  sediment,  not  directly  derived  from  volcanic 
eruptions,  is  mingled  with  them,  and  the  whole  is  heated  or  raised 
above  the  water,  effects  would  be  produced  not  precisely  corresponding 
with  those  where  the  modifying  action  has  been  alone  exercised  upon 
the  direct  products  of  volcanoes.  Tuffs  of  this  kind  can  scarcely  but 
be  often  formed,  and  their  examination  in  connexion  with  volcanoes 
now  in  action,  or  which,  geologically  speaking,  have  recently  been  in 
that  state,  will  be  found  important  as  explaining  the  origin  of  certain 
mixtures  of  igneous  and  sedimentary  rocks,  even  amid  very  ancient 
deposits. 

In  regions,  such  as  Iceland,  where  volcanic  action  is  widely  spread 
amid  its  mineral  products  rising  above  the  level  of  the  sea,  and  where 
modifications  due  to  the  action  of  vapours  and  gases  passing  through 
lava  streams,  cinders,  and  ashes,  may  be  so  great,  there  would  appear 
good  evidence  of  the  changes  to  which  such  mineral  products  may  be 
exposed.  Professor  Bunsen  has  pointed  out  several  which  he  considers  to 
be  now  in  progress  in  Iceland.  "  The  Icelandic  mineral  springs,"  he  re- 
marks, "to  which  belong  all  the  systems  of 'geysers  and  suffiones,  are 
distinguished  from  all  others  in  Europe  by  the  proportionally  large  quan- 
tity of  silica  which  they  contain ;  and,  if  we  except  the  acidulous  springs, 
which  are  confined  to  the  western  part  of  the  island,  the  so-called  beer- 
springs  (olkilder)  of  the  natives,  we  may  divide  the  springs  of  Iceland 
into  two  main  groups,  according  to  their  chemical  properties,  one  of 
which  would  comprise  the  acid  and  the  other  the  alkaline  silica  springs." 

Whether  the  water  of  these  springs  has  been  derived  directly  from 
the  atmosphere  by  means  of  rain,  or  melted  snow  and  ice,  or  from  sea- 
water  finding  its  way  to  the  interior  of  volcanoes,  the  aqueous  vapours 
thence  thrown  off  being  condensed  in  their  rise  upwards,  to  it  and  to 
the  substances  with  which  it  can  mingle,  we  have  to  refer  many  modifi- 
cations which  evidently  take  place  in  the  mineral  matter  through  which 
it  passes.  The  experiments  instituted  on  this  subject,  and  the  conclu- 
sions deduced  from  them,  and  from  a  personal  examination  of  the 
springs  of  Iceland,  by  Professor  Bunsen,  are  highly  valuable.  With 
respect  to  the  action  of  pure  heated  water  alone  for  some  hours  upon 
the  palagonite-tuff  above  noticed,  he  found  that  at  the  temperature  of 
212°  Fahr.  (100°  centigrade)  or  2264  (108°  cent.),  silicic  acid,  potash, 
and  soda,  were  dissolved.*  When  the  water  was  saturated  with  car- 

*  Cavendish  Society's  Works  ;  Chemical  Reports  and  Memoirs,  1848,  p.  364.  "1,000 
grammes  of  water  after  12  hours'  digestion  yield,  in  this  manner,  a  solution  containing 
the  following  proportions : — 


366  SOLUTION    OF    PALAGONITE    IN    ACIDS. 

bonic  acid,  and  allowed  to  act  upon  pulverized  palagonite,  all  the  con- 
stituents, with  the  exception  of  alumina  and  oxide  of  iron,  were  dis- 
solved in  the  form  of  bicarbonates.*  When  the  palagonite  was  heated 
for  ten  hours,  in  water  saturated  with  sulphuretted  hydrogen,  sulphide 
of  iron  was  formed,  and  the  solution  contained  silica  and  the  sulphides 
of  calcium,  magnesium,  sodium,  and  potassium,  f  Palagonite  was  found 
to  be  "  entirely  dissolved  in  hydrochloric  and  sulphurous  acids,  except 
a  small  quantity  of  silica  left  as  a  residue.  "J  Thus  many  and  great 
modifications  and  changes  may  be  effected  in  this  variety  of  volcanic 

Grammes. 
Silica    .         .     J   .        .        .        .        0-03716 

Soda 0-00824 

Potash  .  0-00162 


Total    ....        0-01702" 

*  "  1,000  grammes  of  this  water,  after  four  hours'  digestion,  yielded  the  following 
constituents: — 

Grammes. 

Silica 0-09544 

Bicarbonate  of  lime  .  .  .  0-16893 
magnesia  .  .  0-05333 
soda  .  .  .  0-06299 
potash  .  .  .  0-00189 


•  Total        .        .        .        0-38368" 
f  The  solution  contained,  for  1,000  grammes  : — 

Grammes. 

Silica 0-1175 

Sulphide  of  calcium        .         .        .  0-2748 

magnesium  .        .         .  0-0727 

sodium         .        .        .  0-0438 

potassium    .        .        .  6-0410 

Total 0-5498 

J  "We  see,"  observes  Professor  Bunsen,  "from  the  relations  existing  among  these 
salts  themselves  (alluding  to  those  mentioned  in  the  text  and  previous  notes),  and  with 
the  silica,  that  the  constituents  of  palagonite  take  very  different  parts  in  the  decompo- 
sition which  is  induced  by  hot  water,  carbonic  acid,  and  sulphuretted  hydrogen  respec- 
tively ;  whilst,  as  we  have  already  seen,  this  mineral  is  entirely  dissolved  in  hydro- 
chloric and  sulphurous  acids,  except  a  small  quantity  of  silica  left  as  a  residue.  The 
alkaline  siliceous  springs,  in  which  there  is  a  smaller  quantity  of  this  volcanic  gas, 
assume,  consequently,  a  very  different  character  from  the  waters  of  the  suffiones ; 
since  it  is  evident  that  the  composition  of  the  water  and  the  nature  of  the  argillaceous 
deposits  produced  from  these  actions,  must  stand  in  a  definite  relation  to  the  greater 
or  smaller  resistance  opposed  by  the  separate  constituents  of  palagonite  to  the  action 
of  the  weaker  volcanic  acids,  that  is  to  say,  to  the  water,  carbonic  acid,  and  sulphu- 
retted hydrogen  gas."  .  .  .  .  "  When  the  alkaline  silicates,  removed  by  the  heated 
water  from  the  palagonite,  are  brought  into  contact  with  carbonic,  hydrochloric,  and 
sulphuric  acids  (the  latter  of  which  is  formed  by  the  oxidation  of  the  sulphurous  acid 
through  the  oxide  of  iron  in  the  palagonite),  these  alkalies  must  be  converted  into 
carbonates,  sulphates,  and  chlorides,  whilst  the  silicic  acid  remains  dissolved  in  the 
alkaline  carbonates  and  in  the  water,  and  is  partially  separated  from  them  by  evapora- 
tion, as  siliceous  tuff, — a  fact  already  observed  by  Black  in  1792." 


SOLFATARAS.  367 

tuff;  pointing  to  those  which  may  take  place  in  other  volcanic  regions, 
the  results  in  each  depending  on  local  conditions. 

In  many  districts,  as  well  those  in  some  portions  of  which  volcanic 
action  is  now  well  exhibited,  as  in  those  where  it  is  becoming  extinct, 
as  far  as  respects  the  ejection  of  molten  rock,  cinders,  and  ashes,  dis- 
charges of  aqueous  vapours  are  effected ;  sometimes  alone,  at  others 
accompanied  by  some  of  the  usual  volcanic  gases. 

Some  mention  has  already  been  made  (pp.  46  and  49,)  of  thermal  or 
warm  springs,  found  to  rise  as  well  in  regions  not  marked  by  volcanic 
action  on  the  surface,  as  in  those  where  that  action  is  now  apparent,  or 
may  be  inferred  to  have  existed  at  no  very  distant  geological  period.* 
In  some  volcanic  countries  the  various  modifications  under  which  aqueous 
vapour,  and  the  gases  connected  with  volcanic  action  are  emitted,  can  be 
well  studied.  The  observer  can  readily  suppose  that,  while  in  the  great 
eruptions  these  are  so  driven  off  as  to  have  effected  little  combination 
while  in  the  crater,  minor  action  would  leave  sufficient  time  for  the  con- 
densation of  the  aqueous  vapour  into  water,  and  the  combination  of  the 
latter  with  volcanic  gases,  the  whole  acting  upon  the  rocks  through 
which  it  has  to  pass,  abstracting  matter  from  them  as  above  noticed. 

The  Solfatara,  near  Puzzuoli,  has  long  been  known  in  the  volcanic 
region  of  Naples,  from  the  emission  of  aqueous  vapour  and  certain  gases, 
manifesting  a  kind  of  subdued  volcanic  action  unaccompanied  by  the 
ejection  of  lava,  cinders,  or  ashes.f  Dr.  Daubeny  found  the  gas  evolved 
to  be  sulphuretted  hydrogen,  with  a  minute  portion  of  muriatic  acid.J 
Solfataras,  or  modifications  of  them,  are  noticed  as  existing  in  many 
volcanic  regions  in  different  parts  of  the  world.  Professor  Bunsen  has 
shown  the  connexion  of  the  solfataras  of  Iceland  (the  Ndmar  of  the  Ice- 
landers) with  the  acid  springs  of  that  country.  He  remarks  that  they 
"  owe  their  slight  acid  reaction  more  commonly  to  the  presence  of  a 

*  While  noticing  the  dispersion  of  hot  springs,  and  their  issue  from  all  kinds  of  rock, 
Humboldt  (Kosmos)  mentions  that  the  hottest  permanent  springs  yet  known  are  those 
discovered  by  himself,  "  at  a  distance  from  any  volcano — the  'Aquas  calientes  de  las 
Trincheras,'  in  South  America,  between  Porto  Cabello  and  New  Valencia;  and  the 
'Aquas  de  Comanzillas,'  in  the  Mexican  territory,  near  Guanaxuato."  The  first  of 
these  has  a  temperature  of  97°  centigrade  (206-6°  Fahr.),  according  to  M.  Boussingault, 
who  visited  this  spring  in  1823. 

f  An  ancient  lava  current,  of  a  trachytic  kind,  is  supposed  to  be  traceable  from  the 
mountain  to  the  sea. 

%  "  Description  of  Volcanoes,"  p.  211.  After  pointing  out  the  probable  effects  of  the 
two  gases  upon  the  trachyte  of  the  mountain,  the  sulphuretted  hydrogen  uniting  with 
the  bases  of  the  several  earths  and  alkalies,  and  its  consequent  decomposition,  Dr. 
Daubeny  accounts  for  the  absence  of  muriatic  compounds  with  these  bases,  by  noticing 
that,  "if  they  existed  they  would  be  immediately  decomposed  by  the  sulphuric  acid 
generated;  and  that  muriatic  acid  itself  is  incapable  per  se  of  decomposing  trachyte, 
except  it  be  concentrated,  and  the  rock  pounded,  as  shown  from  the  fact  of  its  continu- 
ance during  so  many  ages  in  the  domite  of  Auvergne  in  a  free  condition." 


368  THE    GEYSERS,    ICELAND. 

small  quantity  of  ammonia-alum,  or  soda,  and  potash-alum,  than  to  their 
inconsiderable  traces  of  free  sulphuric  or  muriatic  acids."* 

While  such  springs  in  Iceland  thus  illustrate  the  condensation  of  some 
of  the  aqueous  vapours,  mixed  with  gases  discharged  in  that  volcanic 
region,  the  Geysers  also  well  illustrate  that  of  the  aqueous  vapours  under 
other  conditions.  Allusion  has  been  previously  made  (p.  46)  to  those 
long-celebrated  discharges  of  steam  and  water,  the  Geysers,  and  to 
siliceous  deposits  from  them.  According  to  Professor  Bunsen,  the 
thermal  group  to  which  the  Geysers  belong,  occurs  southward  from  the 
highest  point  of  Hecla,  and  about*  20  geographical  miles  from  it.  Their 
main  direction  is  about  N.  17°  E.,  "  almost  parallel  with  the  chain  of 
Hecla,  and  with  the  general  direction  of  the  fissures."  The  rock  be- 
neath the  incrustations  of  the  springs  is  palagonite-tuff,  a  vein  of  clink- 
stone running  lengthwise  from  the  western  margin  of  the  springs.  The 
following  are  analyses,  by  Dr.  Sandberger  and  M.  Damour,  of  the  water 
of  the  Great  Geyser  :f 

*  Cavendish  Society  Works;  Chemical  Memoirs  and  Reports,  1848,  p.  327. 

f  The  cause  assigned  by  Professor  Bunsen  for  the  alternate  states  of  repose  and 
activity  of  this  great  natural  fountain,  is  very  different  from  that  usually  inferred.  By 
very  careful  experiments  by  M.  Descloizeaux  and  himself,  it  was  ascertained,  1.  "  That 
the  temperature  of  the  column  of  the  Geyser  decreases  from  below  upwards,  as  had 
already  been  shown  by  Lottin  and  Robert.  2.  That,  setting  aside  small  disturbances, 
the  temperature  goes  on  increasing  regularly  at  all  points  of  the  column  from  the  time 
of  the  last  eruption.  3.  That  the  temperature  in  the  unmoved  column  of  water  did  not, 
at  any  period  of  time  up  to  a  few  minutes  before  the  great  eruption,  reach  the  boiling- 
point  that  corresponds  to  the  atmospheric  and  aqueous  pressure  at  the  point  of  obser- 
vation ;  and  4,  That  it  is  at  mid-height  in  the  funnel  of  the  Geyser,  where  the  tempera- 
ture approaches  nearest  to  the  boiling-point,  corresponding  to  the  pressure  of  the 
column  of  water,  and  that  it  approaches  nearest  to  this  point  in  proportion  to  the  ap- 
proximation of  the  period  of  a  great  eruption."  Diagrams  are  given  in  illustration, 
and  indeed  are  almost  necessary  to  the  view  taken.  It  may,  however,  be  stated,  that 
there  is  a  constant  addition  of  heated  water  below  in  the  tube  or  funnel,  and  an  evapo- 
ration of  the  water  above,  and  that  the  whole  is  in  such  a  condition  that  every  cause 
that  tends  to  raise  this  column  of  water  only  a  few  metres  would  bring  a  large  portion 
of  it  into  a  state  of  ebullition.  Vapour  is  generated,  and  it  is  calculated  that  an  excess 
of  1°  (centigrade)  over  the  corresponding  boiling-point  of  the  water,  "  is  immediately 
expended  in  the  formation  of  vapour,  generating  in  the  present  case  a  stratum  of  vapour 
nearly  equally  high  with  the  stratum  of  water  1  metre  in  height.  By  this  diminution 
in  the  superincumbent  water  a  new  and  deeper  portion  of  the  column  of  water  is  raised 
above  the  boiling-point ;  a  new  formation  of  vapour  then  takes  place,  which  again 
occasions  a  shortening  in  the  pressing  liquid  strata,  and  so  on,  until  the  boiling  has 
descended  from  the  middle  to  near  the  bottom  of  the  funnel  of  the  Geyser,  provided 
always  that  no  other  circumstances  have  more  speedily  put  an  end  to  this  process." 

"  It  appears  from  these  considerations,  that  the  column  of  water  in  the  funnel  of  the 
Geyser  extending  to  a  certain  distance  below  the  middle,  is  suddenly  brought  into  a 
state  of  ebullition,  and  further,  as  may  be  shown  by  an  easy  method  of  computation, 
that  the  mechanical  force  developed  by  this  suddenly-established  process  of  vaporiza- 
tion is  more  than  sufficient  to  raise  the  huge  mass  of  the  waters  of  the  Geysers  to  that 
astounding  elevation  which  imparts  so  grand  and  imposing  a  character  to  these  beautiful 
phenomena  of  eruption.  The  amount  of  this  force  may  easily  be  ascertained  by  calcu- 
lating from  the  temperature  of  the  preceding  experiments  (those  above  alluded  to),  the 


THE     GEYSERS,    ICELAND.  369 


Sandberger. 

Damour. 

Silica        .... 

.     0-5097    . 

0-5190 

Carbonate  of  soda     . 

.     0-1939     . 

0-2567 

Carbonate  of  ammonia 

.     0-0083     . 

.            .  . 

Sulphate  of  soda 
Sulphate  of  potash    . 
Sulphate  of  magnesia 
Chloride  of  sodium    . 

.     0-1070     . 
.     0-0475    . 
.     0-0042     . 
.     0-2521     . 

0-1342 
0-0180 
0-0091 
0-2379 

Sulphide  of  sodium  . 

.    0-0088    . 
.     0-0557    . 

0-0088 
0-0468 

Water 

998-7695 

Not  only  do  the  vapours  and  gases  escaping  from  volcanic  vents  de- 
compose, under  variable  conditions,  the  rocks  through  which  they  rise 
or  against  which  they  may  be  driven  in  the  atmosphere,  and  often  the 
latter  extends  to  some  distance  from  the  place  of  escape  (well  shown  in 
the  case  of  winds  prevailing  in  particular  directions),  but  deposits  of 
different  kinds  are  effected,  thrown  down  from  the  waters  containing 
them.  Professor  Bunsen  has  carefully  investigated  the  well-known 
siliceous  deposits  from  the  Geysers  of  Iceland,  previously  noticed  (p.  46, 

known  latent  and  specific  heat  of  the  aqueous  vapour,  and  the  height  of  the  column  of 
vapour,  which  would  be  developed  by  the  ascent,  to  the  mouth  of  the  Geyser,  of  a  section  of 
the  column  of  water.  If  we  designate  the  height  of  such  a  column  of  water  in  the  funnel 
of  the  Geyser  by  h ;  its  mean  temperature  expressed  in  centesimal  degrees  by  t ;  the  latent 
heat  of  the  aqueous  vapour  by  w ;  the  density  of  the  latter  compared  with  that  of  the  water 
by  s ;  and  the  coefficient  of  the  expansion  of  the  vapour  by  d ;  we  shall  find  that  the  ex- 
cess of  heat  of  the  water  above  the  boiling-point  under  the  pressure  of  one  atmosphere  is 
t — 100.  But  the  height  A,  of  the  section  of  the  column  of  water,  which  at  the  mouth  of 
the  Geyser,  that  is  to  say,  under  the  pressure  of  one  atmosphere,  would  be  converted  into 
vapour  by  the  quantity  of  heat,  t  —  100,  would  be  to  the  whole  height  of  the  water 

h  (t  —  IQO) 

column  A,  as  (t  —  100) :  w.  A  column  of  water  of  the  height  ^  would  there- 
fore be  evaporated  at  the  mean  temperature  t,  if  the  water  were  under  the  pressure  of 
one  atmosphere.  Hence  it  directly  follows,  that  the  height  H,  of  the  column  of  vapour 
sought  at  100°  (centigrade)  and  0-76  metre  (29-921  English  inches)  will  be 

H  _  h  (*  —  100)  (1  +  100  d] 

w  s 

On  applying  this  formula  to  the  value  of  the  numbers  found  by  observation,  we  obtain 
the  remarkable  result  that,  in  the  period  of  time  immediately  preceding  an  eruption,  a 
column  of  water  of  only  12  metres  (39  feet  4-442  in.  English)  in  length,  which  projects 
5  metres  (16  feet  4-851  inches  English)  to  17  metres  (55  feet  9-294  inches  English) 
above  the  base  of  the  tube,  generates  for  the  diagonal  section  of  the  Geyser,  a  column 
of  vapour  638-8  metres  (2093  feet  2-245  inches  English)  in  height  (assumed  to  be  at 
100°  centigrade,  and  under  the  pressure  of  one  atmosphere),  this  column  being  developed 
continuously  from  the  upheaved  mass  of  water,  as  the  lower  strata  reach  the  mouth  of 
the  Geyser.  The  whole  column  of  the  Geyser,  reckoned  from  the  point  where  the  tem- 
perature amounts  to  100°  centigrade  down  to  the  base,  is  capable,  according  to  a  calcu- 
lation of  this  kind,  of  generating  a  similar  column  of  vapour,  1041  metres  (3415  English 
feet)  in  height." — Bunsen,  On  the  intimate  connexion  existing  between  the  Pseudo- 
Volcanic  Phenomena  of  Iceland ;  Works  of  the  Cavendish  Society,  Chemical  Reports 
and  Memoirs,  pp.  346-349. 

24 


370  SILICEOUS    DEPOSITS    FROM    THE    GEYSERS. 

note).  Referring  to  the  analysis  of  the  water  of  the  Great  Geyser, 
above  mentioned,  and  remarking  that  the  silica  is  dissolved  in  the  water 
by  alkaline  carbonates,  and  in  the  form  of  a  hydrate,  he  observes  that 
"  no  trace  of  silica  is  precipitated  on  the  cooling  of  the  water,  and  it  is 
only  after  the  evaporation  of  the  latter  that  silica  is  deposited  in  the 
form  of  a  thin  film  on  the  moistened  sides  of  the  vessel  where  evapora- 
tion to  dryness  takes  place,  whilst  the  fluid  itself  is  not  rendered  turbid 
by  hydrated  silica  until  the  process  of  concentration  is  far  advanced." 
Professor  Bunsen  then  points  out,  that  in  consequence  of  these  circum- 
stances, the  incrustations  increase  in  proportion  as  the  surface  of  evapo- 
ration expands  with  the  spread  of  the  water.* 

The  same  land  presents  us  with  other  deposits  from  waters  and  gaseous 
emanations,  of  importance  geologically,  as  showing  some  of  the  modes 
in  which  mineral  matter  may  be  accumulated  or  disseminated.  Here 
again  the  researches  of  Professor  Bunsen  supply  us  with  valuable  infor- 
mation. He  points  out  that  the  acid  silica  springs,  besides  inconside- 
rable traces  of  hydrochloric  and  sulphuric  acids,  and  small  quantities  of 
ammonia-alum,  or  potash  and  soda-alum,  contain  "  sulphates  and  chlo- 
rides of  calcium,  magnesium,  sodium,  potassium,  and  iron,  also  silica 
and  sulphurous  acid,  or  in  the  place  of  the  latter,  sulphuretted  hydrogen 
gas."  They  are  especially  characterized  by  deposits  of  gypsum  and 
sulphur.  Professor  Bunsen  found  the  composition  of  the  water,  in 
10,000  parts,  taken  from  the  Reykjahlider  solfatara,  in  August,  1846, 

to  be : — 

Sulphate  of  lime, 1-2712 

Sulphate  of  magnesia, 1-0662 

Sulphide  of  ozide  of  ammonium,         .        .         .  0-7333 

Sulphate  of  alumina, 0-3261 

Sulphate  of  soda, 0-2674 

Sulphate  of  potash, 0-1363 

Silica, 0-4171 

Alumina,! 0-0537 

Sulphuretted  hydrogen,  , 0-0820 

Water,  .  9995-6467 


*  Chemical  Reports  and  Memoirs ;  Works  of  the  Cavendish  Society,  1848,  p.  344. 
Professor  Bunsen  remarks,  that  the  peculiar  forms  of  the  Geysers  result  from  certain 
conditions.  "As,"  he  observes,  "  the  basin  of  the  spring  has  no  part  in  this  incrusta- 
tion, it  becomes  converted  into  a  deep  tube  as  it  is  gradually  inclosed  by  a  hillock  of 
siliceous  tuff,  combining,  when  it  has  reached  a  certain  height,  all  the  requirements 
necessary  to  convert  it  into  a  Geyser.  If  such  a  tube  be  narrow,  and  be  filled  with  tolerable 
rapidity  by  a  column  of  water  strongly  heated  from  below  by  the  volcanic  soil,  a  con- 
tinuous Geyser  must  necessarily  be  produced,  as  we  find  them  in  so  many  parts  of  Ice- 
land. For  it  will  easily  be  understood  that  a  spring,  which  originally  did  not  possess 
a  higher  temperature  at  its  mouth  than  that  which  would  correspond  to  the  pressure  of 
the  atmosphere,  may  easily,  when  it  has  been  surmounted  by  a  tube,  formed  by  gradual 
incrustation,  attain  at  its  base  a  temperature  of  upwards  of  100°  centigrade  (212°  Fah- 
renheit), owing  to  the  pressure  of  the  fluid  resting  in  the  tube." 

f  It  is  remarked  respecting  the  alumina,  "the  small  quantity  of  which  brings  it 


GYPSUM    DEPOSITS     OF    ICELAND.  371 

The  clay  and  gypsiferous  accumulations  resulting  from  these  waters, 
or  rather  from  the  general  action  of  their  constituent  parts  upon  the 
rocks  traversed  by  them,  and  upon  each  other,  possess  much  interest. 
The  palagonite-tuff  is  decomposed,  and  clay,  often  variegated  in  colour, 
is  deposited,  and  sulphate  of  lime  is  also  formed.  The  gypsum  occurs 
as  isolated  crystals,  and  "  in  connected  strata  and  floor-like  depositions, 
which  not  unfrequently  project  as  small  rocks,  where  the  loose  soil  has 
been  carried  away  by  the  action  of  the  water.  These  depositions  are 
sometimes  sparry,  corresponding  in  their  exterior  very  perfectly  with 
the  strata  of  gypsum  so  frequently  met  with  in  the  marl  and  clay  for- 
mations of  the  trias."*  In  the  clay  deposits  from  the  Icelandic  fume- 
roles  iron  pyrites  is  found  in  small  crystals,  mentioned  by  Professor 
Bunsen,  as  "often  very  beautifully  developed."  The  sulphur  accumu- 
lations of  Iceland,  the  Professor  attributes  to  the  same  cause,  as  Dr. 
Daubeny  does  generally  (p.  324),  namely,  the  reciprocal  reaction  of 
sulphurous  acid  and  sulphuretted  hydrogen  gas. 

With  regard  to  the  presence  of  nitrogen,  ammonia,  and  their  com- 
pounds, so  frequently  observed  in  connexion  with  volcanic  action, 
opinions  seem  somewhat  divided ;  while  some  consider  that  the  nitrogen 
is  actually  evolved  from  the  craters  and  other  volcanic  vents,  part, 
perhaps,  of  the  air  disseminated  in  water  finding  its  way  to  volcanic 
foci,  others  infer  that  ammoniacal  products,  found  in  connexion  with 
volcanoes,  have  had  a  different  origin.  Dr.  Daubeny,  treating  of  vol- 
canic action,  remarks  : — "  Nor  is  the  access  of  atmospheric  air  to  vol- 
canoes more  questionable  than  that  of  water ;  so  that  the  appearance  of 
hydrogen  united  with  sulphur,  and  of  nitrogen,  either  alone  or  combined 
with  hydrogen,  at  the  mouth  of  the  volcano,  seems  a  direct  proof  that 
oxygen  has  been  abstracted  by  some  process  or  other  from  both."f  On 

within  the  limits  of  the  errors  incidental  to  the  experiment,"  that  it  may  have  been 
dissolved  in  excess  by  the  alum  of  the  water. — Chemical  Reports  and  Memoirs,  1848, 
p.  332. 

*  Bunsen,  Works  of  the  Cavendish  Society,  Chemical  Reports  and  Memoirs,  1848, 
p.  336.  "Their  deposition,"  the  Professor  adds,  "is  owing  to  the  fact  that  has  not 
hitherto  been  sufficiently  regarded  in  the  explanation  of  geological  phenomena,  viz.  : — 
that  substances  crystallizing  from  solutions  are  more  readily  deposited  on  a  surface 
identical  with  their  own  (although  at  a  considerable  distance  from  the  limits  of  their 
solubility),  than  on  substances  different  from  themselves.  These  depositions  of  gypsum 
increase,  therefore,  in  these  formations  in  the  same  manner  as  we  observe  small  crys- 
tals to  enlarge  in  a  solution,  without  any  deposit  being  formed  on  the  sides  of  the 
vessel ;  much  salt  being  removed  from  the  solution  (not  by  a  change  of  tempera- 
ture, but  owing  to  the  cohesive  force  emanating  from  the  crystal),  so  that  no  further 
deposit  can  be  made  on  the  particles  of  bodies  of  a  different  nature.  The  process  of 
crystallization  here  comes  within  the  domain  of  mechanical  forces,  since  it  causes,  by 
the  expansive  growths  of  the  layers  of  gypsum,  the  upheaval  of  the  moistened  clay 
deposit,  or  compresses  it  towards  the  exterior,  as  the  first-named  masses  increase  in 
quantity." 

f  Daubeny,  Transactions  of  the  British  Association  for  the  Advancement  of  Science, 
vol.  v.  for  1837,  and  Description  of  Volcanoes,  2d  edition,  1848,  p.  655. 


372       FUSIBILITY    OF    MINERAL    VOLCANIC    PRODUCTS. 

the  other  hand,  Professor  Bunsen  seems  disposed  to  consider  the  subli- 
mations of  muriate  of  ammonia  as  due  to  the  overflow  of  vegetation  by 
lava  currents,  at  the  same  time  referring  to  nitrogen  and  its  compounds, 
and  to  their  being  scarcely  ever  absent  from  volcanic  exhalations,  adding 
that  "  they  undoubtedly  belong  originally  to  the  atmosphere,  or  to  or- 
ganic nature,  their  occurrence  being  due  to  the  water  which  holds  them 
in  solution  and  conveys  them  from  the  air  to  these  subterranean  depths."* 
If  we  assume  that  water  from  the  atmosphere  or  sea,  more  or  less  con- 
taining air  (p.  161),  does  find  a  passage  into  volcanoes  or  their  foci,  it 
may  not  be  improbable  that  both  causes  can  contribute  to  the  effects 
recorded. 

The  observer  will  have  seen  that  volcanic  products  are,  as  a  mass, 
easily  melted,  notwithstanding  that  during  times  where  the  particles  of 
matter  could  freely  adjust  themselves  in  a  definite  manner,  certain 
mineral  bodies  were  formed  of  a  less  fusible  character,  and  that  from 
the  decomposition  of  ejected  lava,  cinders,  and  ashes,  certain  other  sub- 
stances are  produced,  such  as  siliceous  and  purer  argillaceous  deposits 
of  a  more  refractory  kind.  Looking,  however,  at  the  mass  of  matter, 
it  continues  readily  fusible,  whether  partaking  of  the  trachytic  or  dole- 
ritic  character,  or  of  a  mixture  of  both.  It  will  readily  strike  him  that 
sheets  of  trachytic  or  doleritic  tuff  could  be  easily  acted  on  by  heat,  so 
that  even  altered  as  they  may  have  been  previously,  a  considerable 
area,  if  a  sufficiently  elevated  temperature  could  be  applied  to  it,  would 
begin  to  yield,  rising  upwards  if  any  elevatory  force  were  acting  from 
beneath,  and  that,  finally,  a  fracture  would  be  effected,  so  far  as  any 

*  Pseudo-Volcanic  Phenomena  of  Iceland,  p.  330.  "In  July,  1846,"  observes  Pro- 
fessor Bunsen,  "  only  a  few  months  subsequent  to  the  eruption  of  the  volcano  (Hecla), 
when  I  was  sojourning  in  that  district,  the  lower  portion  of  the  lava  stream  appeared 
studded  over  with  smoking  fumeroles,  in  which  so  large  a  quantity  of  beautifully  crys- 
tallized muriate  of  ammonia  was  undergoing  a  process  of  sublimation,  that,  notwith- 
standing the  incessant  torrents  of  rain,  hundreds  of  pounds  of  this  valuable  salt  might 
have  been  collected.  On  surveying  the  stream  from  the  summit  of  Hecla,  it  was  easy 
to  perceive  that  the  formation  of  muriate  of  ammonia  was  limited  to  the  zone  in  which 
meadow  lands  were  overflowed  by  the  lava.  Higher  up,  where  even  the  last  traces  of 
a  slunted  cryptogamic  vegetation  disappear,  the  formation  of  this  salt  likewise  ceased. 
The  large  fumeroles  of  the  back  of  the  crater,  and  even  of  the  four  new  craters,  yielded 
only  sulphur,  muriatic  and  sulphuric  acids,  without  exhibiting  the  slightest  trace  of 
ammoniacal  products.  When  we  consider  that,  according  to  Boussingault,  an  acre  of 
meadow  land  contains  as  much  as  32  pounds  of  nitrogen,  corresponding  to  about  122 
pounds  of  muriate  of  ammonia,  we  shall  hardly  be  disposed  to  ascribe  these  nitroge- 
nous products  of  sublimation  in  the  lava  currents  to  any  other  circumstance  than  the 
vegetation  which  has  been  destroyed  by  the  action  of  the  fire.  The  frequent  occurrence 
in  Southern  Italy  of  tuff  decomposed  by  acid  vapours  containing  muriate  of  ammonia, 
likewise  confirms  the  hypothesis  regarding  the  atmospheric  origin  of  this  salt.  For  the 
same  body  of  air  which  can  annually  convey  to  a  piece  of  meadow  land  a  quantity  of 
ammonia  corresponding  to  these  large  nitrogenous  contents,  must  at  least  be  capable  of 
depositing  an  equal  quantity  of  alkali  on  tuff-beds  saturated  by  acid  water ;  which  may 
be  actually  observed  in  some  rare  instances  both  in  Southern  Italy  and  Sicily." 


FISSURES    FILLED    BY    MOLTEN    LAVA.  373 

sufficient  coherence  of  parts  remained,  where  the  resistance  became  un- 
equal to  the  force  employed. 

That  volcanic  action  does  work  through  points,  however  these  may 
be  complicated,  as  from  time  to  time  changed,  volcanic  craters  show, 
and  that  it  has  at  least  sometimes  continued  to  find  vent  through  the 
same  points,  or  thereabouts,  for  long  periods,  is  not  only  attested  by 
volcanoes  which  have  been  observed  during  the  historic  period,  but  also 
by  those  to  the  products  of  which,  intermingled  with  other  accumula- 
tions, geological  dates  may  be  assigned. 

That  the  temperature  of  volcanoes  may  even  change  externally,  so 
that  snows  reposing  upon  them  at  one  time  are  suddenly  melted  from 
them  at  another,  we  have  evidence  both  in  high  northern  latitudes  (Ice- 
land) and  in  warm  regions  (Cotopaxi).  Volcanic  products  being,  like 
rocks  generally,  bad  conductors  of  heat,  these  changes  are  sufficient  to 
show  the  variable  amount  of  temperature  to  which  portions,  at  least,  of 
volcanic  mountains  may  be  exposed  from  changes  in  the  conditions  to 
which  it  may  be  due.  That  the  layers  and  variably-shaped  masses  of 
substances  composing  volcanoes,  no  matter  how  accumulated,  have  been 
exposed  to  tension  and  subsequent  fracture,  is  proved  by  the  rents  in 
them  which  have  been  filled  by  molten  matter.  In  the  view  beneath. 

Fig.  126. 


(fig.  126),  in  the  Val  del  Bove,  Etna,*  exhibiting  the  now  hard  lava 
protruding,  from  that  weathering  which  the  whole  has  experienced  from 

*  Taken  from  Dr.  Abich's  "  Views  of  Vesuvius  and  Etna." 


3T4 


LAVA    EJECTED    THROUGH    FISSURES. 


atmospheric  influences,  we  see  that  the  original  volume  of  the  previously 
deposited  volcanic  products  has  been  increased  by  the  amount  of  the 
molten  matter  so  introduced.  The  following  section  (fig.  127),  showing 


Fig.  127. 


' 

a        b          c         d         f 

the  same  thing,  is  not  unfrequent  amid  volcanic  craters  and  ravines. 
In  it,  ef  represent  a  thickness  of  volcanic  tuff  or  lava  layers,  traversed 
by  dykes  (as  they  are  termed),  a  b  c  d,  of  lava  which  has  entered  fissures 
made  by  the  rupture  of  the  beds  e  /,  the  force'acting  from  beneath,  so 
that  while,  for  the  length  seen,  some  fissures  have  their  walls  equidistant 
from  the  top  to  the  bottom  of  the  section,  at  a  and  c  they  diminish  up- 
wards. In  all  these  cases,  the  layers  or  beds  are  not  disturbed  further 
than  by  fracture,  those  on  either  side  of  the  dykes  preserving  their  con- 
tinuous lines  of  original  accumulation.  This  need  not  always  be  the 
case,  as  will  be  readily  inferred,  since  after  a  fracture  is  made,  should 
the  liquid  or  viscous  lava  rise  with  much  force  from  considerable  pres- 
sure of  a  column  of  molten  rock  with  which  it  may  be  connected,  with 
a  comparative  cooling  of  the  upper  part  of  the  lava  as  it  rose,  increasing 
the  solidification  of  the  particles,  the  upper  layers  of  tuff  or  lava  broken 
through  may  be  heaved  upwards  by  the  friction  of  thejiprising  lava, 
this  even  overflowing,  as  appears  to  be  frequently  the  case.  Of  this 
kind  the  section  beneath  (fig.  128),  taken  from  a  view  by  Dr.  Abich, 
of  a  dyke  exposed  by  the  fall  of  part  of  the  crater  of  Vesuvius,  is  pro- 
bably an  instance. 

Fig.  128. 


The  observer  has  next  to  consider  the  magnitude  and  direction  of 
these  fissures.     Perhaps  volcanic  islands,  such  as  those  in  the  Atlantic 


LAVA    EJECTED    THROUGH    FISSURES.  375 

and  Pacific,  are  as  favourable  situations  for  studying  volcanic  fissures 
as  are  to  be  found,  not,  however,  that  great  facilities  do  not  present 
themselves  elsewhere.*  The  rent  or  series  of  rents  which  traversed  the 
side  of  Mauna  Loa,  during  the  ejection  of  lava  in  1843,  is  not  only  re- 
markable for  its  length,  25  miles,  but  also  for  the  comparatively  tranquil 
manner  in  which  it  was  effected,  the  inhabitants  not  being  aware  of  its 
formation  by  any  earthquake  motion,  but  from  finding  a  torrent  of 
liquid  lava  poured  out.f  A  fissure  so  produced  would  seem  to  point  to 
much  softening  of  the  subjacent  rocks,  so  that  when  fractures  were  pro- 
duced, though  25  miles  in  length,  comparatively  little  resistance,  from 
cohesion,  remained  in  the  rocks.  From  an  examination  of  Maui  (Ha- 
waiian Group),  Mr.  Dana  infers  that  at  its  last  eruption,  a  huge  segment 
of  that  volcano  must  have  been  broken  off,  by  which  two  great  valleys 
were  formed  (one  two  miles  wide),  through  which  great  opening  the 
lavas  were  poured  out.J  Here  would  appear  to  have  been  far  greater 
resistance  and  a  more  sudden  overpowering  of  it  by  the  force  exerted. 
According  to  the  accounts  given,  Jorullo  was  the  result  of  an  uprise  of 
ground,  finally  traversed  by  a  fissure  (p.  344).  With  respect  to  fissures 
traversing  active  volcanoes  from  which  lava  has  issued,  there  is  abun- 
dant evidence.  The  great  outflow  of  lava  from  Skaptar-jokull,  in  1783 
(p.  341),  was  from  fissures  at  the  base  of  the  mountain.  Great  fissures 
have  been  made  in  Etna,  and  the  numerous  subordinate  craters  seem 
little  else  than  points  in  those  formed  at  various  times  through  which 
volcanic  matter  has  been  ejected. §  Respecting  the  fissures  on  Etna, 
M.  Elie  de  Beaumont  remarks,  that  they  occur  for  the  most  part  in 
nearly  vertical  planes,  often  so  cutting  the  crater,  as  it  were,  to  star  it, 
the  lower  part  of  the  fissures  usually  filled  with  lava,  the  higher  with 
scoriae,  and  with  pieces  of  tuff  and  lava  fallen  from  the  upper  part. 

*  Respecting  the  Hawaiian  Group,  Mr.  Dana  (Geology  of  the  United  States  Ex- 
ploring Expedition,  p.  282)  infers: — 1.  That  there  were  as  many  separate  rents  or  fis- 
sures in  the  origin  of  the  Hawaiian  Islands  as  there  are  islands.  2.  That  each  rent 
was  widest  in  the  southeast  portion.  3.  That  the  southeasternmost  rent  was  the 
largest,  the  fires  continuing  there  longest  to  burn.  4.  That  the  correct  order  of  ex- 
tinction of  the  great  volcanoes  is  nearly  as  follows  (leaving  out  Molokai  and  Lanai, 
which  were  not  visited  by  Mr.  Dana) — a,  Kauai ;  b,  Western  Oahu ;  c,  Western  Maui, 
Mount  Eeka ;  d,  Eastern  Oahu ;  e,  Northwestern  Hawaii,  Mauna  Kea ;  /,  Southeast 
Maui,  Mount  Hale-a-kala;  and  g,  Southeast  Hawaii,  Mauna  Loa.  "This  order,"  he 
observes,  "is  shown  by  the  extent  of  the  degradation  on  the  surface.  Each  successive 
year,  since  the  finishing  of  the  mountain,  has  carried  on  this  work  of  degradation,  and 
the  amount  of  it  is,  therefore,  a  mark  of  time,  and  affords  evidence  of  the  most  decisive 
character."  (p.  283.) 

f  Dana,  "Geology  of  the  United  States  Exploring  Expedition,"  p.  217. 

j  Ibid.,  p.  259. 

|  It  is  stated  that  there  are  52  of  these  subordinate  volcanic  hills  on  the  west  and 
north  of  the  summit  of  Etna,  and  27  on  the  east  side,  "  some  covered  with  vegetation, 
others  bare  and  arid,  their  relative  antiquity  being  probably  denoted  by  the  progress 
vegetation  has  made  upon  their  surface." — Daubeny,  Volcanoes,  2d  edition,  p.  272. 


376       DIRECTION  OF  FISSURES  IN  VOLCANOES. 

He  mentions  that  the  fissure  formed  in  1832,  was  so  far  a  shift,  or  fault, 
that  one  of  the  sides  of  the  dislocation  rose  about  a  yard  higher  than 
the  other.*  The  great  fissure,  which  in  1669  traversed  the  slope  of 
the  great  gibbosity  of  Etna  and  the  Piano  del  Largo,  is  described  as 
having  ranged  from  near  Nicolosi  to  beyond  the  Torre  del  Filosofo,  and 
to  have  been  about  two  yards  wide  at  the  surface,  a  vivid  light  being 
emitted  from  the  incandescent  lava  rising  in  it.f  An  observer  should 
carefully  ascertain  the  directions  of  such  rents  or  fissures,  whether 
large  or  small,  and  always  with  reference  to  the  complication  which 
may  arise  from  variable  resistances,  even  in  the  prolongation  of  the 
same  fissures,  to  the  force  employed,  seeing  especially  if  the  greater 
fractures  have  continued  to  preserve  any  definite  directions  at  different 
intervals  of  time. 

M.  Elie  de  Beaumont  has  called  attention  to  the  fact  that  these  frac- 
tures so  often  starring  Etna,  and  into  which  the  molten  lava  is  intro- 
duced, there  hardening  and  remaining,  must  produce  a  tumefaction  or 
elevation  of  the  whole,  each  eruption  of  the  mountain,  so  characterized, 
having  a  tendency  to  elevate  the  mass  of  the  volcano.J  The  same 
reasoning  is  applicable  to  all  volcanoes  rent  and  fissured  in  a  similar 
manner,  and  the  abundance  of  the  resulting  dykes  of  lava  is  often  a 
prevailing  feature  in  many.  They  are  sometimes  interlaced  so  as  to 
show  differences  in  date,  those  of  one  time  cutting  those  of  another, 
exhibiting  proofs  of  repeated  fractures  through  the  same  general  mass 
of  volcanic'matter. 

In  examining  some  volcanic  regions,  the  observer  will  have  to  con- 
sider, as  above  noticed  (p.  322),  the  probable  differences  which  would 
arise  in  the  structure  and  arrangement  of  the  accumulations  from  a 
part  or  the  whole  of  them  having  been  produced  beneath  water.  At 
considerable  depths  in  the  ocean,  beyond  those  at  which  an  equal  tem- 
perature of  39-5°  (p.  119)  would  appear  to  prevail,  not  only  the  pressure 
but  also  the  constancy  of  that  temperature  and  the  mass  of  water  pos- 
sessing it  have  to  be  borne  in  mind.  Assuming  a  communication  made, 
whether  by  an  elevation  of  the  sea-bottom  and  the  bursting  of  a  tume- 
faction formed  by  forces  acting  from  beneath,  or  by  one  of  those 
adjustments  of  the  earth's  surface  by  which  more  or  less  considerable 
fractures  are  produced,  he  will  have  to  recollect  that  a  great  volume  of 
water,  with  a  low  temperature,  would  be  at  once  brought  to  bear  upon 
it,  and  that  not  only  are  the  usual  volcanic  gases  absorbed  by  water, 
but  that  the  very  pressure  itself  might  tend  to  drive  them  into  the 

*  Recherches  sur  la  Structure  et  sur  1'Origine  du  Mont  Etna,  par  M.  L.  Elie  de 
Beaumont;  "Me*moires  pour  servir  a  une  Description  G6ologique  de  la  France,"  1838, 
t.  iv.  p.  111. 

f  Ibid.,  p.  108. 

j  "Mdmoires  pour  servir  a  une  Description  Gdologique  de  la  France,"  t.  iv.  p.  118. 


SOFTENING    AND    RAISING    OF    TUFFS    AND    LAVAS.      377 

liquid  state.*  It  would  be  out  of  place  here  to  enter  into  the  probable 
effects  produced  under  such  conditions,  further  than  to  notice  that, 
supposing  the  communication  made,  and  the  elevatory  force  sufficient 
to  lift  a  body  of  molten  lava,  so  that  it  could  pass  out  of  the  volcanic 
orifice  or  crack,  the  observer  has  to  consider  the  effects  which  would 
follow.  However  any  intense  heat  might  permit  the  existence  of  the 
vapours  and  gases  observed  at  subaerial  volcanoes,  before  the  rupture 
was  effected,  as  soon  as  the  water  came  into  contact  with  them,  a  ready 
supply  of  that  at  39*5°  pouring  in,  the  more  heated  water  ascending,  as 
so  heated,  they  would  disappear  as  they  rose.  If  disseminated  amid 
the  lava  thrown  out,  the  great  pressure  upon  the  latter  would  produce 
its  effects  upon  them,  while  the  low  temperature  would  soon  act  on  the 
external  liquidity  of  the  lava  itself. 

From  such  a  state  of  things  to  the  minor  depths  and  surface  of  the 
water,  great  modifications  would  be  expected,  solid  lava  (supposing  the 
struggle  between  the  forces  brought  into  action  to  be  such,  as  on 
the  whole,  to  permit  a  gain  on  the  side  of  the  volcanic  products),  pro- 
bably prevailing  beneath,  while  there  was  an  admixture  of  more  scori- 
aceous  matter  above,  as  the  accumulations  rose  into  the  atmosphere. 
The  whole  mass  would  be  liable  at  all  times  to  be  cracked  and  fissured, 
molten  lava  rising  into  the  rents  according  to  the  pressure  of  the  time 
upon  it,  and  the  tumefaction  mentioned  by  M.  Elie  de  Beaumont  pro- 
gressing. 

The  extent  to  which  sheets  of  matter  could  be  spread  in  various 
directions  and  at  different  times  around  submarine  volcanic  vents,  would 
necessarily  depend  upon  circumstances ;  among  them,  the  absence  of 
piles  of  cinders  and  ashes  into  cones,  such  as  are  formed  by  the  dis- 
charge of  vapours  and  gases  through  lava  into  the  atmosphere,  being 
important,  so  that  when  fissures  were  produced  molten  matter  flowed 
more  freely  out,  in  the  manner,  so  far  as  liquidity  and  the  absence  of 
cinders  and  ashes  are  regarded,  of  the  streams  which  poured  out  on  the 
flanks  of  Mauna  Loa,  in  1843. 

It  has  been  seen  that  volcanic  vents  may  remain  for  a  long  time 
dormant  or  closed,  and  then  lava,  cinders,  and  ashes  be  driven  out  of 
them.  The  probable  differences  which  would  arise  in  such  cases  with 
volcanic  accumulations  beneath  the  sea  and  those  above  its  level,  re- 
quire attention.  It  may  be  inferred  that,  beneath  given  depths  of 
water,  though  a  tendency  to  greater  thickness  should  prevail,  where  the 
rents  have  been  more  frequent,  and  the  lavas  have  more  frequently 
been  thrown  out,  there  may  be  such  a  mechanical  resistance  to  the  new 

*  Dr.  Faraday  has  shown  (Philosophical  Transactions,  1823),  that  sulphurous  acid 
gas  becomes  liquid  under  the  pressure  of  two  atmospheres,  at  a  temperature  of  45° 
Fahr. ;  sulphuretted  hydrogen  under  that  of  17  atmospheres  at  50° ;  carbonic  acid 
under  36  atmospheres  at  32° ;  and  hydrochloric  acid  gas  under  40  atmospheres  at  50°. 


378  THE    CALDERA,    ISLAND    OF    PALMA. 

application  of  an  elevatory  force,  that  an  increase  of  heat  may  soften 
and  even  melt  some  of  the  prior-formed  accumulations,  for  the  most 
part  readily  fusible.  Thus  a  dome-shaped  mass  may  be  raised,  not 
finally  splitting,  in  given  localities,  at  its  surface,  until  even  above 
water  ;  and  the  quiet  cracking  of  Mauna  Loa  for  the  length  of  25  miles, 
would  appear  to  show  us  that  conditions  may  arise,  even  in  subaerial 
volcanoes,  permitting  the  heating  and  softening  of  a  volcanic  crust  to 
within  comparatively  moderate  distances  from  that  crust. 

That  such  dome-like  elevations  of  volcanic  products  have  been  formed, 
MM.  Von  Buch,  Elie  de  Beaumont,  Dufr&ioy,  and  others  consider  they 
have  sufficient  proof.  Some  notice  has  been  above  given  (p.  318),  of 
the  equivocal  .appearances  which  may  be  presented  by  the  "craters  of 
elevation"  and  the  "craters  of  eruption."  The  Caldera,  in  the  Island 
of  Palma,  Canaries,  is  adduced  by  Von  Buch  as  a  good  example  of  the 
"craters  of  elevation."  A  large  precipitous  cavity  or  crater  is  there 
surrounded  by  beds  of  basalt  and  conglomerate,  composed  of  basaltic 
fragments,  dipping  regularly  outwards,  and  is  broken  only  by  a  deep 
gorge  on  one  side,  through  which  access  can  be  obtained  to  this  central 
cavity.  White  trachyte,  and  a  compound  of  hornblende  and  white  fel- 
spar, are  also  noticed  among  these  rocks.  There  being  no  mixture  of 
scoriae  or  ashes,  and  the  beds  of  molten  rock  as  well  as  the  conglomerate ' 
presenting  a  uniform  stratification,  it  is  inferred  that  the  whole  was 
formed  under  different  circumstances,  such  as  beneath  water,  from  the 
ordinary  eruptive  accumulations  of  a  volcano,  and  had  been  upraised  in 
a  dome-like  manner,  until  finally  the  rupture  was  effected,  and  the  least 
resistance  being  in  one  direction,  the  lateral  gorge  was  produced,  the 
whole  presenting  the  appearance  of  the  pear-shaped  termination  of  the 
fissures  in  figs.  115  and  116. 

M.  Elie  de  Beaumont  has  given  a  valuable  description  of  Etna,  illus- 
trating the  same  views.*  The  Val  del  Bove  shows  an  accumulation  of 
many  hundred  layers  of  fused  rock,  somewhat  resembling  the  modern 
lavas  of  this  mountain,  interstratified  with  others  composed  of  frag- 
mentary and  pulverulent  substances,  the  beds  varying  in  thickness  from 
half  a  yard  to  several  yards,  those  of  fused  rock  commonly  thinner  than 
the  fragmentary  deposits.  The  surfaces  of  the  former  are  rough,  and 
their  outer  part  is  penetrated  by  cells  to  the  depth  of  8  or  12  inches ; 
whence  beds  only  20  inches  or  2  feet  thick  are  cellular  throughout. 
The  thicker  beds  are  solid  in  the  middle,  and  resemble  certain  trachytes, 
labradorite  replacing  orthoclase.  The  fragmentary  beds  are  true  tuffs, 

*  "Me'moires  pour  servir  a  une  Description  Gdologique  de  la  France,"  torn.  iv. 
According  to  M.  Elie  de  Beaumont,  the  order  of  the  Etna  formations  is  as  follows : — 
1.  Granitoid  rocks,  known  only  by  ejected  fragments.  2.  Calcareous  and  arenaceous 
rocks.  3.  Basaltoid  rocks.  4.  Rolled  pebbles,  forming  a  line  of  hills  at  the  junction 
of  the  Plain  of  Catania  and  the  first  slopes  of  Etna.  6.  Ancient  lavas,  forming  the 
escarpments  round  the  Val  del  Bove ;  and  G,  Modern  eruptions,  (p.  53.) 


ETNA. 


379 


their  structure  similar  to  those  found  in  the  Cantal  and  Mont  Dore,  the 
component  fragments  composed  of  the  same  substances  as  the  fused 
beds,  sometimes  scoriaceous,  at  others  compact.  The  beds  of  the  Val 
del  Bove  undulate  in  different  directions,  varying  from  horizontality  to 
inclinations  of  20°  and  30°,  without  their  structure  or  thickness  being 
altered  in  a  constant  manner.  They  are  traversed  by  a  multitude  of 
lava  dykes,  the  rock  of  which  is  of  the  same  kind  as  that  of  the  fused 
beds.  Though  these  take  various  directions,  it  is  considered  that  there 
is  a  tendency  on  the  whole  to  one  ranging  E.N.E. 


380 


SECTIONS    OF    ETNA    AND    VESUVIUS. 


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FORM    AND    STRUCTURE    OF    ETNA.  381 

The  general  form  of  Etna  will  be  seen  from  the  accompanying  view 
(fig.  129)  taken  from  one  of  those  in  the  atlas  of  M.  von  Walterhausen.* 
By  it  the  very  slight  rise  of  the  general  mass  to  the  central  crater  will 
be  observed,  as  also  the  great  break  in  front,  known  as  the  Val  del  Bove, 
where  the  more  ancient  volcanic  accumulations  are  considered  to  be  ex- 
posed. While  this  view  may  thus  be  useful  in  showing  the  general  out- 
line of  the  mountain,  so  far  as  views  embracing  considerable  areas 
may  do  so,  the  annexed  section  from  west  to  east  (fig.  130), f  will  more 
correctly  give  the  real  shape  of  Etna,  taken  through  the  Val  del  Bove, 
therefore  somewhat  across  the  outline  represented  in  the  view,  and  ex- 
hibit the  steep  descent  through  the  cliffs  of  that  great  break  or  depres- 
sion on  the  flank  of  the  mountain. 

M.  Elie  de  Beaumont  quotes  M.  Mario  Gemellaro  as  pointing  out  that 
the  central  mass  of  Etna  is  composed  of  two  cones  passing  into  each 
other ;  one,  interior,  formed  of  ancient  volcanic  products,  the  other,  ex- 
terior, formed  of  modern  accumulations.  These  two  cones  are  upon  the 
same  axis,  the  ancient  nearly  east  from  the  modern  cone,  whence  they 
do  not  completely  embrace  each  other,  the  modern  not  altogether  cover- 
ing the  ancient,  and  the  products  of  the  latter  being  exposed  on  the 
eastern  side  of  the  mountain,  especially  in  the  Val  del  Bove.J  This  con- 
siderable and  sudden  gap  in  Etna,  M.  Elie  de  Beaumont  agrees  with  Sir 
Charles  Lyell  §  in  referring  to  a  great  subsidence  of  that  part  of  the 
mountain,  in  the  same  manner  as  the  much  larger  volcanic  mass  of  the 
Papandayang  fell  in  at  Java  in  1772,  and  that  of  Carguairazo  subsided 
on  the  19th  of  July,  1698 ;  a  volcano  considered  previously  to  have 
rivalled  its  neighbour  Chimborazo  in  height.  M.  Elie  de  Beaumont  re- 
fers to  the  possibility  of  the  lava  which  lifted  the  ancient  mass  of  Etna 
having  been  abstracted,  so  that  the  needful  previous  support  of  the  por- 
tion now  occupied  by  the  Val  del  Bove  being  removed,  depression  was 
the  result.  He  considers  Etna  to  have  been  an  irregular  crater  of  eleva- 
tion, the  uplifting  force  not  having  there  acted  in  the  same  simple  man- 
ner as  at  the  Isle  of  Palma,  Teneriffe,  and  Monte  Somma  (Vesuvius). || 

*  Maps  and  Views  of  Etna. 

j-  Taken  from  Dr.  Abich's  "Erlauternde  Abbildungen  Geologischer  Erscheinungen 
beobachet  am  Vesuv  und  Aetna,"  pi.  9,  Berlin,  1837.  In  this  section,  the  scale  for 
height  and  distance  is  the  same. 

|  "  Memoires  pour  servir  a  une  Description  Gdologique  de  France,"  t.  iv.  p.  124. 

g  "Principles  of  Geology,"  4th  edition. 

||  "  Memoires  pour  servir  a  une  Description  Ge"ologique  de  France,"  t.  iv.  p.  188.  M. 
Elie  de  Beaumont  further  observes,  that  "the  force  which  raised  the  gibbosity  of  Etna 
appears  to  have  acted  not  on  a  single  and  central  point,  but  in  a  straight  line,  repre- 
sented by  the  axis  of  the  ellipse,  of  which  the  southern,  northern,  and  eastern  flanks  of 
the  Val  del  Bove  form  a  part ;  and  it  seems  to  have  acted  unequally  on  the  diiferent 
parts  of  this  straight  line,  so  that  its  western  extremity,  answering  to  the  actual  volca- 
nic vent,  has  been  more  raised  than  the  rest.  An  elevation  of  this  kind  could  not  be 
produced  without  the  upraised  masses  being  broken,  and  the  rents  ought  chiefly  to  coin- 
cide with  the  line  of  elevation,  or  diverge,  radiating,  from  its  extremities." 


382  FOSSILIFEROUS    TUFF    OF    MONTE    SOMMA. 

M.  Elie  de  Beaumont  infers  that  the  first-formed  deposits  were  nearly 
horizontal,  successive  fissures  presenting  channels  for  the  outpouring  of 
very  fluid  lava,  which  spread  round  in  various  directions,  in  the  manner 
that  sheets  of  basalt  are  seen  to  have  done  in  many  countries,  and  espe- 
cially in  Iceland,  cinders  being  also  ejected,  so  as  to  alternate  with  the 
fluid  rock.  Upon  the  accumulations  thus  produced,  the  elevatory  force 
is  considered  to  have  acted  in  the  manner  described. 

In  like  manner,  the  part  of  Vesuvius  known  as  Monte  Somma  has 
been  inferred  tojbe  the  remains  of  a  crater  of  elevation,  which  has  been 
broken  through,  so  that  it  became  in  a  great  measure  covered  by  the 
eruptions  of  more  modern  times,  those  chiefly  which  followed  the  great 
outbreak  of  79.  The  section*  (fig.  131)  will  serve  to  show  the  general 
outline  of  this  volcano,  as  well  as  the  portion  of  the  cone  (Monte  Somma) 
which  existed  prior  to  that  eruption.  After  describing  the  volcanic  tuff 
of  the  environs  of  Naples,  showing  that  it  is  composed  almost  entirely 
of  the  debris  of  trachyte,  the  greater  portion  of  the  fragments  contained 
in  it  pumice,  that  it  was  in  part,  at  least,  fossiliferous,f  and  inferring 
that  it  was  arranged  in  beds  under  water,!  M.  Dufr^noy  observes  that 
the  tuff  of  Monte  Somma  is  the  continuation  of  the  same  accumulations, 
and  quotes  M.  Pilla  as  having  discovered  fossil  shells  in  it.§  He  points 
out  that  among  the  limestone  fragments  in  the  tuff  of  Monte  Somma, 
some  are  covered  by  small  serpulce  of  the  same  species  as  those  which 
adhere  to  the  rocks  on  the  coast  of  Sicily,  and  that  these  fossils  not  be- 
ing in  the  least  altered,  they  prove,  even  more  than  the  general  disposi- 
tion of  the  tuff,  that  it  has  been  formed  beneath  water,  and  subsequently 
raised  to  its  present  height  on  the  Monte  Somma.  This  tuff,  with  its 
fragments  or  pebbles  of  limestone  (commonly  saccharoid),  and  of  micace- 
ous rocks,  M.  Dufrenoy  considers,  with  the  lava  associated  with  it  on 
Monte  Somma,  to  have  been  upraised,  in  a  vaulted  manner,  by  volcanic 

*  From  Abich's/'  Erlauternde  Abbildungen  Geologischer  Erscheinungenbeobachtet  am 
Vesuv  und  Aetna,"  pi.  9.  Berlin,  1837.  The  scale  for  this  section  is  the  same  for 
height  and  distance,  but  it  differs  from  that  of  the  section  of  Etna  on  the  same  page. 

•}•  M.  Dufrdnoy  (M6moires  pour  servir  a  une  Description  Gdologique  de  la  France,  t. 
iv.  p.  240)  adds  to  the  evidence  of  Mr.  Poulett  Scrope,  who  pointed  out  (Geol.  Transac- 
tions, 2d  series,  vol.  ii.  p.  351)  that  this  tuff  contained  the  remains  of  ostrea,  cardium, 
buccinum,  and  patella,  of  species  now  living  in  the  Mediterranean ;  and  of  Sir  Charles 
Lyell  (Principles  of  Geology)  respecting  the  fossiliferous  tuff  of  Ischia,  that  ostrea,  car- 
dium, and  pecten  have  been  obtained  from  the  quarries  in  the  hill  of  Posilippo,  an  ostrea 
and  a  peclunculus  at  St.  Elmo,  above  Naples,  and  fossils  in  other  places. 

J  M.  Dufrdnoy  mentions  (Mdmoires  pour  servir,  £c.,  t.  iv.  p.  238),  that  this  tuff  often 
presents  cavities  from  6  inches  to  2  feet  in  height,  almost  always  taking  a  vertical  direc- 
tion. They  are  numerous  in  the  tuff  of  Naples  itself,  and  in  the  escarpments  on  the 
highroad  to  Nesita.  Their  parallelism  leads  him  to  infer  that  they  have  been  caused 
by  the  abundant  escape  of  gas  which  traversed  the  beds  before  their  solidification.  M. 
Dufr6noy  (p.  241)  also  notices  concretions  in  the  tuff,  chiefly  in  the  argillaceous  beds. 

\  The  fossils  found  by  M.  Pilla  are  Turritella  terebra,  Cardium  ciliare,  Corbula  gibba, 
and  a  portion  of  an  Echinite. 


MIXED  MOLTEN  ROCKS  AND  CONGLOMERATES.    383 

forces  acting  from  beneath,  the  eruptions  finally  finding  vent  through 
this  elevated  mass,  and  forming  the  present  Vesuvius.  The  rocks  com- 
posing Monte  Somma  and  Vesuvius  are  pointed  out  as  different.  While 
the  lavas  of  Monte  Somma  resemble  crystalline  rock,  such  as  granite  and 
trachyte,  the  Vesuvian  products  are  scoriaceous.  The  former  are  com- 
posed of  leucite,  augite,  labradorite,  and  some  rare  nodules  of  olivine ; 
while  the  latter,  when  compact  and  crystalline,  are  formed  of  crystals  of 
the  order  of  felspar,  but  differing  from  ordinary  felspar,  albite,  and  la- 
bradorite. They  moreover  contain  crystals  of  green  augite,  some  nodules 
of  olivine,  and  some  rare  plates  of  mica.  As  with  the  lava  and  tuff  beds 
of  the  Val  del  Bove,  Etna,  the  lava  and  tuff  of  Monte  Somma  are  tra- 
versed by  numerous  lava  dykes. 

Without  multiplying  examples  of  mixed  beds  of  conglomerate,  tuff, 
and  lava,  so  occurring  as  to  render  it  probable  that  these  volcanic  accu- 
mulations had  been  effected  beneath  water,  mention  may  be  made  of 
the  evidence  on  that  head  obtained  by  Mr.  Dana  among  the  islands  of. 
the  Pacific,  as  the  descriptions  given  of  such  aggregations  at  Oahu,  and 
Maui  (Hawaiian  Group),  and  Tahiti,  possess  much  interest  in  their  geo- 
logical bearings.  Some  of  the  rounded  masses  in  the  conglomerate  of 
Kauai  are  stated  to  contain  30  cubic  feet,  lying  against  each  other,  the 
interstices  between  filled  in  with  pebbles  and  finer  matter.  At  Oahu, 
there  are  some  finely  laminated  tuffs,  which  as  much  point  to  their  for- 
mation beneath  water  as  the  conglomerates.*  Molten  rocks  and  con- 
glomerates are  mentioned  as  alternating  at  Tahiti,  some  of  the  stones 
in  the  latter  being  six  inches  in  diameter. f  In  such  islands  we  have 
merely  the  upper  portions  of  volcanoes  above  the  level  of  the  sea.  As 
respects  the  evidence  of  their  uprise  from  situations  where  large  rounded 
blocks  and  pebbles  could  be  formed,  the  simple  tumefaction  of  the  vol- 
canic mound,  from  the  causes  above  noticed  (p.  376),  would  alone  aid 
the  uplifting  of  beaches  and  various  deposits,  in  minor  depths,  to  heights 
proportionate  to  the  introduction  of  the  matter  filling  dykes  traversing 
the  mass,  and  to  the  extension  of  the  various  deposits  of  ashes  and  cin- 
ders, and  of  lava,  by  heat,  as  covering  after  covering  was  accumulated, 
independently  of  any  great  force  applied  from  beneath,  and  tending  to 
dome  out  and  perhaps  throw  off  the  flanks. 

The  observer  will  have  to  consider  the  probable  figures  which  beds 
would  take  round  volcanic  islands.  If  we  are  to  suppose  some  volca- 
noes, now  inland  in  various  parts  of  the  world,  to  have  been  once  islands, 
the  depth  of  water  around  them  at  different  times  would  much  influence 
the  arrangement  of  their  mineral  products.  We  should  expect  the 

*  Dana,  "  Geology  of  the  United  States  Exploring  Expedition,"  pp.  239,  261,  267,  268. 

f  Ibid.  p.  295.  Mr.  Dana  describes  the  general  dip  of  these  beds  to  be  from  the  cen- 
tral part  of  the  island  outwards,  the  central  rocks  being  more  compact  than  those  on 
the  exterior,  and  less  vesicular,  more  trachytic  and  syenitic  (p.  296). 


384 


PEAK    OF    TENERIFFE. 


deposits  which  now  take  place  around  and  amid  the  Hawaiian  Islands 
to  be  much  modified,  as  regards  general  arrangement,  from  those  of 
any  volcanoes  in  shallow  seas.  We  must  refer  to  previous  notices  of 
volcanic  ash  and  cinder  accumulations  in  tideless  (p.  94)  and  tidal  seas 
(p.  122),  and  the  working  out  of  soft  from  hard  volcanic  matter  by  the 
breakers  (fig.  80,  p.  203),  as  pointing  to  these  modifications.  To  these 
may  be  added  the  condition  of  volcanic  islands,  such  as  those  in  various 
parts  of  the  ocean  exposed  to  almost  ceaseless  breaker  action,  separating 
the  harder  from  the  softer  volcanic  products,  the  volcanic  mass  gra- 
dually rising,  from  time  to  time ;  great  subaerial  eruptions,  and  perhaps 
submarine  also,  being  effected.  Very  complicated  arrangement  of  parts 
could  scarcely  but  arise,  and  much  admixture  of  molten  matter  with 
conglomerates  and  finer  volcanic  sediment,  be  the  result,  and  this  inde- 
pendently of  any  accumulations  at  considerable  depths,  which,  as  they 
rose,  would  become  acted  upon  by  the  breakers  in  a  similar  manner ;  to 
be  afterwards  covered  with  subaerial  accumulations,  should  volcanic 
action  continue  above  water  in  the  elevated  mass.  The  accompanying 
view  of  the  Peak  of  Teneriffe  (fig.  132)  by  M.  Deville,*  taken  from  near 
Santa  Ursula,  may  serve  to  illustrate  the  slope  of  that  mountain,  con- 
sidered fundamentally  due  to  the  elevation  of  beds  of  tuff  and  molten 
rock  around  the  central  portion,  upon  which  the  subaerial  eruptions 
have  formed  the  present  Peak,  as  also  the  cutting  back  of  the  mass  at 
the  level  of  the  sea  by  the  breakers. 

Fig.  132. 


As  to  the  elevation  of  volcanic  accumulations,  the  island  of  Santorin 
has  attracted  considerable  attention,  not   only  from  the  discovery  of 

*  "Etudes  Ge*ologiques  sur  les  lies  <le  Te'ndriffe  et  de  Fogo,"  1847. 


SANTORIN    GROUP.  385 

organic  remains  in  the  tuffs,  now  raised  above  the  sea,  but  also  from 
its  general  form  and  its  history.  Dr.  Daubeny  infers — with  respect  to 
this  island,  or  rather  islands,  the  larger  known  to  the  ancients  as  Thera, 
and  the  second  in  size  as  Therasia,  though  there  may  be  some  uncer- 
tainty as  to  the  whole  of  the  little  group  having  been  thrown  up  in  his- 
torical times — that  some  considerable  convulsions  may  have  occurred, 
to  which  early  ancient  writers  refer.*  Whatever  obscurity  may  hang 
over  the  exact  times  at  which  the  Santorin  Group,  or  parts  of  it,  were 
upraised  above  the  level  of  the  sea,  there  appears  none  as  to  changes 
having  been  effected  in  its  isles  and  islets  by  volcanic  action  in  remote 
historical  times.  Although  this  may  be  a  circumstance  to  be  expected 
in  any  volcanic  mound,  so  situated  that  movements  of  its  sides  or  central 
portions,  as  well  as  eruptions,  should  raise  the  substances  composing  it 
higher  above  water  than  at  any  previous  time,  or  which  should,  on  the 
other  hand,  permit  depressions,  or  even  produce  'oscillations  of  an  order 
sometimes  to  raise  volcanic  matter  above,  or  at  others  to  depress  it  be- 
neath the  level  of  the  sea,  it  is  still  of  importance,  as  affording  us  infor- 
mation so  far  back  as  2,000  years  and  more. 

Nearer  our  own  times,  it  seems  certain  that  a  portion  of  this  volcanic 
mass  was  raised  above  water  in  1573,  forming  a  rock  known  as  the  Little 
Kaimeni ;  that  there  was  an  eruption  of  pumice  near  Santorin  in  1638 ; 
and  that,  in  1707,  a  new  rock  rose  between  the  Little  and  Great  Kai- 
meni, "  which  increased  in  size  so  rapidly,  that  in  less  than  a  month  it 
became  half  a  mile  in  circumference,  and  had  risen  20  or  30  feet  above 
the  level  of  the  water,  constituting  a  third  island,  which  was  called  New 
Cammeni,  a  name  which  it  still  bears,  "f  Some  persons  landing  on  the 
upraised  rock  to  collect  oysters  adhering  to  it,  were  compelled  to  leave 
it  from  the  violent  shaking  of  the  ground.  The  commencement  of  the- 
island  was  first  observed  on  the  23d  of  May,  1707.  In  July,  black 
smoke  accompanied  the  upheaval  of  the  rocks,  and  much  sulphuretted 
hydrogen  appears  to  have  been  discharged.  Stones,  cinders,  and  ashes 
were  shortly  afterwards  ejected;  showers  of  the  two  latter  spreading  to 

* 'Daubeny,  "Description  of  Volcanoes,"  2d  ed.  p.  320.  Dr.  Daubeny  refers  to  the 
statement  of  Pliny,  that  130  years  after  the  separation  of  Therasia,  the  island  of  Thera 
•was  thrown  up;  "a  statement,"  he  observes,  "confirmed  by  Justin  and  Plutarch,  as  to 

the  fact,   though  not  as  to  the  date." "  It  is  to  this  event  that   Seneca 

seems  to  refer,  where  he  speaks  of  an  island  thrown  up  in  the  ^Egean  Sea,  by  an  accu- 
mulation of  stones,  of  various  sizes,  piled  one  upon  another." "Pliny  also 

speaks  of  another  phenomenon  of  the  same  kind,  as  happening  in  his  own  time,  for  he 
tells  us  that  in  the  reign  of  Claudius,  A.D.  46,  a  new  island  called  Thia  appeared  near 
Thera.  But  as  he  mentions  it  as  only  two  stadia  distant  from  Hiera,  it  is  possible  that 
the  island  may  have  been  joined  to  the  latter  by  a  subsequent  revolution,  as  by  that 
recorded  to  have  taken  place  in  the  year  726,  by  which  Hiera  is  said  to  have  been 
greatly  augmented  in  point  of  size." 

•j-  Daubeny  (Description  of  Volcanoes,  p.  321),  who  quotes  from  Father  Goree,  an 
eyewitness  of  the  fact,  seen  from  Scaro  and  all  that  side  of  Santorin. 

25 


386 


SANTORIN    GROUP. 


considerable  distances.  The  volcanic  action  continued  for  nearly  a  year, 
more  or  less;  indeed,  during  ten  subsequent  years.*  As  Dr.  Daubeny 
remarks,  this  elevatory  action  has  not  yet  ceased,  inasmuch  as  a  reef 
found  by  the  fishermen  to  have  been  raised,  during  a  short  time,  to 
within  30  or  40  feet  of  the  surface,  was  in  1829  ascertained,  by  M. 
Lalande,  to  have  no  more  than  nine  feet  water  over  an  area  of  2,400 
by  1,500  feet,  the  ground  gradually  sinking  around  from  the  centre  ; 
and  less  water,  by  two  feet,  was  obtained  about  two  months  afterwards 
by  M.  Bory  de  St.  Vincent. 

Fig.  133. 


/  81  ;         S3 
(I3fi\  t,s 


.  IS! 


m  \  ",.'"" 

' ...    'ISO 
a,  a,  a,  a,  Thera  or  Santorin ;  6,  Therasia. 

The  accompanying  cut  (fig.  133)  is  a  map  of  these  islands,  with  a  plan 
of  the  banks  and  form  of  the  ground  beneath  the  sea,  as  shown  by  the 

*  "  In  July,  the  appearances  were  more  awful,  as  all  at  once  there  arose,  at  a  dis- 
tance of  about  60  paces  from  the  island  already  thrown  up,  a  chain  of  black  and  cal- 
cined rocks,  soon  followed  by  a  torrent  of  black  smoke,  which,  from  the  odour  that  it 
spread  around,  from  its  effect  on  the  natives  in  producing  headache  and  vomiting,  and 
from  its  blackening  silver  and  copper  vessels,  seems  to  have  consisted  of  sulphuretted 
hydrogen.  Some  days  afterwards  the  neighbouring  waters  grew  hot,  and  many  dead 
fish  were  thrown  upon  the  shore.  A  frightful  subterranean  noise  was  at  the  same  time 
heard,  long  streams  of  fire  rose  from  the  ground,  and  stones  continued  to  be  thrown 
out,  until  the  rocks  became  joined  to  the  White  Island,  originally  existing.  Showers  of 
ashes  and  pumice  extended  over  the  sea,  even  to  the  coasts  of  Asia  Minor  and  the  Dar- 
danelles, and  destroyed  all  the  products  of  the  earth  in  Santorino.  These,  and  similar 
appearances,  continued  round  the  island  for  nearly  a  year,  after  which  nothing  re- 
mained of  them  but  a  dense  smoke.  On  the  15th  July,  1708,  the  same  observer  (Father 
Goree),  had  the  courage  to  attempt  visiting  the  island,  but  when  his  boat  approached 
within  500  paces  of  it,  the  boiling  of  the  water  deterred  him  from  proceeding.  He 
made  another  trial,  but  was  driven  back  by  a  cloud  of  smoke  and  cinders  that  proceeded 
from  the  principal  crater.  This  was  followed  by  ejections  of  red-hot  stones,  from  which 
he  very  narrowly  escaped.  The  mariners  remarked,  that  the  heat  of  the  water  had 
carried  away  all  the  pitch  from  their  vessel."— Daubeny,  "Description  of  Volcanoes," 
p.  322. 


SUBMAKINE    CHARACTER    OF    SANTORIN    GROUP.        387 

late  survey  of  Captain  Graves,  R.  N.  The  crateriform  cavity  in  the 
centre,  with  its  depth  of  213  fathoms  (1,278  feet),  will  be  at  once  appa- 
rent, with  the  shallow  depth  on  the  west,  dividing  it  from  the  Mediter- 
ranean in  that  direction.  Equally  interesting  is  the  deep  channel 
running  to  the  northward,  with  as  much  as  990  feet  in  it,  reminding 
us  of  those  figures  and  descriptions  of  the  craters  particularly  brought 
under  notice  by  Von  Buch,  where  a  great  rent  appears  to  have  been 
effected  on  one  side,  forming  a  ravine  entrance  to  their  central,  and 
often  otherwise  inaccessible  interiors.  Such  a  form  also  will  again 
remind  the  observer  of  the  pear-shaped  termination  of  fissures  noticed 
above  (figs.  115  and  116),  one  which  would  so  readily  accord  with  the 
power  of  a  force  acting  from  beneath  upwards,  so  that  if  this  was  ex- 
erted in  the  centre  of  the  group  of  Santorin,  and  a  fissure  extended 
northerly  through  the  deep  channel  there  presenting  itself,  there  appears 
no  mechanical  difficulty  in  supposing  a  somewhat  yielding  covering,  ren- 
dered so,  in  a  great  measure,  by  heat,  opening  outwards  in  such  a  man- 
ner that  the  chief  fissure  would  suffice  for  any  required  separation  of 
parts,  a  certain  amount  of  cohesion  still  remaining.  The  observer  will 
find  it  needful,  in  estimating  the  effects  which  would  be  produced  in 
this,  or  in  a  somewhat  similar  manner,  to  regard  the  whole  mass  with 
reference  to  proportion  and  real  sections,*  so  that  no  undue  value  should 
be  attached  to  heights  or  distances ;  and  also  to  the  masses  of  limestone 
of  Mount  Elias  and  the  hill  on  the  north  of  it,  a  range  of  that  limestone 
on  the  eastern  side  of  the  island  (marked  by  straight  lines  on  the  map, 
fig.  133),  having  to  be  taken  into  account.  It  is  also  easy  to  conceive 
— indeed,  the  variable  intensities  of  different  eruptions  from  the  same 
volcanic  vent  point  to  the  fact — that  the  action  which  at  one  time  may 
elevate  a  considerable  mass,  may  at  another,  and  after  time,  be  unable 
to  cause  more  than  a  central  movement  in  a  volcanic  vent.f 

Professor  Edward  Forbes  and  Captain  Spratt,  R.  N.,  who  visited 
Santorin  in  1841,  state  that  "  the  aspect  of  the  bay  is  that  of  a  great 
crater  filled  with  water,  Thera  and  Therasia  forming  its  walls,  and  the 
other  islands  being  after-productions  in  its  centre.  "J  In  the  Little 
Kaimeni  they  found  the  elevated  sea-bottom,  formed  of  fine  pumiceous 
ash,  to  be  fossiliferous.§  They  were  informed  that  similar  beds  of  shells 

*  Those  constructed  with  the  same  scale  for  heights  and  distances. 

f  When  noticing  the  uprise  of  ground  and  eruptions  witnessed  at  Santorin  by  the 
Father  Goree,  in  1707  and  1708,  Dr.  Daubeny  calls  attention,  as  important  to  the 
natural  history  of  volcanoes,  "that  in  this  case,  as  in  many  others,  the  mountain  ap- 
pears to  have  been  elevated  before  the  crater  existed,  or  gaseous  matters  were  thrown 
out.  According  to  Bourguignon,  smoke  was  not  observed  till  26  days  after  the  ap- 
pearance of  the  raised  rocks." — "Description  of  Volcanoes,"  p.  322. 

J  In  a  letter  from  Professor  E.  Forbes  to  Dr.  Daubeny,  quoted  by  the  latter  in  hi 
"Description  of  Volcanoes,"  2d  ed.,  p.  324,  1848. 

\  Professor  E.  Forbes  informs  me  that  the  following  shells  were  there  obtained : — 


388 


SANTOKIN    GROUP    FROM    THE    NORTHWARD. 


QUIET    DEPOSITS    INSIDE    THE    SANTORIN    GROUP.        389 

were  found  on  the  cliffs  of  Santorin  itself.  "  In  the  main  island,  the 
volcanic  strata  abut  against  the  limestone  mass  of  Mount  St.  Elias,  in 
such  a  way  as  to  lead  to  the  inference,  that  they  were  deposited  on  a 
sea-bottom,  on  which  the  present  mountain  rose  as  a  submarine  mass  of 
rock."*  The  preceding  view  (fig.  134),  kindly  communicated  by  Captain 
Spratt,  R.  N.,  is  highly  illustrative  of  the  general  appearance  of  the  in- 
terior of  the  Santorin  Group,  of  the  position  of  the  central  islets,  and  of 
the  kind  of  stratification  which  occurs  around  the  central  opening. 

In  a  group  of  this  kind,  independently  of  any  eruptions  through  the 
central  cavity  or  crater,  which  it  would  appear  have  taken  place  even  in 
later  historic  times,  breaker  action  upon  the  interior  cliffs,  upon  the  softer 
substances  especially,  would  tend  to  degrade  them,  and  deposit  the  de- 
tritus, so  derived,  in  the  central  depression,  a  deep  cavity  in  a  tideless 
sea,  as  the  Mediterranean  may  be  considered,  as  far  as  regards  geologi- 
cal effects.  In  like  manner,  also,  heavy  seas  rolling  over  the  gap  facing 
the  southwest,  between  Therasia  and  Cape  Akroteri  (Santorin),  where 
Aspro  Island  rises  above  the  shallow  bank  connecting  the  chief  islands 
(the  brim  of  the  volcanic  basin,  slightly  covered  with  water),f  tend  to 
force  in  detrital  matter.  Deposits  at  the  bottom  of  the  central  cavity, 
varying  in  depth  from  960  to  1,278  feet  in  its  curved  passage  round  the 
Kaimeni,  would  seem  well  at  rest,  except  as  regards  upheaval  or  de- 
pression from  volcanic  action  there  prevailing.  In  cases  where  animal 
life  might  become  extensively  destroyed  by  the  boiling  of  the  waters,  a 
ready  supply  of  the  germs,  even  of  those  inhabiting  deep  water,  could 
be  furnished  by  the  deep  channel  opening  to  the  northward ;  one  also 
through  which  the  heated  waters  could  flow  outwards  on  the  surface, 
while  cooler  water  supplied  their  place  by  the  inflow  beneath.  As  re- 
gards the  exposure  of  this  channel  to  wind-wave  action,  a  glance  at  the 
charts  of  the  JEgean  Sea  will  show,  that  it  is  comparatively  well  shel- 
tered by  Nio,  Sikino,  and  Polykandro,  with  the  bank  connecting  those 
islands,  on  the  north  and  northwest,  while  Siphano,  Paros,  and  Naxos 
prevent  any  great  range  of  sea  exposure  still  further  beyond  those 
islands. 

Examining  the  charts  of  coasts  or  islands  where  volcanoes  occur,  vari- 

Pectunctulus  pilosus,  Area  tetragona,  Cardita  trapezia,  Trochus  ziziphinus,  T.  fanulum,  T. 
exiguus,  T.  Coutourii,  Turbo  rugosus,  T.  sanguineus,  Phasianella  pulla,  Turritella  tricostata, 
Necera  cuspidata,  Cerithium' Lima,  Pleurotoma  gracile. 

*  "  My  own  impression  is,"  adds  Professor  E.  Forbes,  "that  this  group  of  islands  con- 
stitutes a  crater  of  elevation,  of  which  the  outer  ones  are  the  remains  of  the  walls,  whilst 
the  central  group  is  of  later  origin,  and  consists  partly  of  upheaved  sea-bottoms  and 
partly  of  erupted  matter,  erupted  however  beneath  the  surface  of  the  water." 

f  Commencing  with  the  southern  point  of  Therasia,  the  soundings  show  this  submerged 
brim  of  the  crater  to  be  successively  42,  36,  54,  06,  54,  and  42,  feet  (depths  at  which 
wind-wave  action  would  cause  much  disturbance  on  the  bottom,  especially  during  heavy 
gales),  a  point,  marked  as  a  sunken  rock,  rising  higher  between  the  south  end  of  The- 
rasia and  Aspro  Island. 


390 


ISLAND    OF    ST.    PAUL. 


ous  instances  will  be  found  by  the  observer  in  which  the  sea  more  or  less 
enters  the  central  cavities  or  craters,  or  where,  by  a  little  more  cutting 
away  of  the  remaining  walls  of  the  crater  by  breaker  action,  or  a  slight 
change  of  level,  bringing  some  lower  part  of  its  lip  further  down,  a  simi- 
lar entrance  of  the  sea  would  be  effected.  The  Island  of  St.  Paul  may 
be  taken  in  illustration  of  a  crater  just  so  far  laid  open  by  breaker  ac- 
tion, that  the  portion  of  the  brim  of  the  basin  through  which  the  sea 
enters  is  nearly  dry  at  low  tide.  It  will  be  seen  by  the  accompanying 
plan  (fig,  135),  that  this  little  island,  scarcely  2J  geographical  miles 

Fig.  135. 


from  N.W.  to  S.E.,  and  about  1J  mile  broad  from  N.E.  to  S.  W., 
rising  in  the  Indian  Ocean,  between  the  south  of  Africa  and  the  west  of 
Australia,  Madagascar  being  the  nearest  mass  of  dry  land,  and  more 
than  2,000  miles  distant,  is  the  mere  summit  of  a  volcano.  With  its 
companion,  Amsterdam  Island,  it  forms  a  remarkable  protrusion  through 
the  ocean  amid  a  mass  of  waters,  an  excellent  example  of  the  uplifting 
of  volcanic  matter  through  them.  That  such  mere  points  should  be 
easily  removed  by  breaker  action,  unless  some  hard  rocks  should  be  ac- 
cumulated, would  be  expected,  and  the  foregoing  plan  (fig.  134)  and  ac- 
companying view  (fig.  135),*  would  seem  to  show  that  its  abrasion  by 

Fig.  136. 


fed  c  b  a 

a.  Nine-Pin  Rock ;  b.  Entrance  to  crater-lake  ;  c.  Cliff,  vrell  exhibiting  the  united 
action  of  breakers  and  atmospheric  influences  ;  d.  Dark-coloured  rock,  dipping  seaward; 
e.  Section  of  a  dark-coloured  bed  ;  /.  The  southern  point  of  the  island. 

such  means  is  now  being  accomplished.     The  high  cliffs,  several  hundred 
feet  in  elevation,  appear  the  remains  of  the  accumulations  cut  back  by 

*  From  that  accompanying  the  Admiralty  chart  of  the  Island  of  St.  Paul,  by  Captain 
Blackwood,  R.  N. 


BREAKER    ACTION    ON    ST.    PAUL'S    ISLAND.  391 

the  breakers,  so  ceaselessly  at  work  in  such  a  situation,  the  amount  of 
removal  on  the  N.E.  of  the  island  being,  to  a  certain  extent,  shown 
where  the  anchorage  (a)  of  the  surveying  ship,  the  "Fly,"  is  marked  in 
that  direction  on  the  chart,  as  upon  sand  and  stones,  and  beyond  which 
the  depth  suddenly  increases  seaward.  The  greatest  height  of  the  island 
is  stated  to  be  820  feet.  The  Nine-Pin  Rock  (a,  fig.  136)  is  merely  a 
harder  portion  left  by  the  breakers,  and  it  may  be  inferred,  the  present 
breaker  action  continuing  to  remove  the  matter  of  St.  Paul's  Island,  and 
no  new  eruptions  adding  to  its  mass,  that  in  time  such  points  might 
alone  remain  above  water  to  attest  the  former  presence  of  a  volcanic 
crater,  the  walls  of  which  once  rose  several  hundred  feet  above  the  level 
of  the  sea.* 

The  distribution  of  volcanoes  over  the  face  of  the  globe  will  strike  the 
observer  as  necessarily  important  when  searching  for  their  cause  and 
studying  their  effects.  It  will  also  at  once  be  apparent  to  him  that  in- 
dependently of  the  modifications  which  may  arise  in  local  conditions,  so 
that  the  same  vent  may  be  active-  at  one  time,  with  variable  degrees  of 
intensity,  and  dormant  at  another,  there  may  be  great  general  condi- 
tions becoming  so  permanently  changed,  that  a  region  once  marked  by 
volcanic  action  may  so  far  be  considered  as  ceasing  to  be  so,  that  some 
very  considerable  modification  in  such  portion  of  the  earth's  crust  must 
be  effected  to  produce  a  return  of  that  action.  In  consequence  of  such 
complicated  conditions,  it  becomes  almost  impossible  to  separate  active 
volcanoes  from  those  termed  extinct,  inasmuch  as  we  can  scarcely  be 
certain  that  many  of  the  latter  may  really  be  such,  and  not  in  a  com- 
paratively dormant  state.  Asa  matter  of  convenience,  therefore,  rather 
than  of  principle,  it  has  usually  been  considered  desirable  to  separate 
volcanoes  known  to  have  been  active  from  those  never-recorded  to  have 
been  so,  though  often  preserving  the  forms  which  they  took  under  sub- 
aerial  eruptions  and  lava  outflows,  atmospheric  influences  having  little 
changed  such  forms.  This  division,  however  convenient  in  the  present 
state  of  the  subject,  should  not  mislead  the  observer,  nor  will  it  do  so 
when  he  regards  volcanic  action  on  a  larger  scale,  and  igneous  products 
generally,  during  the  long  lapse  of  geological  time  of  which  we  can  obtain 
any  relative  records. 

It  has  long  been  remarked  that  active  volcanoes  are  chiefly,  though 
not  altogether,  situated  amid,  or  at  moderate  distances  from,  oceans  and 
seas,f  a  circumstance  also  considered  important  as  regards  their  pro- 
ducts, especially  as  respects  aqueous  vapours  and  certain  of  the  gases 

*  In  the  view  above  given  there  is  an  apparent  interstratification  of  differently  shaded 
rocks,  perhaps  of  lavas  and  tuff.  During  the  abrading  process  by  the  breakers,  these 
would  necessarily  be  acted  upon  according  to  their  relative  hardness  and  positions. 

f  M.  Arago  pointed  out  in  1824  (Annuaire),  that  about  five  or  six  only  of  the  173  re- 
puted active  volcanoes  of  the  world  were  not  so  circumstanced. 


392  VOLCANOES    DISTRIBUTED    IN    THE    OCEAN. 

evolved.  It  would  be  out  of  place  to  enter  upon  the  hypotheses  framed 
in  consequence,  further  than  to  call  the  attention  of  the  observer  to 
points  which  appear  important  for  the  effective  study  of  his  subject. 
First,  however,  as  respects  the  facts  recorded.  Upon  glancing  at  any 
of  the  maps  of  the  world  whereon  the  existing  knowledge  of  volcanoes, 
considered  sufficiently  active,  is  laid  down,  we  find  them  in  the  ocean 
separating  America  from  Europe  and  Africa,  ranging  in  points,  or  groups 
of  points,  from  Jan  Mayen's  Island  on  the  north,  by  Iceland,  the  Azores, 
Canary  and  Cape  de  Verde  Islands,  Ascension,  and  Trinidad  (South 
Atlantic),  to  Tristan  da  Cunha  on  the  south.  On  one  side  of  the  same 
waters  the  line  of  the  West  Indian  volcanoes  presents  itself.  In  the 
Indian  Ocean  appear  the  somewhat  scattered  groups  of  the  Islands  of 
Bourbon,  Mauritius,  and  Rodriguez,  and  the  small  isolated  points 
of  St.  Paul  and  Amsterdam  Islands.  In  the  central  portion  of  the 
Pacific  are  the  Hawaiian,  Marquesas,  and  Society  Islands  groups,  with 
Easter  Island.  On  the  north  of  the  same  ocean  is  the  range  of  the 
Aleutian  vents,  having  a  somewhat  W.S.W.  and  E.N.E.  direction  (as 
if  upon  a  great  fissure),  into  the  northwest  of  North  America.  To  the 
westward  of  the  Aleutian  volcanoes  a  range  of  vents,  commencing  with 
the  somewhat  lofty  volcanoes  in  Kamtschatka,  proceeds  in  a  southwest 
direction  through  the  Kurile  Islands  to  and  beyond  Japan.  Southward 
of  the  latter,  and  having  a  north  and  south  direction,  are  the  volcanoes 
of  the  Benin  and  Mariana  Islands.  On  the  S.E.  of  Japan  a  series  of 
vents  commences,  which,  ranging  down  by  Formosa  and  the  Philippines, 
passes  round  in  the  form  of  a  huge  fish-hook,  by  the  N.E.  point  of  Cele- 
bes, Gilolo,  the  volcanic  isles  between  New  Guinea  and  Timor,  Floris, 
Sumbawa,  Java,  and  Sumatra,  to  Barren  Island,  where  a  central  active 
cone  rises  amid  water,  entering  from  the  sea  on  one  side,  bounded,  ex- 
cept on  that  side,  by  a  series  of  rocks.*  Returning  to  the  Pacific,  we 
find  the  volcanic  group  of  the  Galapagos  in  that  ocean,  off  the  coast  of 
Quito. 

As  respects  volcanoes  on  continents,  or  in  seas  more  or  less  intermin- 
gled with  them,  the  vents  of  South  America  constitute  by  far  the  most 
important  range.  After  quitting  the  volcanoes  of  Tierra  del  Fuego,  a 
space  intervenes  northward  for  several  degrees  of  latitude  in  which  they 
have  not  been  noticed.  Then  succeeds  the  long  line  of  the  volcanoes  of 
Chili,  several  rising  to  considerable  heights  above  the  sea.  Another 
break  then  occurs,  after  which  volcanoes  appear  in  the  Andes  of  Quito, 

*  Von  Buch  views  this  island  as  highly  illustrative  of  a. cone  of  eruption  in  the  midst 
of  a  crater  of  elevation;  and  Dr.  Daubeny  observes,  that  "  if  we  compare  this  locality 
with  Santorin,  there  will  be  found  nothing  but  the  absence  in  the  latter  case  of  an  ac- 
tive vent  in  the  centre  of  the  bay  whereby  to  distinguish  it ;  and  from  Monte  Somma  it 
chiefly  differs  in  its  lower  level,  which  causes  the  bottom  of  the  crater  to  be  sunk  be- 
neath the  waters  of  the  ocean." — "  Description  of  Volcanoes,"  p.  413,  where  also  a  view 
of  Barren  Island  is  given. 


AMERICAN    VOLCANOES.  393 

Cotopaxi  being  one  of  them.  Passing  the  Isthmus  of  Darien,  the  vents 
of  Guatemala  come  in,  succeeded  more  northerly  by  those  of  Mexico. 
Continuing  in  the  same  direction  volcanoes  become  scarce  in  North  Ame- 
rica, a  few  points  only  being  noticed  in  California,  upon  the  Columbia, 
on  the  Island  of  Sitka,  and  in  Russian  America,*  where  the  Aleutian 
range  joins  in.  Active  volcanoes  in  Europe  are  confined  to  the  Neapo- 
litan States  and  Santorin,  the  latter  being  inferred  to  be  merely  for  the 
time,  dormant.  On  the  continent  of  Africa  no  active  vents  are  known, 
Jebel  Tarr,  in  the  Red  Sea,  being  as  much  Asiatic  as  African.  With 
respect  to  Asia,  the  great  mass  of  that  continent  appears  (omitting  the 
Kamtschatkan  peninsula),  to  be  at  least  in  a  great  measure  without  active 
vents.  Though  doubts  are  expressed  respecting  such  vents,  the  state- 
ments regarding  volcanoes  in  Central  Asia  are  deserving  of  every  atten- 
tion, and  numerous  warm  springs  would  appear  there  to  be  found,  under 
circumstances  which  may  connect  them  with  volcanic  action. f 

The  observer  will  perceive  that  the  statement  as  to  these  communica- 
tions with  the  surface  of  the  earth  being  chiefly  found  amid  oceans 
and  seas,  or  not  far  from  them,  seems  borne  out.  Volcanoes  in  Mexico 
and  those  of  Central  Asia,  assuming  that  there  are  still  active  volcanoes 
there,  would  appear  the  principal  exceptions.  J  As  respects  the  former, 
it  has  been  held  by  the  advocates  of  the  necessity  of  water  as  one  of  the 
causes  of  volcanic  action,  that  there  may  be  a  connexion  along  a  great 
fissure  extending  in  an  east  and  west  direction  across  Mexico,  vents  being 
established  upon  it  at  Colima,  Jorullo,  Popocatepetl,  and  Orizaba.  With 
regard  to  Central  Asia,  it  can  be  inferred  that  it  is  a  region  which  may 
have  once  been  in  a  great  measure  occupied  by  an  inland  sea,  waters 
being  then  supplied  to  the  volcanic  foci,  as  is  now  supposed  by  some  to 
happen  in  the  volcanic  regions  of  the  Mediterranean. § 

*  Wrangell's  Volcano,  on  the  Atna. 

f  With  respect  to  the  volcanoes  of  Central  Asia,  Humboldt,  after  observing  that  Abel 
Rcmusat  first  called  the  attention  of  geologists  to  them  (Annales  des  Mines,  t.  v.  p.  137), 
remarks  (Kosmos,  Sabine's,  7th  edit.  p.  232),  that  there  is  "  a  great  volcanic  chain,  the 
Thian-schan  (Celestial  Mountains),  to  -which  belong  the  Pe-schan,  from  whence  lava 
issues,  the  Solfatara  of  Urum-tsi,  and  the  still  active  <  fire  mountain'  (Ho-tscheu)  of 
Turfan,  almost  equidistant  from  the  shores  of  the  Polar  Sea  and  of  the  Indian  Ocean 
(1,400  and  1,528  miles).  Pe-schan  is  also  fully  1,360  miles  from  the  Caspian  Sea,  and 

172  and  208  miles  respectively  from  the  great  lakes  of  Issikoul  and  Balkasch." 

"It  is  impossible  not  to  recognise  currents  of  lava  in  the  descriptions  given  by  the 
Chinese  writers  of  smoke  and  flame  bursting  from  the  Pe-schan,  accompanied  by  burn- 
ing masses  of  stone  flowing  as  freely  as  'melted  fat,'  and  devastating  the  surrounding 
district,  in  the  first  and  seventh  centuries  of  our  era." 

J  Respecting  the  range  of  the  Mexican  volcanoes,  Humboldt  remarks  (Kosmos,  Sa- 
bine's, 7th  edit.  p.  232),  that  Jorullo,  Popocatepetl,  and  the  Volcano  de  la  Fragua,  are 
respectively  80,132,  and  156  geographical  miles  from  the  ocean. 

$  Reference  to  the  remarkable  fact  that  in  the  island  of  Cephalonia  a  stream  of  sea- 
water,  in  sufficient  quantity  and  volume  to  turn  a  mill,  is  constantly  flowing  from  the 
sea  inland,  where  it-  becomes  swallowed  up,  has  been  made,  as  illustrating  the  employ- 


394   VARIABLE  PROXIMITY  OF  WATER  TO  VOLCANOES. 

Should  the  presence  of  water  be  considered  only  a  secondary  cause 
of  volcanic  action,  it  would  follow  that  during  the  changes  of  levels  which 
have  taken  place  over  large  areas  on  the  earth's  surface,  circumstances 
may  arise  that  should  at  one  time  permit  the  easy  access  of  water  to 
great  fissures  or  apertures  of  any  form,  and  at  another  prevent  it; 
thus  aiding  in  changing  active  volcanic  regions  into  those  termed  ex- 
tinct, independently  of  the  termination  of  other  and  perhaps  more  gene- 
ral conditions  from  which  volcanic  action  may  arise.  If  we  regard  the 
variable  amount  of  dry  land  which  would  be  exposed  above  water  by 
changes  of  the  relative  level  of  sea  and  land,  such  as  has  been  above 
noticed  in  the  British  Islands  (fig.  99),  it  would  appear  that  parts  of 
France  might  constitute  islands  at  one  time  to  which  sea  water  could 
have  more  ready  access  (from  proximity)  to  any  volcanic  foci  beneath, 
than  at  another.  Thus,  supposing  such  supply  needed,  if  it  were  stopped 
by  changes  removing  the  sea  to  greater  distances,  a  region  containing 
active  volcanoes  at  the  one  period,  might  present  only  extinct  craters 
at  another.  This,  even  under  the  hypothesis  of  the  water  being  essen- 
tial, might  not  necessarily  be  always  the  real  cause  of  change,  inasmuch 
as  the  general  conditions,  productive  of  volcanic  action  in  such  districts, 
may  have  been  exhausted,  so  that  whether  the  supply  of  water  was  or 
was  not  altered,  that  action  became  extinct. 

Whatever  may  have  caused  volcanic  fires  to  have  ceased,  there  are 
whole  regions,  independently  of  portions  of  districts  in  parts  of  which 
active  volcanoes  still  exist,  or  have  been  known  in  historic  times,  which 
offer  clear  evidence  of  volcanic  action  having  prevailed,  sometimes  ex- 
tensively, in  them  at  no  very  remote  geological  period,  loose  piles  of 
cinders  and  ashes,  and  lava  streams  being  found  nearly  as  fresh  as  when 
ejected.  The  district  of  Auvergne,  in  Central  France,  has  for  about  a 
century  engaged  attention,  as  one  of  extinct  volcanic  action.*  This 

ment  of  water  in  volcanic  action,  that  supply  of  water  being  converted  into  gases  and 
vapours,  producing  earthquakes  and  volcanic  eruptions. — See  Mr.  Strickland,  "  Geol. 
Trans.,"  2d  Series,  vol.  v.  p.  408,  and  "  Geological  Proceedings,"  vol.  ii.  pp.  220,  393; 
also  Daubeny's  "Description  of  Volcanoes." 

*  It  is  now  about  a  century  since  (1752)  that  Guettard  published  his  "Me'moire  sur 
quelques  Montagnes  de  la  France,  qui  ont  et<5  des  Volcans  (Mdmoires  de  1'Acaddmie 
des  Sciences)."  As  regards  general  views  of  the  extinct  volcanoes  of  France,  the  ob- 
server will  find  them  in  Mr.  Scrope's  "Geology  of  Central  France,"  1827;  in  the 
"Mdmoires  pour  servir  a  une  Description  G6ologique  de  la  France,"  (1830-38,)  and 
the  "Explication  de  la  Carte  Gdologique  de  la  France,"  1841,  by  MM.  Dufrenoy  and 
Elie  de  Beaumont,  and  in  Dr.  Daubeny's  "Description  of  Volcanoes,"  2d  edit.,  1848. 
More  than  70  years  since  M.  Desmarest  published  a  map  of  Auvergne,  always  adverted 
to  with  satisfaction  by  those  who  have  visited  that  region.  As  Sir  Charles  Lyell  re- 
marks ("Principles  of  Geology,"  7th  edit.,  p.  51),  "Desmarest,  after  a  careful  exami- 
nation of  Auvergne,  pointed  out,  first,  the  most  recent  volcanoes  which  had  their  craters 
still  entire,  and  their  streams  of  lava  conforming  to  the  level  of  the  present  river- 
courses.  He  then  showed  that  there  were  others  of  an  intermediate  period,  whose 
craters  were  nearly  effaced,  and  whose  lavas  were  less  intimately  connected  with  the 


MINERAL    COMPOSITION    OF     BASALT.  395 

seems  to  have  continued  for  a  long  period,  various  points  of  communica- 
tion having  been  established  between  the  interior  of  the  earth  and  the 
atmosphere  at  different  times,  and  changed  and  modified  results  the 
consequence.  In  addition  to  Auvergne,  similar  accumulations  are  found 
in  France,  in  the  Cantal,  the  Velay,  the  Vivarais,  the  Cevennes,  and 
in  the  vicinity  of  Marseilles  and  Montpellier.  In  Germany  they  are 
seen  in  the  districts  of  the  Eifel,  the  Siebengebirge,  and  other  places. 
Hungary,  Transylvania,  and  Styria,  present  their  trachytic  and  other 
igneous  products.  Extinct  volcanic  action  is  also  traced  in  Spain  and 
Sardinia ;  Italy  offers  its  extinct  as  well  as  active  volcanic  accumulations, 
as  does  also  Greece,  when  including  its  islands.  In  Asia  Minor,  extinct 
volcanoes  are  found,  and  more  especially  in  the  wide  district  of  the 
Katakekaumene.*  With  respect  to  the  Holy  Land,  the  destruction  of 
Sodom  and  Gomorrah  has  been  attributed  to  volcanic  eruptions,  and 
volcanic  accumulations  are  elsewhere  noticed  in  the  same  land,  and  in 
Persia  and  its  adjoining  countries.  Doubtless,  also,  many  other  regions, 
not  yet  explored  by  the  geologist,  will  be  found  to  present  similar  accu- 
mulations, and  indeed  they  have  been  noticed  in  the  great  continent  of 
America. 

In  various  parts  of  the  world,  as  well  in  regions  where  lava  streams 
intermingled  with  ash  and  cinders,  either  piled  up  conically  or  more 
evenly  distributed,  are  not  apparent,  as  in  those  where  active  or  extinct 
volcanoes  exist,  certain  rocks  are  found  to  which  the  name  basalt  has 
been  given.  In  the  application  of  this  name  care  has  not  always  been 
taken  to  distinguish  the  same  compound  considered  chemically  and  mine- 
ralogically,  so  that  in  the  matter  of  fusibility  alone,  substances  so  termed 
differ  somewhat  materially. f  Fine  varieties  of  greenstone  (diabase), 

present  valleys ;  and,  lastly,  that  there  were  volcanic  rocks,  still  more  ancient,  without 
any  discernible  craters  or  scoriae,  and  bearing  the  closest  analogy  to  rocks  in  other 
parts  of  Europe." 

*  Messrs.  Hamilton  and  Strickland  (Geol.  Trans.,  2d  series,  vol.  vi.  1841,  and  "  Tra- 
vels in  Asia  Minor,"  1842,  by  the  former  geologist),  consider  the  volcanic  products  of 
the  Katakekaumene,  as  referable  to  three  periods.  The  volcanic  accumulations  of  the 
last  period  are  as  fresh  as  amid  active  vents,  the  ashes  and  scoriae  still  loose  and  piled 
up  as  after  immediate  ejection,  the  lava  streams  rugged,  a  few  straggling  plants  alone 
finding  fitting  conditions  for  their  growth. 

f  During  the  experiments  on  the  fusibility  of  rocks,  to  which  allusion  has  been  above 
made,  we  found  marked  differences  in  that  of  the  so-termed  basalts.  Allowing  for 
changes  by  the  different  conditions  under  which  substances,  originally  similar,  may 
have  been  placed,  so  that  while  one  may  have  been  deprived  of  certain  substances, 
another  may  have  mineral  matter  added  to  it,  there  were  still  evidently  original  diffe- 
rences. It  has  been  stated  by  De  Saussure  (Journal  de  Physique),  that  basalt  melts  at 
76°  of  Wedgwood.  The  experiments  of  Sir  James  Hall  (Trans.  Royal  Soc.  of  Edinburgh, 
vol.  v.),  went  to  show  that  whinstone,  or  basalt  as  it  has  been  called,  from  the  vicinity 
of  Edinburgh,  became  soft  at  a  temperature  from  28°  to  55°  Wedgwood,  a  heat,  as  Dr. 
Daubeny  remarks  (Description  of  Volcanoes,  p.  616),  inferior  to  that  of  a  common 
glass-house. 


396 


CHEMICAL    COMPOSITION    OF    BASALT. 


consisting  of  orthoclase  and  hornblende,  have  as  often  been  termed  ba- 
salt, as  those  of  labradorite  and  augite  (dolerite).  If,  with  M.  Rose, 
hornblende  and  augite  be  considered  only  modifications  of  the  same 
mineral,  this  would  leave  the  difference  of  these  two  varieties  of  basalt 
to  consist  in  that  of  the  two  felspars.  The  basalt  of  the  Mont  Dor  has 
been  stated  to  contain  both  the  augite  and  hornblende  forms  of  this 
mineral.  Basalt  has  again  been  supposed  essentially  to  consist  of  augite, 
magnetic  iron,  and  a  mineral  of  the  zeolitic  family.*  The  uncertainty 
in  the  employment  of  the  term  basalt,  would  appear  to  require  attention. 
Thus  the  rocks  which  encircle  the  Peak  of  Teneriffe,  and  usually  noticed 
under  that  head,  are  referred  by  Dr.  Abich  to  his  class  of  trachyte- 
dolerites.  While  endeavouring  to  trace  the  sources  whence  certain 
igneous  rocks  may  have  been  obtained,  even  sometimes  with  reference  to 
the  melting  of  masses  which  may  have  been  accumulated  by  means  of 
water,  or  have  been  intermingled  with  such  deposits,  mineralogical  and 
chemical  distinctions,  as  far  as  they  can  fairly  be  carried  out,  would 
appear  very  desirable. f  While  at  times  extensive  sheets  of  basalt  cover 
great  areas,  at  others  they  are  mingled  with  ordinary  volcanic  products, 
apparently,  therefore,  ejected  under  similar  conditions.  Basalt  is  some- 
times highly  vesicular,  at  others  very  compact ;  these  modes  of  occur- 
rence are  observable  over  areas  of  different  extent,  both  considerable 
and  limited. 

*  Referring  to  the  composition  of  this  zeolitic  mineral,  Dr.  Daubeny  observes  (De- 
scription of  Volcanoes,  p.  18),  that  it  "  is  such  as  to  imply  that  it  may  have  been  formed 
out  of  labradorite  by  the  addition  of  water,  the  presence  of  which  in  all  zeolites  is  the 
cause  of  the  bubbling  up  under  the  blowpipe,  which  has  occasioned  them  to  be  distin- 
guished by  that  general  appellation."  Following  out  this  view,  it  seems  highly  desirable 
to  consider  how  far  a  change  may  be  brought  about  in  a  compound  of  augite,  magnetic 
iron,  and  labradorite,  so  that  the  latter  became  modified  by  water  after  ejection.  The 
vesicles  of  basalts,  as,  for  example,  those  of  the  north  of  Ireland,  are  often  filled  with 
zeolitic  minerals,  the  results  of  infiltrations  into  them,  quite  as  much  as  agates,  &c., 
also  found  amid  the  same  rocks.  In  fact,  in  certain  districts  the  vesicles  are  filled  with 
a  variety  of  substances,  the  zeolites  forming  only  a  part  of  them. 

f  As  respects  the  chemical  composition  of  basalt,  including  that  of  Teneriffe  (trachy  te- 
dolerite  of  Dr.  Abich),  the  following  table  of  basalts,  from  Saxony  (1),  by  Mr.  Phillips, 
from  Banlieu  (2),  by  M.  Beaudant,  and  from  Teneriffe  (3),  by  Dr.  Abich,  may  be 
useful: — 


1 

2 

3 

Silica        .          ... 

44-50 

69-5 

57-76 

Alumina.  .... 

16-75 

11-5 

17-56 

Protoxide  of  iron,  . 
Peroxide  of  iron,    . 
Oxide  of  manganese, 
Lime,   

20-00 

6-i2 
9-50 

19-7 
0-5 

i-3 

4-64 
2-09 
0-82 
6-46 

Magnesia,     .     .     . 
Potash,     .... 
Soda     .     . 

2-25 
°-60 

i-e 

5-9 

2-76 
1-42 

6-82 

Chlorine,  .... 

0-30 

Water. 

2-00 

trace 

GLOBULAR    STRUCTURE    OF    BASALT.  397 

As  regards  the  relative  antiquity  of  basalt,  we  find  it  noticed  as  well 
among  the  ancient  as  the  more  modern  volcanic  products  of  Central 
France,  and  among  the  more  modern  of  the  Vivarais  in  the  south  of 
France,  as  also  in  those  of  the  Eifel.*  It  is  noticed  as  intermingled 
among  the  ancient  volcanic  rocks  of  the  Siebengebirge,  as  also  of  later 
date  in  the  same  district.  Basalt  is  described  as  among  the  ancient 
igneous  rocks  of  Iceland.  It  occurs  in  many  parts  of  the  world  where 
its  relative  date  is  not  so  apparent,  sometimes  forming  the  isolated  caps 
of  hills,  and  resting  upon  other  rocks,  in  a  manner  pointing  to  the  con- 
siderable or  partial  destruction  of  some  great  sheet  of  this  rock.  This 
has  been  supposed  the  case  with  the  basaltic  hills  in  parts  of  Germany. 
The  largest  area  occupied  by  basalt  seems  to  be  in  India,  where  rocks 
of  this  class  appear  to  occupy  one  of  200,000  square  miles.f  With 
respect  to  this  rock,  a  fine  exhibition  of  it  is  found  in  the  north  of  Ire- 
land, where  the  Giant's  Causeway  and  the  adjacent  country  have  long 
attracted  attention.  Though  on  a  much  smaller  scale,  the  Island  of 
StafFa,  Hebrides,  has  also  long  been  equally  celebrated  for  its  basalt. 
In  the  north  of  Ireland  its  eruption  was  posterior  to  the  formation  of 
"the  chalk  of  the  same  district,  but  the  portion  of  the  tertiary  period  to 
which  this  should  be  referred  is  not  clear. 

Though  by  no  means  confined,  among  igneous  rocks,  to  basalt,  the 
spherical  and  columnar  structures  often  developed  in  that  rock  have  also 
long  attracted  much  attention.  The  minor  spherical  structure  seen  on 
the  small  scale  in  some  volcanic  rocks,  and  also  in  artificial  glass,  and 
which  has  been  previously  noticed,  would  appear  to  have  been  produced 
on  the  larger  scale,  under  certain  conditions,  in  basalts.  Sometimes  this 
globular  structure,  as  shown  during  the  decomposition  of  the  rock,  is 
irregular,  so  that  the  whole  has  the  appearance  of  balls  of  various  dimen- 
sions piled  up  without  much  order  (fig.  1ST) ;  at  others,  a  great  order 

Fig.  137. 


prevails,   and  the  concretions  are  either  roughly  arranged  above  one 
another  in  wide  spheroidal  shapes,  or  so  pressed  against  each  other  as 

*  On  this  point,  Dr.  Daubeny  remarks  (Description  of  Volcanoes,  p.  42),  when  men- 
tioning the  occurrence  of  basalt  with  the  fresh-water  limestones,  near  Clermont,  and 
the  proof  by  M.  Elie  de  Beaumont  of  this  basalt  forming  dykes  amid  the  fresh-water 
formation  of  the  Liinagne  (Memoires  pour  servir,  &c.,  torn,  i.),  that  while  it  occasion- 
ally underlies  the  trachyte  and  subjacent  tuffs  of  the  districts,  "its  general  relation  to 
both  these  rocks  indicates  that  it  is  of  more  modern  eruption." 

f  Lieut. -Colonel  Sykes  (Geological  Transactions,  2d  series,  vol  iv.  p.  409)  observes, 
that  in  the  Dukhun  there  are  proofs  of  a  continuous  trap  formation,  covering  an  area' 
of  from  200,000  to  250,000  square  miles. 


398  COLUMNAR    STRUCTURE     OF    BASALT. 

to  produce  prisms,  sometimes  of  very  symmetrical  forms.  In  1804,  Mr. 
Gregory  Watt  showed  by  his  experiments  on  basalt,  that  when,  in  the 
cooling  of  a  molten  mass  of  that  rock,  this  structure  was  developed,  and 
"  two  spheroids  came  into  contact,  no  penetration  ensued,  but  the  two 
bodies  became  mutually  compressed  and  separated  by  a  plane,  well  de- 
fined and  invested  with  a  rusty  colour,"  and  he  observed,  when  several 
spheroids  met,  that  they  formed  prisms.* 

From  the  arrangement  observed  by  Mr.  Gregory  Watt,  he  inferred 
that  "  in  a  stratum  composed  of  an  indefinite  number,  in  superficial  ex- 
tent, but  only  one  in  height,  of  impenetrable  spheroids,  with  nearly  equi- 
distant centres,  if  their  peripheries  could  come  in  contact  on  the  same 
plane,  it  seems  obvious  that  their  mutual  action  would  form  them  into 
hexagons ;  and  if  these  were  resisted  below,  and  there  was  no  opposing 
cause  above  them,  it  seems  equally  clear  that  they  would  extend  their 
dimensions  upwards,  and  thus  form  hexagonal  prisms,  whose  length 
might  be  indefinitely  greater  than  their  diameters.  The  further  the 
extremities  of  the  radii  were  removed  from  the  centre,  the  nearer  would 
their  approach  be  to  parallelism;  and  the  structure  would  be  finally 
propagated  by  nearly  parallel  fibres,  still  keeping  within  the  limits  of 
the  hexagonal  prism  with  which  their  incipient  formation  commenced; 
and  the  prisms  might  thus  shoot  to  an  indefinite  length  into  the  undis- 
turbed central  mass  of  the  fluid,  till  their  structure  was  deranged  by  the 
superior  influence  of  a  counteracting  cause." 

It  will  require  the  careful  study  of  this  class  of  rocks,  more  particu- 
larly in  a  decomposed  state,  for  the  observer  to  ascertain  the  extent  to 
which  the  view  of  Mr.  Gregory  Watt  may  be  applicable.  Where  one 
plane  of  a  sheet  of  basalt  may  have  been  exposed  to  cooling  influences, 
so  that  the  spheroidal  structure  could  be  first  'developed  in  it,  and  in  the 
manner  suggested,  and  also  so  that  no  other  spheroidal  bodies  could  be 
developed  in  the  general  body  of  the  rock,  and  thus  interfere  with  the 
extension  of  the  original  spheroid,  there  would,  when  this  could  find 
space  for  development,  not  appear  much  difficulty  in  following  this  view. 
In  those  basaltic  dykes  that  are  sufficiently  common  in  some  districts, 
where  we  may  suppose  that  the  walls  of  the  fissure,  which  had  been  filled 

Fig.  138. 


by  the  molten  rock,  presented  equal  cooling  conditions,  we  sometimes 
•see,  as  in  the  preceding  section  (fig.  138),  that  the  prisms  shoot  out  at 

*  Observations  on  Basalt,  and  on  the  transition  from  the  vitreous  to  the  stony  tex- 
ture which  occurs  in  the  gradual  refrigeration  of  the  melted  basalt,  Phil.  Trans.  1804. 


JOINTED    COLUMNS    OF    BASALT. 


399 


right  angles  to  the  walls  of  the  containing  rock  (b  c),  as  if  each  set  com- 
menced at  the  sides  (d  and  e\  confusion  arising  at  the  central  portion 
(af\  on  the  conditions  having  been  there  such  that  the  prismatic  struc- 
ture was  not  developed.*  In  cases,  also,  where  not  a  trace  of  joints  can 
be  observed,  as  in  the  annexed  section  (fig.  139),  where  the  columns  (c\ 
are  seen  to  rise  at  right  angles  to  the  supporting  rock  (a  6),  which  may 

Fig.  139. 


be  of  any  kind,  igneous  or  accumulated  in  water,  the  prisms  reaching  to 
the  height  of  100  feet  or  more,  an  original  cooling  lower  plane  may  have 
produced  the  prisms  throughout.  Also  in  those  curved  columns  of  basalt, 
where,  as  in  the  following  sketch  (fig.  140),  no  joints  are  apparent,  even 
upon  the  weathering  of  the  rock,  we  may  suppose  that  some  tendency 

Fig.  140. 


of  an  original  set  of  spheroids  to  develope  themselves  more  in  one  direc- 
tion than  another,  from  some  local  cause,  has  been  so  continued  as  to 
produce  the  general  curve  observed. 

When  the  jointing  of  the  prisms  is  marked,  though  no  doubt,  upon 
the  view  of  Mr.  Gregory  "Watt,  the  prolongation  of  additions  to  the  ra- 

Fig.  141.  Fig.  142. 


diating  arrangement  of  parts  would  render  the  pauses  of  that  which  would 
be  otherwise  concentric  coatings  of  a  spheroidal  mass,  somewhat  flat 
planes,  across. the  prisms,  so  that  the  preceding  structures  (figs.  141, 142). 

*  It  sometimes  happens  that  the  central  portions  of  a  basaltic  dyke  are  more  prisma- 
tic than  the  sides,  as  if  the  cooling  had  been  too  rapid  at  the  sides  for  the  production 
of  this  arrangement  of  parts.  Again,  the  prisms  are  sometimes  found  ranging  from 
wall  to  wall  of  the  fissure,  as  if  artificially  cut  prismatic  blocks  of  rock  had  been  piled 
in  it  on  their  sides. 


400 


FINGAL'S  CAVE,    STAFFA. 


might  be  thereby  accounted  for,  facts  are  occasionally  seen,  where  the  de- 
composition of  the  joints  would  rather  point  to  the  production  of  separate 
centres  of  radiation.  Certain  joints  of  the  great  bed  of  prismatic  basalt 
which,  dipping  into  the  sea,  forms  the  well-known  Giant's  Causeway,  in 
the  north  of  Ireland,  would  seem  to  countenance  such  a  view.  These 
joints  are  observed  to  have  minor  pieces,  a,  a,  a,  supplemental,  as  it  were, 
to  the  main  joints,  filling  up  corners ;  giving  an  idea  of  each  joint  hav- 
ing been  a  separate  sphere,  the  minor  pieces  completing  the  arrange- 
ment of  particles  in  the  corners,  where  sphere  pressing  against  sphere, 
these  remained  to  be  filled  up.  At  times  the  minor  pieces  constitute 
more  of  the  whole  sharp  corners  of  the  prisms,  as  represented  beneath 
(fig.  143). 

Fig.  143. 


Of  the  intermixture  of  conditions  producing  flows  of  melted  rock  at  one 
time  from  the  same  general  vent,  or  system  of  vents,  which  should  take 
the  prismatic  form,  and  at  another  exhibit  no  tendency  to  that  structure, 
the  Giant's  Causeway  and  adjacent  district  in  the  north  of  Ireland  will 
afford  the  observer  a  good  example.  The  same  mixture  of  prismatic 
and  more  solid  basalt  is  also  to  be  found  in  the  Island  of  Staffa,  where, 

Fig.  144. 


as  shown  in  the  preceding  sketch  (fig.  144),*  the  action  of  the  Atlantic 
breakers  has  worn  out  the  celebrated  Fingal's  Cave. 

*  Reduced  from  M'Culloch's  "  Western  Islands  of  Scotland." 


SALSES  OR  MUD  VOLCANOES.  401 

» 

fakes  or  Mud  Volcanoes. — Mineral  matter  is  raised  from  beneath 
and  thrown  out  upon  the  surface  of  the  ground,  and  vapours  and  gases 
are  evolved,  the  latter  sometimes  inflammable,  in  a  manner  which  so 
differs  from,  or  forms  a  modification  of  the  volcanic  action  previously 
noticed,  as  to  merit  separate  attention.  Amid  the  changes  effected 
during  the  modification  of  ordinary  volcanic  action,  it  may  readily  hap- 
pen, as  has  been  seen,  that  aqueous  vapours  and  certain  gases  alone 
escape  from  old  volcanic  vents,  and  masses  of  mud  may  be  ejected,  as 
from  Tongariro,  New  Zealand  (p.  323).  In  these  cases,  the  gases 
evolved  would  tend  to  show  the  observer  the  connexion  between  volcanic 
action,  such  as  it  is  manifested,  with  a  very  general  resemblance,  in  so 
many  situations  scattered  over  the  face  of  the  globe,  and  any  localities 
he  may  be  examining  ;  more  especially  if  volcanic  rocks  prevailed  in  the 
vicinity.  As  the  subject  at  present  rests,  it  requires  more  attention 
than  has  always  been  assigned  it,  inasmuch  as  somewhat  similar  appear- 
ances may  be  brought  about  by  different  means.  While  a  modification 
of  volcanic  action  may  connect  certain  of  these  salses  or  mud  volcanoes, 
as  they  have  been  termed,  with  the  general  cause  of  that  action,  others 
may  depend  upon  causes  which,  though  producing  effects  of  local  impor- 
tance, could  scarcely,  as  regards  the  crust  of  the  globe,  be  considered 
as  exerting  any  great  geological  influence,  while,  as  manifesting  alte- 
rations in  the  condition  of  the  matter  composing  even  limited  portions 
of  the  accumulations  on  the  earth's  surface,  they  require  consideration. 
With  respect  to  gaseous  emanations,  they  are  not  only  found  so 
connected  with  volcanic  regions,  that  their  origin  can  scarcely  be 
doubted ;  but  also  in  localities  where  that  action  is  either  not  apparent, 
or  where  other  sources  may  be  reasonably  assigned  them.  Of  the  latter 
kind  are  those  discharges  of  carburetted  hydrogen,  which  rise  in  several 
coal  districts ;  this  gas  occasionally  evolved  in  such  volume  as  to  be 
economically  employed.*  In  these  cases,  our  experience  in  working 
collieries  shows  us  that  such  gases  are  abundantly  produced  from  cer- 

*  At  Fredonia,  State  of  New  York,  this  gas  has  long  been  collected  in  a  gasometer 
for  the  lighting  of  the  place;  and,  according  to  Humboldt  (Kosmos),  it  has  been  used  in 
the  Chinese  province  of  Tse-tchuan,  for  more  than  1,000  years.  M.  Imbert  states,  that 
an  inflammable  gas  is  employed  in  evaporating  saline  water  at  Thsee-lieou-tsing. 
"  Bamboo  pipes  carry  gas  from  the  source  to  the  place  where  it  is  to  be  consumed. 
These  tubes  are  terminated  by  one  of  pipe-clay,  to  prevent  their  being  burnt.  A  single 
source  (of  gas)  heats  more  than  300  kettles.  The  fire  thus  produced  is  exceedingly 
brisk,  and  the  caldrons  are  rendered  useless  in  a  few  months.  Other  bamboos  conduct 
the  gas  intended  for  lighting  the  streets  and  great  rooms  or  kitchens." — "  Bibliotheque 
Universelle,"  and  "  Edinburgh  Philosophical  Journal,"  1830.  The  wells  whence  this 
inflammable  gas  rises  were  sunk  for  the  purpose  of  obtaining  the  saline  water.  This 
they  first  afforded ;  but  the  water  failing,  they  were  sunk  much  deeper,  when,  instead 
of  water,  the  gas  rushed  out  suddenly  with  considerable  noise  (Humboldt,  "  Fragmens 
Asiatiques").  This  seems  a  good  instance  of  tapping,  as  it  were,  a  supply  of  inflamma- 
ble gas,  pent  up  in  a  compressed  state. 

26 


402  EXHALATION    OF    CARBURETTED    HYDROGEN. 

•  , 

tain  coal  beds  and  associated  carbonaceous  shales,  the  result  of  a  decom- 
position of  those  bodies  by  which,  among  other  changes,  a  portion  of 
the  constituent  carbon  and  hydrogen  is  evolved  in  a  gaseous  state.  That 
fissures,  or  other  natural  rock  channels,  should  permit  the  escape  of 
this  gas  to  the  surface,  and  that  the  causes  for  its  production  continuing, 
it  should  have  been  known  during  a  long  lapse  of  time,  would  be  ex- 
pected. Emanations  of  carburetted  hydrogen  are  well  known  in  the 
coal  districts  of  Europe  and  America. 

When  beds  of  lignite,  coal,  or  shales  highly  impregnated  with  bitumin- 
ous matter,  can  be  acted  on  by  heat,  so  that  these  substances  may  be 
placed  under  somewhat  of  the  conditions  of  the  coals  in  a  gas-work,  we 
should  expect  results  corresponding  with  the  resistance  to  the  escape  of 
the  gas  which  any  associated  or  superincumbent  rock-deposits  may 
offer,  with  the  additional  force  exerted  by  any  steam  which  may  be 
derived  from  disseminated  water,  the  latter  sometimes  forming  no  in- 
considerable power  for  overcoming  superincumbent  resistance.  In  such 
instances,  the  heat  produced  by  the  decomposition  of  iron  pyrites,  so 
often  disseminated  amid  carbonaceous  and  bituminous  deposits,  should 
scarcely  be  neglected,  a  sufficient  supply  of  air  and  water  being  effected. 
Indeed,  the  "  burning,"  as  it  is  usually  termed,  of  bituminous  shales 
exposed  in  cliffs,*  and  through  which  easily  decomposed  iron  pyrites  are 
disseminated,  is  sufficient  to  show  that  this  circumstance  should  receive 
attention,  however  exaggerated  the  views  taken  respecting  the  effects  of 
such  causes  may  once  have  been. 

The  country  around  Baku,  a  port  on  the  Caspian,  would  appear  instruc- 
tive, not  only  as  respects  the  emanation  of  inflammable  gas,  but  also 
with  regard  to  the  production  of  one  class  of  salses,  or  mud  volcanoes. 
That  district  is  described  as  impregnated  with  petroleum  and  naphtha, 
to  such  an  extent  that  the  inhabitants  of  Baku  employ  no  other  fuel. 
About  ten  miles  N.E.  from  the  town  there  are  many  old  temples  of  the 
Guebres,  in  each  of  which  inflammable  gas,  burning  with  a  pale  flame 
and  smelling  strongly  of  sulphur,  rises  in  jets  from  the  ground. f  A 

*  The  Kimmeridge  clay  of  the  Weymouth  coast,  in  which  there  is  much  shale  in 
places  so  bituminous  as  to  have  been  distilled  for  the  bitumen  in  it,  offers  from  time  to 
time  a  good  example  of  the  "burning"  of  a  cliff  from  the  decomposition  of  iron  pyrites 
amid  bituminous  shale  by  the  action  of  the  weather.     The  heat  generated  has  been 
occasionally  so  considerable  as  to  fuse  some  of  the  clay  or  shale. 

•j-  It  would  be  expected  that  these  natural  jets  of  inflammable  gas  would  be  utilised, 
wherever  ascertained  to  be  emitted,  by  those  to  whom  a  perpetual  fire  could  be  of 
importance  in  their  religious  rites.  Captain  Beaufort  (Karamania)  describes  a  jet  of 
inflammable  gas,  named  the  Yanar,  near  Deliktash,  on  the  coast  of  Karamania,  pro- 
bably once  thus  used.  "  In  the  inner  corner  of  a  ruined  building,  the  wall  is  under- 
mined, so  as  to  leave  an  aperture  of  three  feet  in  diameter,  and  shaped  like  the  mouth 
of  an  oven ;  from  thence  the  flame  issues,  giving  out  an  intense  heat,  yet  producing  no 
smoke  on  the  wall."  Though  the  wall  was  scarcely  discoloured,  small  lumps  of  caked 
soot  were  found  in  the  neck  of  the  opening.  The  Yanar  i-;  considered  to  be  very  ancient, 


MUD    VOLCANOES    OF    TAMAN    AND    KERTCH.  403 

large  jet  is  stated  to  issue  from  an  adjoining  hillside,  and  the  whole 
country  around,  for  a  circumference  of  two  miles,  is  so  impregnated 
with  this  gas  that  a  hole  being  made  in  the  ground  it  immediately 
issues,  the  inhabitants  thrusting  canes  into  the  earth,  through  which  the 
gas  rises  and  is  used  in  cooking.*  It  was  near  Jokmali,  to  the  east  of 
Baku,  that,  on  the  27th  November,  1827,  flame  burst  out,  where  flame 
had  not  previously  been  known,  rising  to  a  considerable  height,  for 
three  hours,  after  which  it  became  lowered  to  three  feet,  burnt  for  20 
hours,  and  was  then  succeeded  by  an  outburst  of  mud,  covering  an  area 
of  more  than  1,000,000  square  feet  to  the  depth  of  two  or  three  feet.f 
Large  fragments  are  mentioned  as  having  been  thrown  out,  and  hurled 
around.  J  A  column  of  flame  rose  so  high  at  an  eruption  near  Baklichli, 
west  of  Baku,  that  it  could  be  seen  at  the  distance  of  24  miles.  The 
country  is  considered  to  afford  other  traces  of  similar  eruptions. 

While  these  eruptions  have  taken  place  near  Baku,  on  the  east  of 
the  Caucasus,  similar  outbursts  of  flame  and  mud  have  occurred,  under 
similar  circumstances,  in  the  neighbourhood  of  Taman  and  Kertch,  at 
the  western  extremity  of  the  same  range.  These  have  been  long 
known,  and  taking  place,  in  an  area  which  comprises  the  Cimmerian 
Bosphorus,  where  the  Sea  of  Azof  communicates  through  a  shallow 
channel  with  the  Black  Sea,  they  become  important  in  effecting  surface 
changes,  tending  still  further  to  close  this  channel  upon  the  outflow  of 
the  river  waters  poured  into  the  Sea  of  Azof,  chiefly  by  the  Don  and 
its  tributaries,  and  not  evaporated  in  it.  These  salses,  or  mud  vol- 
canoes, are  found  on  both  sides  of  the  strait,  and  are  situated,  like 
those  of  Baku,  in  a  district  replete  with  bituminous  matter.  M.  Dubois 
de  MontpeVeux  gives  sections  showing  the  area  to  be  principally  com- 
posed of  a  highly  bituminous  (tertiary)  shale,  sometimes  with  lignite, 
alternating  with  sands.  From  these  bituminous  beds  asphalt  is  pre- 
pared, and  there  is  evidently  much  bituminous  matter,  including  naphtha, 
disseminated  in  its  various  forms ;  indeed,  naphtha  springs  are  mentioned 
as  rising  near  the  crater-cavity  of  Khouter.  In  some  situations  the 
salses  seem  to  have  vomited  forth  flame  and  niud  from  the  same  spots 
at  different  times,  at  others  these  suddenly  rise  from  places  not  previ- 
ously known. §  The  gases  evolved  from  the  salses  at  Baku,  Taman,  and 

and  possibly  the  jet  described  by  Pliny.  The  hill  whence  it  issues  is  formed  of  crum- 
bling serpentine  and  loose  blocks  of  limestone.  A  short  distance  down  it  there  is  ano- 
ther aperture,  whence,  from  its  appearance,  another  jet  of  a  similar  kind  is  inferred 
once  to  have  risen. 

*  "Edinburgh  Philosophical  Journal,"  vol.  vi. 

I  Humboldt,  "Fragmens  Asiatiques." 

j  Humboldt,  "Kosmos," — Mud  Volcanoes. 

\  Dubois  de  Montpereux  (Voyage  autour  du  Caucase,  t.  v.  p.  51)  mentions,  respect- 
ing these  mud  volcanoes,  that  Koukou-oba  was  in  eruption  in  February,  1794 ;  and 
Koussou-oba  on  the  26th  April,  1818  ;  that  the  chief  eruption  of  Gnila-Gora,  near  Tern- 


404  MUD    VOLCANOES    OF    MACULABA. 

Kertch,  and  from  the  vicinity  of  Tiflis,  where  similar  facts  are  noticed, 
seem  not  so  well  known  as  is  desirable.  M.  Dubois  de  Montpereux 
mentions  the  emission  of  sulphuretted  hydrogen  when  the  mud  of 
Khouter  was  disturbed,  and  there  was  also  a  sulphurous  spring  not  far 
distant.  M.  de  Verneuil  gives  an  elevation  of  250  feet  to  some  of  the 
conical  mud  accumulations  of  Taman  and  the  Eastern  Crimea.*  Iron 
pyrites  seem  to  be  found  amid  the  ejected  mud.  As  might  be  expected, 
these  jets  of  flame,  smoke,  and  mud,  occur  as  well  in  the  shallow  water 
adjoining  the  dry  land  as  upon  the  latter,  even  adding  to  and  modifying 
its  form.  In  1814,  flames  rose  through  the  Sea  of  Azof,  mud  was 
thrown  out,  and  an  island  gradually  produced.  Among  the  stones 
ejected  at  these  eruptions  are  limestones  and  shales  not  known  among 
the  surrounding  strata. f 

The  mud  volcanoes  of  Maculaba,  near  Girgenti,  whence  mud  and 
bituminous  matter  are  thrown  out,  Dr.  Daubeny  attributes  to  the  com- 
bustion of  the  beds  of  sulphur  there  associated  with  the  blue  clays, 
amid  which  these  mud  eruptions  take  place.  J  He  ascertained  that  the 
gases  given  off  consisted  of  carbonic  acid  and  carburetted  hydrogen. 
At  the  time  of  his  visit  the  cavities  were  small,  and  filled  with  water, 
somewhat  above  the  usual  temperature  of  that  in  the  country,  mixed 
with  mud  and  bitumen,  through  which  the  gases  bubbled  up.§  Dr. 
Daubeny  refers  similar  phenomena  at  Terrapilata,  near  Caltanisetta, 
and  at  Misterbianco,  near  Catania,  to  the  same  causes. 

To  ascertain  how  far  such  salses  or  mud  volcanoes  may  arise  from 
other  than  strictly  volcanic  causes,  or  be  merely  some  secondary  effects 
produced  by  them,  it  becomes  very  desirable  not  only  that  the  geolo- 

rouk,  was  in  February,  1815  ;  that  an  island  appeared  in  front  of  the  Isle  of  Tyrambe, 
on  the  10th  May,  1814,  and  that  the  mud  volcano  of  Taman  was  never  in  a  greater 
state  of  activity  than  in  April,  1835.  He  comments  on  these  eruptions  having  occurred 
at  one  time  of  the  year,  remarking,  with  Pallas,  that  the  only  known  autumnal  eruption 
was  on  the  5th  September,  1799,  when  the  first  island  was  thrown  up.  In  the  Geolo- 
'  gical  Atlas  accompanying  the  "Voyage  autour  du  Caucase,"  there  is  a  plan  (pi.  xxvi.) 
in  which  the  various  salses  or  mud  volcanoes  of  Taman  and  Kertch  are  laid  down ;  and 
in  the  Carte  Ge'ne'rale  Geologique  of  the  same  work,  the  districts  of  Baku  and  Tiflis 
are  included.  Section,  pi.  xxv.  shows  the  alternations  of  bituminous  shales  and  sands 
whence  a  mud  volcano  broke  out  near  Koutchougourei,  bordering  the  Sea  of  Azof. 

*  "Bulletin  de  la  Soc.  Gdol.  de  France." 

f  Sir  E.  Murchison,  "  Geology  of  Russia,"  p.  576. 

j  "  Description  of  Volcanoes."  Alluding  to  the  combustion  of  the  sulphur,  Dr.  Dau- 
beny remarks,  that  "the  sulphurous  acid  being  retained  by  the  moisture  of  the  rock, 
and  gradually  converted  into  sulphuric  acid,  would  act  upon  the  calcareous  particles, 
and  give  rise  to  the  extrication  of  carbonic  acid  gas,  whilst  if  any  bituminous  matters 
were  present,  the  heat  generated  might  cause  a  slow  decomposition,  and  resolve  them 
into  petroleum  and  carburetted  hydrogen,"  p.  267. 

$  It  is  stated  that  at  times  "  the  mud  has  been  known  to  be  thrown  up  to  the  height 
of  200  feet,  accompanied  by  a  strong  odour  of  sulphur." — Daubeny,  "Volcanoes," 
p.  266. 


NITROGEN  EVOLVED  NEAR  TAMAN.  405 

gical  structure  of  the  country  should  be  well  examined,  but  also  that  the 
gases  evolved  should  be  carefully  ascertained.  According  to  Humboldt 
and  M.  Parrot,  almost  pure  nitrogen  is  found  among  the  gases  evolved 
from  the  mud  volcanoes  of  the  peninsula  of  Taman,  and  the  former 
mentions  hydrogen  mixed  with  naphtha  as  emitted  from  salses  of  this 
kind.  We  have  seen  that  carburetted  hydrogen  and  carbonic  acid  are 
emitted,  and  that  sulphuretted  hydrogen  is  noticed  amid  the  mud  of 
one  thrown  out  near  Kertch.  Stones  being  ejected  in  the  Taman  and 
Kertch  district  different  from  those  forming  the  adjacent  rocks,  would 
certainly  point,  as  Sir  R.  Murchison  has  remarked,*  to  an  action  more 
deep-seated  than  the  combustion  of  the  bituminous  beds  amid  which  the 
salses  are  found,  and  certainly  deposits  of  that  kind  might  cover  vol- 
canic vents,  which,  though  usually  in  a  dormant  state,  may  from  time 
to  time  manifest  some  minor  activity,  furnishing  aqueous  vapour  (cooled 
into  water  of  moderate  temperature  before  it  rises  to  the  surface),  and 
producing  conditions,  from  the  distillation  of  some  of  the  bituminous 
deposits,  by  which  carburetted  hydrogen  may  be  evolved  and  carbonic 
acid  formed.  In  cases  where  nearly  pure  nitrogen  is  emitted,  as  near 
Taman,  it  would  appear,  assuming  that  substance  to  have  been  derived 
from  the  atmosphere,  as  if  common  air  passing  into  the  earth,  perhaps 
mixed  with  water,  had  been  deprived  of  its  oxygen  beneath,  during  the 
combustion  of  the  bituminous  substances,  the  water  driven  off,  if  not 
decomposed,  and  the  nitrogen  uncombined,  evolved.  Be  this  as  it  may, 
any  differences  or  resemblances  in  the  gaseous  substances  emitted 
require  consideration.  Naphtha  and  the  thicker  bitumens  are  at  pre- 
sent so  scattered  over  various  parts  of  the  world,  that  though  certain 
localities  may  abound  with  them  more  than  others,  they  appear  to  show 
little  beyond  the  conversion  of  some  organic  matter,  accumulated  under 
variable  conditions,  into  that  form.f  Inflammable  gases  have  also  been 
found  evolved  from  the  earth,  not  only  in  connexion  with  bituminous 
and  coal  deposits,  but  under  other  circumstances,  where  no  volcanic 
action  is  required  for  their  production,  as,  for  example,  at  the  salt 

*  "  Geology  of  Russia  in  Europe  and  the  Ural,"  vol.  i.  p.  576. 

|  Naphtha  springs  seem  to  continue,  in  some  cases,  at  least,  in  the  same  state  during 
a  long  lapse  of  time,  pointing  to  the  long  duration  of  the  needful  conditions.  Thus, 
according  to  Dr.  Holland  ("Travels  in  the  Ionian  Isles,  Albania,  &c."),  the  petroleum 
springs  of  Zante  are  in  the  same  state  as  when  described  by  Herodotus.  The  pitch  lake 
of  Trinidad  is  a  good  example  of  a  considerable  collection  of  the  more  solid  bitumens. 
It  is  estimated  at  about  three  miles  in  circumference,  though  its  exact  boundaries  are 
difficult  to  trace,  in  consequence  of  the  soil  which  covers  parts  of  it,  from  which  crops 
of  tropical  productions  are  obtained  (Nugent,  Geol.  Trans.,  vol.  i.)  According  to  Cap- 
tain Alexander  (Edinburgh  Phil.  Journal,  January,  1833),  masses  of  this  pitch  advance 
into  the  sea  at  Pointe  la  Braye.  The  same  author  notices  an  assemblage  of  salses  or 
mud  volcanoes  at  Pointe  du  Cae,(40  miles  southward  from  the  pitch  lake,  the  largest 
about  150  feet  in  diameter. 


406  EARTHQUAKES. 

mines  of  Gottesgabe,  at  Heine,  in  the  county  of  Tecklenberg,*  and 
from  borings  for  salt  in  America5f  and  China.J 

With  regard  to  the  rise  of  boracic  acid  with  the  steam  at  the  lagunes 
near  Volterra,  in  Central  Italy,  accompanied  by  carbonic  acid  and 
sulphuretted  hydrogen,  it  has  been  referred  to  volcanic  action  beneath 
the  rocks  in  which  the  lagunes  are  situated.  That  great  heat  exists 
beneath  is  certain,  but  how  far  this  heat  may  now  be  considered  volcanic 
and  distinct  from  a  more  general  dispersion  of  an  elevated  temperature 
beneath  the  surface  of  the  ground,  more  intense  at  some  points  than  at 
others,  seems  not  so  certain.  The  boracic  acid  is  found  in  combination 
with  ammonia,  as  well  as  free,  and  Dr.  Daubeny  remarks  that  its  pre- 
sence in  the  steam  may  arise  from  the  aqueous  vapour  passing  over  this 
substance,  and  carrying  it  upwards  in  mechanical  suspension,  as  steam, 
by  experiment,  has  been  found  capable  of  effecting. § 

Earthquakes. — It  has  been  seen  that  prior  to,  and  sometimes  during, 
volcanic  eruptions,  the  country  in  the  vicinity  has  been  disturbed  by 
vibrations,  as  if  from  time  to  time  certain  resistances  to  these  volcanic 
forces  were  suddenly  overcome.  The  rending  of  rocks  by  fissures,  such 
as  have  been  previously  noticed,  could  scarcely  but  produce  vibrations, 
supposing  the  needful  tension  and  cohesion  of  parts.  It  is  by  no  means 
required  that  these  fissures  should  always  rise  to  the  surface  of  the 
ground ;  indeed,  in  many  volcanic  accumulations,  the  rents  formed,  and 
subsequently  filled  with  molten  rock,  are  observed  to  terminate  before 
they  reach  it.  From  the  absence  of  the  proper  cohesion  of  parts  amid 
great  masses  of  ashes  and  cinders,  these  may  so  yield,  that  though  a 
fissure  might  be  suddenly  produced  in  more  solid  matter  beneath  them, 
they  could  adjust  themselves  above  in  a  very  general  manner  over  its 
upward  termination. 

It  would  be  anticipated  that,  all  other  things  being  equal,  vibrations 
of  the  ground  around  volcanoes  would  be  more  intense  after  a  vent  had 
long  been  closed  and  dormant,  so  that  time  for  the  consolidation  of  tuff 

*  The  gas  is  obtained  from  the  abandoned  pits,  and  is  considered  to  consist  of  carbu- 
retted  hydrogen  and  olefiant  gas.  It  was  employed  by  M.  Roders,  the  inspector  of  the 
mines,  for  lighting  and  cooking,  being  conveyed  to  the  houses  by  pipes. 

f  While  boring  for  salt  at  Rocky  Hill,  in  Ohio,  near  Lake  Erie,  the  borer  suddenly 
fell  after  they  had  driven  to  the  depth  of  197  feet.  Salt  water  immediately  rushed 
forth,  and  was  succeeded  by  a  considerable  outburst  of  an  inflammable  gas,  which 
being  ignited  by  a  fire  in  the  vicinity,  consumed  all  within  its  reach. 

J  At  Thsee-lieou-tsing  (previous  note,  p.  401),  according  to  M.  Klaproth,  a  jet  of 
inflammable  gas  from  a  locality  also  producing  salt  water,  was  burning  from  the  second 
to  the  thirteenth  century  of  our  era,  at  about  80  li  S.W.  from  Kioung-tcheou. 

\  By  employing  the  heat  of  the  superabundant  vapour,  the  water  collected  in  artifi- 
cial ponds  is  sufficiently  evaporated  to  dispense  with  fuel,  and  the  boracic  acid  obtained 
at  small  cost.  These  lagunes  furnish  about  1,650,000  Ibs.  of  boracic  acid  annually, 
sufficient,  when  purified  and  mixed  with  soda,  forming  borax,  nearly  for  the  supply  of 
Europe. — Daubeny,  "Volcanoes,"  p.  156. 


CONNEXION  OF  VOLCANOES  AND  EARTHQUAKES.   407 

beds  had  elapsed,  the  whole  well  braced  together  by  lava  streams  of 
various  dimensions,  than  when  the  vent  was  still  open,  the  volcano 
active,  and  the  ashes  and  cinders  incoherent.  It  may  also  be  inferred 
that  a  certain  thickness  of  trachyte,  dolerite,  or  basalt,  if  not  too  much 
divided  by  columnar,  or  other  joints,  would  offer  greater  resistance  to 
any  given  volcanic  force  employed  than  tuff  beds,  unless  these  were  so 
changed  and  consolidated  as  to  assume  the  character  of  palagonite,  or 
others  of  that  class.  Again,  different  effects  would  be  expected  from 
the  resistance  of  intermingled  sheets  of  tuff  and  rocks  which  had  been 
in  fusion,  such  as  those  described  as  occurring  in  the  Val  del  Bove, 
Etna,  and  where  similar  substances  are  mixed,  as  narrow  lava  streams 
and  irregular  piles  of  matter,  in  both  cases  prior  fissures,  more  or  less 
filled  by  dykes  of  lava,  considerably  modifying  the  effects  produced. 

A  connexion  has  often  been  inferred  to  exist  between  volcanic  erup- 
tions and  vibrations  of  the  ground  at  distances  far  beyond  the  immediate 
vicinity  of  the  former,  as  if  the  volcanoes  were  great  safety-valves, 
through  which,  under  ordinary  circumstances,  a  certain  amount  of  force 
escaped,  mere  local  disturbances  being  thereby  produced;  while  at 
others,  from  the  overloading  of  the  valves,  or  a  greater  exertion  of 
power,  larger  portions  of  the  earth's  crust  were  shaken.  Without 
including  dormant  or  extinct  volcanoes,  active  vents,  as  has  been  seen 
(p.  392),  are  so  widely  dispersed  over  different  parts  of  the  world,  that 
considerable  areas  may  readily  be  disturbed  by  vibrations  more  or  less 
depending  upon  general  conditions,  of  which  the  discharge  of  molten 
rock,  vapours,  and  gases,  at  certain  points,  is  only  one  of  the  effects 
thereby  produced.  Hence,  as  respects  this  mode  of  viewing  the  subject, 
volcanic  eruptions  and  earthquakes  may  be  intimately  connected,  vol- 
canic eruptions  being  equally  regarded  in  the  same  general  manner, 
and  several  other  adjustments  of  the  earth's  surface  included,  by  which 
great  fissures  have  been  formed,  and  huge  masses  of  rocks  squeezed, 
broken,  and  thrust  up  into  great  ridges  and  mounds  of  varied  forms  and 
magnitude. 

Many  instances  are  given  of  the  inferred  connexion  between  earth- 
quakes and  volcanic  eruptions,  as,  for  example,  the  sudden  disappear- 
ance of  smoke  in  the  volcano  of  Pasto,  when  the  province  of  Quito,  192 
miles  distant,  was  so  violently  shaken  by  the  great  earthquake  of  Rio- 
bamba,  on  the  4th  of  February,  1797,  and  the  sudden  tranquillity  of 
Stromboli  from  its  otherwise  constant  activity,  during  the  great  earth- 
quake in  Calabria,  in  1783.  As  we  are  quite  assured  that  in  minor 
areas  there  is  often  much  vibration  of  the  ground  prior  to  such  erup- 
tions, and  that  subsequently  to  them  tranquillity  is  restored,  at  least  for 
a  time,  an  observer  would  be  led  to  inquire  how  far  such  apparent 
causes  arid  effects  may  be  extended.  Herein  caution  is  much  needed, 
so  that,  from  a  preconceived  opinion,  accidental  circumstances  may  not 


408   CONNEXION  OF  VOLCANOES  AND  EARTHQUAKES. 

have  an  undue  value  assigned  them,  some  of  the  inferences  drawn 
respecting  the  immediate  connexion  between  given  earthquakes  and  the 
eruptions  from  certain  volcanoes  being  scarcely  borne  out  by  the  facts 
adduced. 

It  would  be  anticipated  that  in  regions  of  volcanoes,  such  as  those  of 
South  America,  great  vibrations  of  the  ground  should  be  experienced, 
these  vibrations  extending  to  variable  distances,  not  only  according  to 
their  intensity,  but  also  to  the  kinds  of  rocks  through  which  they  are 
transmitted.  In  certain  regions  earthquakes  are  sometimes  of  such 
frequent  occurrence,  that  except  when  of  particular  intensity,  they  are 
so  little  regarded,  that  those,  and  similarly  circumstanced  portions  of 
the  earth's  surface,  may  be  considered  in  a  more  unstable  state  than 
others.  The  great  earthquake  of  Chili,  in  1835,  was  merely  one  of  a 
more  intense  kind  in  a  district  often  shaken  by  such  vibrations.  It  is 
described  as  having  been  felt  from  Copiapo  to  Chiloe  in  one  direction, 
and  from  Mendoza  to  Juan  Fernandez  in  another ;  and  the  volcanoes  of 
that  part  of  the  Andes  are  noticed  as  having  been  in  an  unusual  state 
of  activity  prior  to,  during,  and  subsequent  to  it.  In  a  previous  earth- 
quake (1822)  the  same  region  of  South  America  was  shaken  through  a 
distance,  from  north  to  south,  of  about  1200  miles. 

With  respect  to  the  areas  actually  disturbed  by  earthquakes,  as  waves 
are  necessarily  raised  by  them  in  the  sea  adjoining  the  lands  shaken, 
or  by  the  vibration  of  the  rocks  beneath  it,  attention  has  to  be  directed 
as  to  the  amount  of  dry  land  disturbed,  and  the  extent  to  which  any  ad- 
joining portion  of  the  sea  bottom  may  have  been  simultaneously  shaken. 
For  instance,  this  has  to  be  done  with  the  great  earthquake  of  Lisbon, 
the  area  disturbed  being  represented  as  spread  over  a  large  portion  of 
the  Northern  Atlantic,  and  comprising  a  part  of  North  America,  with 
some  of  the  West  India  Islands  (Antigua,  Barbadoes,  and  Martinique), 
on  the  one  side,  and  a  part  of  Northern  Africa  and  a  large  portion  of 
Western  Europe  on  the  other.  In  such  a  case  the  extent  to  which  the 
sea-wave  produced  by  earthquakes  may  have  been  propagated,  has  to 
be  well  considered.*  The  known  amount  of  dry  land  shaken  in  Europe 
was  alone  very  large,  comprising  Portugal,  Spain,  France,  the  British 
Islands,  the  southern  portions  of  Norway  and  Sweden,  Denmark,  Ger- 
many, Switzerland,  and  the  north  of  Italy. 

As  respects  earthquakes,  the  transmission  of  the  vibrations  has  to  be 
regarded  with  especial  reference  to  the  kind  of  substances  through  which 
an  earthquake-wave  may  have  to  pass,  so  that  even,  for  illustration, 

*  Sir  Charles  Lyell  (Principles  of  Geology,  7th  edit.,  p.  344),  calls  attention  to  the 
great  Lisbon  shock,  as  having  come  in  from  the  ocean,  remarking  that  "  a  line  drawn 
through  the  Grecian  Archipelago,  the  volcanic  region  of  Southern  Italy,  Sicily,  Southern 
Spain,  and  Portugal,  will,  if  prolonged  westward  through  the  ocean,  strike  the  volcanic 
group  of  the  Azores;"  hence  inferring,  as  probable,  their  submarine  connexion  with 
the  European  line. 


MOVEMENT    OF    THE    EARTH-WAVE.  409 

assuming  the  impulses  given  to  be  equal,  the  extent  of  the  vibrations 
and  their  amount  might  be  very  materially  modified.*  Mr.  Mallet  infers 
that  an  earthquake  "  is  the  transit  of  a  wave  of  elastic  impression 
in  any  direction,  from  vertically  upwards  to  horizontally  in  any  azimuth, 
through  the  crust  of  the  earth,  from  any  centre  of  impulse,  or  from  more 
than  one,  and  which  may  be  attended  with  tidal  and  sound  waves,  de- 
pendent upon  the  impulse,  and  upon  the  circumstances  of  position  as  to 
sea  and  land."  At  the  same  time,  he  admits  that  the  truth  of  this  view 
has  not  yet  been  fully  and  experimentally  demonstrated. 

The  movement  of  the  great  earth-wavef  is  commonly  classed  as  un- 
dulatory  or  vertical,  as  the  ground  may  be  observed  to  roll  onward  in  a 
given  direction,  or  simply  rise  and  fall  in  a  nearly  perpendicular  manner. 
We  have  descriptions  in  the  one  case,  of  the  surface  of  the  ground  mov- 
ing in  a  wave-like  manner,  and  in  the  other,  of  a  mere  sudden  rise  and 
fall,  as  far  as  regards  a  particular  locality.  Of  the  latter,  the  great 
earthquake  experienced  at  Riobamba,  in  1797,  would  appear  an  excel- 
lent example,  many  bodies  of  the  inhabitants  having,  according  to  Hum- 
boldt,  been  hurled  to  a  height  of  several  hundred  feet  on  the  hill  of  La 
Cullca,  beyond  the  small  river  of  Lican.J  We  may  readily  infer,  that 
these  two  classes  of  earthquake  movements  are  only  modifications  of  the 
same  thing,  and  that  while  a  spot,  such  as  the  tow-n  of  Riobamba,  situ- 
ated immediately  over  that  where  the  impulse  was  given,  should  be  lifted 
suddenly  upwards,  the  same  shock  would  appear  to  travel  outwards  to 
various  distances  around,  in  the  manner,  as  often  noticed,  of  waves  on 
the  surface  of  water  into  which  a  stone  has  been  cast. 

With  respect  to  the  vorticose  movement,  which  has  been  often  re- 
garded as  another  class  of  earthquake  motion,  we  may  also,  with  Mr. 
Mallet,  consider  it  as  only  a  modification  of  the  same  kind  of  shock. 
With  regard  to  the  two  obelisks  at  the  Convent  of  St.  Bruno,  at  Stefano 
del  Bosco,  the  stones  of  which  were  twisted  on  a  vertical  axis  in  a  simi- 
lar manner,  without  falling,  during  the  great  Calabrian  earthquake  of 

*  Mr.  Mallet  Naval  Manual  of  Scientific  Inquiry,  Art.  Earthquakes,  p.  197,  in 
order  to  illustrate  the  transmission  of  waves  through  different  materials,  supposes  a 
person  to  stan&upon  a  line  of  railway,  near  the  rail,  and  that  a  heavy  blow  be  struck 
upon  the  latter  a  few  hundred  feet  distant.  "  He  will,"  Mr.  Mallet  remarks,  "  almost 
instantly  hear  the  wave  through  the  iron  rail ;  directly  after  he  will  feel  another  wave 
through  the  ground  on  which  he  stands  ;  and,  lastly,  he  will  hear  another  wave  through 
the  air ;  and  if  there  were  a  deep  side-drain  to  the  railway,  a  person  immersed  in  the 
water  would  hear  a  wave  of  sound  through  it,  the  rate  of  transit  of  which  would  be 
different  from  any  of  the  others — all  these  starting  from  the  same  point  at  the  same 
time." 

f  (Admiralty  Manual  of  Scientific  Inquiry,  Art.  Earthquakes.) — Mr.  Mallet  defines 
the  ''great  earth-wave"  as  the  "true  shock,  a  real  roll  or  undulation  of  the  surface 
travelling  with  immense  velocity  outwards  in  every  direction  from  the  centre  of  impulse." 

|  "  Kosmos,"  Art.  Earthquakes. 


410  SEA-WAVES    PRODUCED    BY    EARTHQUAKES. 

1783,*  and  inferred  well  to  illustrate  this  movement,  Mr.  Mallet  has 
shown,  that  this,  and  other  cases  of  a  similar  kind,  may  be  explained  by 
the  transmission  of  the  ordinary  shock,  under  a  modification  of  circum- 
stances by  which  the  rectilinear  is  converted  into  a  curvilinear  motion. f 
In  the  same  manner,  when  the  complicated  structure  of  some  parts  of 
the  earth's  surface  is  considered,  particularly  where  igneous  rocks  have 
been  extended  among,  or  otherwise  much  intermingled  with,  other  accu- 
mulations, the  observer  may  have  reason  to  infer  that,  during  the  trans- 
mission of  an  earthquake-wave,  the  various  parts  of  the  whole  may  some- 
times be  so  circumstanced,  that  a  kind  of  twist  may  be  locally  given 
to  considerable  masses. 

Taking  the  great  earth-wave  as  the  base  of  all  the  movements,  how- 
ever modified  this  may  be  according  to  conditions,  the  waters  of  seas, 
lakes,  or  rivers,  resting  or  flowing  upon  the  solid  crust  of  the  globe,  will 
have  the  shock  communicated  to  them.  When  we  look  at  the  present 
distribution  of  land  and  sea,  and  consider  earthquakes  in  their  generality, 
these  are  quite  as  likely,  if  not  more  so,  to  have  been  produced  by  im- 
pulses received  beneath  parts  of  the  great  ocean  as  on  the  dry  land. 
As  the  rate  at  which  the  earth-wave  would  travel,  under  such  circum- 
stances, would  be  greater  than  that  at  which  the  vibration  transmitted 
to  the  water  would  proceed,  two  waves,  as  Mr.  Mallet  has  pointed  out, 
will  result.  One  will  arise  from  the  vibration  along  the  surface  of  the 
ground,  in  contact  with  the  bottom  of  the  superincumbent  water,  and 
becoming  apparent  in  shallow  water ;  the  other  from  the  heaping  up  of 
the  water  above  a  vertical  uprise  of  the  sea  bottom,  such  as  we  may  sup- 
pose given  if  Riobamba,  in  1797,  had  been  beneath  the  sea.  The  first 
is  named  by  Mr.  Mallet,  the  "forced  sea-wave,"  seen  when  the  shock 
or  earth-wave  passes  beneath  or  into  shallow  water,  whether  the  earth- 
quake travels  from  seaward  inland,  or  the  reverse :  the  second  he  terms 
the  "great  sea-wave."  The  geological  importance  of  the  "forced  sea- 
wave,"  would  seem  much  to  depend  upon  the  distance  at  which  any 
shore  or  shallow  water  may  be  from  the  spot  where  a  chief  vertical  move- 
ment, either  inland  or  beneath  the  sea,  has  been  given.  If  this  were  in 
the  ocean  far  distant  from  the  land,  or  shallow  water,  the  movement 
communicated  to  the  sea  would  be  small,  as  also  if  the  shock  came  from 
the  dry  land  with  little  intensity,  either  from  the  original  impulse  hav- 
ing been  unimportant,  or  of  its  force  being  nearly  expended.  Should, 

*  Figures  and  descriptions  of  these  obelisks  are  given  by  Sir  Charles  Lyell,  in  his 
"  Principles  of  Geology,"  and  in  Dr.  Daubeny's  "  Description  of  Volcanoes,"  taken  from 
the  Transactions  of  the  Royal  Academy  of  Naples. 

f  Mr.  Mallet  remarks  (Admiralty  Manual  of  Scientific  Inquiry,  Art.  Earthquakes), 
that  "  this  motion  arises  from  the  centre  of  gravity  of  the  body  lying  to  one  side  of  a 
vertical  plane  in  the  line  of  shock,  passing  through  that  point  in  the  base  on  which  the 
body  rests,  in  which  the  whole  adherence,  by  friction  or  cement  of  the  body  to  its  sup- 
port, may  be  supposed  to  unite,  and  which  may  be  called  the  centre  of  adhesion." 


* 
SEA-WAVES    PRODUCED    BY    EARTHQUAKES.  411 

however,  the  vertical  movement  of  the  earth-wave  be  close  to  a  coast, 
whether  on  the  sea  or  land  side,  or  beneath  shallow  water,  then  the 
" forced  sea-wave"  may  merge  in  the  "great  sea-wave,"  sufficient  dis- 
tance not  existing  to  permit  much  distinction.  The  one  wave  would 
precede  the  other  under  ordinary  conditions,  the  "great  sea-wave" 
throwing  huge  masses  of  water  upon  the  land,  mechanically  disturbing 
sea-bottoms  to  a  great  extent,  and  often  producing  effects  of  considera- 
ble geological  importance.  As  Mr.  Mallet  has  remarked,  while  a  "  great 
sea-wave"  may  be  so  broad  and  low  in  deep  water  as  not  to  be  observed 
in  the  open  ocean,  it  could  break  with  great  force  on  a  coast  or  in  shal- 
low water. 

It  will  be  convenient,  as  has  been  pointed  out  by  Mr.  Mallet,  so  to 
classify  observations  on  earthquakes,  that  things  accessory  may  be  sepa- 
rated from  those  which  are  material.  Unfortunately,  as  has  been  re- 
marked by  Sir  Charles  Lyell,*  it  is  only  in  comparatively  recent  times 
that  earthquake  phenomena  have  been  studied  with  reference  to  their 
real  geological  bearing,  accounts  of  the  lives  and  properties  destroyed, 
with  now  and  then  a  notice  of  a  new  lake  or  island  produced  at  the  time, 
having  chiefly  occupied  attention.  Whatever  may  cause  the  shock, 
whether  from  a  portion  of  the  earth  being  suddenly  thrown  into  motion, 
without  violent  rupture,  viewing  the  subject  on  the  large  scale,  or  from 
sudden  and  violent  fracture,  the  observer  has  to  consider  not  only  the 
depth  beneath  the  surface,  where  the  impulse  may  be  given,  but  also  the 
mineral  masses  through  which  the  waves  have  to  be  transmitted,  both 
as  regards  the  kind  and  relative  position  of  those  masses. 

During  violent  volcanic  eruptions,  when,  as  for  instance,  in  that  of 
Tomboro,  in  Sumbawa,  on  the  5th  April,  1815,  the  detonations  were 
heard  as  far  as  970  miles,  and  with  such  distinctness,  and  so  loud  at  Ma- 
cassar, 217  miles  distant,  that  a  vessel  of  war  was  sent  out  with  troops 
in  search  of  supposed  pirates  engaged  in  the  neighbourhood ;  it  may  be 
assumed  that  vibrations  of  the  earth  would  radiate  around,  as  from  any 
point,  a,  in  the  annexed  plan  (fig.  145),  which  may  represent  any  district 

Fig.  145. 


having  such  a  centre  of  disturbance.     Assuming  the  roar  of  any  great 
volcanic  eruption,  such  as  that  at  Tomboro,  to  arise  from  the  violent  dis- 


"  Principles  of  Geology,"  7th  edit.,  p.  431. 


412  TRANSMISSION    OF    E ARTH QUAK E -WAVES 

charge  of  the  vapours,  gases,  cinders,  and  ashes  through  the  crater, 
the  vibrations  thereby  produced  in  the  adjacent  mineral  accumulations 
would  be  felt  more  or  less  horizontally,  according  to  the  variable  compo- 
sition and  solidity  of  the  substances  shaken.  Should  the  cause  of  the 
earthquake-waves  be  deep-seated,  the  vibrations  on  the  surface  would 
correspond  with  the  radiation  of  the  waves  from  their  centre  of  origin, 
so  that  there  would  be  a  point  where  the  shock  would  be  felt  vertically.* 
If  b  c  (fig.  146)  be  supposed  a  section  of  part  of  the  earth's  crust,  and 

Fig.  146. 


a  a  point  in  a  curve,  250  miles  beneath  the  surface,  where  an  impulse  is 
given  producing  earthquake-waves,  these  would  strive  to  radiate  around, 
so  far  as  resistances  or  facilities  would  permit,  in  spherical  shells.  If 
the  substance  through  which  the  wave  passed  was  homogeneous,  as  for 
example,  a  piece  of  iron,  the  wave  would  first  traverse  the  distance  a  e, 
then  ad,  af,  and  ag^  in  succession,  the  shock  being  felt  most  vertically 
as  regards  the  surface  of  the  iron  at  e,  and  more  laterally  at  /,  and  most 
so,  as  regards  the  section,  at  g.  Geological  investigations  show  us  that 
the  composition  of  the  mineral  substances,  forming  so  much  of  the  earth's 
surface  as  we  have  the  power  of  examining,  their  state  of  solidification, 
and  their  mode  of  accumulation,  are  very  variable.  Hence,  if  in  the 
foregoing  section,  instead  of  a  homogeneous  body,  we  may  suppose  a 
great  mass  of  mineral  matter,  granite  for  example,  supporting  two  accu- 
mulations, one  at  6,  arranged  in  beds  of  a  hard  coherent  substance,  such 
as  compact  limestone,  and  another  at  (?,  formed  of  strata  slightly  ce- 
mented, or  loose  sands  and  pebbles,  the  observer  will  see  that  the  shock 
striking  at/,  might  be  transmitted  readily  along  the  planes  of  the  lime- 
stone beds,  while,  though  the  shock  would  strike  the  loose  accumulations 
at  e  more  laterally,  the  wave  might  be  there  more  complicated,  from  the 
want  of  sufficient  coherence  of  parts. 

*  The  great  Lisbon  earthquake  of  1755,  felt  so  severely  around  a  space  near  that  city, 
has  been  considered  a  good  example  of  a  radiating  earthquake  with  a  deep-seated  source. 
The  earthquake  of  1828,  experienced  in  the  Netherlands  and  Rhenish  Provinces,  is  in- 
ferred to  have  been  radiating,  though  less  deeply  seated.  The  area  most  shaken  form- 
ed an  ellipse,  comprising  Brussels,  Lidge,  and  Maestricht,  and  the  shocks  radiated  to 
Westphalia,  and  to  Middelburg  and  Vliessingen.  Referring  to  the  great  Calabrian 
earthquake  of  1783,  also  considered  somewhat  central,  Dr.  Daubeny  remarks  (Descrip- 
tion of  Volcanoes,  2d  ed.,  p.  515),  after  mentioning  certain  movements  noticed,  that 
such  earthquakes  may  have  "the  impelling  force  situated  along  a  particular  line  of 
country,  although  at  the  points  at  which  it  is  exerted  in  its  greatest  intensity,  the  vi- 
brations are  propagated  with  greater  or  less  violence  in  all  directions  around." 


COMPLICATED    BY    DIFFERENT    MINERAL    STRUCTURES.    413 

Numerous  modifications  of  the  arrangements  above  noticed  will  readily 
suggest  themselves,  more  particularly  as  regards  the  interruptions  to 
the  course  of  earthquake-waves  by  contorted  and  variably  intermingled 
masses  of  solid  and  loosely  aggregated  rocks  in  mountainous  districts, 
by  the  long  wide-spread  sheets  of  interstratified  and  dissimilar  sub- 
stances in  some  regions,  by  the  fractures  and  alterations  of  mineral 
masses  in  others,  and  by  the  mixture  of  active  volcanic  districts  with 
those  of  very  different  origin.  It  would  be  inferred  that,  on  the  minor 
scale,  a  shock  may  be  modified  in  apparent  direction  and  intensity  when 
felt  amid  horizontal,  or  nearly  horizontal  beds,  composed  of  different 
rocks,  such  as  in  the  following  plan  (fig.  147),  where  /  may  represent  a 

Fig.  147. 


limestone,  e  g  a  clay,  d  h  a  sandstone,  and  c  i  a  conglomerate,  resting 
in  a  trough-shaped  cavity,  as  shown  in  the  annexed  section  (fig.  148)  of 


the  same  piece  of  country,  formed  of  hard  slates  and  limestones,  which 
had,  previously  to  the  deposit  of  the  first-named  beds,  been  thrown  into 
a  vertical  position.  Taking  the  shock  to  pass  in  the  direction  a  5,  it 
could  easily  traverse  the  line  of  vertical  rocks  beneath  in  that  direction, 
while  both  the  duration  and  intensity  may  be  found  modified  in  any 
town  situated  upon  the  central  limestone,  perhaps  a  stripe  many  miles 
in  length,  joining  finally  with  a  considerable  sheet  of  the  same  sub- 
stance. It  sometimes  happens  that  earthquakes  do  not  affect  certain 
upper  beds,  while  the  shock  is  continued  beneath  and  transmitted 
onwards.  Humboldt  states,  that  such  upper  strata,  rarely  if  ever 
shaken,  are  by  the  Peruvians  termed  bridges.* 

*  "  Kosmos"  (earthquakes).  Remarking  on  this  circumstance,  Humboldt  observes 
(Notes),  that  "  these  local  interruptions  to  the  transmission  of  the  shock  through  the 
upper  strata,  seem  analogous  to  the  remarkable  phenomenon  which  took  place  in  the 
deep  silver  mines  of  Marienberg,  in  Saxony,  at  the  beginning  of  the  present  century, 
•when  earthquake  shocks  drove  the  miners  in  alarm  to  the  surface,  where,  meanwhile, 
nothing  of  the  kind  had  been  experienced.  The  converse  phenomenon  was  observed 
in  November,  1823,  when  the  workmen  in  the  mines  of  Fahlun  and  Persberg  felt  no  move- 
ment whatever,  whilst  above  their  heads  a  violent  earthquake  shock  spread  terror  among 
the  inhabitants  of  the  surface." 


414  LOCALLY    EXTENDED    RANGE     OF    MOUNTAINS. 

Careful  observation  shows  that  shocks  are  more  readily  transmitted 
in  certain  lines  in  particular  localities  than  others,  much  necessarily 
depending  on  the  direction,  either  vertically  or  laterally,  from  whence 
these  vibrations  come,  the  minor  adjustment  of  parts  so  lost  occasionally 
amid  the  whole  mass  shaken,  as  not  to  be  very  readily  appreciated. 
This  could  scarcely  otherwise  than  happen,  when  the  source  of  the 
shocks  remains  for  any  length  of  time  sufficiently  fixed,  and  the  relative 
position  and  structure  of  the  rocks  composing  a  region,  continue  un- 
altered.* Changes  in  this  arrangement  have  been  noticed  even  within 
the  last  60  years,  sufficient  to  show  that,  either  from  local  modifications 
in  the  causes  of  earthquakes,  or  in  their  effects,  adjustments  of  the  kind 
may  become  permanently  altered.  Humboldt  mentions  that  since  the 
destruction  of  Cumana,  on  the  14th  of  December,  1797,  the  range  of 
earthquake  vibration  in  that  district  has  so  changed,  that  every  shock 
has  since  that  time  extended  to  the  peninsula  of  Maniquarez,  which  did 
not  previously  happen.  He  also  points  to  the  gradual  advance  of  the 
almost  uninterrupted  earthquake  shocks  from  south  to  north,  up  the 
valleys  of  the^  Mississippi,  the  Arkansas,  and  the  Ohio,  between  1811 
and  1813,  as  showing  that  the  subterranean  obstacles  to  the  propaga- 
tion of  the  earthquake-waves  had  been  as  gradually  removed. f 

When  earthquake-waves  traverse  mountain  chains,  as  they  have  been 
known  to  do,  across  the  lines  of  their  general  range,  the  composition  of 
such  mountains  requires  much  attention.  If  merely  long  ridges  of  a 
homogeneous  rock,  such  as  granite  or  the  like,  that  may,  as  in  the  sub- 
joined section  (fig.  149),  descend  beneath  various  subaqueous  accumula- 


tions, c  and  d,  an  earthquake-wave  could  readily  be  transmitted  across 
the  ridges  a  and  b  from  e  to  /,  in  preference  to  lines  corresponding  with 
them,  should  this  be  the  general  direction  of  the  wave  in  acconiance 
with  the  impulse  given.  In  estimating  the  transmission  of  an  earth- 
quake-wave through  any  portion  of  the  earth's  crust,  the  observer  will 
thus  have,  as  it  were,  to  dissect  the  portion  shaken,  endeavouring  to 
separate  the  minor  from  the  major  effects,  duly  weighing  the  probability 

*  The  Cordilleras,  extending  from  north  to  south,  and  a  transverse  line  ranging  from 
the  Island  of  Trinidad  to  New  Granada,  arc  considered  to  be  shaken  in  a  marked  man- 
ner. "  In  a  line  with  both  these  ranges,"  observes  Dr.  Daubeny,  "  frightful  earthquakes 
have  occurred,  as  at  Lima,  Callao,  Riobamba,  Quito,  Pasto,  Cumana,  Caraccas,  &c., 
by  which  40,000  persons  have  been  known  to  be  at  one  time  destroyed.  In  all  these 
cases  the  greater  effects  have  not  only  been  confined  to  the  range  of  the  mountains, 
but  have  pursued  the  direction  of  the  coast." — Description  of  Volcanoes,  p.  516. 

f  Kosmos,  Art.  Earthquakes. 


FISSURES    PRODUCED     DURING    EARTHQUAKES.          415 

of  the  undulation  passing  through,  or  along  such  mountain  chains  as 
the  Alps,  Andes,  and  Himalaya,  according  to  the  depth  of  its  cause. 
He  has  also  to  see  if  the  shocks  experienced  along  great  lines,  corre- 
sponding with  those  of  accumulations,  however  contorted  and  broken 
these  are,  may  be  merely  regarded  as  subordinate  to  a  major  motion, 
modified  according  to  conditions,  or  be  conformable  to  the  general 
range  of  the  earthquake-wave,  regarded  with  reference  to  the  total  mass 
shaken.*  The  rocks  of  the  same  region  may  be  differently  affected  if 
the  wave  be  propagated  from  a  great  depth,  than  when  the  undulation 
has  been  produced  by  a  less  deep-seated  cause.  The  transmission  of 
the  wave  amid  them  might,  in  the  first  case,  be  a  mere  modification  of 
some  great  movement,  common,  as  in  the  Lisbon  earthquake,  to  a  large 
portion  of  the  earth's  crust,  while  in  the  second,  the  same  rocks  may  be 
directly  acted  upon  in  the  first  instance.  Hence  the  importance  of 
observations  as  to  how  far,  during  any  given  earthquake,  particular 
districts,  even  great  mountain  ranges,  may  be  considered  to  transmit  a 
primary  wave,  or  some  modification  of  it. 

As  the  earthquake-wave  would  pass  with  different  velocities  through 
different  rocks,f  it  would  follow  that  while  the  particles  may  so  yield 
in  some  that  fracture  may  riot  be  produced,  cracks  and  dislocations 
could  be  effected  in  others.  Even  in  the  simple  arrangement  of  sheets 
of  the  one  class  above  the  other,  the  whole  acted  on  laterally  by  an 
earthquake-wave,  one  set  of  rocks  may  be  dislocated,  the  other  return- 
ing to  its  original  state,  in  the  same  manner  as  if  the  observer  were  to 
cover  a  sheet  of  copper  with  plaster  of  Paris,  and  throw  both  into  vibra- 
tion, when  the  latter  would  be  broken,  while  the  copper  remained  sound. 
It  is  easy  to  conceive,  independently  of  the  different  conditions  of  the 
upper  to  the  lower  beds  of  rock,  composing  a  series  of  horizontal  or 
nearly  horizontal  deposits,  as  regards  difference  of  pressure  upon  them, 
that  the  lower  may  be,  from  heat  beneath,  not  in  so  fragile  a  state  as 

*  As  regards  the  range  of  earthquake-waves  along  or  across  mountain  chains,  Hum- 
boldt  remarks  (Kosmos,  Art.  Earthquakes),  after  adverting  to  mountains  transmitting 
shocks  in  lines  corresponding  with  the  walls  of  the  fissures  along  which  they  may  be 
raised,  that  earthquake-waves  sometimes  "intersect  several  chains  almost  at  right 
angles ;  an  example  of  which  occurs  in  South  America,  where  they  cross  both  the  littoral 
chain  of  Venezuela  and  the  Sierra  Parime.  In  Asia,  shocks  of  earthquakes  have  been 
propagated  from  Lahore  and  the  foot  of  the  Himalaya  (22d  of  January,  1832),  across 
the  chain  of  the  Hindoo  Coosh,  as  far  as  Badakschan,  or  the  Upper  Oxus,  and  even  to 
Bokhara."  As  regards  earthquake-waves  traversing  mountain  ranges,  Dr.  Daubeny 
(Description  of  Volcanoes,  2d  edit.,  p.  516)  quotes  also  that  of  1828,  which  crossed  the 
Appenines  from  Voghera,  by  Bochetta,  to  Genoa. 

f  Mr.  Mallet  points  out  (Admiralty  Manual  of  Scientific  Inquiry,  Art.  Earthquakes), 
that  "  an  erroneous  notion  of  the  dimensions  of  the  great  earth-wave  must  not  be  formed 
from  its  being  called  an  undulation — its  velocity  of  translation  appears  to  be  frequently 
as  much  as  30  miles  per  minute,  and  the  wave  or  shock  moving  at  this  rate  often  takes 
10  or  12  seconds  to  pass  a  given  point;  hence  its  length  or  amplitude  is  often  several 
miles." 


416     SETTLEMENT    OF    UNCONS 0 LID ATED    DETRITAL    BEDS 

those  above,  and  be  capable  of  more  ready  vibration  without  fracture. 
Thus  many  cracks  and  fissures  may  be  made,  not  penetrating  to  great 
depths,  and  yet  extending  sufficiently  beneath  the  surface  to  permit  the 
ejection  of  water,  mud,  sand,  or  other  easily  expelled  body,  out  of  them, 
and  some  of  these  may  again  so  close  as  to  envelope  any  substances 
which  may  have  fallen  into  them,  while  others  continue  permanently 
open,  the  new  adjustment  of  parts  produced  by  the  earthquake-wave 
not  permitting  a  perfect  return  to  the  old  conditions.  Of  such  fissures 
formed  during  earthquakes  there  is  abundant  evidence,  their  forms  very 
variable,  as  would  be  anticipated  from  the  complicated  rock  accumula- 
tions frequently  shaken,  their  complexity  of  structure  often  concealed 
by  coverings  of  deposits,  perhaps  only  a  few  hundred  feet  thick,  while 
the  mass  thrown  into  vibration  may  extend  downwards  many  thousands 
of  feet,  if  not  many  miles.  Inverted  conical  cavities  have  been  so  fre- 
quently noticed  after  earthquakes  in  plains  and  loosely  aggregated 
deposits,  that  they  deserve  attention.  Water  is  usually  mentioned  as 
having  risen  through  them,  as  if,  during  the  earthquake,  it  had  been 
violently  driven  through  points  in  the  loose  ground.* 

That  at  the  junction  of  loose  or  slightly  consolidated  deposits,  such 
as  sands  and  gravels,  with  hard  rocks,  the  latter  rising  through  the 
former,  so  that  when  the  whole  became  violently  shaken  there  should 
be  settlements  of  incoherent  substances,  with  fissures  and  mounds  of 
adjustment,  would  be  anticipated,  and  is  on  record.  During  the  great 
earthquake  of  Calabria,  in  1783,  this  seems  to  have  occurred  to  consi- 
derable extent.  In  the  great  Jamaica  earthquake  of  1692,  this  shaking 
off,  as  it  were,  of  loose  materials,  appears  to  have  produced  the  "  swal- 
lowing up,"  as  it  has  been  termed,  of  Port  Royal.  Documents  which  have 
been  preserved  fortunately  show  that  the  part  of  that  town  which  then 
disappeared  was  built  upon  sands  accumulated  against  and  around  a 
rock,  which,  though  shaken  by  the  earthquake,  retained  its  place  as 
respects  the  level  of  the  adjoining  sea.  The  darkly-shaded  parts,  P 
and  C,  in  the  annexed  plan  (fig.  150),  represent  those  which  remained 

*  Circular  cavities  were  formed  in  the  plains  of  Calabria  during  the  earthquake  of 
1783.  They  are  described  as  commonly  of  the  size  of  carriage-wheels,  sometimes  filled 
with  water,  more  frequently  by  sand.  Water  appears  to  have  spouted  through  them. 
(Lyell's  Principles  of  Geology,  where  a  view  and  section  of  these  cavities  are  given.) 
During  the  earthquake  of  1829,  in  Mercia,  numerous  small  circular  apertures  were 
formed  in  a  plain  near  the  sea,  whence  black  mud,  salt  water,  and  marine  shells  were 
ejected.  (Lyell's  Principles,  and  Ferussac's  Bulletin,  1829.)  After  the  earthquake  of 
1809  at  the  Cape  of  Good  Hope,  the  sandy  surface  of  Blauweberg's  Valley  was  studded 
with  circular  cavities,  varying  from  six  inches  to  three  feet  in  diameter,  and  from  four 
inches  to  a  foot  and  a  half  in  depth.  Jets  of  coloured  water  are  stated  to  have  been 
thrown  out  of  these  holes  during  the  earthquake  to  the  height  of  six  feet.  (Phil.  Maga- 
zine, 1830.)  During  the  Chili  earthquake  of  1822,  sands  were  raised  up  in  cones,  many 
of  which  were  truncated,  with  hollows  in  their  centres. — Journal  of  Science. 


ADJOINING    HARD    ROCKS    DURING    EARTHQUAKES.      417 


standing  after  this  earthquake,  and  are  considered  to  be  based  on  a 
white  compact  limestone,  common  in  that  part  of  Jamaica,     a,  a,  a,  a, 


Fig.  150. 


and  L  form  the  boundary  of  Port  Royal  prior  to  the  earthquake ; 
N,  N,  N,  the  restoration  by  sand,  drifted  by  prevalent  breaker  and 
wind  action,  at  the  close  of  the  last  century,  and  I,  I,  L,  and  H,  subse- 
quent additions  effected  by  a  continuance  of  the  same  causes  to  about 
the  first  quarter  of  the  present  century.*  The  settlement  of  the  loose 
sand,  combined  with  the  sea-wave  caused  by  the  earthquake,  appears  to 
have  produced  all  the  effects  observed  during  this  earthquake  at  Port 
Koyal,  no  mention  being  made,  amid  all  the  details  extant,  of  any  per- 
manent change  in  the  relative  level  of  the  sea  and  the  part  of  the  town 
preserved. f  In  like  manner  landslips  take  place  on  the  sides  of  moun- 
tains and  from  sea-cliffs  during  earthquakes,  some  often  of  considerable 

*  There  are  documents  to  show  the  rate  at  which  the  long  stripe  of  sands,  known  as 
the  Palisades,  was  prolonged,  so  as  to  join  the  mainland  of  Jamaica  with  the  ground 
on  which  Port  Royal  is  built.  From  the  evidence  of  Captain  Hala,  who  accompanied 
Penn  and  Venables  to  Jamaica,  in  1655,  it  appears  that  the  sands  of  the  Palisades  (the 
drift  of  the  prevalent  winds  and  breakers,  as  noticed  in  the  text)  were  separated  from 
the  town  by  a  narrow  ridge  of  sand  just  appearing  above  water,  an  accumulation  within 
about  17  years,  for  at  that  time  Port  Royal  formed  an  island.  Prior  to  the  earthquake 
the  junction  was  complete,  as  represented  on  the  plan. 

f  Heavy  brick  houses  were  built  on  the  sand,  and  it  is  stated  (Philosophical  Trans- 
actions, 1694),  that  "the  ground  gave  way  as  far  as  the  houses  stood,  and  no  further, 
part  of  the  fort  and  the  Palisades  on  the  other  end  of  the  houses  standing."  Sir  Hans 
Sloane  says,  "  The  whole  neck  of  land  being  sandy  (excepting  the  fort,  which  was 
built  on  a  rock,  and  stood),  on  which  the  town  was  built,  and  the  sand  kept  up  by  the 
Palisades  and  wharfs,  under  which  was  deep  water,  when  the  sand  tumbled,  on  the 
shaking  of  the  earth,  into  the  sea,  it  covered  the  anchors  of  ships  riding  by  the  wharfs, 
and  the  foundations  yielding,  the  greatest  part  of  the  town  fell,  great  numbers  of  the 
people  were  lost,  and  a  good  part  of  the  neck  of  land,  where  the  town  stood,  was  three 
fathoms  covered  with  water."  Long  (History  of  Jamaica)  says,  "The  weight  of  so 
many  large  brick  houses  was  justly  imagined  to  contribute,  in  a  great  measure,  to  their 
downfall,  for  the  land  gave  way  as  far  as  the  houses  erected  on  this  foundation  stood, 
and  no  further."  Dr.  Miller,  of  Jamaica,  was  informed  that  it  was  a  tradition  at  Port 
Royal,  prior  to  1815,  among  the  descendants  of  the  early  settlers,  that  the  great  damage 
was  produced  by  the  slipping  of  the  sand  during  the  earthquake. 

27 


418  BREAKING    OF    GREAT    SEA-WAVE    ON    COASTS. 

magnitude.  When  the  numerous  slips  of  this  kind  which  occur  in  moun- 
tainous and  even  hilly  districts,  and  along  coasts,  are  considered,  as  well 
as  the  frequent  fall  of  rocks  from  the  effects  of  ordinary  atmospheric 
influences,  it  could  scarcely  otherwise  than  happen  that  when  such 
districts  are  violently  shaken,  settlements  of  varied  kinds  are  effected. 
Looking  at  the  sources  of  springs,  and  especially  of  those  which  rise 
through  joints  and  fissures,  that  these  should  be  disturbed,  and  that 
matter  should  be  subsequently  thrown  out  mechanically  suspended  in 
the  water,  would  also  be  anticipated. 

The  "  great  sea-wave"  produced  by  earthquakes  (p.  410),  sometimes 
aids  materially  in  the  modification  of  the  coasts  shaken,  seizing  and 
transporting  before  it  masses  of  matter  which  could  not  be  moved  under 
ordinary  circumstances,  and'  tearing  up  deposits  thrown  down  in,  or 
raised  to,  shallow  situations.  The  magnitude  of  these  waves  is  occa- 
sionally very  considerable,  though  no  doubt  this  may  often  have  been 
much  exaggerated  from  the  terror  of  those  endeavouring  to  escape  from 
them.  In  the  Jamaica  earthquake  of  1692,  "a  heavy  rolling  sea"  fol- 
lowed the  shock, at  Port  Royal,  and  the  " Swan"  frigate,  which  was  by 
the  wharf,  careening,  was  borne  by  it  over  the  tops  of  houses,  and  some 
hundreds  of  persons  were  saved  by  clinging  to  her.  The  sea-wave  of 
the  Lisbon  earthquake  of  1755  rose  to  the  height  of  40  feet  in  the 
Tagus,  leaving  the  bar  dry  as  it  rolled  inwards,  followed  by  others, 
each  less  in  importance,  until  the  water  again  returned  to  its  ordinary 
repose.  The  sea-wave  of  the  same  shock  was  60  feet  high  at  Cadiz,  18 
feet  at  Madeira,  and  under  modified  conditions  was  felt  on  the  coasts  of 
Great  Britain  and  Ireland,  rising  8  to  10  feet  on  the  coast  of  Cornwall. 
The  shock  was  experienced  at  sea  so  severely,  that  vessels  were  thought 
to  have  struck  the  ground,  and  it  is  worthy  of  remark,  as  regards  the 
locality  over  which  the  "  great  sea-wave"  may  have  had  its  origin,  that 
on  board  a  ship  120  miles  west  of  St.  Vincent,  the  men  on  deck  were 
violently  thrown  perpendicularly  upwards  to  the  height  of  a  foot  and  a 
half.*  The  coasts  of  Chilif  and  Peru  have  suffered  from  similar  waves, 
and  in  the  great  Calabrian  earthquake  of  1783  the  shore  of  Scilla  was 
inundated  by  one  rushing  20  feet  high  over  the  low  grounds.  Such 
waves  are,  indeed,  sufficiently  common,  though  seldom  prominently 
noticed  unless  productive  of  considerable  effects.  The  sudden  rise  and 
fall  of  the  sea  observed  in  so  many  harbours  of  the  world,  as  well  in 
tidal  as  tideless  seas,  evidently  independent  of  the  tides  in  the  former, 

*  Lyell,  "Principles  of  Geology,"  7th  edit.,  p.  475. 

•j-  Sir  Charles  Lyell  remarks  (Principles  of  Geology,  7th  edit.,  p.  478),  respecting  the 
destruction  of  the  ancient  town  of  Conception  (called  Penco),  in  1751,  an  earthquake 
sea-wave  rolling  over  it,  that  "a  series  of  similar  catastrophes  has  also  been  traced 
back  as  far  as  the  year  1590,"  including  one  in  1730.  In  1835  the  town  also  suffered 
from  a  "great  sea-wave." 


FLAME    AND    VAPOURS    FROM    EARTHQUAKE    FISSURES.    419 

and  not  due  to  wind-wave  undulations  prolonged  to  the  shores,  often 
seem  little  else  than  the  continuation  of  these  waves  reaching  coasts 
where  the  earthquake  itself  has  not  been  noticed. 

While  the  earthquake  movement  is  thus  communicated  to  the  waters 
of  the  ocean,  minor  volumes  of  water,  even  small  lakes  and  rivers  of 
all  kinds,  cannot  be  otherwise  than  more  or  leas  affected  by  it.  Accord- 
ing to  the  form  of  the  bottom,  situation  as  regards  the  range  of  the 
shock,  and  size  of  the  lakes  and  enclosed  seas,  the  intensity  of  the 
earthquake-wave  being  the  same,  will  necessarily  be  the  effects  pro- 
duced. The  inland  seas  and  lakes  would  be  like  so  many  basins  or 
troughs  of  varied  forms  filled  with  water.  We  can  conceive  important 
geological  modifications  on  the  shores  of  districts  adjoining  Lake  Supe- 
rior, for  example,  when  situated  immediately  above  such  an  impulse  as 
threw  up  men  vertically  to  considerable  heights  at  Riobamba,  in  1797, 
or  jerked  sailors  upwards  off  the  decks  of  a  vessel,  120  miles  from 
shore,  during  the  earthquake  of  Lisbon  in  1755.  In  connexion  with 
the  earth-wave  around  the  centre  of  the  great  Lisbon  shock,  the  waters 
of  Loch  Lomond,  even  though  this  earth-wave  was  then  transmitted  so 
far,  are  represented  to  have  been  thrown  two  feet  four  inches  high  on  the 
shores.  As  respects  rivers,  should  the  shocks  pass  up  their  courses, 
and  the  undulations  be  considerable,  their  waters  would  be  precipitated 
onwards,  or  rolled  back  into  the  troughs  or  hollows  formed,  as  the 
vibration  passes  onwards,  gushes  of  water  rolling  afterwards  down  their 
channels  in  accordance  with  the  temporary  interruptions  to  their  usual 
flow.  Should  fissures  be  formed  during  the  undulation,  and  not  remain 
more  permanently  open,  the  river  waters  rushing  into  them  might  be 
suddenly  discharged  out  of  them  upon  their  again  closing.* 

Accounts  of  earthquakes  contain  such  frequent  mention  of  gases  and 
flames  evolved  from  fissures  during  shocks,  that  although  there  may  be 
many  exaggerations  and  mistakes  on  this  point,  there  would  appear 
little  doubt  of  their  occurrence.  The  emission  of  flame  is  interesting, 
whether  it  be  produced  by  the  escape  of  gases  simply  inflaming  by 
rising  into  the  atmosphere,  or  from  causes  more  resembling  those  ob- 
served in  volcanoes  (p.  323).  In  the  latter  case  we  should  have  to 
infer  the  fracture  of  rocks  down  to  the  needful  supply  of  volcanic  gases. 

*  The  effects  produced  by  the  earthquakes  in  the  Valley  of  the  Mississippi  in 
1811-12,  are  highly  instructive.  Sir  Charles  Lyell  has  not  only  collected  valuable 
information  respecting  them,  but  has  also  personally  examined  the  region  then  shaken. 
The  ground  near  New  Madrid  is  mentioned  as  having  been  so  disturbed  that  the  Mis- 
sissippi was  arrested  in  its  course,  and  a  temporary  reflux  produced.  Large  lakes 
were  formed  in  the  course  of  an  hour,  twenty  miles  in  extent,  and  others  were  drained. 
Hundreds  of  deep  chasms  were  produced,  which  remained  open  many  years  afterwards, 
and  during  the  shock  large  volumes  of  water  and  sand  were  thrown  out  of  them.  Sir 
Charles  Lyell  found,  in  1846,  the  remains  of  many  of  these  fissures  extending  for  half 
a  mile  and  upwards. — Principles  of  Geology,  7th  edit.,  1847. 


420  SOUNDS    ACCOMPANYING    EARTHQUAKES. 

The  emission  of  steam  as  well  as  flame  would  seem  still  more  to  show 
that  the  fissure  was  opened  down  to  depths  where  considerable  heat 
existed.  In  the  instance  of  the  earthquake  of  Cumana  in  1828,  where 
the  water  hissed  and  bubbled  up  round  a  vessel  in  the  harbour,  as  if  a 
hot  iron  had  been  thrust  in  it,  and  when,  on  weighing  the  anchor,  it 
was  found  that  the  links  on  part  of  her  chain  cable  had  been  elongated 
from  two  inches  in  diameter  to  the  length  of  three  and  four  inches, 
there  would  appear  proof  of  some  sudden  communication  by  a  fissure 
with  great  heat.*  In  regions  composed  either  wholly  or  in  part  of 
such  accumulations  as  those  of  the  great  coal  deposits  of  Europe  and 
North  America,  and  where  fissures  descended  to  depths  whence  great 
heat  could  rise  upwards  through  them,  not  only  might  such  gases  as 
carburetted  hydrogen,  disseminated  amid  such  deposits,  and  to  a  certain 
extent  liberated,  be  inflamed,  but  even  from  the  access  of  atmospheric 
air  for  a  time,  the  broken  parts  of  the  coal  beds  themselves  might  be 
burnt,  producing  certain  secondary  effects  in  such  districts,  f 

The  shocks  are  often,  but  not  always,  accompanied  by  noises,  trans- 
mitted through  the  ground.  These  are  necessarily  of  very  different 
kinds,  from  the  varied  conditions  under  which  they  may  be  transmitted. 
According  to  Humboldt,  the  great  shock  of  Riobamba  (4th  February, 
1797),  was  unaccompanied  by  any  noise,  while  at  the  cities  of  Quito 
and  Ibarra  the  great  detonation  of  the  same  shock  occurred  eighteen 
or  twenty  minutes  afterwards.  As  an  example  of  the  great  distance 
to  which  subterranean  noises  may  be  transmitted,  without  earthquake 
shocks,  he  adverts  to  the  noise  like  thunder  heard  over  an  area  of 
several  thousand  square  miles  in  the  Caraccas,  the  plains  of  Calaboso, 
and  on  the  banks  of  the  Rio  Apure  during  the  eruption  of  St.  Vincent, 
in  1812,  this  being,  as  Humboldt  remarks,  in  point  of  distance,  as  if  an 
eruption  of  Vesuvius  should  be  heard  in  the  north  of  France.  He  also 
points  out,  that  in  the  great  earthquake  of  October,  1746,  at  Lima  and 
Callao,  a  noise  like  a  subterranean  thunder-clap  was  heard  a  quarter 

*  "  During  the  earthquake  of  1828  at  Cumana,  an  English  vessel  in  the  harbour  was 
suddenly  enveloped  in  mist,  and  noise  like  distant  thunder  was  heard.  At  the  same 
time  a  shock  was  felt,  and  the  surrounding  water  hissed  as  if  a  hot  iron  had  been 
introduced  into  it,  sending  up  a  number  of  bubbles,  accompanied  by  a  smell  of  sulphur. 
Multitudes  of  dead  fish  floated  on  the  surface.  On  weighing  anchor,  it  was  found  that 
one  of  the  chains  which  connected  it  with  the  vessel,  lying  on  soft  mud,  had  been 
melted,  and  the  rings,  which  were  two  inches  in  diameter,  had  been  stretched  to  the 
length  of  three  or  four  inches,  and  become  much  thinner  than  before."  Daubeny 
(Description  of  Volcanoes,  p.  628). 

•f-  Any  accumulation  of  gas,  or  of  substances  rendered  liquid  by  pressure  ready  to 
assume  the  gaseous  form  when  this  is  removed,  would  be  expected  to  escape  upwards 
should  earthquake  fissures  traverse  or  extend  to  them.  Humboldt  notices  (Kosmos) 
that  during  the  earthquake  of  New  Granada  (16th  November,  1827),  carbonic  acid 
issued  from  fissures  in  the  Magdalena  River,  suffocating  snakes,  rats,  and  other  animals 
living  in  holes. 


EARTHQUAKE    ELEVATIONS    AND    DEPRESSIONS.         421 

of  an  hour  later  at  Truxillo,  unaccompanied  by  any  shaking  of  the 
ground.  These  are  merely,  as  will  be  apparent,  the  transmission  of 
the  earth-wave  through  fair  conductors,  such  as  most  solid  rocks,  beyond 
distances  where  any  tremulous  motion  of  the  ground  is  apparent. 
When  noises  precede  earthquake  shocks  of  importance,  and  these  are 
sometimes  noticed,  they  would  chiefly  appear  to  arise  from  vibrations 
insufficient  to  be  termed  earthquakes,  succeeded  by  those  which  arrest 
attention,  the  greater  earth-waves  being  alone  regarded.  The  con- 
tinued subterranean  sounds  heard  during  a  month  at  Guanaxuato,  in 
1784,  afford  a  good  example  of  such  noises,  unaccompanied  by  vibra- 
tions sufficiently  sensible  to  be  termed  earthquakes.* 

The  permanent  elevations  and  depressions  of  land  accompanying 
earthquakes  require  to  be  well  considered,  apart  from  the  great  earth- 
waves  and  their  consequences,  since  such  waves  may  be  merely  move- 
ments resulting  from  the  cause  producing  these  permanent  relative 
changes  of  level,  sometimes  extending  over  considerable  areas.  The 
observer  will  readily  see  that  a  force  acting  from  the  interior  of  the 
earth  outward,  rending  and  otherwise  disturbing  portions  of  its  solid 
crust,  could  throw  such  portions  into  motion,  causing  earth-waves, 
which,  though  often  so  terribly  disastrous  to  man  and  his  works,  are 
nevertheless  insignificant  when  measured  by  a  very  minor  part  of  the 
earth's  radius.  We  have  seen  (p.  376),  that  molten  matter  raised 
upwards  into  cracks  formed  in  the  relatively  small  mass  of  a  volcano 
will  increase  its  volume,  raising  the  ground  around  in  a  manner  which 
may  produce  changes  of  importance  when  near  shores.  An  observer 
would  therefore  be  prepared  to  expect  that  where  there  may  be  no  very 
ready  outlet,  such  as  a  crater  or  the  sides  of  a  volcano  may  present, 
for  a  greater  mass  of  molten  matter  pressing  to  overcome  superincum- 
bent obstacles  to  its  escape,  greater  fractures,  extending  over  wider 
areas,  may  be  formed,  throwing  the  fractured  and  adjoining  rock  masses 
into  movement,  molten  rock  remaining  in  its  new  position  as  far  as 
circumstances  will  permit.  In  such  a  case  the  earthquake  would  be 
merely  a  secondary  effect  consequent  on  the  exertion  of  force  raising 
the  ground  upwards.  Although  allusion  has  been  made  to  molten 
matter  raised  upwards  over  a  large  instead  of  a  minor  area,  the  surface 

*  "Kosmos,"  Art.  Earthquakes.  Humboldt  obtained  good  evidence  on  this  subject. 
The  noise  began  on  the  9th  of  January,  1784,  at  midnight.  From  the  13th  to  the  16th 
of  the  same  month,  "it  was  as  if  there  were  heavy  storm-clouds  under  the  feet  of  the 
inhabitants,  in  which  slow  rolling  thunder  alternated  with  short  thunder-claps.  The 
noise  ceased  gradually  as  it  commenced;  it  was  confined  to  a  small  space,  for  it  was 
not  heard  in  a  basaltic  district  at  the  distance  of  only  a  few  miles."  "  Neither  at  the 
surface,  nor  in  the  mines,  1598  English  feet  in  depth,  could  the  slightest  trembling  of 
the  ground  be  perceived."  "  Thus,"  he  adds,  "  as  chasms  in  the  interior  of  the  earth 
close  or  open,  the  propagation  of  the  waves  of  sound  is  either  arrested  in  its  progress, 
or  continued  until  it  meets  the  ear." 


422         EARTHQUAKE    ELEVATIONS    AND    DEPRESSIONS. 

of  the  earth  might  be  rent,  earthquakes  produced,  and  land  perma- 
nently elevated,  as  will  be  noticed  hereafter,  by  the  mere  expansion  of 
a  considerable  portion  of  the  earth's  crust,  the  resistances  upwards 
being  in  the  end  somewhat  suddenly  overcome. 

From  the  adjustment  of  the  minor  volume  of  a  volcanic  mountain,  to 
that  of  great  masses  of  the  earth's  crust,  by  which  parts  may  be  either 
raised  or  depressed,  and  this  by  such  sudden  movements  that  earth- 
waves  of  various  magnitudes  are  communicated  to  the  adjacent  rocks, 
the  observer  would  expect  no  slight  modifications.  The  geological  im- 
portance of  the  rise  or  depression  of  land,  especially  on  sea-coasts,  at 
the  time  of  earthquakes,  being  fully  recognised,  it  is  very  desirable  that, 
whenever  opportunities  present  themselves,  exact  researches  as  to  the 
amount  of  rise  or  depression  above  or  beneath  a  somewhat  permanent 
datum  level  should  be  undertaken.  The  mean  tide  level  on  oceanic 
coasts  is  very  desirable  for  this  purpose,  when  available,  and  may  often 
readily  be  obtained  with  sufficient  accuracy.  In  certain  estuaries  an 
alteration  in  the  bottom  of  the  seaward  portion  might  influence  the  tides, 
so  that  a  greater  or  less  amount  of  water  could  flow  upwards  to  situa- 
tions where  no  real  change  of  the  relative  level  of  land  and  the  main  sea 
had  been  effected.  An  observer  will  see,  by  reference  to  charts  of  estu- 
aries, especially  those  with  extensive  bars  at  their  mouths,  how  materi- 
ally tides  might  be  influenced  in  their  action  by  moderate  elevations  or 
depressions  at  their  mouths.  In  some,  where  the  amount  of  water  en- 
tering with  the  flood  tide  is  so  important  in  keeping  a  channel  clear  upon 
the  ebb,  especially  where  a  shallow  coast  is  exposed  to  heavy  breaker 
action,  the  volume  of  water  passing  up  or  down  might  be  most  materially 
modified. 

Modern  observations  on  the  western  coast  of  America,  which,  fortu- 
nately for  these  researches,  is  so  truly  oceanic,  uncut  by  great  rivers, 
have  successfully  established  the  rise  of  extensive  lines  of  coast  during 
earthquakes.  At  the  time  of  that  of  November,  1822,  felt  from  north 
to  south  for  a  distance  of  about  1200  miles,  the  coast  was  raised  four 
feet  at  Quintero,  and  three  feet  at  Valparaiso  above  its  former  level ; 
and  Mrs.  Graham  records  that  oysters  and  other  molluscs  were  elevated 
out  of  the  sea,  becoming  offensive  as  they  decomposed.*  Dr.  Meycn 
found,  nine  years  afterwards,  sea-weed  and  shells  adhering  to  the  coast 
thus  raised,  and  infers  it  was  so  to  the  height  of  about  four  feet  along 
Central  Chili.  Sir  Charles  Lyell,  detailing  the  evidence  as  to  the  rise 
of  land  at  the  time  of  this  earthquake,  considers  that  if  the  estimate  of 
the  mass  moved  be  correct,  namely,  that  superficially  it  extended  over 
100,000  square  miles,  the  area  elevated  would  be  equal  to  half  that  of 
France,  and  five-sixths  that  of  Great  Britain  and  Ireland,  so  that  only 

*  Geological  Transactions,  2d  series,  vol.  i. 


EFFECTS    PRODUCED    IN    THE    RUNN    OF    CUTCH.          423 

giving  two  miles  for  the  depth  of  the  mass  raised,  200,000  cubic  miles 
of  mineral  matter  were  elevated  above  their  previous  position  at  that 
time.* 

At  the  time  of  the  earthquake  on  the  coast  of  Chili  in  1835,  when  the 
towns  of  Conception,  Talcahuano,  and  Chilian  suffered  so  seriously  from 
the  shocks,  f  much  land  was  also  raised.  Captain  Fitzroy,  who  was  then 
engaged  in  a  survey  of  the  coast,  states  that  the  sea  did  not  for  some 
days  fall,  by  four  or  five  feet,  to  the  usual  marks ;  and  that  "  even  at 
high  water,  beds  of  dead  mussels,  numerous  chitons,  and  limpets,  and 
withered  sea-weed,  still  adhering,  thoughw  lifeless,  to  the  rocks  on  which 
they  had  lived,  everywhere  met  the  eye."J  The  amount  of  rise  gradu- 
ally diminished,  so  that  about  two  months  afterwards,  the  coast  was 
within  two  feet  of  its  former  level,  so  that  a  kind  of  settlement  after  the 
first  upheaval  seems  to  have  been  effected. 

During  the  earthquake  of  Cutch,  in  June  1819,  the  surface  of  a  wide 
area  was  so  acted  upon,  that  part  became  depressed  beneath,  and  part 
elevated  above,  its  former  general  level.  The  Runn  of  Cutch,  as  it  is 
termed,  is  the  lowest  part  of  a  considerable  district  situated  between  the 
eastern  branch  of  the  delta  of  the  Indus  and  the'  Loonee  River.  The 
area  is  estimated  at  about  7000  square  miles,  and  is  so  slightly  above 
the  level  of  the  sea,  that  during  the  monsoons  the  sea  is  driven  up  from 
the  Gulf  of  Cutch  and  the  creeks  at  Luckput,  overflowing  a  large  part 
of  it,  the  subsequent  evaporation  of  the  water  sometimes  leaving  a  de- 
posit of  salt  about  an  inch  thick.  It  is  also  described  as  liable  to  be 
occasionally  overflowed  in  parts  by  river  water.  As  a  whole,  it  seems 
to  be  a  district  peculiarly  favourable  for  having  any  modifications  of  its 
surface  marked  by  changes  in  the  position  of  water  flowing  over,  resting 
upon,  or  bounding  it.  From  the  facts  accumulated  respecting  the  earth- 
quake of  1819,  by  Sir  Charles  Lyell,§  it  would  appear  that  immediately 
after  the  chief  shock  ||  a  mound  was  found  to  be  raised  across  the  eastern 

*  "  Principles  of  Geology,"  7th  edit.,  p.  436. 

f  Though  there  was  one  chief  shock,  there  are  considered  to  have  been  more  than 
300  minor  shocks  subsequently,  between  the  20th  of  February  and  the  4th  March. — 
Lyell,  "Principles,"  7th  edit.  p.  433. 

J  Captain  Fitzroy  adds  (Voyages  of  Adventure  and  Beagle,  vol.  ii.),  with  respect  to 
the  Island  of  Santa  Maria,  southeast  from  Conception,  that  its  southern  extremity 
"had  been  raised  eight  feet,  the  middle  nine,  and  the  northern  end  upwards  of  ten 

feet." "An  extensive  rocky  flat  lies  around  the  northern  parts  of  Santa  Maria. 

Before  the  earthquake  this  flat  was  covered  by  the  sea,  some  projecting  rocks  only 
showing  themselves  ;  now  the  whole  flat  is  exposed,  and  square  acres  of  it  are  covered 
with  dead  shell-fish,  the  stench  arising  from  which  is  abominable.  By  this  elevation  of 
the  land,  the  southern  port  of  Santa  Maria  has  been  almost  destroyed,  little  shelter  re- 
maining there,  and  very  bad  landing." 

$  "Principles  of  Geology,"  7th  edit.,  pp.  437-441. 

||  Shocks  are  mentioned  as  having  been  felt  from  the  16th  of  June,  the  day  of  the 
great  earthquake,  to  the  20th,  when  it  is  said  an  eruption  broke  out  at  the  volcano  of 
Denodur,  30  miles  N.W.  from  Bhooj,  the  vibrations  then  ceasing.  The  chief  shock  was 


424  QUIET    RISE    OR    SUBSIDENCE    OF    LAND. 

branch  of  the  Indus,  more  than  50  miles  in  length  from  east  to  west,  and 
in  some  places  16  miles  in  breadth,  with  a  height  of  10  feet.  This  was 
named  by  the  inhabitants  the  Ullah  Bund,  or  Mound  of  God.  At  the 
same  time  a  submergence  of  land  was  effected  on  the  south  of  the  Ullah 
Bund,  into  which  the  sea  flowed  up  the  eastern  channel  of  the  Indus, 
converting  an  area  of  2000  square  miles  of  land  into  a  great  sea  lagoon. 
The  village  of  Sindree,  situated  on  the  land  bordering  the  river  prior  to 
the  earthquake,  was  submerged,  the  tops  of  the  fort  and  houses  being 
alone  visible  above  the  waters.*  At  Luckput,  further  down  the  Indus, 
the  river,  which  was  there  fordable  at  low  water,  being  then  only  about  a 
foot  deep,  became  afterwards  18  feet  deep  at  the  same  time  of  tide.  Other 
portions  of  the  channel  were  also  found  to  be  deepened.  The  course  of 
the  Indus  is  described  as  much  unsettled  after  the  earthquake,  and  the 
river  finally  cut  through  the  Ullah  Bund  in  1826,  throwing  such  a  body 
of  water  into  the  salt  lagoon,  formed  during  the  earthquake,  as  to  ren- 
der the  water  fresh  for  many  months,  though  it  became  again  salt  in 
1828. f  Being  in  the  course  of  such  a  river,  it  would  be  expected  that 
this  submergence  would  be  obliterated  by  the  usual  transport  of  detritus 
into  it,  a  change  now  in  progress,  the  lagoon  having  been  found  dimi- 
nished both  in  size  and  depth  in  1838. 

Quiet  Rise  or  Subsidence  of  Land. — In  volcanic  regions  where  there 
is  sufficient  activity  to  show  that  the  vents  are  merely  in  a  half-dormant 
state,  or  where,  from  time  to  time,  though  the  eruptions  may  occur  occa- 
sionally after  even  considerable  intervals  of  comparative  repose,  volcanic 
action  produces  very  marked  effects  on  the  surface,  we  should  expect 
that  there  would  sometimes  be  quiet  elevations  or  depressions  of  the 
ground.  Differences  in  the  relative  level  of  sea  and  land  could  be  caused 
by  the  variations  of  heat  to  which  the  hard  rocks  or  other  mineral  accu- 
mulations may  be  exposed,  such  differences  producing  effects  likely  to 
be  appreciated  by  the  inhabitants  of  coasts  only  in  proportion  as  the 
areas  acted  upon  may,  or  may  not,  be  more  or  less  covered  by  water,  or 
be  left  dry.  Changes  of  temperature  which  could  in  so  short  a  time  de- 
prive a  volcanic  mountain,  such  as  Cotopaxi  in  the  hot,  or  such  as  those 
in  Iceland  in  the  cold  regions,  of  their  snows,  could  scarcely  but  be  at- 

felt  destructively  at  Ahmedabad,  and  feebly  at  Toonah,  400  miles  more  distant. — Lyell, 
"Principles,"  p.  437. 

*  Remarking  upon  the  houses  not  having  been  thrown  down  (Bhooj,  the  principal 
town  of  Cutch  was  converted  into  a  heap  of  ruins  by  this  earthquake),  Sir  Charles  Lyell 
observes  that,  "  had  they  been  situated,  therefore,  in  the  interior,  where  so  many  forts 
were  levelled  to  the  ground,  their  site  would,  perhaps,  be  regarded  as  having  remained 
comparatively  unmoved.  Hence  we  may  suspect  that  great  permanent  upheavings  and 
depressions  of  soil  may  be  the  result  of  earthquakes,  without  the  inhabitants  being  in 
the  least  degree  conscious  of  any  change  of  level." 

f  It  is  represented  as  having  been  more  salt  than  the  sea,  and  the  natives,  according 
to  Sir  A.  Burnes,  supposed  that  it  was  so  from  a  solution  of  the  salt  with  which  the 
"Runn  of  Cutch"  is  impregnated. — Lyell,  "  Principles,"  p.  439. 


RISE    AND    DEPRESSION    OF    THE    COAST    AT    PUZZTJOLI.   425 

tended  with  the  expansion  of  the  accumulations  acted  upon.  How  far 
minor  volcanic  areas  may  permanently,  so  far  as  regards  a  certain 
amount  of  time,  remain  elevated  or  depressed,  would  depend  upon  the 
conditions  under  which  such  areas  may  be  generally  placed.  A  minor 
volcanic  area  exhibiting  considerable  activity  at  one  time  may  present  a 
mass  of  mineral  matter  more  heated,  and  be,  consequently,  more  ex- 
panded than  at  another  when  this  activity  may  cease,  even  only  for 
several  centuries. 

In  tracing  back  the  elevation  or  depression  of  a  coast  by  means  of  the 
human  works  which  appear  to  have  risen  or  have  been  submerged, 
relatively  to  the  level  of  an  adjoining  sea,  assuming  that  there  are  no 
difficulties  respecting  the  permanency  of  the  latter,  as  there  might  be, 
especially  as  regards  tidal  seas,  there  may  be  much  uncertainty  as  to 
how  far  the  one  or  the  other  has  been  slow  and  tranquil.  The  sudden 
uprise  or  depression  of  land  during  earthquakes  does  not  necessarily 
suppose  such  undulations  and  vibrations  of  the  ground  as  always  to 
overthrow  the  works  of  man,  though  on  coasts  the  resistance  offered  by 
them  to  a  great  sea- wave,  rolling  furiously  over  the  shore,  in  conse- 
quence of  the  earth-wave,  may  often  be  very  limited.  Great  caution  is 
evidently  needed  on  this  head,  so  that  a  slow  continuous  elevation  or 
depression  of  the  land,  relatively  to  the  level  of  the  sea,  be  well  sepa- 
rated from  its  sudden  rise  or  fall  at  the  time  of  an  earthquake. 

As  regards  a  minor  area  in  a  volcanic  district  exhibiting  relative 
changes  of  level  within  the  historic  period,  the  coasts  of  part  of  the 
Bay  of  Baiae,  Naples,  have  been  regarded  as  affording  sufficient  proof. 
Whether  these  changes  may  have  been  more  or  less  sudden,  or  were 
gradual  and  continued  through  a  somewhat  long  time,  has  not  been 
altogether  settled.  Looking  at  the  kind  of  country  acted  upon,  a 
change  of  level,  sometimes  slow,  at  others  sudden,  would  not  appear 
inconsistent  with  the  facts  noticed.  With  respect  to  the  probable  dates 
at  which  the  changes  of  level  were  effected,  the  Temple  of  Jupiter 
Serapis,  at  Puzzuoli,  has  been  considered  as  affording  good  approxima- 
tions. The  main  fact  is,  that  three  marble  columns,  somewhat  more 
than  40  feet  high,  slightly  out  of  the  perpendicular,  are  smooth  and 
uninjured  to  the  height  of  12  feet,  above  which,  for  9  feet,  they  are 
perforated  by  the  Lithodomus,  a  common  and  existing  boring  mollusc 
of  the  Mediterranean.  The  remainder  of  the  columns,  all  of  which 
exhibit  the  same  fact,  at  the  same  heights,  only  exhibit  the  usual  effects 
of  atmospheric  exposure.  On  the  pavement  of  the  temple  are  other 
broken  columns  of  marble  perforated  in  certain  parts,  some  of  them 
bored  not  only  on  the  exterior,  but  also  in  the  cross  fracture.  The 
inference  from  these  facts  has  been,  that  the  lower  'parts  of  the  columns 
were  protected  by  some  deposit  during  submergence  beneath  the  sea, 
'the  columns  standing  erect,  or  nearly  so,  while  the  part  above  was  per- 


426     ELEVATION    AND    DEPRESSION    OF    MASSES    OF    LAND 

forated,  and  consequently  in  water  sufficiently  clean  for  the  animals  to 
live  in,  bore,  and  obtain  their  food,  the  remainder  rising  above  the  sea, 
or  only  submerged  to  a  depth  beneath  which  the  Lithodomus  usually 
lives.  This  supposes  the  building  of  the  temple  on  dry  land,  its  sub- 
mergence beneath  the  sea  to  between  20  and  30  feet,  and  its  subsequent 
emergence,  as  now  seen ;  so  that  the  platform  of  the  temple  is  about 
one  foot  or  thereabouts  beneath  the  high  water  mark  of  the  small  tides 
of  the  Bay  of  Naples.  From  the  various  circumstances  connected  with 
this  locality,  Sir  Charles  Lyell  infers,  respecting  the  ground  forming 
the  foundation  of  the  temple,  that  "  first,  about  80  years  before  the 
Christian  era,  when  the  ancient  mosaic  pavement  was  constructed,  it 
was  about  12  feet  above  its  actual  level,  or  that  at  which  it  stood  in 
1838 ;  secondly,  towards  the  close  of  the  first  century  after  Christ  it 
was  only  six  feet  above  its  actual  level ;  thirdly,  by  the  end  of  the  fourth 
century  it  had  nearly  subsided  to  its  present  level ;  fourthly,  in  the 
middle  ages,  and  before  the  eruption  of  Monte  Nuovo,  it  was  about  19 
feet  below  its  present  level ;  lastly,  at  the  beginning  of  the  present  cen- 
tury it  was  about  two  feet  two  inches  above  the  level  at  which  it  now 
stands"  (in  1838).* 

The  evidences  of  recent  changes  of  the  relative  level  of  sea  and  land, 
even  as  respects  the  works  of  man  in  the  vicinity,  are  not  confined  to 
the  temple  of  Serapis.  Mr.  Babbage  mentions  that  at  the  sixth  pier  of 
the  Bridge  of  Caligula,  at  Puzzuoli,  a  line  of  perforations  by  the 
Lithodomm,  and  other  indications  of  a  water  level,  are  found  four  feet 
above  the  sea,  as  also  at  ten  feet  above  the  present  sea  level  on  the 
twelfth  pier,  and  points  to  the  broken  columns  of  the  Temples  of  the 
Nymphs  and  of  Neptune,  as  remaining  now  standing  in  the  sea.f  With 
respect  to  the  columns  of  the  latter  temple,  Sir  Charles  Lyell  observes, 
that  as  they  now  stand  erect  in  five  feet  water,  just  rising  to  the  surface 
of  the  sea,  their  pedestals  buried  in  the  mud,  if  the  sea  bottom  be 
raised,  and  the  covering  accumulations  removed,  they  might  exhibit 
similar  appearances  to  those  observed  at  the  Temple  of  Serapis. { 
Roman  roads  are  mentioned  as  under  water,  one  between  Puzzuoli  and 
the  Leucrine  Lake,  and  another  near  the  Castle  of  Baise.  A  road  with 
some  fragments  of  Roman  buildings  is  beneath  the  level  of  the  sea  on 
the  Sorrento  side  of  the  Bay  of  Naples ;  and  in  the  island  of  Capri,  one 
of  the  palaces  of  Tiberius  is  covered  by  water.§ 

Independently  of  these  evidences  connected  with  the  works  of  man, 

*  "  Principles  of  Geology,"  7th  edition,  in  which  Sir  Charles  Lyell  gives  the  results 
of  his  personal  examination  of  the  district,  as  published  in  the  early  editions  of  the 
same  work,  and  the  chief  facts  mentioned  by  other  authors. 

f  Proceedings  of  the  Geological  Society  of  London  (March,  1834),  vol.  ii.  p.  74. 

J  "  Principles  of  Geology,"  7th  edition,  p.  491. 

g  Professor  James  Forbes,  "  Physical  Notices  of  the  Bay  of  Naples,"  Brewster's  Edin- 
burgh Journal  of  Science,  vol.  i.,  new  series.  * 


FKOM    INCREASE    OR    DECREASE    OF    THEIR    HEAT.      427 

of  changes  of  the  relative  level  of  sea  and  land,  there  is  also  geological 
evidence  of  the  same  movements  within  a  comparatively  recent  period. 
Mr.  Babbage  mentions  a  line  of  perforations  by  the  Lithodomus,  like 
those  on  the  columns  of  the  Temple  of  Serapis,  32  feet  above  the  pre- 
sent level  of  the  sea,  in  an  inland  cliff  opposite  the  Island  of  Nisida.* 
Sir  Charles  Lyell  points  to  this  cliff  and  other  facts  as  capable  of  prov- 
ing these  changes,  even  if  human  works  in  the  Bay  of  Naples  had  not 
afforded  the  evidence  above  noticed;  and  which,  taken  in  connexion 
with  that  furnished  by  the  geological  facts  observed,  would  appear  to 
show  an  unequal  elevation  and  depression  of  the  land  in  different  parts 
of  an  area  comprising  this  bay. 

In  accounting  for  the  gradual  sinking  and  rising  of  the  ground  on 
which  the  Temple  of  Serapis  is  based,  and  of  which  he  concludes  there 
is  sufficient  evidence,  Mr.  Babbage  adverts  to  the  changes  of  volume 
which  might  be  produced  in  the  subjacent  accumulations  by  the  diffe- 
rence of  heat  in  them  at  different  times ;  an  important  consideration, 
not  only  as  respects  a  minor  area  of  this  kind,  but  also  the  elevation 
and  depression  of  great  masses  of  land,  constituting  even  considerable 
portions  of  continents. f  He  observes,  that  "in  consequence  of  the 
changes  actually  going  on  at  the  earth's  surface,  the  surfaces  of  equal 
temperature  within  its  crust  must  be  continually  changing  their  form, 
and  exposing  thick  beds,  near  the  exterior,  to  alterations  of  tempera- 
ture ;"  and,  that  "  the  expansion  and  contraction  of  these  strata  will 
probably  form  rents,  raise  mountain  chains,  and  elevate  even  conti- 
nents. "I  With  respect  to  these  greater  results,  Mr.  Babbage  refers  (1), 
to  the  increase  of  temperature  found  as  we  descend  beneath  the  surface 
of  the  earth ;  (2),  to  the  expansion  of  solid  rocks  by  heat,  while  clay 
and  some  other  substances  contract  under  the  same  circumstances  ;  (3), 
to  different  mineral  accumulations  conducting  heat  unequally ;  (4),  to 
the  different  radiation  of  heat  from  the  earth,  or  at  different  parts  of  its 

*  "Observations  on  the  Temple  of  Serapis,  at  Puzzuoli,  near  Naples;  with  remarks 
on  certain  causes  which  may  produce  geological  cycles  of  great  extent." — Proceedings 
of  the  Geological  Society  of  London  (March,  1834),  vol.  ii.  p.  74. 

-j-  With  respect  to  the  changes  of  volume  produced  in  rocks  by  differences  in  tempe- 
rature, though  we  may,  in  a  work  entitled  "  Sections  and  Views,  illustrative  of  Geolo- 
gical Phenomena,"  p.  70,  and  published  in  1830,  have  called  attention  to  them  when 
remarking  respecting  one  of  the  diagrams,  that  "to  one  who  looks  at  such  a  diagram, 
it  will  be  obvious  that  slight  and  unequal  contractions  of  the  mass  of  the  earth  would 
produce  changes  we  should  consider  important;  and  it  may  occur  to  him,  that  mere 
thermometrical  differences  beneath  the  earth's  crust  might  be  sufficient  to  raise  whole 
continents  above  the  level  of  the  sea,  or  plunge  them  beneath  it,"  it  may  be  as  well 
here  to  state,  as  was  done  in  our  "Researches  in  Theoretical  Geology,"  (1834)  p.  163, 
in  which  there  were  more  extended  remarks  to  the  same  effect,  that  Mr.  Babbage's  ob- 
servations were  entirely  original,  and  that  we  did  not  entertain  "opinions  similar  to  his 
respecting  the  probable  effects  of  the  causes  he  notices  before  he  stated  them  to  us." 

J  Proceedings  of  the  Geological  Society  of  London  (March,  1834),  vol.  ii.  p.  75. 


428  GRADUAL    RISE    OF    LAND    IN    SWEDEN. 

surface,  according  as  it  is  covered  with  forests,  with  mountains,  with 
deserts,  or  with  water;  and  (5),  to  existing  atmospheric  agents  and 
other  causes  constantly  changing  the  condition  of  the  surface  of  the 
globe.  Applying  these  views  to  the  ground  on  which  the  Temple  of 
Serapis  is  placed,  Mr.  Babbage  supposes  it  to  have  had  an  elevated 
temperature  when  this  temple  was  first  erected,  and  that  it  "  subse- 
quently contracted  by  slowly  cooling  down ;  and  that  when  this  con- 
traction had  reached  a  certain  point,  a  fresh  accession  of  heat  from 
some  neighbouring  volcano,  by  raising  the  temperature  of  the  beds, 
again  produced  a  renewed  expansion,  which  restored  the  temple  to  its 
present  level."* 

Quitting  the  minor  area  of  Naples,  where  complications  may  arise 
from  the  volcanic  character  of  the  district,  it  fortunately  occurs,  that 
in  Northern  Europe  observations  have  been  sufficiently  long  and  care- 
fully continued  to  prove  that  a  mass  of  land  in  Norway  and  Sweden  has 
been  slowly  and  tranquilly  rising  above  the  level  of  the  sea  during  his- 
toric times.  About  a  century  and  a  half  since,  facts  were  known  which 
induced  Celsius  to  infer  that  the  level  of  the  Baltic  and  Northern  Ocean 
was  sinking,  as  was  likely  to  be  concluded  at  that  time  with  respect  to 
any  relative  change  of  the  levels  of  sea  and  land.  Although  Playfair 
may  have  pointed  out  that,  in  accordance  with  the  views  of  Hutton,  it 
was  more  probable  that  the  land  had  risen,  it  was  not  until  Von  Buch 
had  personally  visited  the  district  in  1807  that  the  latter  inference  be- 
came established  as  a  fact.  He  concluded,  "  that  the  whole  country 
from  Frederickshall,  in  Norway,  and  perhaps  as  far  as  St.  Petersburgh, 
was  slowly  and  insensibly  rising  ;"f  inferring  that  the  northern  portion 
was  rising  faster  than  the  southern.  Referring  to  the  marks  cut  in 
rocks  at  levels  in  calm  weather,  considered  to  represent  the  standard 
level  of  the  Baltic,  it  was  concluded  by  officers  charged  with  the  exami- 
nation in  1820-21,  that  there  had  been  a  relative  change  of  level,  though 
the  rise  had  not  been  generally  to  the  same  extent.  In  1834,  Sir 
Charles  Lyell  examined  the  marks  then  cut  by  these  officers,  and  con- 
cluded that  the  land  had  risen  four  or  five  inches  in  certain  localities  in 
the  north  of  Stockholm.  He  convinced  himself  at  the  time,  "  after 
conversing  with  many  civil  engineers,  pilots,  and  fishermen,  and  after 
examining  some  of  the  ancient  marks,  that  the  evidence  formerly  ad- 
duced in  favour  of  the  change  of  level,  both  on  the  coasts  of  Sweden 
and  Finland,  was  full  and  satisfactory.  The  alteration  of  level  evidently 
diminishes  as  we  proceed  from  the  northern  parts  of  the  Gulf  of  Bothnia 
towards  the  south,  being  very  slight  around  Stockholm."! 

*  Proceedings  of  the  Geological  Society  of  London,  vol.  ii.  p.  75. 
f  "  Travels  in  Norway." 

j  " Principles  of  Geology,"  7th  edition,  p.  300,  and  "On  the  Proofs  of  a  Gradual 
Elevation  of  certain  parts  of  Sweden,"  Philosophical  Transactions,  1835. 


RAISED    COASTS    IN    SCANDINAVIA.  429 

The  elevation  of  the  area  noticed  is  considered  to  extend  to  the 
North  Cape,  so  that  further  traces  of  it  become  lost  beneath  the  North- 
ern Ocean.  Taking  a  general  view  of  the  evidence,  Sir  Roderick  Mur- 
chison  has  concluded,*  that,  assuming  an  east  and  west  line  traversing 
Sweden  in  the  parallel  of  Solvitsborg,  there  has  been  in  recent  times  on 
the  north,  and  continues  to  be,  an  elevation,  and  on  the  south  a  depres- 
sion. As  regards  the  slow  depression  of  Scania,  Professor  Nilsson 
infers,  that  this  has  been  in  progress  for  several  centuries  ;f  and  Pro- 
fessor Forchhammer  considers  that  the  Isle  of  Saltholm  has  not  sensibly 
changed  its  level,  with  respect  to  the  sea,  for  600  years ;  while  the  Isle 
of  Bornholm  appears  to  have  risen  one  foot  in  a  century,  this  elevation 
having  been  continued  for  1600  years. J 

With  respect  to  very  exact  measurements,  as  regards  small  changes 
in  the  relative  level  of  sea  and  land  in  inland  seas,  such  as  those  of  the 
Baltic,  from  the  configuration  of  which  and  their  mode  of  communication 
with  the  main  ocean,  disturbing  influences  may  arise,  no  doubt  without 
reference  of  the  general  area  to  some  more  constant  level,  such  as  that 
of  mean  tide  in  some  adjoining  ocean,  there  may  be  difficulties ;  but 
looking  at  the  evidence  as  a  whole,  it  would  appear  decisive  of  a  slow 
change  in  the  relative  level  of  sea  and  land  in  the  manner  inferred. § 
Geological  evidence  supports  the  views  derived  from  the  circumstances 
mentioned ;  for,  while  the  oceanic  coast  shows  deposits  raised  above  the 
present  level  of  the  sea,  and  containing  the  remains  of  shells  still  exist- 
ing in  it,  even  barnacles  and  small  zoophytes  adhering  to  the  rocks  on 
which  they  fastened  while  beneath  the  water,  on  the  Baltic  side  there 
are  also  raised  accumulations  containing  shells  characteristic  of  that 
sea.  Although  these  facts  might  not  show  that  the  land  had  been 

*  Address  to  the  Royal  Geographical  Society  of  London,  1845. 

|  Communication  to  Sir  Charles  Lyell  (Address  of  the  latter  to  the  Geological  Society 
of  London,  1837).  Professor  Nilsson  mentioned,  among  other  circumstances,  that  a 
large  stone,  the  distance  from  which  on  the  shore  of  Scania  was  measured  by  Linngeus 
in  1749,  was,  in  1836,  one  hundred  feet  nearer  the  water's  edge,  and  that  in  the  seaport 
towns,  "  all  along  the  coast  of  Scania,  there  are  streets  below  the  high-water  level  of 
the  Baltic,  and,  in  some  places,  below  the  level  of  the  lowest  tide.  Thus  when  the  wind 
is  high  at  Malmo,  the  water  overflows  one  of  the  present  streets ;  and  some  years  ago 
some  excavations  showed  an  ancient  street  in  the  same  place,  eight  feet  below,  and  it 
was  then  seen  that  there  had  evidently  been  an  artificial  raising  of  the  ground,  doubt- 
less in  consequence  of  that  subsidence.  There  is  also  a  street  at  Trelleborg,  and  ano- 
ther at  Skanor,  a  few  inches  below  high-water  mark;  and  a  street  at  Ystad  is  just  on 
a  level  with  the  sea,  at  which  it  could  not  have  been  originally  built." 

J  "  On  Changes  of  Level  which  have  taken  place  in  Denmark  in  the  present  times," 
Transactions  of  the  Geological  Society  of  London,  vol.  vi.,  1841. 

\  The  average  rate  of  rise  in  Sweden  is  estimated  at  about  three  feet  four  inches  in 
a  century.  With  regard  to  the  various  authorities  on  the  subject  of  this  change,  we 
would  refer,  for  his  usual  impartial  statements,  to  the  Vicomte  d'Archiac's  "  Histoire 
des  Progres  de  la  Geologic,"  chap.  v.  ;  Soulevements  et  Abaissements  Contemporains, 
t.  i.  p.  045. 


430   GRADUAL  DEPRESSION  OF  LAND  IN  GREENLAND. 

raised  in  historic  times,  they  are   important,   as   proving  a  relative 
change  of  level  at  a  recent  geological  period.* 

Changes  in  the  relative  levels  of  sea  and  land,  Jtnd  which  can  be  mea- 
sured by  that  of  the  ordinary  tidal  wave  of  an  oceanic  coast,  are  not 
confined  to  the  north  of  Europe.  Facts  appear  to  show,  that  there  has 
been  a  gradual  sinking  of  the  west  coast  of  Greenland  during  at  least  a 
century.  Dr.  Pingel  has  shown  that  in  a  frith,  called  Igalliko  (lat.  60° 
43'  N.),  a  house  built  on  a  small  rocky  island  is  now  submerged ;  that 
the  foundations  of  a  storehouse  of  the  colony  of  Juliariahaab,  founded 
in  1776,  are  only  now  dry  at  low  water ;  that  near  the  village  of  Fiske- 
nass  (lat.  63°  4'  N.),  they  have  been  obliged  to  shift  the  poles  for  the 
women's  boats,  the  old  poles  still  standing  in  the  sea ;  and  that  to  the 
northeast  of  Godthaab  (lat.  64°  10'  N.),  the  remains  of  a  winter-house 
are  now  beneath  high  water.  Dr.  Pingel  mentions,  that  no  original 
Greenlander  builds  his  house  so  near  the  water's  edge.  This  author 
adds,  that  from  information  highly  deserving  of  credit,  ruins  of  ancient 
Greenland  winter-houses  at  Napparsok,  45  (English)  miles  north  of  Ny- 
Sukkertop  (lat.  65°  20'  N.),  are  to  be  seen  under  water. f  Thus,  for 
about  368  English  miles  there  would  appear  evidence  of  this  subsidence, 
and  it  is  supposed  to  extend  to  Disco  Bay,  about  256  miles  further  north. 

It  has  been  supposed  that  the  movement  noticed  in  the  Bay  of  Naples 
has  not  been  confined  to  it,  and  that,  however  local  some  of  the  oscilla- 
tions of  the  ground  may  be,  in  consequence  of  the  volcanic  action  con- 
nected with  it,  there  is  a  slow  elevation  in  progress  affecting  Italy  from 
the  neighbourhood  of  Naples  to  Venice.  It  has  been  inferred  that  there 
is  a  change  of  the  relative  level  of  sea  and  land  near  the  latter  city  of 
about  six  inches  in  a  century,  and  that,  extending  to  Naples,  this  eleva- 
tion (varying  in  the  proportion  of  155  to  660  southwards),  is  felt  for  at 
least  the  distance  of  520  miles. J  With  respect  to  elevations  in  the 
Mediterranean  connected  with  the  works  of  man,  Captain  Spratt  and 
Professor  E.  Forbes  mention  an  antique  sarcophagus  in  the  water  of  the 
Bay  of  Macri  (the  ancient  Telmissus),  perforated  by  boring  molluscs  up 

*  M.  Alex.  Brongniart  found  balani  still  on  the  rocks,  beneath  a  mass  of  shells,  of 
the  same  species  as  now  live  in  the  adjoining  sea,  and  216  (English)  feet  above  its  level, 
near  Uddevalla  (Tableau  des  Terrains  qui  composent  1'Ecorce  du  Globe,  p.  89).  Sir 
Charles  Lyell  had,  in  1834,  an  opportunity  of  verifying  this  observation,  not  only  by 
discovering  balani  adhering  to  the  rocks,  but  also  small  zoophytes  (Cdlepora?)  beneath 
a  mass  of  similar  shells  at  Kured,  two  miles  north  of  Uddevalla,  at  more  than  100  feet 
above  the  adjoining  sea.  With  respect  to  the  raised  accumulations  on  the  Baltic  side, 
the  same  geologist  found  them  more  than  100  feet  above  the  adjoining  sea  at  Soder- 
telje,  16  miles  southwest  from  Stockholm.  The  shells  in  these  deposits  are  well  charac- 
terized as  Baltic,  and  Sir  Charles  Lyell  points  out  that  the  marine  molluscs  found  in 
the  Baltic,  though  "very  numerous  in  individuals,  are  dwarfish  in  size,  scarcely  even 
attaining  a  third  of  the  average  dimensions  which  they  acquire  in  the  salter  waters  of 
the  ocean." — Principles,  7th  edition,  p.  503. 

f  Pingel,  Proceedings  of  the  Geological  Society  of  London,  vol.  ii.  p.  208. 

J  MM.  Ant.  Niccolini  and  Em.  Campo-Lonze",  as  quoted  by  M.  d'Archiac,  "Histoire 
des  Progres  de  la  Ge"ologie,"  t.  i.  p.  659. 


MOVEMENTS    OF     COASTS     IN    THE    MEDITERRANEAN.     431 

to  a  third  of  its  height,  showing  a  depression  and  subsequent  elevation 
of  the  coast.*  Not  only  are  there  traces  of  terraces  on  the  limestones 
of  Greece,  with  lines  perforated  by  boring  molluscs,  such  as  now  inhabit 
the  adjoining  sea,  but  M.  Boblaye  also  points  out  a  cavern  near  Napoli 
di  Romania,  raised  five  or  six  yards  above  the  level  of  the  Mediterra- 
nean, containing  a  breccia,  the  formation  of  which  he  refers  to  historic 
times,  inasmuch  as  fragments  of  antique  pottery  are  included  in  it.f 
Continuing  researches  of  this  kind  in  the  Mediterranean,  we  find,  on 
the  authority  of  M.  de  la  Marmora,  that  on  the  coast  of  Sardinia  there 
is  a  deposit  now  raised  above  the  sea,  in  which,  mingled  with  terrestrial, 
fluviatile,  and  marine  shells,  are  the  remains  of  ancient  pottery.  The 
bed  is  described  as  sloping  gently  seawards,  so  as  to  represent  part  of 
an  ancient  coast  with  a  portion  of  its  adjoining  sea-bottom.  The  remains 
of  pottery  are  found  where  an  ancient  coast,  inhabited  by  man,  may  be 
supposed  to  have  ranged,  the  marine  shells  of  the  same  species  as  now 
found  in  the  adjoining  sea  becoming  abundant  outwards  where  the  old 
sea-bottom  occurred.  At  about  150  feet  on  the  northwest  of  Cagliari, 
oysters  (Ostrea  edulis),  are  found  adhering  to  the  rock  on  which  they 
grew;  and  M.  de  la  Marmora  discovered,  also  on  the  northwest  of 
Cagliari,  among  the  pottery,  a  round  ball  of  baked  earth,  about  the 
size  of  an  apple,  with  a  hole  in  the  centre,  as  if  to  pass  a  cord  through. 
M.  de  la  Marmora  considers  that  this  ball  may  have  belonged  to  fisher- 
men following  their  calling  on  this  coast,  and  who  used  such  balls  instead 
of  lead  before  the  change  of  level  elevating  the  deposit  to  its  present 
situation.  J 

The  circumstances  above  noticed  will  be  sufficient  to  show  the  ob- 
server, that  movements  of  the  ground,  as  well  gradual  as  somewhat 
more  sudden,  have  taken  place  since  the  localities  mentioned  have  been 
inhabited  by  man,  and  that  there  may  have  been  oscillations  'of  the 
land  in  certain  situations.  These  movements  cannot  be  termed  per- 
manent, in  a  strictly  geological  sense,  since  the  history  of  the  surface  of 
our  planet  is  one  of  change  and  modification,  with  respect  to  the  dis- 
tribution of  land  and  water ;  but  they  may,  for  the  most  part,  be  so 
regarded  with  reference  to  the  lapse  of  many  centuries,  during  which 
man  may  modify  or  change  his  mode  of  existence  on  the  areas  so  acted 
upon.  Whatever  the  cause  of  these  movements  may  be  on  the  great 
scale,  and  however  the  action  which  is  commonly  termed  volcanic,  may 
merely  constitute  a  modification  of  the  effects  due  to  some  general  in- 
fluence by  which  whole  continental  masses  are  upraised  or  depressed 
beneath  the  sea-level,  we  have,  in  earthquakes  and  the  slow  elevation 
and  depression  of  land  now  taking  place,  manifestations  of  the  unstable 
support  on  which  the  present  mineral  surface  of  the  earth  reposes. 

*  "Travels  in  Lycia,  Mylias,  and  the  Cibyratis,"  vol.  ii.  p.  189,  1846. 
|  "Journal  de  Gdologie,"  torn.  iii.  J  Ibid. 


432       SUNK  FORESTS  AND  RAISED  BEACHES. 

That  earthquakes  on  the  large  scale  may  be  due  to  the  rending  of  por- 
tions of  the  earth's  crust  so  acted  upon  that  some  previous  resistance 
to  an  upraising  or  depressing  force  is  suddenly  overcome,  while,  in  the 
gradual  movements  of  elevation  or  depression,  the  resistance  is  quietly 
overpowered,  may  not  be  improbable.  To  the  cause  of  this  unstable 
state  of  the  earth's  surface,  the  observer  will,  no  doubt,  be  induced  to 
inquire  more  particularly  when,  searching  amid  the  various  accumu- 
lations which  he  will  find  recording  the  -past  history  of  our  planet,  he 
sees  proofs  of  elevations  and  depressions  of  old  surfaces  to  which  those 
above  mentioned  are  almost  as  nothing.  It  would  be  out  of  place  here 
to  enter  upon  the  hypotheses  which  have  been  framed  respecting  it ;  at 
the  same  time,  it  may  not  be  undesirable  to  recall  attention  to  the 
results  produced  by  changes  on  the  earth's  surface,  by  which  dry  land 
is  lowered  and  sea-bottoms  raised  higher,  and  which  Mr.  Babbage  has 
pointed  out  when  accounting  (p.  428)  for  the  oscillations  of  the  ground 
on  which  the  Temple  of  Serapis  is  based,  inasmuch  as,  whether  the 
explanation  be  sufficient  or  insufficient  for  all  the  phenomena  observed, 
it  can  scarcely  be  disregarded,  if  we  look  for  any  source  of  heat  beneath 
the  surface  of  the  earth,  either  partial  or  central.* 

Submarine  Forests  and  Raised  Beaches. — These  names  for  compara- 
tively recent  changes  in  the  relative  levels  of  land  and  sea,  since  the  vege- 
tation of  the  former  and  the  animal  life  in  the  latter  have  been  much 
the  same  as  now  found  adjacent  on  the  one  or  in  the  other,  though  not 
perhaps  too  well  chosen,  since  there  have  been  many  depressions  and 
elevations  of  land  marked  by  the  submergence  of  terrestrial  vegetable 
life  and  the  emergence  of  marine  remains  in  beaches  at  various  geologi- 
cal times,  is  here  retained  as  convenient  for  the  present,  and  as  the 
facts  they  represent  appear  to  belong  to  a  period  when,  though  the 

*  Mr.  Babbage  (Proceedings  of  the  Geological  Society  of  London,  February,  1834, 
vol.  ii.  p.  75)  observes,  that  "Whenever  a  sea  or  lake  is  filled  up  by  the  continued 
wearing  down  of  the  adjacent  lands,  new  beds  of  matter,  conducting  heat  much  less 
quickly  than  water  carries  it,  are  formed ;  and  that  the  radiation,  also,  from  the  sur- 
face of  the  new  land,  will  be  different  from  that  from  the  water.  Hence  any  source  of 
heat,  whether  partial  or  central,  which  previously  existed  below  that  sea,  must  heat 
the  strata  underneath  its  bottom,  because  they  are  now  protected  by  a  bad  conductor. 
The  consequence  must  be,  that  they  will  raise,  by  their  expansion,  the  newly  formed 
beds  above  their  former  level,  and  thus  the  bottom  of  an  ocean  may  become  a  conti- 
nent. The  whole  expansion,  however,  resulting  from  the  altered  circumstances,  may 
not  take  place  until  long  after  the  filling  up  of  the  sea,  in  which  case  its  conversion  into 
dry  land  will  result  partly  from  the  filling  up  by  detritus,  and  partly  from  the  rise  of 
the  bottom.  As  the  heat  now  penetrates  the  newly  formed  strata,  a  different  action 
may  take  place;  the  beds  of  clay  or  sand  may  become  consolidated,  and  may  contract 
instead  of  expanding.  In  this  case  either  large  depressions  will  occur  within  the  limits 
of  the  new  continent,  or,  after  another  interval,  the  new  land  may  again  subside,  and 
form  a  shallow  sea.  This  sea  may  be  again  filled  up  by  a  repetition  of  the  same  pro- 
cesses as  before,  and  thus  alternations  of  marine  and  fresh-water  deposits  may  occur, 
having  interposed  between  them  the  productions  of  dry  land." 


SUNK    FORESTS    OF    WESTERN    EUROPE.  433 

traces  of  man  and  his  works  may  not  be  found  in  connexion  with  them, 
they  seem  not  far  removed  from  the  time  of  man.  The  evidence  is  no 
doubt  negative  as  to  the  absence  of  man  from  the  coasts  where  these 
changes  may  have  been  effected,  certain  conditions  being  needed  for 
the  preservation  either  of  his  remains  or  those  of  his  works,  and  cer- 
tainly some  of  the  changes  of  this  kind  may  readily  have  occurred  since 
man  was  created  on  our  planet,  though  no  traces  of  human  existence 
either  in  the  contemporary  accumulations  themselves,  or  in  their  mode 
of  occurrence,  have  been  detected.  While  alterations  in  the  relative 
levels  of  land  and  sea  have  occurred  in  countries  long  inhabited  by 
civilized  races,  and  are  now  being  effected  where  sufficient  interest  is 
taken  to  record  them,  it  is  scarcely  to  be  supposed  that  the  like  have 
not  taken  place  in  regions  inhabited  by  man  in  a  less  advanced  state, 
the  more  especially  as  the  study  of  geology  teaches  us  that  such,  as 
will  be  hereafter  seen,  have  occurred  during  a  long  lapse  of  geological 
time. 

It  can  rarely  happen  that,  without  some  historic  record  of  the  event, 
the  submergence  of  a  coast  to  any  marked  depth  can  be  well  ascertained. 
The  water,  except  under  very  rare  and  favourable  circumstances,  would 
remove  the  traces  of  the  old  coast  lines  from  our  view,  and  new  accu- 
mulations, mechanical  or  chemical,  would  tend  still  further  to  conceal 
them.  .  As  regards  the  evidence  of  a  submergence  of  the  shores  of 
Europe  for  a  considerable  extent  on  its  western  and  oceanic  front,  we 
fortunately  possess  good  evidence  in  those  trees  and  accumulations  of 
other  plants  around  them,  which  have  been  termed  Submarine  Forests. 
These  are  to  be  found  under  the  same  general  conditions,  from  the  shores 
of  Scandinavia  to  those  of  Spain  and  Portugal,  and  around  the  British 
Islands.  So  common  to  the  whole  are  their  general  characters,  that 
without  supposing  an  absolute  contemporaneous  submergence,  or  one  of 
equal  amount  throughout,  there  still  remains  a  change  of  the  relative 
level  of  sea  and  land  of  a  marked  kind  over  the  whole  of  this  area. 
These  "forests"  sometimes  occur-  on  the  seaward  front  of  a  minor 
valley,  and  of  others  of  far  larger  dimensions,  even  beneath  the  accu- 
mulations of  a  considerable  estuary,  and  are  found  stretching  inland  for 
considerable  distances  under  deposits  of  gravels,  sands,  and  clays,  the 
latter  sometimes  slightly  elevated  above  the  sea,  and  occupying  some- 
what large  tracts  of  country. 

The  slopes  on  which  the  "forests"  rest  are  variable,  though  usually 
dipping  seaward  at  a  very  slight  angle.  If  the  observer  will  imagine, 
that  during  low  water,  on  any  tidal  coast,  a  change  of  relative  level  of 
land  and  sea  were  effected,  so  that  the  low  water  line  became  that  of 
high  water,  he  may  form  a  good  idea  of  the  varied  slopes  and  different 
areas  on  which  the  trees  and  other  plants  may  have  grown,  and  which, 
now  partially  or  wholly  submerged,  constitute  "  submarine  forests." 

28 


434  MODE    OF    OCCURRENCE    OF    SUNK    FORESTS. 

While  they  are. often  wholly  beneath  the  level  of  high  water,  at  others 
they  are  partly  beneath  it,  and  partly  rise  to,  or  above  it.  The  follow- 
ing section  (fig.  151)  will  illustrate  the  mode  of  occurrence  of  several, 
where,  after  a  submergence,  other  accumulations  have  been  effected 
over  a  portion,  if  not  the  whole  ;  and  so  that  while  a  part  may  be  laid 
bare  by  the  action  of  the  breakers,  others  may  be  concealed  seaward 
beneath  the  water,  or  be  covered  by  gravels,  sands,  or  clays  inland. 

Fig.  151. 


Let  «,  5,  represent  the  level  of  high  water,  and  c,  d,  that  of  low  tide, 
€,/,  a  line  marking  the  general  plane  of  the  "  submarine  forest,"  g,  a 
beach  thrown  up  in  the  usual  manner,  and  A,  sand,  'clay,  or  any  other 
accumulation  covering  up  the  "forest;"  then  it  usually  happens,  espe- 
cially after  such  a  state  of  the  tides  and  weather  as  shall  remove  a  part 
of  the  beach,  that  the  trees  and  other  vegetation  are  alone  visible  on 
the  shore  at  levels  corresponding  with  those  at  which  the  tide  may  cut 
the  general  plane  of  the  "  forest."  The  extension  of  the  trees  and 
other  vegetation  seaward  may  never  be  known  except  in  the  case  of  a 
roadstead  for  shipping,  such  as  at  the  Mumbles,  near  Swansea,  or  on 
fishing-grounds,  where  the  anchors  or  nets  may  bring  up  portions  of 
them.  In  like  manner  inland  their  spread  in  such  directions  may  only 
be  made  apparent  by  canals,  docks,  or  other  works  cutting  through  the 
superincumbent  accumulations,  as  has  been  done  in  many  localities. 

Although  this  movement  over  so  considerable  an  area  may  not  always 
have  been  tranquil,  the  very  common  state  of  the  vegetation  preserved 
would  lead  to  the  inference  that  it  had  very  frequently  been  so ;  for,  as 
in  the  following  section  (fig.  152),  the  trees  a,  a,  a,  a,  a,  are  in  their 

Fig.  152. 


J^fc^^ 

jf-^rj-.Sj?,-:.^ ', J ->^->r: ^o7.;  .7  T^/'~'^ *"£& ^A.v^X^/Si^^-      "   * 

^  i        — ••-. ,  ••  — a    i -f=s*-.-'    .   ' " — '     '  ___ •• — ^^wdC.... 


actual  places  of  growth,  though  prostrate  trees,  £,  may  be  often  found 
among  them,  and  the  matted  remains  of  branches,  leaves,  and  various 
plants,  as  well  as  certain  animal  remains,  such  as  the  horns  of  deer  and 


LOCALITIES    OF    SUNK    FORESTS.  435 

oxen,  c,  c,  intermingled  with  the  roots  or  accumulated  round  them,  and 
constituting  part  of  the  old  ground,  d,  d,  are  undisturbed.  For  further 
illustration  the  supporting  rocks,  e,  e,  which  may  be,  and  are  of  all 
kinds,  as  also  some  covering  beds,  /,  /,  supposed  inland,  are  also  repre- 
sented. 

When  an  observer  is  studying  any  of  the  numerous  situations  where 
these  "  forests"  are  to  be  seen,  it  will  be  desirable  that  he  should  do  so 
with  reference  to  the  locality,  and  its  connexion  with  any  larger  area  ; 
to  the  mode  of  growth  of  the  .trees,  and  distribution  of  the  other  remains 
of  vegetation  mingled  with  them,  and  their  agreement  with,  or  diffe- 
rence from,  any  plants  of  a  similar  kind  now  found  in  the  vicinity, 
whether  as  regards  kind  or  mode  of  accumulation ;  to  the  remains  of 
animals  found  intermingled  with  the  vegetation,  and  to  the  probable 
form  of  the  area  occupied  by  the  "forest,"  as  well  inland  as  seaward. 
Various  nooks  and  corners  of  oceanic  bays,  where  we  may  suppose 
vegetation  could  have  flourished  under  differences  of  level,  so  that  more 
dry  land  was  exposed,  should  be  examined  as  well  as  very  sheltered 
situations  in  places  less  open  to  the  ravages  of  the  sea.  Thus  a  part  of 
the  coast  of  Tiree,*  Hebrides,  and  of  another  in  the  Bay  of  Skail],f 
Mainland  of  Orkney,  though  both  exposed  to  the  ocean,  furnish  the 
remains  of  these  "forests"  as  well  as  the  ramifications  of  old  estuaries 
amid  the  shores  of  the  British  Channel  and  Severn,!  and  the  low 
grounds  of  Lincolnshire  and  Cambridgeshire,  now  bounded  on  the 
eastern  coast  of  England  by  "  the  Wash."§  As  regards  the  tideless 
Baltic,  trunks  of  oaks  and  pines  (Pinus  sylvestris)  and  other  trees, 
the  roots  in  their  natural  positions,  often  several  times  above  each 
other,  and  the  whole  five  feet  beneath  the  level  of  that  sea,  are  found 
on  different  points  of  the  coast  near  Greifswald,  near  Gnageland, 

*  The  Rev.  C.  Smith,  "  Edinburgh  New  Philosophical  Journal,"  1829. 

|  Watt,  "Edinburgh  Philosophical  Journal,"  vol.  iii.  Stems  of  small  fir  trees,  ten 
feet  long  and  five  or  six  inches  in  diameter,  were  here  found  partly  imbedded  in  and 
partly  resting  on  the  vegetable  matter,  chiefly  composed  of  leaves. 

J  The  "forest"  passes  beneath  a  considerable  portion  of  the  flat  low  land  commonly 
known  as  the  Bridgewater  Levels,  and  it  is  to  be  found  in  numerous  other  portions  of 
the  old  area  of  the  estuary.  The  part  exposed  on  the  coast  of  Stolford  has  been 
described  by  Mr.  L.  Homer  (Geological  Transactions,  vol.  iii.  p.  380),  who  pointed  out 
that  many  of  the  remains  of  trees  were  rooted  as  they  grew,  while  others  were  pros- 
trate, some  20  feet  in  length.  Remains  of  the  Zostera  oceanica  were  dispersed  amid  the 
vegetable  matter  in  which  the  trees  occur.  Dr.  Buckland  and  Mr.  W.  D.  Conybeare 
(Geol.  Trans.,  2d  series,  vol.  i.  p.  310)  mention  oak,  fir,  and  willow  trees,  sometimes 
of  large  dimensions,  partly  rooted  as  they  grew  and  partly  prostrate,  15  to  20  feet 
beneath  the  surface  of  the  Bridgewater  Levels.  Furze  bushes  and  hazel  trees  with  their 
nuts  are  intermingled  with  them. 

\  The  vegetable  accumulations  of  this  kind  have  long  been  known  in  Lincolnshire 
and  Cambridgeshire.  In  1799,  M.  Correa  de  Serra  described  (Philosophical  Transac- 
tions) the  "  submarine  forest"  of  Lincolnshire  as  composed  of  roots,  trunks,  branches, 
and  leaves  of  trees  and  shrubs,  intermixed  with  aquatic  plants,  many  of  the  roots  still 
standing  in  the  position  in  which  they  grew,  while  the  trunks  were  laid  prostrate. 
Birch,  fir,  and  oak  were  distinguishable. 


436       REMAINS    OF    MAMMALS    AND    INSECTS    AMID    THE 

on  the  southeast  side  of  the  Haff,  in  the  Island  of  Usedom,  and  in  the 
vicinity  of  Colberg.  They  are  separated  from  the  sea  for  variable 
breadths  of  coast  by  sandy  dunes,  under  which  they  do  not  extend, 
there  gradually  disappearing.  In  the  vegetable  mass  accompanying 
the  trees,  terrestrial,  marsh,  and  fresh-water  plants,  with  their  seeds, 
are  alone  discovered,  remains  of  marine  vegetation  not  being  found.* 

Occasionally  the  bones  of  quadrupeds,  and  the  traces  of  their  foot- 
prints, are  discovered  in  these  "  forests,"  as  also  the  remains  of  insects, 
which  are  important  as  enabling  the  observer  to  consider  the  distribu- 
tion of  the  terrestrial  animal  life  as  well  as  that  of  the  plants  of  the 
time.  Thus,  among  the  vegetable  accumulations  apparently  of  this 
date  on  the  banks  of  the  Humber,  remains  of  the  red  deer  (Cervus 
JElephas)  and  the  fallow  deer  (C.  Dama)  have  been  detected ;  and  in 
the  "submarine  forest"  of  Minehead,  Somersetshire,  the  bones  and 
antlers  of  the  red  deer  are  discovered  amid  the  upright  stumps  of  trees 
(chiefly  oaks)  now  below  the  level  of  the  sea  and  covered  by  it  at  high 
water,  the  trees  rooted  as  they  grew.  The  latter  is  especially  an  inte- 
resting circumstance,  as  the  red  deer  are  still  found  wild  in  the  adjoin- 
ing forest  of  Exmoor,  so  that  the  change  of  level  has  been  effected 
since  the  red  deer  inhabited  the  district.  Extending  our  researches 
into  Cornwall,  we  find  that  a  change  of  level  may  have  happened,  sub- 
merging vegetation  in  its  place  of  growth,  even  after  the  introduction 
of  man  into  Western  England ;  for,  at  the  Carnon  tin  stream-works, 
north  of  Falmouth,  whence  pebbles  of  tin  ore  have  been  extracted  from 
beneath  the  bottom  of  an  estuary,  human  skulls  are  stated  to  have  been 
discovered  with  the  bones  of  deer,  among  the  trees  and  other  vegetable 
remains  covering  the  stanniferous  gravel.  Trees,  partly  in  their  places 
of  growth,  their  roots  descending  among  the  tin  pebbles,  have  been 
found  48  feet  below  high-water  mark  at  the  Pentuan  tin  stream-works, 
Cornwall,  covered  by  estuary  and  fluviatile  accumulations,  and  which 
may  be  the  equivalent  of  the  Carnon  bed,f  not  far  different  in  depth 

*  German  translation  of  De  la  Beche's  Geological  Manual.  "  In  some  places  the 
Arundo  phragmites  so  abounds  that  the  peaty  mass  seems  entirely  composed  of  it.  The 
lower  layers  contain  Ccratophyllum  dcmersum,  Potamogeton  pusillum^  Najas  major,  and 
Nymphcea  lutea.  Scirpus  palustris  and  Hippuris  vulgaris  are  also  found  -with  the  Arumlo. 
Seeds,  especially  of  the  Menyanthes  trifoliata,  are  also  frequent  in  the  lower  layers.  The 
ground  beneath  the  peat  contains  fresh-water  shells ;  Paludina  impura,  Lam.,  Planorlis 
imlricatus,  Cyclostoma  acutum,  and  Limncus  vulgaris" 

f  The  section  showed  a  bed,  about  18  inches  thick,  of  wood,  leaves,  nuts,  &c.,  beneath 
about  50  feet  of  silts  and  sands,  with  shells,  the  vegetable  accumulation,  with  its 
human  skulls  and  remains  of  deer,  resting  on  the  pebbles  of  tin  ore,  and  of  quartz, 
slate,  granite,  &c.,  commonly  termed  the  tin  ground.— Kenwood,  "Trans.  Geol.  Soc.  of 
Cornwall,"  vol.  iv.  p.  68. 

At  the  Pentuan  tin  stream-works,  where  mining  operations  were  continued  under  the 
sea-level  for  the  extraction  of  the  tin-ore  pebbles,  the  vegetable  accumulation,  the 
roots  of  trees  passing  down  to  the  "  tin  ground,"  was  (at  the  Happy  Union  Works)  about 
30  feet  below  the  level  of  low  water,  and  48  feet  beneath  that  of  high-water  spring 


SUNK    FORESTS    OF    SOUTHWESTERN    ENGLAND.         437 

beneath  the  same  level.  Whatever  may  have  been  the  relative  date 
when  the  skulls  were  entombed,  supposing  the  Carnon  accumulation  in 
which  they  were  discovered  not  to  be  precisely  equivalent  to  the  "  sub- 
marine forest"  disclosed  by  the  mining  operations  at  Pentuan,  it  would 
still  appear,  as  we  have  elsewhere  remarked,*  "  that  after  the  causes 
which  produced  the  tin  ground  or  stanniferous  gravel  (of  Cornwall)  had 
ceased,  the  relative  levels  of  sea  and  land  were  such  in  this  district  that 
a  growth  of  plants  and  trees,  not  dissimilar  from  that  of  the  present 
day,  took  place  upon  the  gravel,  and  that  subsequently  these  levels 
became  altered,  so  that  the  sea  covered  the  lower  parts  of  the  valleys 
previously  above  water.  In  the  creeks  thus  formed,  silt,  mud,  and  sand 
were  deposited,  entombing  the  remains  of  marine  and  estuary  shells  of 
the  same  species  as  those  which  now  exist  on  the  coast,  and  finally, 
from  the  continued  drift  of  alluvial  matter  down  the  valleys,  river 
detritus  covered  up  these  marine  or  estuary  deposits  when  they  had 
accumulated  to  the  necessary  height." 

As  regards  the  British  "submarine  forests,"  they  not  only  show  that 
red  and  fallow  deer,  species  now  living,  roamed  among  them  when  they 
were  above  water  and  in  full  growth,  and  possibly  that  man  may  have 
been  an  inhabitant  of  Western  England  at  the  time,  but  also  that  they 
were  tenanted  by  species  of  at  least  one  large  quadruped  which  is  now 
extinct.  Of  this  evidence  has  been  obtained  in  the  "  submarine  forests" 
on  the  coasts  of  South  Wales.  Among  other  places  where  they  are 
found  on  the  shores  in  that  district,  there  is  a  considerable  tract  of  low 

tides.  The  trees  had  been  submerged  so  that  oyster-shells  were  found  attached  to  their 
stumps.  "  The  roots  of  the  oak  are  in  their  natural  position,"  observes  Mr.  Colenso, 
"and  may  be  traced  to  their  smallest  fibres  (in  the  tin  ground)  even  so  deep  as  two 
feet ;  from  the  manner  in  which  they  spread,  there  can  be  no  doubt  that  the  trees  have 
grown  and  fallen  on  the  spot  where  their  roots  are  found."  Resting  upon  this  accu- 
mulation is  a  bed  of  silt,  about  two  feet  thick,  in  which  there  are  also  wood  and  hazel- 
nuts,  and  with  these  vegetable  remains  the  bones  and  horns  of  deer,  oxen,  &c.  Mr. 
Colenso  further  states,  that  the  shells  dispersed  through  this  bed,  commonly  in  layers, 
present  the  appearance  of  their  animals  having  lived  and  died  on  the  places  where 
their  remains  are  now  discovered.  Above  this  accumulation  follow  in  ascending  order ; 
— a,  a  bed  of  sand,  four  inches  thick,  containing  marine  shells ;  b,  silt  or  clay,  two 
feet  thick;  e,  sand,  20  feet  thick  ("in  all  parts  of  this  sand  there  are  timber  trees, 
chiefly  oaks,  lying  in  all  directions,  and  also  the  remains  of  animals,  such  as  parts  of 
red  deer,  &c.  Human  skulls  have  also  been  found  in  it,  as  also  those  of  whales") ;  <?, 
a  bed  of  rough  river  sand  and  gravel,  here  and  there  mixed  with  sea  sand  and  silt, 
about  20  feet  thick,  extending  to  the  surface.  Mr.  Colenso  states,  that  a  short  time 
before  he  described  the  section  (1829),  the  remains  of  a  row  of  wooden  piles  had  been 
found  in  this  sand,  sharpened  for  the  purpose  of  driving,  and  that  they  appeared  to 
have  been  used  in  the  construction  of  a  wooden  bridge  for  foot  passengers.  They 
crossed  the  valley,  and  were  about  six  feet  long,  their  tops  being  about  24  feet  from 
the  present  surface,  just  on  a  level  with  the  present  low  water  at  spring  tides.  He 
remarks,  that  if  the  relative  sea  level  had  been  then  as  now,  such  a  bridge  would  have 
been  useless. 

*  "Report  on  the  Geology  of  Cornwall,  Devon,  and  West  Somerset,"  p.  406  (1839). 


438          FOOT-PRINTS    OF    DEER    AND    OXEN    AMID    THE 

ground  extending  from  the  mouth  of  the  Neath  River  eastward  beyond 
Port  Talbot,  fringed  by  a  covering  of  blown  sand-hills.  Beneath  these 
and  the  low  ground,  natural  and  artificial  operations  have  occasionally 
exposed  the  vegetable  accumulation,  the  stumps  of  trees  with  their 
roots  standing  as  they  grew,  with  prostrate  trunks,  and  the  usual  cha- 
racteristics of  the  "forest."  On  the  surface  of  the  clay  in  which  the 
trees  are  rooted,  foot-prints  have  been  here  and  there  detected,  as  if  in 
passages  amid  the  trees  by  which  animals  found  their  way  through 
them,  these  foot-prints  of  various  forms  and  sizes,  some  clearly  those  of 
deer,  while  now  and  then  a  large  impression  would  be  observed  resem- 
bling that  of  some  gigantic  ox,  having  feet  spreading  far  more  widely 
than  any  domestic  ox,  even  of  the  largest  size,  now  known.  This  is 
not  an  isolated  fact,  for  more  westward  (about  28  miles),  while  docks 
were  being  constructed  at  the  port  of  Pembre,  Caermarthenshire,  and 
some  covering  sands  removed,  the  "submarine  forest,"  which  there 
occurs  beneath  much  of  the  estuary  of  the  Burry  and  Llwchwr  was 
exposed,  and  similar  foot-prints  were  found,  some  of  a  great  ox  mingled 
with  those  of  the  deer.  Having  attracted  attention,  drawings  of  these 
impressions  were  made  at  the  time.  As  the  horns  and  skull  of  the  Bos 
primigenius  were  discovered  near  the  same  place,  apparently  derived 
from  the  same  beds,  it  may  be  that ,  the  foot-prints  mentioned  might 
have  been  those  of  this  large  animal. 

We  would  thus  seem  to  arrive  at  a  period  for  the  growth  of  these 
"  forests"  in  England,  when  not  only  species  of  existing -British  animals 
then  wandered  among  them,  but  also  one,  if  not  more,  of  the  now  extinct 
mammals,*  leading  into  the  times  when  elephants,  hyaenas,  and  other 
extinct  quadrupeds  also  tenanted  this  country.  Indeed,  when  contem- 
plating from  any  of  the  adjacent  heights  the  range  of  country  which 
includes  the  estuary  of  the  Burry  and  Llwchwr,  with  its  "  submarine 
forest,"  and  also  one  of  the  limestone  caves  of  that  part  of  the  country, 
wherein  the  remains  of  hyaenas,  rhinoceroses,  and  other  animals  are 
found,  the  cave's  mouth  fronting,  and  not  far  above  the  range  and  level 
of  the  "forest,"  an  observer  has  some  difficulty  in  very  clearly  sepa- 
rating the  time  when  the  forest  grew  and  the  red  deer  of  the  present 
time,  the  great  extinct  ox,  and  the  rhinoceros  may  have  ceased  to  be 
contemporaneous,  anterior  to  the  submergence  of  the  land  beneath  the 
level  of  the  adjoining  ocean,  in  such  a  manner  that  not  only  the  stumps 
of  trees  remained  rooted  in  the  ground  in  which  they  grew,  but  the 
foot-prints  of  mammals  which  roamed  amid  the  forest  of  this  period 

*  It  becomes  interesting,  as  connected  with  the  subject,  to  ascertain  how  far  any  of 
the  localities  where  the  antlers  and  bones  of  the  Megaccros  Ilibernicus  are  found  may  be 
connected  with  the  tracts  of  "  submarine  forests."  The  general  evidence  respecting 
this  gigantic  and  extinct  deer  would  appear  to  be,  that  its  remains  are  discovered  in 
fresh-water  shell  marls  or  gravels  beneath  existing  bogs. 


ROOTED    TREES    OF    SUNK    FORESTS    IN    SOUTH    WALES.     439 

also  remained  uninjured  during  the  time  when  they  "were  covered  over 
by  silt  and  sand. 

While  thus  there  is  evidence  of  a  change  in  the  relative  levels  of  sea 
and  land,  by  which  the  latter  has  been  lowered  several  feet  beneath  the 
former  along  the  oceanic  shores  of  Europe  for  about  20°  of  latitude, 
there  is  also  evidence  of  changes  of  levels  on  the  same  coasts  of  the 
reverse  kind,  beaches  and  worn  cliffs  affording  proofs  of  them,  and  the 
remains  df  molluscs  showing  that  such  changes  occurred  after  these 
were  of  the  same  species  as  those  which  now  inhabit  the  adjoining  seas. 
Reference  has  been  previously  made  (p.  282,  &c.)  to  the  mollusc  re- 
mains of  existing  species  found  entombed  in  deposits,  of  the  inferred 
comparatively  recent  and  very  cold  condition  of  Northern  Europe ;  a 
time  when  molluscs  of  an  Arctic  character  reached  more  southwards 
than  at  present.  Still  referring  to  the  same  period,  and  to  the  evidence 
pointing  to  a  submergence  and  emergence  of  the  lands  of  the  British 
Islands  to  the  amount  of  1000  to  1500  feet,  and  probably  also  of  much 
of  Western  Europe  to  variable  depths  and  heights,  many  tracts  of  old 
coasts  and  beaches  would  be  expected,  their  greater  or  less  state  of 
preservation  depending  upon  local  circumstances  as  well  as  on  the  more 
general  influences  of  different  climates.  Amid  the  varied  cliffs  and 
beaches  left  by  so  considerable  an  emergence,  if  we  are  to  suppose  it 
slow,  intervals  of  comparative  stability  intervening,  the  observer  would 
anticipate  much  difference  of  level  in  the  cliffs  and  beaches  he  may  dis- 
cover, expecting,  nevertheless,  all  other  circumstances  being  the  same, 
that  the  cliffs  and  beaches  would  be  the  less  injured  in  proportion  as 
they  were  the  more  recent. 

The  coasts  of  Europe  present  many  examples  of  cliffs  and  beaches 
elevated  above  the  present  level  of  the  adjoining  seas,  the  beaches 
containing  fragments  of  the  shells  of  molluscs  still  inhabiting  the  latter. 
The  coasts  of  the  British  Islands,  from  their  position,  and  the  variable 
conditions  under  which  they  occur  relatively  to  exposure  or  comparative 
shelter  from  the  Atlantic,  and  the  variable  rise  and  fall  of  tides,  afford 
excellent  opportunities  for  the  study  of  these  cliffs  and  beaches.  And 
with  respect  to  the  consideration  of  such  changes  of  level,  the  observer 
should  bear  in  mind  the  alterations  that  may  b,e  effected  by  the  conver- 
sion of  an  estuary,  facing  the  tidal  wave  coming  in  from  the  Atlantic 
or  any  other  ocean,  into  a  more  spread  area  of  water  by  submergence 
of  the  land,  and  by  converting  the  latter  into  the  former  by  an  emer- 
gence, the  wearing  away  of  cliffs  or  the  accumulation  of  beaches  con- 
tinuing up  to  high-water  mark.  For  example,  if  the  land  of  New 
Brunswick  and  Nova  Scotia  were  depressed  beneath  the  ocean  (and  no 
very  considerable  submergence  would  be  required),  so  that  the  tidal 
wave  flowed  freely  over  from  the  present  Bay  of  Fundy  to  the  Gulf  of 
St.  Lawrence,  there  would  be  an  end  of  the  causes  (p.  103)  producing 


440  RAISED    BEACHES    CONCEALED    BY    DETRITUS. 

the  very  high  rise  of  tide  in  that  bay,  and,  consequently,  its  plane  of 
lines  of  cliffs  and  beaches.  The  same  would  also  happen,  though  on  a 
minor  scale,  if  the  land  bounding  the  Bristol  Channel,  and  its  continua- 
tion, the  Severn,  was  so  depressed  beneath  its  present  relative  level, 
that  the  great  rise  of  tide  (46  to  50  feet)  at  King's  Road  (Bristol)  and 
Chepstow  was  no  longer  produced,  the  tidal  wave  sweeping  onwards 
without  much  obstruction,  and  passing  round  on  the  north  and  south  of 
Wales,  then  becoming  an  island.  In  such  cases  the  inclined  plane  cor- 
responding to  the  high-water  mark  would  be  depressed  at  different 
depths  beneath  the  general  level.  In  like  manner  the  observer  should 
well  weigh  the  changes  and  modifications  by  which  similar  estuaries  or 
bays  during  emergence  from  the  sea  may  have  such  tides  produced  in 
them  as  are  now  found,  so  that  after  having  cliffs  worn  out,  or  beaches 
thrown  up  at  some  more  equal  level,  these  more  inclined  planes  of  the 
one  or  the  other  may  be  formed.  The  modifications  of  the  relative 
heights  at  which  cliffs  and  beaches  may  be  contemporaneously  formed 
on  all  tidal  coasts,  according  to  the  general  level  of  land  and  sea  for 
the  time,  require  very  great  care,  as  also  the  probable  conversion  of 
tidal  into  tideless  seas,  and  the  reverse,  tideless  seas  (employing  that 
term  with  reference  to  tides  capable  of  producing  very  appreciable  geo- 
logical effects,  and  not  strictly)  affording  as  a  whole  (due  reference 
being  made  to  the  disturbing  influences  of  winds)  a  better  general  level 
than  the  high-water  line  on  coasts  variably  affected  by  the  action  of 
tides  upon  them.* 

From  the  effects,  chiefly  of  atmospheric  influences,  by  which  the  sides 
of  hills  and  mountains  are  decomposed,  and  the  disintegrated  portions 
descend  downwards  into  the  valleys  and  low  grounds,  as  in  the  following 
section  (fig.  153),  where  certain  rocks,  6,  £>,  slates,  for  example,  decom- 

*  It  is  much  to  be  desired,  that  the  governments  of  different  countries  having  sea- 
coasts  would,  at  convenient  points,  ascertain  the  level  of  mean  tides  (not  a  difficult 
operation),  connecting  the  spots  where  this  may  be  accomplished,  as  marks  on  the 
coast  itself  at  the  actual  level  found  may  be  in  time  obliterated  from  the  action  of  the 
sea  or  atmospheric  influences,  with  copper  bolts,  or  other  bench-marks  in,  or  on  some 
inland  cliff,  religious  edifice,  or  other  building  likely  to  be  preserved.  By  connecting 
such  original  bench-marks,  and  also  others  inland,  by  a  carefully  considered  system  of 
levels,  not  only  might  any  variations  in  the  relative  levels  of  sea  and  land  be  hereafter 
detected,  but  also  movements  of  the  like  kind  on  the  great,  though  tranquil  scale,  bo 
ascertained  inland,  the  means  of  obtaining  the  needful  evidence  even  extending  con- 
siderable distances  into  the  great  continents.  With  this  view  the  British  Association 
for  the  Advancement  of  Science  had  lines  of  level  run,  in  1837-8,  uniting  bench-marks 
connected  with  the  tides  in  the  English  Channel  at  Axmouth,  Devon,  and  in  the  Bristol 
Channel,  at  Porteshead,  near  Bristol,  and  at  Minehead.  The  careful  levels  worked  out 
during  the  progress  of  the  Ordnance  Survey  in  the  British  Islands  permit  excellent 
connexions  with  the  level  of  mean  tides  around.  If  the  various  European  governments 
possessing  sea-coasts  were  to  establish  proper  tide-marks,  and  form  connexions  by 
levelling  between  them,  the  relative  levels  of  sea  and  land  in  Europe  could  be  so  ascer- 
tained that  any  changes  in  it  could  readily  be  detected. 


RAISED    BEACHES    AT    PLYMOUTH. 


441 


posed  on  the  surface  of  the  hills,  a,  a,  are  more  or  less  covered  by  this 
detritus,  accumulating  in  depressions,  such  as  the  valley  c,  many  a  cliff 


Fig.  153. 


and  beach  is  covered  up,  so  that  inland  the  opportunities  are  less  fre- 
quent usually  for  observing  them  than  near  the  sea,  where  a  coast  may 
be  so  cut  back  by  breakers  as  to  exhibit  the  beach  and  cliff  beneath  this 
kind  of  covering.  Let,  for  illustration,  the  following  section  (fig.  154), 


Fig.  154. 


one  which  is  not  uncommon  in  Western  England,  represent  a  raised  beach, 
concealed  by  a  covering,  a,  a,  composed  of  decomposed  rock  and  other 
detritus,  descending  from  an  adjoining  hill ;  e,  /,  being  the  level  of  high 
tide.  Should  there  be  a  heavy  modern  beach  at  e,  so  that  the  breakers 
have  little  access  to  the  lower  part  of  the  modern  detritus,  a,  a,  even 
the  subjacent  rock  may  be  covered  at  that  point,  b;  but  should  the 
breakers  act  freely,  so  as  to  cut  back  a  cliff,  then  neither  the  first 
distance,  1,  1,  nor  the  second,  2,  2,  would  expose  the  concealed  beach, 
the  latter  only  showing  the  subjacent  rock  at  b.  When,  however,  the 
cutting  back  had  reached  the  distance,  3,  3,  the  beach  may  be  well 
exposed ;  but  should  the  breaker  action  still  further  wear  away  the  cliff 
to  4,  4,  then  no  trace  of  the  beach  would  be  left.  The  subjoined  section 
(fig.  155)  of  the  Hoe,  Plymouth,  may  serve  to  show  how  this  can  really 

Fig.  155. 


happen.  In  it,  d,  d,  represent  the  Devonian  limestones  of  the  locality, 
on  a  part  of  which  the  beach,  <?,  reposes,  about  30  feet  above  the  present 
high-water  mark,  containing  the  remains  of  shells  of  the  same  species  as 
are  now  found  in  the  adjoining  sea.  At  «,  this  is  covered  by  angular 
fragments  of  the  limestone  of  the  hill,  derived  from  the  decomposition 
of  its  upper  part,  of  the  same  kind  which  fills  up  a  cavity  above  at  a'. 
At/,  the  old  cliff  is  seen  behind  the  beach,  c.  This  section  was  exposed 


442 


RAISED    BEACHES    NEAR    FALMOUTII. 


by  blasting  away  the  limestone   rock,  taken  away  for  use  in  large 
quantities.* 

The  following  section  of  part  of  the  Cornish  coast  near  Falmouth 
affords  a  useful  illustration  of  the  manner  in  which  a  raised  beach  may 
be  covered  by  the  detritus  falling  over  from  the  hill  above  ;  in  this  case 
over  the  face  of  an  ancient  cliff,  which  would  be  concealed  except  from 
the  wearing  away  of  the  coast  by  the  breakers.  The  section  is  exposed 

Fig.  156. 


between  Rosemullion  Head  and  Mainporth,  and  the  angular  detritus,  c, 
of  slate  and  more  arenaceous  beds,  clearly  derived  from  the  hill,  A,  is 
well  seen  to  cover  over  the  cliff,  5,  and  the  beach,  a ;  in  all  respects 
corresponding  with  those  in  the  adjacent  coves  and  bays.  In  this  section, 
the  observer  also  finds  a  low  level  of  rocks,  e  a,  formed  at  the  time  when 
the  breakers,  at  another  relative  level,  were  cutting  back  the  ancient 
cliff,  b,  as  similar  planed  portions  of  rocks  are  being  now  cut  back  on 
the  same  coasts  at  a  lower  level.  Not  far  distant  also,  on  the  same 
coast,  at  a  place  named  Nelly's  Cove,  the  subjoined  section  is  exposed, 

Fig.  157. 


wherein  a,  is  the  raised  beach,  5,  the  supporting  rock,  and  c  the  angular 
deposit  derived  from  the  rocks  above,  and  which,  as  it  accumulated,  slid 
into  a  form  corresponding  with  that  of  the  beach  beneath,  and  the  old 

*  The  section  is  given  as  seen  in  1830.  The  raised  beach  was  composed  of  pebbles  of 
limestone,  slate,  reddish  porphyry  (occurring  in  places  in  another  part  of  Plymouth 
Sound),  and  red  sandstones,  all  rocks  of  the  vicinity.  Beneath  the  Plymouth  Citadel, 
where  a  sandy  prolongation  of  this  raised  beach  occurs,  it  is  chiefly  formed  of  fragments 
of  molluscs,  of  the  same  kinds  apparently  as  those  in  the  Sound  adjoining.  Other  raised 
beaches  are  seen  on  the  coasts  of  Plymouth  Sound,  as  under  Mount  Edgecumbe,  at 
Staddon  Point,  and  nearly  opposite  the  Shag  Hock,  on  the  eastern  side,  angular 
detritus  of  the  adjacent  hills  covering  them  all. 


K  A  IS  ED  BEACH  AT  NEW  QUAY,  CORNWALL. 


443 


cliff  behind,  the  covering  detritus,  the  beach,  and  the  supporting  rocks 
being  all  now  in  the  process  of  being  cut  back  by  the  heavy  breakers  of 
the  adjacent  sea,  which  in  time  will  obliterate  all  traces  of  the  beach, 
its  covering,  and  the  old  cliff,  leaving  nothing  but  a  bare  wall  of  the 
rocks  now  behind  the  whole. 

When  formed  of  calcareous  substances,  either  limestone  pebbles  of 
various  sizes,  or  of  comminuted  sea-shells,  raised  beaches  are  sometimes 
as  highly  consolidated  as  the  rocks  which  may  support  them,  carbonate 
of  lime  thrown  down  under  fitting  conditions  from  a  solution  in  water 
of  the  bicarbonate  by  means  of  carbonic  acid  (p.  44)  cementing  the 
whole  together.  Of  the  consolidation  of  a  raised  beach  formed  chiefly 
of  comminuted  sea-shells,  that  at  New  Quay,  on  the  north  coast  of 
Cornwall,  has  long  been  celebrated.  The  following  (fig.  158)  is  a  section 

Fig.  158. 


seen  on  the  Lookout  Hill,  a,  a,  a,  being  slaty  and  arenaceous  beds 
(dipping  at  a  considerable  angle)  upon  which  the  beach,  5,  composed  of 
rounded  pebbles  of  the  adjacent  rocks,  cemented  by  consolidated  sea- 
shell  sand,  reposes.  At  c  are  layers  of  the  same  comminuted  sea-shell 
sand,  not  uncommop.  on  the  shores  and  blown  sandy  dunes  of  the  neigh- 
bouring parts  of  Cornwall,  the  lowest  layers  being  much  consolidated,* 
and  being  covered  at  d  by  an  accumulation  of  angular  fragments  of 
rocks  derived  from  the  hill  above.  The  present  level  of  high  tide  is 
shown  by  the  line  e,  e.  In  this  case  there  would  appear  to  have  been 
some  modification  in  the  condition  of  this  part  of  the  coast,  permitting 
the  deposit  of  the  layers  of  comminuted  sea-shells  after  the  time  during 
which  a  shingle  beach  was  formed,  and  prior  to  the  accumulation  of  the 
covering  of  angular  fragments ;  perhaps,  a  time  when  blown  sands  were 

*  The  consolidation  of  these  sands  is  such  that  they  have  been  long  employed  as  build- 
ing stones  in  the  adjoining  country.  Much  of  it  has  been  used  in  Crantock  Church, 
near  New  Quay,  where  it  appears  to  suffer  little  from  atmospheric  influences.  Ancient 
stone  coffins  made  of  this  modern  sandstone  were  found  in  the  churchyard,  and  one  of 
them  was  to  be  there  seen  in  1838.  Consolidated  sand  of  the  like  kind  is  to  be  found 
in  several  places  beneath  the  Cornish  sandy  dunes,  especially  when  these  are  much 
formed  of  comminuted  sea-shells.  The  consolidation  of  part  of  the  raised  beach  at  New 
Quay  is  so  considerable  that  in  breaking  off  a  portion  in  which  pebbles  of  the  adjoining 
rocks  and  of  quartz  are  mingled  with  the  sand,  the  fracture  will  pass  sometimes  through 
the  pebbles  as  well  as  traverse  the  sands  and  its  cementing  substance. 


444  RAISED    SEA    BOTTOM,    NEAR    NEW    QUAY. 

drifted  over  it,  as  in  parts  of  the  adjacent  coasts  at  the  present  day, 
where  such  sands  are  driven  over  the  shingle  of  ancient  beaches  now 
removed  from  the  action  of  the  sea.  This  view  is  supported  by  a  section 
(fig.  159)  in  Eistral  Bay,  part  (on  the  western  side)  of  the  projecting 
land  on  which  the  other  section  (fig.  158)  is  exposed,  and  where  slates 

Fig.  159. 


and  more  arenaceous  beds,  a,  a,'  forming  a  portion  of  the  same  mass  with 
those  exhibited  beneath  the  Look-out  Hill  (fig.  158,  a,  a,  a),  support 
rolled  pebbles,  often  of  large  size,  mingled  with  smaller  gravel  and  sand, 
the  whole  constituting  a  kind  of  beach,  b.  This  is  surmounted  at  c  by 
frequent  alternations  of  fine  gravel  and  sand,  some  of  the  layers  of  the 
latter  being  more  consolidated  than  others.  At  d,  the  sand  is  less  indu- 
rated, and  at  the  extremities  of  the  dunes  of  the  north  and  south  become 
mingled  with  angular  fragments  of  rocks  derived  from  the  adjacent  hills. 
In  this  instance  there  would  appear  evidence  of  a  portion  of  the  sea 
bottom,  adjacent  to  the  coast,  having  been  elevated  when  the  beach  at 
the  Look-out  Hill  was  uplifted. 

Still  keeping  to  the  north  coast  of  Cornwall,  as  it  appears  useful  to 
illustrate  changes  of  level  of  this  kind,  where  various  modified  eifects, 
arising  from  them,  are  well  exhibited  in  very  accessible  localities  within 
moderate  distances,  the  observer  will  find  good  examples  even  of  raised 
sandy  dunes  ;  thus  obtaining  an  insight  into  the  condition  of  a  range  of 
oceanic  coast,  with  its  modifications  of  shingle  beaches  at  the  foot  of  cliffs, 
shallow  shores  with  their  prolongation  of  blown  sands,  and  accumulations 
in  shallow  coast  waters  of  the  time,  all  upraised  and  variously  acted  upon 
at  the  present  level  of  breaker  action.  At  St.  Ives'  and  Perran  Bays, 
sandy  dunes,  accumulated  when  the  level  of  the  Atlantic  ranged  along 
this  land  30  or  40  feet  higher  than  it  now  docs,  the  latter  having  been 
since  upraised,  are  seen  perched  where  existing  conditions  could  not 
place  them,  their  old  supporting  rocks,  previously  removed  from  breaker 
action,  now  cut  into  cliffs  by  it.  This  is  especially  well  shown  in  the 
former  bay,  near  Gwythian,  where  a  cliff  of  hard  rocks,  rising  35  or  40 
feet  above  the  present  high-water  murk,  is  surmounted  by  a  part  of  an 
ancient  beach,  with  old  s;in<ly  dunes  nbove  it.  After  this  uprise,  the 
slope  of  the  coast  was  such  that  on  the  southwest,  in  the  direction  of 


RAISED    DUNES    OF    BLOWN    SAND.  445 

Hayle  and  Lelant,  conditions  for  the  production  of  sandy  dunes  still 
continued,  so  that  in  this  mass  of  blown  sands,  three  miles  in  length, 
modern  are  partly  driven  over  the  older  accumulations  on  the  sides  and 
in  front  of  the  valley  between  Gwythian  and  Godrevy  Head,  towards 
which,  near  Godrevy,  an  excellent  section  of  a  raised  beach  was,  in 
1838,  to  be  found. 

Masses  of  sand  on  coasts,  acted  upon  by  winds,  and  apparently  not 
produced  by  existing  conditions  on  such  coasts,  have  not  always  been 
accumulated  as  blown  sands  and  then  elevated ;  as,  for  example,  at  Porth- 
dinlleyn,  on  the  coast  of  Caernarvonshire,  where  a  mass  of  sand  covers 
a  clay  and  gravel,  of  the  deposits  termed  glacial,  (p.  283),  and  might, 
at  first  sight,  be  referred  to  raised  and  sandy  dunes.  Careful  investiga- 
tion shows  that  this  sand  is  an  elevated  sea-bottom,  layers  of  a  harder 
and  more  argillaceous  kind  being  interstratified  with  the  more  loose  sand, 
and  retaining  all  the  perforations  made  by  marine  animals  when  these 
layers  were  at  the  bottom  of  the  sea.  Breaker  action  is  now  removing 
these  sands,  brought  within  its  influence  by  the  elevation  of  the  land, 
and  does  not  assist,  with  the  wind,  in  forming  sandy  dunes.  These 
sands  only  constitute  a  portion  of  raised  sea-bottoms,  formed  of  either 
clay,  sand,  and  gravels,  with  larger  blocks  of  rock,  dispersed  over  the 
adjoining  land. 

A  raised  beach  of  a  very  instructive  kind  was  long  since  (1822)  de- 
scribed by  Dr.  Mantell,*  as  occurring  near  Brighton,  where  one,  ele- 
vated several  feet  above  the  sea,  rests  upon  chalk,  the  rock  of  the  coast, 
in  the  same  manner  as  the  beach  at  Nelly's  Cove,  Falmouth  (fig.  157), 
reposes  on  the  old  slates  and  accompanying  beds.  The  beach  near  Brigh- 
ton is  backed  by  an  ancient  cliff  of  chalk,  and,  above  the  beach,  chalk 
rubble,  loam,  &c.,  obscurely  bedded,  contain  many  teeth  and  .bones  of 
the  fossil  elephant,  whence  the  name  "Elephant  Bed"  has  been  given 
it.  Rolled  pieces  of  chalk  and  limestone  are  discovered  among  the  peb- 
bles, "full  of  perforations  made  by  boring  shells."f  In  this  case  the 
beach  would  appear  to,  have  been  formed  prior  to,  or  during  the  existence 
of,  the  mammoth  in  Britain. 

With  regard  to  the  fossil  contents  of  these  beaches,  they  afford  much 
information  as  to  the  exposure  of  the  coasts  of  the  time  to  differences  in 
the  range  of  sea  to  which  they  may  have  been  open ;  tidal  streams  and 
ocean  currents  being  modified  by  alterations  in  the  distribution  of  land 
and  water.  Professor  E.  Forbes  informs  me  that  the  fossil  shells  of  the 
raised  beaches  on  the  shores  of  the  Clyde  are,  in  many  cases,  those  of 
species  which,  though  still  living  in  the  British  seas,  present  a  more 
southern  character  than  the  molluscs  now  existing  in  them,  and  that 

*  Fossils  of  the  South  Downs,  1822. 

f  Mantell,  "Wonders  of  Geology,"  Gth  edit.  (1848),  p.  113,  where  a  section,  and  de- 
tailed description  are  given  of  the  raised  beach  at  Brighton,  east  of  Kemp  Town. 


446    DISTRIBUTION   OF    DETRITUS   IN   THE    ENGLISH    CHANNEL, 

they  are  confined  to  districts  more  southern  and  western  than  the  Frith 
of  Clyde.  He  thence  infers  a  change  in  the  direction  of  the  currents 
from  the  south  (especially  in  that  known  as  Rennell's  Current),  this 
change  being  probably  due  to  the  conformation  of  the  coast  lines  of  the 
time. 

It  is  desirable,  as  has  been  done  by  Mr.  R.  C.  Austen,*  to  connect 
these  raised  beaches  and  elevated  sea-bottoms  of  the  same  geological 
dates,  and  the  submarine  or  sunk  forests,  with  the  present  state  of  the 
seas  adjoining  or  covering  them.  After  carefully  considering  the  sub- 
ject, Mr.  Austen  shows  that  although  the  distribution  of  the  detritus 
derived  from  the  present  coasts  of  France  and  England,  in  the  English 
Channel,  and  from  England  and  Ireland  on  the  sea-bottom  to  the  south 
of  the  latter,  with  the  sediment  brought  down  by  the  rivers  to  those 
coasts,  is  in  accordance  with  the  arrangement  which  would  be  expected 
from  breaker  and  wind-wave  action  and  tidal  streams ;  there  are,  espe- 
cially in  the  central  parts  of  the  English  Channel  and  on  the  outer  range 
of  the  100  and  200  fathom  soundings  towards  the  Atlantic,  bare  rocks, 
shingles  and  coarse  ground,  and  the  shells  of  littoral  molluscs  so  occur- 
ring as  to  point  to  the  submergence  of  former  coasts  and  shallow  water 
adjoining  them.  With  regard  to  the  "  submarine  or  sunk  forests,"  Mr. 
Austen  calls  attention  to  the  necessity  of  not  limiting  their  extension 
beneath  the  sea  outwards  to  the  shores  where  they  are  now  discovered, 
but  to  take  a  more  general  view  of  them  as  parts  of  submerged  dry  land; 
one  which  would  better  accord  with  the  coarse  detritus  at  depths,  or  in 
situations,  where  existing  wind-wave  action  and  tidal  streams  would  not 
transport  it,  and  also  with  the  remains  of  littoral  molluscs,  Patella  vul- 
gata,)  Littorina  littorea,  $c.,  found  in  similar  situations.  The  evidence  ad- 
duced shows  very  uneven  ground  outwards,  especially  towards  the  Atlan- 
tic ;  strewed  over  inwards  by  the  varied  detrital  deposits,  partly  the  ad- 
justment of  existing  circumstances,  partly  the  mixed  result  of  these  and 
former  conditions  when  the  present  sea-bottom  was  more  elevated,  even 
forming  dry  land  connecting  the  British  Islands  with  the  continent. 
Without  a  proper  chartf  showing  the  condition  of  the  sea-bottom  around 
the  British  Islands,  it  would  be  difficult  to  convey  a  correct  idea  of  the 
inferences  to  be  derived  from  it ;  but,  as  illustrating  a  portion  of  this 
bottom,  Mr.  Austen  remarks,  that  "  within  a  distance  from  the  summits 
of  the  Little  Sole  Bank  (parts  of  which  rise  to  within  50  and  60  fathoms 
on  the  south  of  Ireland  and  off  the  mouth  of  the  English  Channel),  not 
so  great  as  from  the  top  of  Snowdon  to  the  sea,  soundings  have  been 

*  "  On  the  Valley  of  the  English  Channel ;"  Journal  of  the  Geological  Society  of  Lon- 
don, vol.  vi.  p.  69. 

j-  The  observer  should  consult  the  chart  appended  to  Mr.  Austen's  Memoir,  in  which 
a  large  amount  of  valuable  information  relating  to  the  sea-bottom  of  the  area  noticed  is 
gathered  together. 


AND  IN  THE  SEA  ON  THE  SOUTH  OF  IRELAND.    447 

obtained  of  529  fathoms  (3174  feet) ;  in  other  words,  the  Sole  Bank  rises 
from  that  level  to  nearly  as  high,  and  more  rapidly,  than  does  the  mass 
of  Snowdon  from  the  sea  level  of  the  Caernarvon  coast  by  the  Menai 
Straits."* 

Amid  the  complications  which  may  arise  in  coasts  where  there  has 
been  gradual  elevation  of  the  land  above  the  mean  tidal  level  of  the 
ocean,  from  the  tidal  differences  above  mentioned  (p.  439),  from  the 
variable  exposure  to  breaker  action,  as  the  shores  become  sheltered  at 
one  time  and  more  exposed  at  another,  from  the  amount  of  concealment 
of  sea  action  on  the  surface  of  land  caused  by  atmospheric  influences, 
combined  with  running  waters,  and  from  unequal  elevation  of  the  land 
itself,  the  observer  will,  no  doubt,  require  much  caution  while  endea- 
vouring to  trace  the  line  of  coast  of  any  one  particular  time.  This  will 
especially  be  the  case  when  there  have  been  oscillations,  as  there  is 
frequently  reason  to  conclude  there  have  often  been,  during  a  time  when 
the  molluscs  of  adjoining  seas  continued  to  be  much  the  same  as  now 
found  in  them. 

In  the  Scandinavian  region,  where  a  slow  rise  of  land  (p.  428),  is  now 
taking  place  more  on  the  north  than  on  the  south,  and  where  surface 
changes,  of  no  great  geological  magnitude,  by  which  the  land  now  sepa- 
rating the  Baltic  from  the  Atlantic  could  so  easily  convert  a  tideless 
sea  into  a  branch  of  the  ocean  (a  tide  rushing  up  the  Gulf  of  Bothnia 
and  producing  its  effects  in  the  same  manner  as  is  now  found  in  the  Bay 
of  Fundy),  traces  of  elevated  ranges  of  coast  are  seen,  which  are  the 
more  interesting,  as  they  serve  to  connect  former  movements  of  thia 
kind  with  that  now  taking  place.  Respecting  the  evidence  on  this  head, 
the  observer  will  find  a  very  valuable  summary  and  general  view  in  the 
observations  of  M.  Elie  de  Beaumont  on  the  researches  of  M.  Bravais 
(connected  with  this  subject),  in  Scandinavia,  f  Shells  of  molluscs  now 

*  "  The  character  of  the  greater  part  of  the  Channel  area,"  continues  Mr.  Austen, 
"if  laid  bare,  would  be  that  of  extensive  plains  of  sand,  surrounded  by  great  zones  of 
gravel  and  shingle,  and  presenting  much  such  an  admixture  and  arrangement  of  mate- 
rials as  we  may  observe  at  present  over  the  Bagshot  district  of  deposits ;  whilst  along 
the  opening  of  the  Channel  there  is  an  obvious  configuration  of  hill  and  valley,  and  an 
amount  of  inequality  equal  to  that  of  the  most  mountainous  part  of  Wales." — Journal, 
&c.,  vol.  vi.  p.  85. 

Referring  to  the  examination  of  the  range  of  the  200  fathom  line  from  Cape  Finisterre 
to  the  parallel  of  the  Lizard,  undertaken  by  Captain  Vanhello  in  1828  and  1829,  Mr. 
Austen  points  out  that  the  irregularity  of  soundings  at  this  line,  which  runs  at  a  com- 
paratively short  distance,  as  we  have  elsewhere  remarked  (Researches  in  Theoretical 
Geology,  p.  190),  outside  that  of  100  fathoms  (represented  in  figs.  65  and  99,  pp.  114 
and  265),  is  far  from  being  confined  to  one  spot,  but  ranges  not  only  southward,  as 
shown  by  Captain  Vanhello,  but  also  to  the  northward.  A  reference  to  fig.  99,  p.  265, 
will  show  that  the  Rockall  Bank,  westward  of  Ireland,  much  resembles  an  island  under 
water  ;  an  uprise  of  only  600  feet  would  make  it  one. 

f  "  Comptes  Rendus,"  vol.  xv.  p.  817  (1842).  Report  on  the  Memoir  of  M.  Bravais, 
Voyage  de  la  Commission  Scientifique  du  Nord  en  Scandinavie,  en  Laponie,  &c. 


448  RAISED    COAST-LINES    IN    SCANDINAVIA. 

found  living,  as  littoral  species,  on  the  shores  of  Norway,  are  discovered 
raised  518  (English)  feet  above  the  sea  in  the  province  of  Drontheim, 
482  feet  at  Skioldal  and  Hellesab'n,  360  feet  around  Lake  Odemark, 
and  206  feet  at  Uddevalla.  Lines  of  erosion  are  also  inferred  to  mark 
the  former  relative  levels  of  sea  and  land  on  the  Norwegian  coasts.  In 
Finmark  traces  of  an  ancient  line  of  sea-coast  were  followed  from  Alten 
Bay  to  Hammerfest.  These  consisted  of  beaches  and  worn  lines  of 
rock,  forming  the  section  of  a  plane  so  inclined  that  while  on  the  south 
of  Altenfiord  it  rose  221  feet  above  the  sea,  it  descended  to  94  feet  near 
Hammerfest.  Beneath  this  first  line  was  a  second,  88  feet  above  the 
sea  in  the  former  locality,  46  feet  at  the  latter,  both  these  lines  falling 
from  south  to  north,  the  reverse  of  the  movement  now  taking  place  in 
northern  Scandinavia.  M.  Bravais  considers  that  an  intermediate  line 
of  ancient  coast  occurs  between  these  more  marked  lines,  which  are  not 
exactly  parallel  with  each  other,  though  they  may  appear  so  for  short 
distances,  showing  the  observer  the  necessity  of  exact  measurements  in 
researches  of  this  kind. 

With  reference  to  the  erosion  of  rocks  in  connexion  with  raised 
beaches  in  an  oceanic  situation,  and  where  sea  levels  are  not  likely  to 
have  been  much  disturbed  by  changes,  altering  tidal  action  during  the 
amount  of  elevation  of  land  inferred,  attention  may  be  called  to  one  of 
the  earliest  observations  of  this  kind  by  Captain  Vetch,  at  the  Island 
of  Jura,  Hebrides.  He  there  found  six  or  seven  lines  of  raised  beaches, 
the  highest  about  40  feet  above  the  present  high-water  mark.  The 
beaches  are  composed  of  shingles  of  quartz  rock  (that  of  the  island),  of 
about  the  size  of  cocoa-nuts,  and  they  are  precisely  similar  to  those 
which  constitute  the  present  beaches  on  the  Loch  Tarbert  side  of  Jura, 
where  these  raised  beaches  are  well  seen.  Their  aggregate  breadth 
varies  "  according  to  the  disposition  of  the  ground ;  where  the  slope  is 
precipitous,  it  may  be  a  hundred  yards ;  where  gentle,  as  on  the  north 
side  of  the  loch,  three-quarters  of  a  mile  from  the  shore."*  The  beaches 
repose  partly  on  bare  rock,  and  partly  on  a  compound  of  clay,  sand,  and 
angular  pieces  of  quartz  rock.  Captain  Vetch  observed  that  caves  are 
found  at  the  same  level  on  the  north  side  of  Loch  Tarbert,  at  a  consi- 
derable height  above  the  sea,  and  as  he  had  never  seen  caverns  formed 
in  the  quartz  rock  of  Isla,  Jura,  or  Fair  Island  (Hebrides),  except  on 
the  shore,  he  considers  these  to  have  been  formed  at  the  time  when 
the  relative  levels  of  sea  and  land  were  such  as  to  cut  the  line  of  these 
caves. 

Temperature  of  the  Earth. — As  the  temperature  of  the  earth  may 
have  an  important  bearing  upon  conclusions  which  an  observer  might 
feel  disposed  to  form  respecting  the  causes  of  certain  phenomena  which 

*  Geological  Transactions,  2d  scries,  vol.  i. 


TEMPERATURE    OF    DIFFERENT    DEPTHS    IN    SIBERIA.     449 

he  may  be  investigating,  it  is  desirable  that  he  should  carefully  direct 
his  attention  to  it,  so  that  its  full  value,  as  a  geological  agent,  may  be 
duly  appreciated.  Mention  has  been  above  made  (p.  216)  of  the  kind 
of  spheroidal  shell  which  passes  through  the  colder  parts  of  the  world, 
cutting  off  the  poles,  and  leaving  a  height  of  from  16,000  to  17,000  feet 
between  the  surface  of  the  sea  level  and  it  in  the  equatorial  regions, 
above  which,  with  certain  modifications,  water  remains  in  a  solid  state. 
Independently  of  the  well-known  action  of  the  sun  on  the  surface  of  the 
earth,  it  is  found  that,  after  due  allowance  has  been  made  for  the  tem- 
perature thus  produced,  there  is  another  temperature,  commencing  at 
certain  distances  beneath  that  surface,  the  cause  of  which  appears  to 
require  another  explanation.  Diurnal  variations  of  temperature  are 
considered  not  to  extend,  viewing  the  subject  generally,  to  a  greater 
depth  than  about  three  feet,  and  annual  variations  are  inferred  to  cease 
at  from  65  to  70  or  80  feet.  Beneath  depths  not  much  differing  from 
the  latter,  the  temperature  of  rocks  has  been  found  to  increase  in  mines, 
as  also  in  the  perforations  into  the  ground  commonly  termed  artesian 
wells.  The  rate  of  this  increase  of  temperature  has  been  found  to  vary, 
as  might  be  expected,  from  certain  local  causes,  such  as  the  relative 
exposure  of  the  mass  of  ground  examined  with  respect  to  the  form  in 
which  it  may  project  into  the  atmosphere,  should  it  be  a  mountain,  its 
proximity  to  any  particular  source  of  heat,  such  as  a  volcanic  region  in 
activity,  and  the  different  circulation  of  water  amid  its  parts,  either 
among  fissures  or  through  beds  of  rocks  of  variable  porosity. 

We  have  seen  (p.  293),  that  in  the  colder  regions  of  the  northern 
hemisphere  frozen  ground  may  descend  to  very  different  depths.  While 
in  Siberia  ice  is  still  found  at  a  depth  of  from  300  to  400  feet,  in  the 
same  latitude  (62°  N.),  in  America  the  frozen  ground  does  not  extend 
beneath  26  feet ;  so  that  very  modified  conditions  must  exist  for  the 
temperature  of  the  two  regions.  While,  however,  this  may  be  the  case, 
it  is  interesting  to  find  (note,  p.  293),  that  the  mineral  accumulations 
passed  through  in  Siberia  show  an  increase  of  temperature  downwards, 
so  that,  while  at  75  feet  beneath  the  surface  it  was  21-2°  (Fahrenheit), 
at  378  feet  it  was  31*1.°  The  circulation  of  water  in  mines  can  scarcely 
otherwise  than  produce  modifications  of  an  important  kind,  as  to  the 
exact  rate  of  increase  of  heat  downwards,  though  the  fact  itself,  in  its 
generality,  may  be  evident,  since  the  excavation  of  the  mine,  and  the 
necessity  of  keeping  it  clear  of  water  while  its  works  are  in  progress, 
will  cause  water  to  descend  from  the  surface  downwards,  more  or  less 
bringing  its  first  temperature  with  it,  to  the  depths  whence  it  is  again 
raised  to  the  surface.*  In  districts,  such  as  those  of  mines  often  are, 

*  In  some  mining  districts,  the  descent  of  water  from  the  surface  downwards,  and 
the  stoppage  of  its  progress  upwards  from  depths  beneath  the  mining  operations,  have 
been  found  so  to  intercept  the  outflow  of  the  previous  natural  springs,  as  to  be  produc- 

29 


450  TEMPERATURE    FOUND     IN    ARTESIAN    WELLS. 

broken  by  numerous  fissures,  this  introduction  of  surface  water,  con- 
tinued for  a  long  time,  may  produce  very  modifying  influences.  Still 
much  may  be  accomplished,  with  care,  in  mines,  by  selecting  portions 
of  rocks  of  the  more  solid  kinds,  and  in  situations  where  the  tempera- 
ture produced  by  the  miners,  their  lights,  and  their  works,  especially 
those  carried  on  by  blasting  with  gunpowder  or  gun-cotton,  may  cause 
the  least  amount  of  error  in  the  needful  experiments.* 

Artesian  wells  have  been  found  very  valuable  in  affording  information 
as  to  the  temperature  of  the  earth  at  different  depths  in  certain  locali- 
ties, the  bore-holes  and  the  waters  rising  in  them  showing  an  increase 
of  temperature  with  the  depth.  Though  numerous  experiments  have 
been  made  upon  the  heat  found  at  different  depths  in  these  wells,  few 
have  attracted  more  attention,  from  the  care  taken  in  conducting  them, 
the  kind  of  ground  perforated,  and  the  depth  of  the  well  itself,  than 
those  at  Grenelle,  near  Paris.  The  rocks  traversed  consist  of  successive 
beds  of  various  kinds,  a  thick  one  of  chalk  being  among  the  most  pro- 
minent, and  are  situated  far  distant  from  any  volcanic  vent  or  any 
known  disturbing  cause  of  that  kind.  After  exhibiting  an  increase  of 
temperature  downwards,  as  the  work  proceeded,  it  was  found  by  MM. 
Arago  and  Walferdin  that  when  the  well  had  reached  the  cretaceous 
clay  known  as  the  G-ault^  at  the  depth  of  1657  feet,  the  temperature 
was  79-5°  (Fahrenheit),  and  it  became  81-7°  lower  down,  at  1798  feet.f 

With  respect  to  the  temperature  obtained  in  artesian  wells,  it  is  de- 
sirable that  the  observer  should  carefully  consider  the  mode  of  occur- 
rence of  the  rocks  of  the  district  in  which  they  may  be  situated,  so.that 

tive  of  much  inconvenience  to  the  inhabitants,  with  respect  to  their  supply  of  water  for 
household  purposes. 

*  M.  Cordier,  who  has  paid  great  attention  to  this  subject,  adopted  the  following 
method  of  obtaining  the  temperature  of  the  rock  itself,  in  certain  coal  mines  in  France. 
The  thermometer  was  loosely  rolled  in  seven  turns  of  tissue-paper,  closed  at  bottom, 
and  tied  by  a  string  a  little  beneath  the  other  extremity  of  the  instrument,  so  that  so 
much  of  the  tube  might  be  withdrawn  as  might  be  necessary  for  an  observation  of  the 
scale,  without  fearing  the  contact  of  the  air ;  the  whole  contained  in  a  tin  case.  This 
was  introduced  into  a  hole  from  24  to  26  inches  in  depth,  and  1£  inch  in  diameter,  in- 
clined at  an  angle  of  10°  or  15°,  so  that  the  air,  once  entered  into  the  hole,  could  not 
be  renewed,  because  cooler,  and  consequently  heavier,  than  that  of  the  levels  or  galle- 
ries. The  thermometer  was  kept  as  nearly  as  possible  at  the  temperature  of  the  rock, 
by  first  plunging  it  amid  pieces  of  rock  or  coal  freshly  broken  off,  and  by  holding  it  a 
few  seconds  at  the  mouth  of  the  hole,  into  which  it  was  afterwards  shut,  a  strong  stopper 
of  paper  closing  the  aperture.  The  thermometer  usually  remained  in  the  hole  about  an 
hour. — "Essai  sur  la  Temperature  de  la  Terre;"  M<jmoires  de  1' Academic,  torn.  vi. 
Other  observations  have  been  made  on  the  temperature  of  the  rocks  in  mines  in  various 
ways,  and  among  them,  holes,  a  yard  or  more  in  depth,  have  been  drilled  in  convenient 
situations,  and  the  temperature  observed  for  a  given  period,  such  as  a  year  or  more. 

•f  It  is  calculated  that,  taking  the  constant  temperature  (53°)  of  the  caves  of  the 
Paris  Observatory,  91 1  feet  beneath  the  surface,  these  temperatures  would  give  an  in- 
crease in  heat  at  the  rate  of  1°  centigrade  (1-8°  Fahrenheit),  for  32-3  metres,  nearly 
106  English  feet  (105  feet  11-659  inches). 


HEAT    OF    WATERS    RISING    THROUGH    FAULTS,    ETC.      451 

the  rise  of  thermal  springs  beneath  the  mineral  accumulations  traversed 
may  not  complicate  the  heat  found.  As,  for  example,  should  it  happen 
that  in  a  country  affording  a  section  similar  to  that  beneath  (fig.  160), 


Fig.  160. 


a  series  of  nearly  horizontal  deposits,  J,  <?,  rests  upon  a  previously  dis- 
turbed assemblage  of  beds,  d,  traversed  by  faults,  e  and  /,  formed  prior 
to  the  accumulation  of  the  upper  beds,  6,  c,  and  that  thermal  waters 
rise  through  these  faults,  as  they  often  do,  and  as  previously  noticed 
(p.  49),  the  ordinary  supply  of  rain  water  entering  at  g,  and  passing  to 
a  lower  porous  bed  e,  the  temperature  of  the  earth  at  any  artesian 
boring,  situate  at  A,  might,  to  a  certain  extent,  be  obtained,  while  ano- 
ther well  sunk  at  i,  being  immediately  near  a  supply  of  thermal  water 
through  the  fault  0,  would  give  a  more  elevated  temperature,  the  higher 
in  proportion  to  the  volume  and  velocity  (p.  49),  with  which  the  pre- 
viously suppressed  ready  outflow  can  now  more  freely  find  vent.  This 
is  by  no  means  an  unnecessary  circumstance  to  be  regarded,  since  in 
districts  such  as  that  of  the  neighbourhood  of  Bath,  there  is  evidence  of 
faults,  some  of  them  of  considerable  size,  having  been  formed  anterior 
to  the  accumulation  of  the  new  red  sandstone  and  oolitic  series  of  that 
country,  the  surface  of  the  fractured  and  contorted  rocks  being  covered 
by  the  nearly  horizontal  beds  of  these  deposits,  and  as  the  thermal 
waters  of  Bath  (116°  Fahrenheit),  appear  to  rise  through  one  of  the  old 
fissures,  a  ready  vent  for  them  occurring  through  the  superincumbent 
beds,  as  at  I  (fig.  160).  The  observer  would  do  well  to  search  in  such 
suspected  districts  for  the  temperature  of  waters  pouring  abundantly 
through  any  faults,  as  at  k.  And  it  is  worthy  of  remark,  that  in  the 
district  above  noticed,  a  thermal  spring  (temp.  74°)  appears  among  the 
older  broken  and  disturbed  rocks  at  the  Hotwells,  Bristol. 

Regarding  the  temperatures  found  at  different  depths  in  artesian 
wells,  and  the  variations  sometimes  observed  therein,  it  will  have  to  be 
borne  in  mind  that  the  different  seams  of  rock  whence  water  may  be 
obtained,  though  not  in  sufficient  abundance  for  the  supply  sought,  will, 
from  any  different  porosity  in  them,  only  permit  waters  to  permeate  or 
flow  through  them  in  such  a  manner  that  a  given  quantity  can  pass 
through  each  in  a  given  time,  thus  influencing  the  circulation  of  any 
heat  which  they  may  carry  with  them  from  one  part  of  a  series  of  beds  to 
another.  If  the  following  section  (fig.  161),  represent  that  of  certain 
beds  of  rocks  traversed  in  sinking  an  artesian  well,  a,  a,  being  a  clay, 
such  as  the  London  clay ;  b  a  porous  bed  of  sand  and  gravel,  gathering 


452        VARIABLE    TEMPERATURES    ARISING    FROM    THE 

surface  waters  at  <?;  d  chalk;  e  sand,  receiving  surface  waters  from  /; 
g  clay  or  marl,  and  i  other  sands  or  gravels  gathering  surface  waters  at 
h,  we  have  very  different  porosities  of  the  beds  which  can  permit  water 


Fig.  161. 


to  pass  somewhat  freely  through  them.  Upon  perforating  through 
these  beds,  as  at  m,  their  relative  permeability  to  water  would  influ- 
ence the  temperature  in  such  an  artesian  well,  a  highly  porous  bed,  6, 
carrying  its  surface  waters  more  readily  to  the  well,  to  rise  through  it, 
than  the  chalk,  d,  beneath,  as  would  probably  also  happen  with  the 
sands  lower  down  at  e.  In  all  cases  of  this  kind,  an  observer  has  to 
allow  for  the  friction  of  the  water  through,  and  capillary  action  in  the 
rock,  which  can  only  permit  the  circulation  of  this  water  according  to 
needful  conditions,  so  that  it  can  only  be  delivered  into  the  artesian 
well  at  a  certain  rate  in  each  case.*  In  the  section  (fig.  161),  a  smaller 
well  is  represented  as  sunk  at  n,  to  the  sands,  e>  /,  and  on  the  bend  of 
the  beds,  where,  in  consequence,  the  heated  waters  are  more  able  freely 
to  ascend,  and  be  replaced  by  heavier  and  colder  water,  always  suppos- 
ing the  whole  to  have  a  temperature  above  40°  Fahrenheit.  In  this 
case  it  might  be  inferred  that  from  the  greater  facility  of  percolation 
from  the  surface,  /,  to  the  bottom  of  the  well,  n,  on  the  one  side,  the 
water  would  produce  a  lower  temperature  in  the  rock  through  which  it 
passed,  than  in  the  same  bed  of  rock  at  m.  At  0,  and  p,  part  of  the 
curves  of  two  porous,  interstratified  with  less  permeable  beds,  k,  ?,  are 
represented  (forming  thus,  as  it  were,  flat  pipes),  for  the  purpose  of 
showing  that,  if  the  curve  were  continued  downwards  on  the  left,  water 
percolating  in  them,  heated  beneath,  and  not  easily  escaping  upwards, 
might  possess  a  somewhat  higher  temperature  than  at  the  same  depths 
from  the  surface  in  the  adjoining  beds  (supposed,  for  illustration,  to  be 
equally  porous),  not  having  the  same  facilities  offered  for  obtaining,  by 
circulation  according  to  temperature  and  densities,  colder  waters  from 
above. 

To  whatever  extent  water,  permeating  amid  rocks,  may  modify  their 
temperature,  the  greatest  density  of  water  will  have  its  influence.  In 

*  It  is  often  practically  found,  in  borings  for  common  wells,  that  the  relative  porosity 
of  the  rock  or  rocks  traversed,  and  the  consequent  possible  delivery  of  water  into  them, 
have  not  been  sufficiently  regarded.  Though  certain  loose  sands  and  gravels  may 
afford  a  volume  of  water  considered  most  abundant,  so  far  as  the  supply  sought  is 
regarded,  rocks  generally  are  but  filters  of  various  degrees  of  porosity,  and  only  capa- 
ble of  permitting  water  to  pass  through  them  in  a  given  quantity  and  time. 


UNEQUAL  PERCOLATION  OF  WATER  THROUGH  ROCKS.  453 

all  regions  where  the  annual  temperature  is  such  as  to  exceed  that  of 
the  greatest  density,  however  the  surface,  and  corresponding  depth 
beneath,  may  be  acted  upon,  after  60  or  80  feet,  the  hotter  waters 
would  tend  to  rise  and  the  colder  to  descend.  In  those,  however,  where 
the  temperature  is  such  that  the  water  takes  a  contrary  course,  instead 
of  cool  waters  descending  to  modify  any  heat  which  the  containing  rock 
might  otherwise  possess,  they  would  ascend.  For  example,  in  the 
Siberian  shaft  (p.  293)  descending  beneath  the  378  feet  at  which  a  tem- 
perature of  31 '1°  was  obtained,  and  allowing  the  same  rate  of  increase 
as  was  found  from  the  depth  of  75  feet,  namely,  about  1°  (Fahrenheit) 
for  each  30  feet,*  it  would  only  be  at  a  depth  of  about  630  feet  that 
water  at  39-5°  (Fahrenheit)  would  be  found. 

It  has  been  inferred  that  ordinary  springs,  in  the  warmer  regions  of 
the  earth,  have  a  higher  temperature  than  the  mean  of  the  climates 
in  the  same  localities,  while  those  in  the  colder  parts  of  the  world  pos- 
sess a  less  heat.  As  this  would  imply  some  modifying  influence  con- 
nected with  the  general  distribution  of  the  temperature  amid  the  rocks 
whence  these  springs  flow,  very  careful  examination  of  the  real  heat  of 
such  springs  becomes  valuable.  As  to  the  springs  which  rise  from 
fissures,  such  as  those  above-mentioned  (p.  451),  a  lower  temperature, 
without  due  precaution,  will  often  be  obtained  than  should  be  assigned 
them,  even  supposing  that  the  waters,  as  they  flow  upwards  from  various 
depths,  lose  much  of  their  original  temperature,  and  acquire  that  of  the 
rocks  amid  which  they  rise.f  The  heat  of  ordinary  springs  has  also  to 
be  carefully  considered  with  reference  to  the  kind  and  mode  of  occur- 
rence of  the  hard  rocks  or  less  coherent  accumulations  of  matter  whence 
they  issue.  If  we  suppose  a,  in  the  following  section  (fig.  162),  to  be 


t 

a  porous  sandstone,  resting  upon  a  bed  of  clay,  5,  #',  the  rain-waters, 
absorbed  by  the  former,  are  prevented  from  permeating  downwards  by 
the  latter,  so  that  the  water  not  retained  amid  the  sandstone,  issues,  as 
springs^  on  the  side  of  the  hill,  at  the  top  of  the  subjacent  clay. 
Should  another  sandstone,  or  any  other  rock,  through  which  water  may 
readily  percolate,  <?,  c',  occur  beneath  the  clay,  this  porous  stratum  also 

*  This  rate  of  increase  of  temperature  very  nearly  coincides  with  that  obtained  at 
Grenelle,  namely,  1-8°  (Fahrenheit)  for  53  feet. 

f  It  is  commonly  needful  to  clear  away  the  ground,  so  that  a  thermometer  may  be 
plunged  in  the  water  where  it  rises  amid  the  rocks  themselves.  And  this  is  especially 
necessary  when  the  volume  of  water  is  far  from  considerable,  and  flows  away  slowly. 
Those  thermometers  in  which  the  bulb  and  a  portion  of  the  glass  project  beyond  the 
graduated  scales,  when  handled  carefully,  will  be  found  the  most  useful  instruments. 


454    TEMPERATURE    OF    WATERS    IN    LIMESTONE    DISTRICTS. 

based  upon  an  impervious  bed,  d,  d'9  the  atmospheric  waters,  with  any 
water  derived  from  the  springs  above  and  absorbed  by  the  lower  porous 
rock,  could  alone  find  a  natural  outflow,  as  springs,  on  the  side  of  the 
hill  d,  t;  while  in  the  opposite  direction,  d',  t\  they  would  saturate 
that  portion  of  the  bed,  laterally  aiding,  by  their  superabundance,  if  we 
infer  the  needful  facility  of  passage,  the  springs  between  c  d.  The 
dotted  line,  t,  t'9  representing  any  depth  beneath  which  a  uniform  tem- 
perature is  preserved  throughout  the  year,  should  water  percolate  slowly 
to  the  surface,  there  would  be — all  other  things  being  equal — a  tendency 
between  a  and  5,  and  c  and  d,  on  the  one  side,  and  a  and  b'  on  the 
other,  to  have  springs  issue  with  nearly  equal  temperatures.  At  w, 
also,  if  a  well  be  sunk,  the  temperature  of  the  water  being  within  the 
depth  of  variable  temperature,  we  should  expect  it  to  be  much  of  the 
same  kind,  the  supply  being  derived  laterally  from  the  same  reservoir 
which  supplied  the  springs  between  c  and  d,  and  the  impervious  bed  d 
(impervious  so  far  as  regards  the  ready  passage  of  water  through  it) 
preventing  appreciable  communication  with,  and  circulation  of,  waters 
of  a  higher  temperature  beneath.  Should  waters  find  their  way,  as 
springs,  by  means  of  joints  or  fissures,  from  the  reservoirs  in  both  porous 
beds,  a,  and  c,  c',  beneath  the  line  of  variable  temperature,  more  rapidly 
in  some  places  than  in  others — or  the  beds  themselves  differ  materially 
in  the  facility  with  which  water  can  pass  through — variations  may  be 
expected,  important  or  not,  according  to  circumstances,  in  the  tempera- 
ture of  springs  issuing  from  them.  All  other  things  being  equal,  the 
lower  reservoir — assuming  that  the  temperature  increases  from  the  sur- 
face downwards — would  be  expected  to  supply  the  water  with  the  more 
elevated  temperature.  It  becomes  needful,  therefore,  that  after  other 
conditions  have  been  ascertained,  the  quantity  of  water  delivered  by  a 
spring  in  a  given  time,  and  the  rapidity  with  which  it  flows,  should  be 
duly  regarded. 

With  respect  to  the  temperatures  of  those  waters  which,  in  limestone 
districts  especially,  rush  out,  often  in  considerable  volume  and  with 
much  force,  from  subterranean  channels,  and  which  result  from  the  loss 
of  many  minor  streams  and  of  rain-water  amid  fissures  and  cavernous 
rocks,  they  may  be  often  very  deceptive.  Should  the  waters  have  been 
absorbed  partly  as  streams,  previously  exposed  to  the  temperature  of 
the  climate  of  the  region,  and  partly  derived  from  slow  percolation 
through  chinks,  joints,  and  the  minor  cavernous  structure  of  the  rock,  a 
mixed  heat  would  follow,  affording  no  correct  data  as  to  the  temperature 
of  the  subterranean  channels  through  which  the  waters  have  passed. 
When,  also,  the  whole  is  derived  from  the  absorption  of  atmospheric 
waters  by  channels  of  various  kinds,  the  rapidity  of  passage  of  the 
waters  downwards  to  the  great  drainage  stream,  and  the  differences  in 
this  respect  have  to  be  considered,  as  also  the  chances,  not  uncommon 


DETRITAL    AND    FOSSILIFERO  US    ROCKS.  .        455 

in  some  districts,  that  great  fissure  waters,  derived  from  considerable 
depths,  may  not  be  mingled  with  the  general  volume  of  those  dis- 
charged. Hence  much  care  is  required  when  an  observer  may  be 
engaged  in  investigating  the  temperatures  of  waters  thus  discharged, 
however  desirable  it  may  be  that  they  should  be  properly  ascertained. 

While  on  the  one  hand  the  observer  has  to  regard  the  adjustment  of 
water,  permeating  amid  the  fissures  and  joints,  or  the  mass  of  rocks,  to 
its  greatest  density,  and  the  variable  mechanical  manner  in  which  this 
may  be  effected,  he  has  also  to  consider  the  depths  at  which  water  itself 
may  cease  to  exist ;  assuming  the  increase  of  temperature  from  the  sur- 
face downwards,  whatever  its  rate,  locally  or  generally,  to  be  certain, 
as  the  general  evidence  would  lead  us  to  believe.  Should  it  be  inferred 
that  the  rate  of  increase  of  heat  usually  supposed  probable,  namely  1° 
Fahrenheit,  for  each  50  to  60  feet,  is  too  great,  and  that  sufficient 
information  as  to  this  rate  has  not  yet  been  obtained,  if  we  take  only  1° 
for  every  100  feet,  we  still  seem  to  obtain  a  comparatively  minor  depth, 
allowing  for  increase  of  pressure  from  the  superincumbent  water,  with 
the  friction  on  the  sides  of  any  fissures,  for  that  portion  of  the  earth's 
crust  in  which  water  may  be  considered  to  circulate  under  the  most 
favourable  conditions.  Taking  the  ordinary  mode  of  calculation,  allow- 
ing for  pressure  at  increased  depths,  and  assuming  tevery  facility  of 
movement  of  the  waters  in  a  fissure,  it  may  be  estimated  that  at  a  com- 
paratively moderate  depth  steam  would  be  found  instead  of  water. 

Waters  in  fissures,  rushing  upwards  with  a  rapid  rate  of  outflow  and 
in  considerable  volume,  may  (as  noticed  p.  50)  bring  with  them  a  greater 
temperature  than  those  finding  their  way  upwards  with  less  velocity  and 
in  smaller  quantity,  the  one  heating  the  waters  communicating  with 
them  laterally,  in  their  course  upwards,  beyond  the  temperature  due  to 
the  containing  rocks  themselves,  and  the  ordinary  percolation  of  water 
through  them  ;  the  others  being  cooled  by  these  lateral  waters.  In  cer- 
tain districts,  such  as  those  where  volcanic  fires  have  once  found  vent, 
and  which  may  be  now  concealed  in  a  dormant  state,  by  various  over- 
spreading aqueous  accumulations,  there  may  be  influences  of  this  kind 
much  modifying  the  exact  depths  at  which  certain  temperatures  would 
otherwise  be  found.  No  doubt,  supposing  a  general  source  of  heat  to 
exist  in  the  earth,  governing  the  outer  temperature  of  its  crust  on  the 
great  scale,  these  would  be  merely  local  variations  in  some  given  tempera- 
ture due  to  the  larger  action  of  the  causes  producing  it,  yet,  when 
endeavouring  to  ascertain  the  distribution  of  the  heat  in  the  whole  por-* 
tion  of  the  globe  to  which  an  observer  can  artificially  obtain  access,  or 
calculate  from  good  data,  all  such  variations  require  attention,  so  that 
the  disturbing  circumstances  may  be  duly  separated  from  the  essential 
causes  of  the  increase  of  heat  downwards  from  the  surface  of  the  earth. 

Mode  of  Accumulation  of  the  Detrital  and  Fossiliferous  RocTcs. — The 


456         DETRITAL    ROCKS    CHIEFLY    OLD    SEA    BOTTOMS. 

observer,  having  well  considered  the  manner  in  which  the  accumulations 
of  mineral  matter  are  at  present  effected,  chemically  and  mechanically, 
through  the  agency  of  water,  as  also  the  mode  in  which  the  remains  of 
animal  and  vegetable  life  may  be  entombed  amid  such  accumulations, 
has  to  study  the  various  layers,  beds,  or  other  forms  of  mineral  matter 
formed  by  aqueous  means,  and  in  which  organic  remains  are  more  or 
less  distributed  in  various  parts  of  the  world.  In  one  respect  he  has 
an  advantage  over  his  previous  investigations,  inasmuch  as  while  he 
could  then  often  only  infer  that  which  takes  place  beneath  seas  and 
lakes,  he  has  in  these  rocks  frequent  opportunities  of  obtaining  direct 
evidence  of  that  which  actually  occurred  beneath  them,  the  large  pro- 
portion of  these  beds  being  the  bottoms  of  various  seas  or  bodies  of  fresh 
water,  deposited  over  each  other,  and  subjected  to  variation  from  local 
causes. 

Inasmuch  as  the  dry  land  of  the  world  is  thus  little  else  than  the 
bottoms  of  seas  and  lakes,  intermixed  with  igneous  matter  vomited 
upwards  at  different  times  from  beneath  the  surface  of  the  earth,  some 
of  the  latter  spread  at  once  on  this  surface,  at  other  times  only  laid  bare 
by  the  removal  of  superincumbent  deposits,  the  observer  will  have  to 
dismiss  from  his  mind  the  existing  dry  lands  and  waters  of  the  world, 
and  substitute  such  other  distributions  of  them  as  may  best  accord  with 
the  evidence  which,  from  time  to  time,  he  will  obtain.  No  matter  how 
highly  raised  into  mountains,  or  slightly  elevated  in  plains,  these  ancient 
bottoms  of  oceans,  seas,  and  bodies  of  fresh  water  may  now  be,  they 
did  not  constitute  dry  land  when  formed,  and  consequently  waters  once 
occupied  the  areas  where  they  now  occur.  We  have  seen  that  to  pro- 
duce detrital  accumulations,  certain  conditions  of  dry  land  are  needed, 
whence  their  component  parts  have  to  be  derived ;  and,  therefore,  to  form 
the  ancient  sea  bottoms  of  any  given  time,  dry  land  appears  required 
out  of  an  area  so  circumstanced,  and  yet  so  near  to  it  as  to  afford  the 
materials  found.  Considerations  of  this  kind  demand  an  enlarged  view 
of  the  physical  geography  of  different  geological  times,  and  such  a  dis- 
regard of  the  existing  distribution  of  land  and  water  that  while  all  due 
weight  is  allowed  for  the  employment  of  a  given  amount  of  mineral 
matter,  over  certain  large  areas,  in  the  production  of  detrital  accumu- 
lations of  different  dates — the  wearing  away  of  one  portion  raised  above 
the  ocean  presenting  materials  for  an  equal  and  subsequent  deposit  be- 
neath it  in  an  adjacent  situation  ;  and  consequently,  that  oscillations  in 
the  relative  levels  of  the  existing  areas  of  our  present  continents  may 
keep  such  matter  much  in  one  large  area, — the  mind  of  the  observer  must 
not  be  too  much  occupied  by  the  present  arrangements  of  land  and  water 
on  the  surface  of  the  earth. 

While  evidence  is  sought  amid  detrital  or  fossiliferous  accumulations, 
of  the  mode  in  which  the  mineral  matter  of  rocks  has  been  chemically 


MIXTUKE    OF    BEDS    WITH    AND    WITHOUT    FOSSILS.      457 

or  mechanically  gathered  together,  and  the  observer  endeavours  to  trace 
among  them  former  beaches,  estuaries,  bays,  promontories,  shallow  and 
deep  seas,  fresh-water  lakes,  and  the  other  modifications  of  water  around 
and  amid  dry  land,  he  has  at  the  same  time  most  carefully  to  study  the 
mode  of  occurrence  of  any  organic  remains  found  in  these  accumulations. 
He  will  have  to  see  if  there  be  evidence  that  the  animals  or  plants  lived 
and  died  in  or  upon  the  beds  where  their  remains  are  now  found ;  or 
whether,  after  death,  such  remains  were  drifted  into  these  situations. 
He  will  also  have  most  carefully  to  refer  to  the  distribution  of  the  ani- 
mals and  plants,  existing  at  any  given  geological  time  according  to 
conditions,  regarding  that  distribution  as  well  on  the  large  scale  as  with 
respect  to  any  minor  area. 

With  respect  to  the  class  of  rocks  usually  named  fossiliferous,  this 
term  has  to  be  regarded  in  an  extended  sense.  It  is  by  no  means 
required  that  the  various  beds  composing  any  given  series  of  sea  bottoms, 
should  all  contain  organic  remains  in  certain  localities.  Frequently,  as 
in  the  subjoined  sketch  (fig.  163),  representing  a  series  of  beds  of  rock, 

Fig.  163. 


a,  5,  Cj  d,  and  e,  exposed  on  a  cliff,  one  of  them  only,  such  as  c?,  may 
contain  them,  the  others  not  affording  any  animal  or  vegetable  exuviae. 
These  beds  are  not,  however,  the  less  interesting  on  that  account,  inas- 
much as  some  cause  for  this  difference  may  present  itself  by  diligent 
investigation,  of  importance  as  bearing  upon  the  conditions,  or  their 
modifications,  under  which  the  whole  series  may  have  been  formed. 
Should  the  beds  be  of  different  substances — as,  for  example,  should  a,  6, 
and  e,  be  formed  of  sands  of  different  kinds,  consolidated,  as  hereafter 
to  be  noticed,  into  sandstones ;  c,  of  gravels  now  hardened  into  a  con- 
glomerate ;  and  d  be  composed  of  mud,  now  constituting  a  shale  ;  the 
mode  of  accumulation  of  the  non-fossiliferous  beds  have  to  be  studied, 
as  well  on  the  small  as  large  scale ;  and  this  study  may  tend  to  show 
how  it  probably  occurred  that  the  mud  contained  the  remains  of  life, 
which  has  existed  on  or  in  this  sea  bottom  of  the  time,  while  no  such 
remains  are  found  in  the  sands  and  gravel. 

Some  rocks  are  only  seen  to  be  fossiliferous  at  rare  intervals,  a  depth 


458        VARIABLE    MODE    OF    OCCURRENCE    OF    ORGANIC 

of  perhaps  only  two  or  three  inches  affording  organic  remains,  these 
occurring  amid  a  great  mass  of  mud,  silt,  and  sand,  as,  for  example, 
among  the  lower  of  the  oldest  fossiliferous  deposits — the  Silurian, — a 
class  of  rocks  for  the  due  appreciation  and  knowledge  of  which  geolo- 
gists stand  so  much  indebted  to  Sir  Roderick  Murchison.  In  certain 
parts  of  this  series,  as  developed  in  the  British  Islands,  there  are 
hundreds  of  feet  in  depth,  in  certain  localities,  where  no  trace  of  an 
organic  remain  is  found,  and  then  a  thin  seam,  replete  with  the  remains 
of  animal  life,  may  be  seen,  showing  that  the  portion  of  the  sea-bottom 
which  it  represents  was  a  me,re  thin  sheet  of  little  else  than  the  crusta- 
ceans, molluscs,  and  corals  of  the  time — partly,  perhaps,  living,  partly 
dead,  or  all  in  one  state  or  the  other.  Nevertheless,  the  whole  series 
of  deposits  of  which  such  seams  constitute  a  portion  (forming,  as  it 
were,  rare  streaks  in  the  general  mass),  is  the  section  of  a  certain^  minor 
area  in  the  sea-bottoms  of  the  time  and  locality,  wherein  the  fitting 
conditions  for  the  development  of  the  germs  and  subsequent  existence 
of  the  perfect  animals  occasionally  presented  themselves.  The  probable 
cause  for  this  distribution  and  mode  of  occurrence  has  to  be  sought  and 
well  considered,  and  herein  the  non-fossiliferous  portion  of  the  general 
mass  becomes  important  for  the  solution  of  the  problem. 

At  other  times  very  variable  kinds  of  beds  are  all  full  of  organic  re- 
mains, as,  for  example,  in  such  a  section  as  that  beneath  (fig.  164),  where 

Fig.  164. 


a  cliff  may  afford  a  view  of  the  various  sea-bottoms  which  have  succeeded 
each  other  in  that  locality,  when  the  whole  was  beneath  water.  If,  for 
illustration,  a  be  a  calcareo-siliceous  sandstone;  £>,  a  coarser-grained 
siliceous  sandstone ;  c,  a  marl  or  clay ;  and  d,  a  fine  argillo-siliceous 
sandstone ;  then,  so  far  as  the  section  extends,  there  was  formed  a  silty 
bottom,  to  which  succeeded  mud,  which  in  its  turn  was  covered  by 
siliceous  sand ;  over  which,  as  the  general  accumulation  proceeded,  a 
finer  sand,  with  the  addition  of  calcareous  matter,  was  deposited. 
There  is  here  evidence  that  the  physical  conditions  affecting  the  area 


REMAINS    AMID    DETRITAL    AND   FOSSILIFEROUS   ROCKS.    459 

wherein  these  deposits  were  effected  must  have  been  modified  or 
changed,  and  an  observer  would  in  consequence  search  for  that  showing 
how  far  any  modification  or  change  in  the  animal  life,  the  remains  of 
which  are  detected  in  the  various  beds,  may  have  been  contemporane- 
ously produced. 

In  seeking  the  boundaries  of  any  ancient  land  which  may  have  fur- 
nished the  mud,  silt,  sand,  and  gravels  of  accumulations  around  it,  of 
whatever  geological  date  the  one  or  the  other  may  be,  it  becomes  evi- 
dently important  to  look  for  traces  of  ancient  beaches,  inasmuch  as 
these  show  the  actual  margins  of  the  seas  of  the  time.  From  the  desire 
at  present  manifested  of  following  out  investigations  of  'this  order,  such 
beaches  have  been  more  frequently  detected  than  might  at  one  time 
have  been  expected.  From  the  researches  of  Professor  Ramsay,  it  has 
been  ascertained  that  during  the  deposit  of  the  Silurian  rocks  of  Wales 
and  Shropshire,  there  was  a  time  when  the  older  accumulations  now 
forming  the  district  of  the  Longmynds,  rose  above  the  sea,  and  were 
bounded  by  beaches ;  while  a  part  of  the  Silurian  series,  named  the 
Caradoc  sandstones,  was  being  deposited  adjacent  to  them.*  Again, 
in  the  Malvern  district,  the  labours  of  Professor  John  Phillips  have 
shown  that  about  the  same  geological  date,  a  portion  of  the  sienites  of 
the  Malvern  Hills  must  have  been  above  the  sea ;  a  beach  deposit,  in 
which  there  are  angular  fragments  of  the  pre-existing  rocks,  occurring 
at  the  Sugar-loaf  Hill,  on  their  western  flank,  f  In  both  cases,  organic 
remains  are  detected  mingled  with  the  shore  accumulations,  and  Pro- 
fessor Edward  Forbes  considers  that  those  which  he  has  examined  in 
the  Longmynd  district  are  of  a  coast  character.!  These  may  not  be 
among  the  oldest  beach  and  littoral  deposits  in  the  British  Islands, 
inasmuch  as  where  conglomerates  are  found  among  the  beds  of  the 
Cambrian  rocks  near  Bangor,  North  Wales,  such  may  also  have  con- 
stituted the  shores  of  still  more  ancient  lands,  furnishing  the  materials 
for  these  conglomerates. 

In  the  ascending  series  of  fossiliferous  rocks,  the  materials  of  which 
were  furnished  at  succeeding  geological  times,  the  like  kind  of  evidence, 
if  carefully  sought  for,  is  to  be  obtained  in  many  localities.  To  take 
the  old  red  sandstone  series,  as  shown  in  the  British  Islands,  while  part 
of  it  may  merely  constitute  a  portion  of  deposits  formed  one  after  the 
other  beneath  the  waters  of  a  sea,  as  in  Devonshire,  other  parts  point 
to  a  littoral  origin.  This  may  be  well  inferred  from  the  mode  of  occur- 
rence of  the  old  red  sandstone  series  in  parts  of  Ireland,  North  Wales, 
and  Scotland,  where  shingles  of  various  sizes,  sometimes  large,  are 
arranged  around  masses  of  older  rocks,  and  follow  many  sinuosities  of 

*  "  Journal  of  the  Geological  Society  of  London,"  vol.  iv.  p.  294. 

f  "  Memoirs  of  the  Geological  Survey  of  Great  Britain,"  vol.  ii.  p.  67. 

J  "Journal  of  the  Geological  Society  of  London,"  vol.  iv.  p.  297. 


460  BEACHES    ON    SHORES    AT    THE    TIME    OF    THE 

the  more  ancient  land  against  which  they  were  piled.  Portions  of  the 
older  land  of  the  time  have  sometimes  an  insular  character,  as,  for 
example,  in  the  County  Kildare,  in  Ireland,  where  the  range  of  heights, 
chiefly  known,  from  one  of  them,  as  that  of  the  Chair  of  Kildare,  seems 
to  have  risen  above  the  sea  of  the  time,  its  rocks  furnishing  materials 
for  the  shingle  on  its  shores,  the  whole  having  been  subsequently 
covered,  or  nearly  so,  by  the  calcareous  deposit  known  as  the  carbo- 
niferous limestone,  the  removal  or  denudation  of  which  (in  its  turn 
furnishing  an  abundance  of  the  shingles  or  gravel  at  other  and  later 
geological  times)  has  in  a  great  measure  disclosed  this  arrangement  of 
parts,  and  left  the  range  of  the  Chair  of  Kildare,  even  now  rising  like 
an  island  above  a  level  district. 

Quitting  these  more  ancient  accumulations,  and  still  not  passing 
beyond  the  area  of  the  British  Islands,  in  order  to  show  how  much  of  this 
kind  of  observation  may  be  carried  out  in  such  a  minor  portion  of  the 
earth's  surface,  we  again  find  marked  evidences  of  beaches,  at  the  time 
commonly  known  as  that  of  the  new  red  sandstone  series,  one  in  these 
islands  following  much  new  adjustment  in  the  relative  distribution  of 
land  and  water,  and  by  which  the  former  bottoms  of  seas  and  of  fresh- 
water deposits  were  irregularly  upraised  (the  coal  measures  probably 
just  above  the  waters,  and  formed  by  continued  depressions  beneath 
their  level).  In  the  southwestern  portion  of  England  and  in  South 
Wales,  the  beaches  of  the  time,  though  they  are  by  no  means  absent  or 
indistinct  in  many  other  districts,  are  particularly  well  exhibited. 

Among  the  Mendip  Hills  (Somerset),  in  various  parts  of  Gloucester- 
shire, Monmouthshire,  and  in  Glamorganshire,  we  have,  from  the  re- 
moval of  subsequent  accumulations  by  denuding  causes,  evidence  of  an- 
cient shores,  as  is  the  case  near  the  Chair  of  Kildare,  though  the  latter 
are  of  earlier  geological  date.  As  at  the  latter,  also,  from  a  repetition 
of  similar  causes,  we  seem  to  have  islands  with  their  beaches  before  us, 
much  as  they  existed  at  this  subsequent  time.  In  investigations  of  this 
kind  it  sometimes  happens  that  sections  are  presented,  or  information 
obtained,  justifying  the  construction  of  sections,  by  which  it  is  shown 
that,  during  the  submergence  of  the  dry  land,  while  the  mud,  silt,  sand, 
and  shingles  were  accumulating  along  the  shores  and  the  islands  of 
the  time,  beach  after  beach  became  buried  up,  a  long  wide-spread  patch 
of  shingles  covering  some  subjacent  ground,  as  it  gradually  sank  beneath 
the  sea  level  of  the  period.  The  subjoined  sections  (figs.  165,  166)  of 
the  ancient  island  of  old  red  sandstone  and  carboniferous  limestone  of 
the  Mendip  Hills,  and  also  of  another  island  of  a  somewhat  similar 
character,  one  of  several  in  the  vicinity  of  Bristol,  may  serve  to  show 
this  circumstance ;  as  also  how  shingles  of  the  same  general  character, 
and  derived  from  subjacent  or  adjoining  rocks,  under  similar  general 
circumstances,  may  be  accumulated  as  a  beach,  on  sloping  ground, 


SILURIAN,    OLD    AND    NEW    RED    SANDSTONE    ROCKS.      461 

during  the  lapse  of  much  geological  time,  while  the  dry  land  of  a  par- 
ticular locality  became  gradually  submerged  beneath  the  sea.     Both 


Fig.  165. 


a,  a,  a,  disturbed  beds  of  carboniferous  limestone ;  b,  b,  conglomerate  of  pebbles 
derived  from  the  subjacent  or  adjoining  rocks,  cemented  by  magnesio-calcareous  mat- 
ter ;  c,  red  marls ;  d,  d}  line  showing  how  denudation  might  cause  successive  accumu- 
lations to  appear  as  of  one  time. 

sections  exhibit  the  beaches,  usually  composed  of  shingles  of  carbo- 
niferous limestone,  now  cemented  by  magnesio-calcareous  matter,  jut- 
ting, as  it  were,  into  the  red  mud  of  the  time  (now  red  marls),  having 
extended  over  one  portion  of  it  during  the  submergence,  and  having 
been  covered  by  another  as  this  proceeded.  One  section  (fig.  165) 
shows  only  the  accumulation  of  the  red  mud  (marl),  while  the  other 
(fig.  166)  exhibits  a  subsequently  formed  deposit  of  dark  mud,  some- 
times calcareous,  alternating  with  an  argillaceous  limestone,  together 
known  as  the  lias.  In  the  red  mud  no  traces  of  a  marine  organic  re- 


a,  a,  beds  of  disturbed  carboniferous  limestone  ;  b,  b,  conglomerate  of  pebbles  de- 
rived from  the  subjacent  or  adjoining  rocks,  cemented  by  magnesio-calcareous  matter; 
c,  red  marl ;  d,  lias ;  B,  Blaize  Castle  Hill,  near  Bristol ;  s,  Mount  Skitham. 

main  have  been  detected  in  that  district,  though  more  northerly,  streaks 
of  them  are  found ;  but  even  supposing  some  rare  organic  remains  may 
hereafter  be  discovered,  there  is  still  evidence  of  a  beach  resting  on  a 
coast,  this  beach  thrown  up  by  seas  during  a  period  when  the  dry  land 
was  becoming  gradually  submerged,  and  a  change  was  effecting  in  the 
existing  conditions,  so  that  the  adjacent  sea  was  no  longer  without 
animal  life,  or  at  least  only  contained  a  small  portion  of  that  affording 
harder  parts  for  preservation  amid  the  deposits  of  the  time,  but 
swarmed  with  molluscs,  fish,  and  reptiles.  The  manner  in  which  the 
filling  up  was  effected  is  well  shown  in  the  section  near  Blaize  Castle 
(fig.  166),  though  evidence  of  this  kind  is  to  be  found  as  well  elsewhere  ; 
one  patch  of  lias  (d,  on  the  right  of  the  figure)  nearly  reaching  over 
the  old  beach,  as  it  actually  does  at  no  great  distance  on  the  westward, 
where  it  covers  up  the  carboniferous  limestone  on  the  margin  of  the 
coal  field  from  Redland,  near  Bristol,  to  Alverston,  on  the  north.  •  The 
observer  will  perceive  that  if  the  denuding  causes  which  have  removed 
so  much  of  the  deposits  of  a  later  geological  date  than  these  old  shingle 


462      BEACHES    OF    THE    NEW    RED    SANDSTONE    PERIOD 


beaches,  had  carried  off  all  traces  of  them  in  the  section  near  Compton 
Martin,  Mendip  Hills  (fig.  165),  so  that  a  surface  corresponding  with 
the  line,  d,  d,  had  only  been  exposed,  there  would  have  been  great 
difficulty  in  assigning  the  different  parts  of  this  shingle  (now  conglome- 
rate) covering  to  their  relative  geological  dates  ;  though,  with  the  old 

Fig.  167. 


1.  Old  Red  Sandstone. 

2.  Carboniferous  Limestone. 

3.  Coal  Measures. 

4.  Dolomitic  Conglomerate. 

5.  New   Red  Marl  and  Sand- 

stone. 

6.  Lias. 

7.'  Inferior  Oolite. 
8.  Alluvial. 


IN    THE    MENDIP     HILLS    AND    NEAR    BRISTOL.  463 

mud  and  sands  outside  of  them,  deposited  at  successive  times,  the  rela- 
tive date  of  the  parts  is  sufficiently  obvious. 

While  on  the  subject  of  this  district,  it  may  not  be  uninstructive,  as 
it  is  one  fertile  in  information,  within  so  very  small  an  area,  to  call  the 
attention  of  the  observer  to  the  successive  coatings  of  fossiliferous 
accumulations  as  they  followed  one  another,  each  spreading  over  a  part 
of  a  preceding  deposit,  as  the  dry  land  of  the  Mendip  Hills  and  adjacent 
country  sank,  and  as  it  would  appear,  gradually,  beneath  the  sea.  For 
this  purpose  the  preceding  map  (fig.  167)  may  be  useful.-  In  it 
the  different  deposits  represented  consist,  in  the  ascending  series,  of  (1) 
old  red  sandstone ;  (2)  carboniferous  or  mountain  limestone ;  (3)  coal 
measures ;  (4)  dolomitic  or  calcareo-magnesian  conglomerate  and  lime- 
stone ;  (5)  the  new  red  sandstone  and  marl ;  (6)  lias ;  (7)  inferior  oolite, 
and  others  of  the  lower  part  of  the  series,  known  as  the  oolitic  or  Ju- 
rassic ;  and  (8)  alluvial  accumulations,  deposits  from  branches  of  the 
adjacent  Bristol  Channel,  where  these  found  their  way  amid  the  sinu- 
osities of  the  land,  often  covering  a  plane  whereon  forests  once  grew,  at 
a  higher  relative  level  of  sea  and  land  than  now  exists,  the  outcrops  of 
these  sheets  of  concealed  vegetable  matter  and  trees  forming  the  "  sub- 
marine forests"  of  Stolford  and  other  places  on  the  present  coast  (p. 
435).* 

The  darkly-dotted  patches  in  the  map  (conglomerates,  4)  will  serve 
to  show  the  mode  of  occurrence  of  the  beaches  surrounding  the  older 
rocks  of  the  Mendip  Hills,  and  an  adjoining  portion  of  country  near 
Wrington,  /.  Although,  from  the  travelling  upwards  of  continuous 
portions  of  these  beaches  during  the  gradual  submergence  of  the  dry 
land,  and  the  subsequent  wearing  of  the  rocks,  including  all  in  the  dis- 
trict, up  to  the  time  of  its  alluvial  plains  inclusive,  they  may  not  give 
the  exact  representation  of  the  beaches  of  one  time,  they  will  stijl  serve 
to  show  the  manner  in  which  they  were  accumulated  round  this  old 
portion  of  dry  land.  Taken  in  connexion  with  similar  facts  observable 
even  so  near  as  Gloucestershire  and  Glamorganshire, f  and  looking  at 
the  size  of  the  rounded  fragments  sometimes  found  in  them,  the  effects 

*  The  names  of  the  various  places  marked  by  crosses  and  letters  in  the  map  (fig.  167) 
are  as  follows  : — a,  Tickenham ;  b,  Nailsea ;  c,  Chelvey ;  d,  Brockley  ;  e,  Kingston  Sey- 
mour ;  /,  Wrington ;  g,  Nempnet ;  k,  Congresbury ;  I,  Banwell ;  m,  Locking ;  n,  Bleadon ; 
o,  Lympsham ;  p,  Burington ;  q,  Compton  Martin ;  r,  Hinton  Blewet ;  *,  East  Harptree ; 
t,  Lilton ;  v,  Chew  Stoke  ;  x,  Chew  Magna  ;  y,  Stowey ;  of,  Shipham ;  b't  Biddesham ;  </, 
Badgworth  ;  df,  Weare ;  ef,  Axbridge  ;  /',  Chapel  Allerton  ;  /,  Chedder ;  h',  Priddy ;  iv, 
Binegar ;  #,  Chewton  Mendip ;  Vt  Wedmore ;  m',  Radstock  ;  nf,  Kilmersdon ;  c/,  Dray- 
cot  ;  /,  Stoke  Rodney ;  qf,  Westbury ;  /,  Wookey ;  «',  Dinder ;  t',  Crosscombe  ;  t/,  North 
Wooton  ;  w,  Wells ;  x'  Shepton  Mallet ;  y',  Downhead  ;  z',  Mells  ;  a",  Elm ;  b",  Whatley ; 
c",  Nunney ;  d",  Cloford;  e",  East  Cranmore;  and/",  Chasterblade. 

f  See  the  Geological  Map,  "Memoirs  of  the  Geological  Survey  of  Great  Britain," 
vol.  i.  pi.  2,  in  which  a  large  area  occupied  by  accumulations  of  this  class  and  time 
will  be  found  represented. 


464  BEACHES    OF    THE    TIME    OF    THE    LIAS. 

of  considerable  breaker  action  is  observable  on  the  shingles,  and  they 
seem  to  have  been  well  piled  up  at  the  bottom  of  old  bays  and  other 
localities  where  favourable  conditions  for  their  production  existed.  The 
following  section  (fig.  168)  will  show  one  of  these  ancient  beaches  facing 


a  a,  limestones,  intermingled  with  sandstones  and  marls,  of  the  upper  part  of  the 
carboniferous  limestone  series  of  the  district,  brought  in  by  a  large  fault,  on  the  N.W. 
of  the  Windmill  Hill,  Clifton ;  b,  boulders  and  pebbles,  in  part  subangular,  of  the  sub- 
jacent rocks,  cemented  by  matter  in  part  calcareo-magnesian,  variably  consolidated ; 
c,  conglomerate  or  breccia,  in  which  the  magnesio-calcareous  matter  is  more  abundant, 
becoming  more  so  at  d,  where  it  further  assumes  the  character  of  the  more  pure  dolo- 
mitic  limestone  in  which  pebbles  and  fragments  do  not  occur. 

the  gorge  of  the  Avon,  near  Clifton,  Bristol,  in  a  depression  between 
Durdham  Down  and  Clifton  Hill,  in  which  some  of  the  rounded  por- 
tions of  the  subjacent  rock  cannot  be  much  less  than  two  tons  in  weight, 
requiring  no  slight  force  of  breaker  action  to  move  them  and  heap  them 
up  as  now  seen. 

The  submergence  of  this  dry  land  continuing  while  geological  changes 
were  being  effected  over  a  wide  area  (in  which  this  district  occurred  as 
a  mere  point),  and  so  that,  without  reference  to  the  modifications  of 
deposits  produced  elsewhere,  the  red  sediment  of  the  seas  near  the 
shores  of  the  land,  then  above  water  in  the  area  of  the  British  Islands, 
was  succeeded  by  others  in  and  above  which  animal  life  swarmed,  the 
beaches  moved  upwards  on  the  slopes  of  adjacent  rocks.  Thus  the 
rolled  pebbles  of  the  latter,  and  of  the  cliffs  of  the  time,  were  occasion- 
ally intermingled  with  the  remains  of  the  animal  life  then  existing. 
Near  Shepton  Mallet  (#',  in  the  map,  fig.  167),  where  the  lias  (6)  rests 
both  on  the  old  red  sandstone  (1),  and  the  carboniferous  limestone  (2), 
there  is  much  of  this  old  shingle  (now  conglomerate).*  The  following 

Fig.  169. 


a  a       /          d  d   g  d 

(fig.  169)  is  a  section,  exhibited  close  to  Shepton  Mallet,  on  the  Bath 

*  These  conglomerates,  which  are  abundant,  and  wherein  the  pebbles  are  chiefly 
derived  from  the  adjacent  carboniferous  limestone,  have  been  long  since  pointed  out  by 
Dr.  Buokland  and  the  Rev.  W.  Conybeare  (1824),  "  Observations  on  the  Southwestern 
Coal  District  of  England;"  Geological  Transactions,  2d  series,  vol.  i.  p.  294. 


LIAS    NEAR    SHEPTON    MALLET,    SOMERSETSHIRE.       465 

Road,  wherein  a  line  of  pebbles  (b)  is  strewed  over  the  previously  up- 
turned edges  of  supporting  carboniferous  limestone  (a,  a\  and  consti- 
tutes a  continuation  of  some  more  arenaceous  and  pebble  beds,  present- 
ing much  the  appearance  of  a  shore,  not  far  distant.*  The  lias  at  £, 
covering  this  pebble  or  shingle  bed,  has  been  thrown  down  (as  it  is 
termed)  by  a  dislocation,  or  fault  /,  so  that  beds  above  that  at  <?,  are 
seen  at  d,  d,  d,  the  latter  again  broken  through  by  a  dislocation  at  g, 
and  the  whole  surface  of  the  hill  being  so  smoothed  off  by  denuding 
causes,  that  a  gently-sloping  plane  is  alone  seen.  Before  we  quit  this 
section,  it  may  be  mentioned,  that  an  observer  in  search  of  the  different 
conditions  under  which  fossiliferous  deposits  may  have  accumulated,  will 
here  see  that  much  less  mud  must  have  been  mixed  with  the  calcareous 
matter  of  the  lias  than  is  usual  in  the  district,  and  which  is  to  be  found 
not  far  distant  from  this  locality.  The  lias  limestone  beds  (d,  d,  d)  are 
here  thick,  for  the  most  part,  and  in  purity  more  resemble  the  carboni- 
ferous limestone  (a,  a)  on  which  they  rest,  showing  a  cleaner  state  of 
the  sea  where  they  were  formed  than  in  those  areas  over  which  the  usual 
mud,  and  muddy  and  silty  limestone  of  the  lias  were  accumulated. 
Coupled  with  the  evidence  of  beaches,  this  greater  freedom  from  mud 
would  seem  to  point  to  the  greater  proximity  of  a  shore  with  minor 
depths  of  sea,  near  and  at  which  the  waters  were  generally  more  dis- 
turbed, so  that  the  lighter  substances  being  readily  held  in  mechanical 
suspension,  they  were  easily  moved  away  by  tides  and  currents  to  more 
fitting  situations  for  deposit. 

This  character  of  a  less  muddy  condition  of  the  lias  is  by  no  means 
confined  to  the  vicinity  of  Shepton  Mallet ;  it  is  to  be  seen  in  several 
places  in  that  part  of  England  and  South  Wales.  It  is  well  shown  in 
parts  of  Glamorganshire,  where,  indeed,  as  in  the  vicinity  of  Merthyr 
Mawr,  care  is  required  not  to  confound  some  of  it  with  the  carboniferous 
limestone  to  which  it  there  bears  no  inconsiderable  mineralogical  resem- 
blance. Here,  again,  the  observer  finds  this  character  in  connexion 
with  old  conglomerates,  resembling  beach  accumulations  of  the  time  of 
the  lias,  pointing  to  the  probable  proximity  of  dry  land,  such  as  may 
be  readily  inferred  to  have  then  existed  in  the  great  coal  district  on  the 

Fig.  170. 


north  of  it,  even  now,  after  so  much  abrasion,  during  depressions  and 
elevations  beneath  and  above  the  sea  during  a  long  lapse  of  geological 
time,  rising  high  above  these  deposits.  In  the  same  neighbourhood 

*  This  was  well  seen  further  up  the  road,  in  1845,  at  which  time  some  new  cuttings 
were  in  progress. 

30 


466 


LIAS    BESTING    ON    DISTURBED 


(Dunraven),  there  is  also  good  evidence  of  the  lias  reposing  upon  a 
clean  surface  of  carboniferous  limestone,  as  will  be  seen  in  the  annexed 
sketch  (fig.  171),  and  in  the  preceding  section  (fig.  170),  wherein  a  repre- 


CARBONIFEROUS  LIMESTONE. 


467 


sents  disturbed  strata  of  the  latter,  and  b  beds  of  the  former,  resting  on 
their  edges.  In  the  section  (fig.  170),  the  lower  beds  (b)  of  the  lias  are 
light-coloured,  and  contain  fragments  from  the  subjacent  carboniferous 
limestone,  these  succeeded  by  argillaceous  gray  limestones  at  <?.  /,  /, 
are  dislocations  or  faults,  traversing  the  beds.  In  this  case,  though  an 
observer  might  suspect  the  vicinity  of  a  coast  from  the  fragments  in  the 
lower  lias,  he  would  desire  further  evidence,  and  by  search  he  would 
find,  round  the  point  d,  in  the  sketch  (fig.  171),  a  conglomerate  (5,  6, 
fig.  172),  reminding  him  of  a  beach  interposed,  to  a  certain  extent  and 
level,  between  the  beds  of  lias  (d,  d\  and  a  worn  slope  of  supporting 
carboniferous  limestone  beds  '(a,  a),  which  here,  from  a  local  curvature, 
are  brought  into  a  horizontal  position.  At  <?,  in  this  section,  the  whitish 
variety  of  the  lias  of  the  district  is  found  in  a  great  measure  free  from 
muddy  admixture.  It  is  even  occasionally  dolomitic,  and  somewhat 
crystalline  in  this  vicinity.* 

Fig.  172. 


Returning  to  the  minor  area  of  the  Mendip  Hills  for  evidence  re- 
specting the  dry  land  and  shores  of  the  locality  and  period,  we  find,  as 
the  land  became  more  and  more  depressed  beneath  the  sea,  that  the  lias, 


Fig.  173. 


a,  gray  lias  limestone  and  marls ;  6,  earthy  whitish  limestone  and  marls ;  c,  earthy 
white  lias  limestone ;  d,  arenaceous  limestone ;  e,  gray  marls ;  g,  red  marls ;  A,  sand- 
stone, with  calcareous  cement ;  t,  blue  marl ;  k,  red  marl ;  I,  blue  marl ;  and  ra,  red 
marls. 

as  it  were,  crept  up  the  sides  of  the  steeper  shores,  accumulating  more 
muddy  matter  outwards,  depressions  being  filled  up,  sometimes  even  on 
the  shores  when  sufficient  tranquillity  permitted  such  a  deposit,  fine 

*  Part  of  these  lower  beds  of  the  lias  of  the  district  is  known  as  Sutton  Stone,  and 
has  been  employed  for  architectural  purposes  during  many  centuries,  being  well  fitted  for 
them. 


468         BORING    MOLLUSCS    OF    THE    INFERIOR    OOLITE. 

sediment  accumulating  above  fine  sediment,  so  that  there  was  a  kind  of 
passage  of  the  lias  into  the  fine  red  marls  beneath  (fig.  173.)* 

The  observer  next  finds  limestone  beds  (7),  known  as  the  inferior 
oolite,  resting  (map,  fig.  167)  from  Cranmore  (e")  on  the  south,  to 
Mells  (z')  on  the  north,  upon  various  older  accumulations ;  old  red  sand- 
stone (1),  carboniferous  limestone  (2),  coal  measures  (3),  and  lias  (6), 
passing  over  the  nearly  horizontal  beds  of  the  latter  as  well  as  the 
variously-curved  beds  of  the  three  former.  The  remains  of  animals  of 
marine  character  show  that  this  accumulation  was  effected  in  a  sea,  and 
therefore,  that  the  depression  of  the  land  above-mentioned  had  con- 
tinued; but,  as  no  distinct  beaches  have  yet  been  discovered  in  con- 
nexion with  this  calcareous  deposit,  the  probable  boundaries  between 
the  sea  and  the  land  are  not  so  apparent.  It  is  not  clear  that  the 
whole  of  the  Mendip  Hills  may  not  have  been  beneath  the  waters, 
though  the  relative  levels  of  the  different  parts  of  the  general  masses  of 
rock,  notwithstanding  the  changes  in  these  levels  produced  by  various 
dislocations,  effected  during  a  long  lapse  of  geological  time,  would  lead 
us  to  infer  that  portions  of  dry  land  may  still  here  and  there  have  risen 
above  the  sea  in  that  minor  area.  Be  this  as  it  may,  when  this  over- 
spread of  calcareous  matter  (inferior  oolite)  took  place,  passing  over  the 
old  margin  of  the  lias,  there  were  bare  patches  of  carboniferous  lime- 
stone (2)  in  the  sea,  and  into  these  the  boring  animals  of  the  time  bur- 
rowed. Their  remains  are  now  found  in  the  holes  worked  by  them ; 
and  when  good  surfaces  are  exposed,  an  observer  might  imagine  himself 
walking  on  limestone  rocks,  dry  at  low  tides,  in  which  the  lithodomous 
molluscs  of  the  present  day  were  in  the  cells  hollowed  out  by  them. 
Not  only  are  these  old  surfaces  thus  bored  by  the  rock-burrowing  mol- 
luscs of  that  period  (the  time  of  the  inferior  oolite  deposit),  but  here 
and  there — as,  for  example,  near  Nunney  (c"), — the  oysters  of  the  same 
date  are  still  found  adhering  to  the  bare  limestone  submarine  sur- 
faces of  the  time.  There  may  be  doubts  as  to  the  depths  at  which  the 
boring  molluscs  worked,  and  the  oysters  adhered  to  these  bare  carbo- 
niferous limestone  rocks ;  the  whole  of  the  old  dry  land  may,  as  before 
mentioned,  have  been  then  under  water;  but  while  the  observer  thus 
loses  his  traces  of  dry  land,  he  has  evidence  that  it  still  continued  to 
descend,  so  that,  at  least,  the  movement  in  that  direction  had  not  ceased. 

The  following  section  (fig.  174)  will  serve  to  illustrate  the  manner  in 

Fig.  174. 


c  b  a 

which  the  older  beaches  (d,  m)  were  overlapped,  as  it  is  termed,  by  the 

*  The  section  selected  is  from  the  vicinity  of  Shepton  Mallet,  reference  to  which  has 
been  previously  made  in  the  text,  p.  464. 


OVERLAP    OF    THE    INFERIOR    OOLITE,    MENDIP    HILLS.     469 

inferior  oolite  (g,  n).  The  sands,  commonly  known  as  the  inferior  oolite 
sands  (/),  separating  the  calcareous  beds  of  the  inferior  oolite  from  the 
lias  (e\  including  in  the  latter  the  upper  beds  of  that  rock  termed  the 
marlstone  (an  accumulation  replete  with  organic  remains),  is  also  over- 
lapped, h  I  is  the  clay  known  as  Fuller's  earth,  i  its  limestone. 

With  regard  to  the  mode  of  occurrence  of  the  inferior  oolite  (7,  map, 
fig.  167),  the  annexed  sketch,  taken  near  Frome,  on  the  road  to  Mells, 

Fig.  175. 


will  show  not  only  the  manner  in  which  it  (a)  frequently  rests  on  sub- 
jacent carboniferous  limestone  (<?),  but  also  the  very  even  surface  which 
the  latter  frequently  presents  over  comparatively  large  areas  in  that 
vicinity.  These  surfaces  are  usually  drilled  not  only  by  the  large 
boring  mollusc  of  the  time,  occasionally  found  in  their  holes,  as  shown 
beneath  (a,  fig.  176),  but  also,  in  a  more  tortuous  manner,  by  another 

Fig.  176. 


animal,  sections  of  the  holes  made  by  which  are  seen  at  5,  b.  At  b  (fig. 
175)  there  is  a  somewhat  arenaceous  parting,  covering  over  the  bored 
surface  of  the  limestone,  an  introduction  of  matter  which  may  have 
served  to  render  that  surface  no  longer  fitted  for  the  habitation  of  the 
lithodomous  animals. 

To  mark  the  date  of  these  borings  still  more  perfectly,  the  same 
vicinity  fortunately  presents  us  with  evidence  (fig.  177)  of  a  portion  of 
the  shingle  (a),  accumulated  at  the  time  of  the  lias  (organic  remains 
characteristic  of  that  deposit  as  it  occurs  in  the  vicinity  being  found  in 
it),  having  been  consolidated  and  planed  down,  by  denuding  causes,  to 
the  same  level  with  the  carboniferous  limestone,  £>,  5,  in  a  cleft  of  which 
it  occurs,  and  having  been  bored  by  the  same  marine  animals  anterior 
to  the  deposit  of  the  inferior  oolite,  c,  c.  Still  further  affording  the 


470 


LAND    AT    THE    TIME    OF    THE    LIAS. 


observer  relative  dates  for  these  perforations,  he  will  find  that  the  beds  of 
the  inferior  oolite  itself  are  thus  bored,  and  by  the  same  kinds  of  animals, 


Fig.  177. 


iji"  ii'ii  .' 

*>      lii!  II  IM",' 


as  can  be  seen  at  the  quarries  of  Doulting,  on  the  south  of  the  Mendips, 
and  near  Ammersdown,  on  the  north,  where,  as  the  beds  became  suc- 
cessively consolidated,  they  afforded  the  needful  conditions,  on  their 
upper  surfaces,  for  the  existence  of  these  marine  animals,  requiring 
shelter  in  hard  rocks. 

Assuming,  for  illustration,  that  the  older  rocks  of  this  small  district 
became  totally  submerged  at  this  time,  the  geologist  will,  as  it  were, 
have  traced  the  state  of  a  minor  area  from  one  where  there  may  have 
been  dry  land  intermixed  with  sea,  to  another  where  the  latter  over- 
spread all  traces  of  the  former.  What  may  thus  be  done  on  the  small 
scale  can  sometimes  be  readily  effected  over  areas  of  far  wider  extent. 
It  can  be  so,  with  care,  over  much  of  the  British  Islands,  as  respects 
the  probable  intermixture  of  land  and  sea,  at  the  time  of  the  accumula- 
tion of  the  new  red  sandstone  series.  To  a  certain  extent  the  study  of 
any  general  geological  map  of  these  islands  will  show  this,  though  not 
altogether,  since  denuding  causes  have  sometimes  so  acted  as  to  remove 
these  rocks  and  subsequent  deposits  from  localities  which  would,  judging 
from  the  mode  of  occurrence  of  the  rocks  in  them,  have  been  beneath 
the  waters  at  the  time  that  other  portions  of  these  beds  were  formed.* 

*  It  becomes  extremely  interesting  to  consider  the  wide-spread  distribution,  over  a 
portion  of  Western  Europe,  of  the  tranquil  conditions  prevalent  at  the  period  when  the 
marls  (termed  new  red  sandstone  marls,  upper  trias  marls,  marnes  irise'es,  and  keuper) 
ceased  to  be  thrown  down  on  the  sea-bottom  of  the  time  with  such  a  common  ohara«- 
ter,  and  the  mud,  and  calcareous  mud  of  a  succeeding  accumulation,  the  lias,  also 
occurred  over  much  of  the  same  area  with  its  common  character,  carefully  looking  for 
the  probable  lands  whence  the  needful  mineral  supply  was  derived,  and  around  or  on 
which  the  terrestrial  plants,  insects,  flying,  coast,  and  oviparous  reptiles,  and  remains 
of  marine  animals  whose  preserved  hard  portions  correspond  with  littoral  creatures  of 
the  present  time,  existed.  The  careful  sketching,  however  approximative  it  might  at 


EVIDENCE    OF    LAND    FROM    FRESH-WATER    DEPOSITS.     471 

Extending  his  views,  it  behoves  the  observer  still  further  to  consider 
the  probabilities  of  dry  land  over  wider  areas,  such  as  would  embrace 
large  portions  of  our  continents,  if  he  expects  to  arrive  at  comprehen- 
sive conclusions  as  to  the  conditions  which  may  have  governed  the  pro- 
duction of  any  given  detrital  or  fossiliferous  accumulation  which  he  may 
have  under  examination.  As  we  have  seen,  it  is  highly  important  for 
him  to  obtain  good  evidence  of  beaches  wherever  they  can  be  observed, 
inasmuch  as  these  give  him  the  boundaries  of  land  and  sea  at  certain 
geological  times.  These,  however,  he  cannot  always  detect,  since  their 
preservation  will  depend  upon  favourable  circumstances,  such,  for  ex- 
ample, as  their  consolidation  at  the  time  of  their  production,  as  is  now 
effected  in  certain  localities,  or  their  occurrence  in  such  sheltered  situa- 
tions, under  altered  conditions  of  sea  and  land,  that  they  may  be  covered 
up  and  not  be  removed  (p.  441). 

Though  fresh-water  deposits,  as  they  are  termed  (from  the  remains 
detected  in  them  being  limited  to  those  of  terrestrial  and  lacustrine  or 
fluviatile  life),  may  not  give  any  definite  boundaries  of  the  land  and  sea 
for  any  given  geological  time,  they  nevertheless  prove  the  existence  of 
dry  land  surrounding  them  at  that  time.  Supposing  the  great  lakes  of 
North  America  to  be  filled  up,  mechanically  or  chemically,  by  mineral 
matter,  enveloping  the  remains  of  the  life  inhabiting  them,  or  drifted 
into  them  by  rivers,  and  these  accumulations  to  be  elevated  into  the 
atmosphere,  forming  hill  and  dale,  and,  crumpled  and  broken,  even 
parts  of  high  mountains  and  deep  valleys,  though  they  would  not  afford 
an  observer  the  land  boundaries  of  the  present  day,  collectively  taken 
they  might  prove  the  existence  of  no  inconsiderable  tract  of  dry  land 
at  a  given  period.  Seeing  the  apparent  necessity  for  land  above 
the  level  of  the  sea  to  be  worn  away  by  atmospheric  influences,  running 
waters,  and  the  action  of  the  sea,  in  order  to  supply  the  materials,  not 
organic,  for  the  mechanical  deposits  accumulated  in  the  seas  of  any 
particular  geological  time,  should  no  traces  of  it  be  found  in  certain 
regions  amid  fossiliferous  rocks,  either  that  land  was  very  distant,  pos- 

first  be,  of  the  probable  area  occupied  by  land  and  sea  in  the  European  area  at  this 
time,  with  the  distribution  of  organic  remains  found  in  the  lias,  distinguishing  its  upper 
and  lower  parts,  would  alone  furnish  matter  for  much  useful  progress  in  inquiries  of 
this  kind.  The  scarcity  of  animal  remains  in  the  upper  red  or  variegated  marls,  and 
the  distribution  of  the  little  areas  where  these  are  detected,  with  the  subsequent  abun- 
dance of  life,  as  shown  by  its  remains,  constitute  in  themselves  interesting  inquiries  for 
those  tracing  out  effects  to  their  probable  causes,  and  who  reason  from  the  known  to 
the  unknown.  The  unequal  distribution  of  the  saurians  of  the  time,  so  numerous  and 
so  varied  in  certain  localities,  and  the  patches  where  drifted  terrestrial  plants  are  dis- 
covered, afford  much  information  that  is  valuable,  it  appearing  sometimes  needful  to 
suppose  that  the  shores  formed  of  the  mud  and  sands  of  immediately  preceding  accu- 
mulations had  been  upraised  above  the  sea  level,  to  account  for  these  distributions. 
Hence  the  probable  oscillation  of  the  land  at  the  time,  above  and  beneath  the  sea,  be- 
comes also  a  part  of  such  researches. 


472    EFFECTS    PRODUCED    ON     COASTS,    RIVERS,    AND    LAKES 

sessed  no  lakes,  at  least  none  in  which  mineral  deposits  were  formed ; 
had  no  rivers  flowing  from  it  into  the  seas,  carrying  onwards  fresh-water 
animals  to  them ;  or  should  there  have  been  fossiliferous  accumulations 
of  a  fresh-water  kind,  they  had  been  removed  subsequently  to  their 
production. 

To  estimate  the  probable  preservation  of  such  deposits  amid  movements 
of  the  earth's  surface,  depressing  dry  land  beneath  the  level  of  the  sea, 
the  observer  should  direct  his  attention  to  the  effects  which  would  follow 
such  a  change.  If  any  large  area  of  dry  land,  wholly  or  partly  bounded 
by  seas,  were  now  elevated  higher  above  the  latter,  there  would  probably 
be  a  fringe  of  submarine  deposits  upraised  at  the  same  time,  while  the 
various  outflows  of  river  waters  would  have  to  adjust  themselves  to  the 
new  sea  level.  Many  estuaries  would  cease  to  be  such  (if  the  boundary 
seas  were  tidal),  and  the  courses  of  their  feeding  rivers  would  require 
adjustments  in  accordance  with  the  change  of  level ;  much  additional 
velocity,  consequently  scouring  power,  the  volume  of  these  waters 
remaining  the  same  as  a  whole,  being  given  to  those  parts  of  their 
channels,  the  adjustments  of  which  had  been  more  or  less  regulated  by 
the  former  sea  level.  Under  such  conditions,  it  would  happen  as  beneath 
(fig.  178),  that  many  a  river  course  was  so  lowered  that  old  river  beds, 

Fig.  178. 


a,  a,  would  be  left  perched  on  the  sides  of  valleys,  above  those  which 
the  river  had  formed  for  itself,  either  by  removing  loose  materials  accu- 
mulated in  the  valley,  v,  during  its  former  adjustments,  or  by  cutting 
through  some  rocky  barrier,  6,  6,  which  the  new  velocity  of  its  course, 
and  power  to  transport  the  means  of  effective  friction,  have  permitted. 
The  new  coast  line  would  be  variably  acted  upon  by  the  breakers.  In 
cases  of  cliffs  of  hard  rocks,  previously  descending  into  the  sea,  so  that 
upon  the  uprise  of  the  land  the  breakers  still  acted  upon  the  cliffs,  no 
material  difference  would  take  place,  except  so  far  as  the  now  shallower 
depths  adjoining  may  be  more  disturbed  than  previously  by  waves,  so 
that  fine  sediment,  formerly  at  rest,  might  be  removed,  and  its  further 
accumulation  in  that  locality  prevented.  With  the  fringes  of  any  littoral 
sea-bottoms  upraised,  the  effects  would  be  very  different.  The  adjust- 


BY  FURTHER  ELEVATION  OF  LAND  ABOVE  SEA.   473 

rnent  to  the  previous  breaker  action  on  shallow  shores,  especially  on 
those  where  the  surplus  sands  were  driven  on  land,  and  accumulated  in 
sandhills  (p.  85),  would  be  destroyed,  and  the  sea  would  remove  the 
loose  materials  before  it,  until  a  new  balance  of  force  and  resistance  had 
been  again  accomplished,  in  the  manner  represented  beneath  (fig.  179). 

Fig.  179. 


d - 

If  in  this  section  a  be  the  surface  of  the  sea,  after  an  elevation  of  the 
adjoining  land,  so  that  a  sea-bottom,  6,  e,  be  brought  within  the  action 
of  the  breakers,  A,  under  which  its  slope  had  been  previously  adjusted, 
then  that  action  would  readily  remove  the  unconsolidated  mud,  silts,  or 
sands  exposed  to  it,  as  well  as  the  remains  of  any  animals  entombed  in 
them  during  their  accumulation,  or  destroyed  when  upraised.  Should 
the  elevation  of  the  land  be  continued,  the  subjacent  detrital  bed,  d,  g, 
with  any  organic  remains  it  also  might  contain,  would,  in  its  turn,  be 
subjected  to  the  same  action,  so  that  upon  exposed  ocean  coasts,  with 
heavy  breakers,  vast  tracts  of  sea-bottoms  might  be  removed,  their 
materials  accumulated  elsewhere  in  the  localities  where  they  could  find 
rest.  As,  under  such  conditions,  there  would  be  depths,  where,  from 
the  disturbance  produced  by  the  waves  above,  a  mere  sifting  of  the 
materials  of  these  bottoms  would  be  effected,  it  is  desirable  that  an 
observe?  should  bear  in  mind  the  mixture  which  might  thence  arise  of 
the  hard  remains  of  marine  animal  life,  entombed  in  the  older  sea- 
bottoms,  with  those  of  the  animals  inhabiting  the  seas  of  the  time,  so 
that,  should  any  change  have  been  effected  in  the  life  of  the  area  by 
the  changes  of  relative  levels,  during  the  interval  of  the  production  of 
the  respective  sea-bottoms,  the  organic  remains  of  both  might  be  much 
mingled,  especially  when  accomplished  in  a  quiet  manner,  so  as  not  to 
injure  the  entire  shells  or  other  remains  of  the  older  accumulation. 

Upon  such  an  elevation  of  land,  if  it  were  horizontal,  as  regards  a 
particular  area,  upon  which  any  fresh-water  lake  might  be  situated,  the 
conditions  affecting  the  deposits  in  it  might  remain  much  the  same, 
except  in  such  cases  as  where  a  discharging  river  into  some  adjoining 
sea  was  so  much  changed,  as.  regards  its  outflow,  that,  instead  of  a 
moderate  velocity,  it  should  acquire  one  so  considerable  that  the  surface 
of  the  lake  itself  became  lowered  from  the  cutting  down  of  a  new  chan- 
nel, by  which  an  adjustment  of  fall  had  been  effected  to  the  relatively 
new  sea  level.  Under  such  circumstances,  the  area  and  volume  of  the 
lacustrine  deposits  thence  exposed  would  depend  upon  the  shallowness 
or  depth  of  the  lake.  When  we  turn  to  great  regions  of  lakes,  such  as 


474      ELEVATION  OF  LAND  OVER  A  WIDE  AREA. 

those  in  North  America,  and  refer  to  the  probability  of  the  unequal 
lifting  of  the  land,  so  that  one  portion  may  be  tilted  more  than  the 
other,  it  is  easy  to  conceive  that  the  waters  of  great  lakes  can  be  so 
removed  that  much  of  their  old  deposits  may  be  exposed  as  dry  land, 
while  accumulations  may  continue  to  proceed  in  the  portions  of  their 
basins  still  submerged.  In  great  lakes,  where  breaker  action  produces 
appreciable  effects,  there  would  be  the  same  tendency  to  remove  loose 
upraised  bottoms,  thus  brought  within  its  influence,  as  on  the  sea-coasts, 
calcareous  deposits  necessarily  offering  resistances  in  proportion  to  their 
hardness,  amounting  even  to  that  of  compact  limestone. 

Turning  now  to  the  elevation  of  land  over  a  wide  area,  so  that  the 
communications  between  seas  intermingled  with  it  and  the  main  ocein 
may  be  cut  off,  great  geological  changes  may  be  effected,  not  only  in 
the  life  of  the  waters  enclosed  by,  or  running  amid  the  land,  but  in  the 
conditions  of  the  dry  land  itself.  As  we  have  seen  (p.  97),  the  evapo- 
ration in  the  Mediterranean  is  so  far  beyond  the  supply  of  water  it 
receives  through  the  Dardanelles,  from  the  Black  Sea,  and  from  the 
rivers  flowing  into  it,  that  if  any  elevation  of  the  land  took  place,  so 
that  the  Straits  of  Gibraltar  were  closed,  a  change  which  the  geologist 
will  learn  from  his  researches  to  consider  as  one  of  no  great  compara- 
tive amount,  this  sea  would  have  to  adjust  itself  to  the  supply  of  water, 
so  that  the  one  should  balance  the  other.  The  result  would  be  a  great 
exposure  of  the  present  shallow  sea-bottom  of  the  Mediterranean,  and 
a  change  of  level  by  which  the  outfalls  of  the  rivers  would  acquire  addi- 
tional velocity,  one  which  would  also  be  communicated  to  the  current 
through  the  Dardanelles,  with  a  new  adjustment  of  levels  in  the  Black 
Sea  and  the  rivers  flowing  into  it,  extending  to  the  Sea  of  Azof. 

The  great  rivers  pouring  their  waters  into  the  Mediterranean  would 
continue  to  produce  their  present  effects  long  after  a  stoppage  to  a 
free  communication  with  the  ocean  was  occasioned  at  the  Straits  of 
Gibraltar,  a  vast  mass  of  detritus  being  borne  into  it  as  now,  entomb- 
ing the  remains  of  animal  and  vegetable  life.  It  is  interesting  to  con- 
sider, that  should  the  adjustment  required  for  evaporation  and  supply 
of  water  lower  the  level  of  the  Mediterranean  sufficiently  far  (450  feet), 
two  basins  would  be  formed  by  a  barrier  passing  between  Sicily  and 
the  coast  of  Africa,*  and  the  mouth  of  the  Dardanelles  would  present 
dry  land  after  the  depression  had  continued  to  222  feet,  so  that  either 
the  descent  of  the  waters  supplied  by  the  Black  Sea  would  be  over  a 
rocky  river  channel,  or  the  removal  of  the  matter  in  the  Dardanelles 
and  Bosphorus  would  effect  a  free  communication  with  the  Black  Sea, 
lowered  to  such  an  extent  as  to  produce  the  most  marked  changes  on 
its  shallower  coasts,  and  most  materially  reduce  its  area. 

Thus  by  the  mere  uprise  of  land  over  a  moderate  area,  one  compris- 

*  See  Captain  Smyth's  "  Charts  of  the  Mediterranean." 


UNEQUAL    ELEVATION    OF    LAND.  475 

ing  Spain  and  the  opposite  land  of  Africa,  very  modifying  effects  would 
be  produced  over  a  wide  range  of  land  and  intermixed  water.  A  glance 
at  maps  of  the  world  will  show  how  readily  other  important  modifica- 
tions of  great  areas  might  be  effected  by  comparatively  local  elevations 
of  land,  such  as  closing  the  outlets  of  the  Baltic  or  the  Red  Sea,  the 
one,  as  at  present,  continuing  to  find  an  outlet  for  any  waters  which 
may  find  their  way  into  it,  the  supply  being  greater  than  the  evapo- 
ration, while  the  reverse  might  be  expected  in  the  latter,  bounded 
by  coasts  to  which  so  little  river  water  flows,  so  that  a  larger  area  than 
the  Dead  Sea  (its  level  1312  feet  beneath  that  of  the  Mediterranean), 
would  be  presented,  all  the  shallow  portions  of  the  Red  Sea  exposed, 
and  such  extension  of  the  sand-drifts  permitted  as  the  new  conditions 
might  offer. 

From  similar  conditions  to  a  complete  removal  of  water,  so  that  wide 
tracts  of  desert  sands  are  produced,  the  observer  will  have  no  difficulty 
in  following.  The  results  obtained  are  the  needful  consequences  of  an 
inadequate  supply  of  water  to  compensate  for  the  evaporation,  so  that, 
while  in  Central  Asia  there  are  still  the  remains  of  the  waters  which 
once  covered  so  wide  an  area  in  that  part  of  the  world,  as  above  noticed 
(pp.  98,  125),  in  Sahara  and  the  other  great  deserts  of  Africa,  whole 
regions  are  strewed  over  with  unconsolidated  sea-bottoms  driven  about 
by  the  winds.* 

All  such  surface  changes,  with  the  various  modifications  resulting 
from  the  unequal  tilting  of  considerable  tracts  of  country  from  one 
course  of  general  drainage  to  another,  as  can  often  be  so  easily  effected 
by  comparatively  moderate  and  unequal  elevations  of  portions  of  dry 
land,  should  be  well  considered  when  weighing  the  probabilities  of  the 
existence  of  such  land  in  any  particular  part  of  the  earth's  surface  at 
some  given  geological  time.  It  will  be  evident  that  many  complicated 
and  intermingled  deposits,  containing  the  remains  of  marine,  fresh- 
water, and  terrestrial  life,  may  be  formed  without  the  submersion  of  a 
great  area  of  dry  land  beneath  the  waters  of  the  ocean,  a  point  of  no 
small  importance  when  the  contemporaneous  spread  of  animal  and  vege- 
table life,  intermingled  with  the  mineral  accumulations  of  the  time,  is 
under  consideration. 

Though  upon  an  elevation  of  land  much  of  the  shallow  sea-bottoms 
adjoining  it  may  be  exposed  to  the  destructive  action  of  the  breakers, 

*  The  observer  will  do  well  to  study  the  evidence  adduced  by  Sir  Roderick  Murchison 
and  his  colleagues  ("  Geology  of  Russia  in  Europe  and  the  Urals,"  vol.  i.  p.  297),  re- 
specting the  character  of  the  wide-spread  deposits  of  the  great  region  in  which  the 
Caspian  is  included,  showing  the  change  of  life  during  a  time  when  the  area  passed 
through  a  condition  of  brackish  water  to  the  mixture  of  dry  land  and  water  which  now 
presents  itself; — an  important  addition  to  our  knowledge  of  the  changes  which  the 
earth's  surface  has  undergone,  over  a  wide-spread  region,  in  comparatively  recent  geo- 
logical times. 


476 


LAKES    ON    THE    OUTSKIRTS    OF    MOUNTAINS. 


as  above-mentioned  (p.  472),  the  same  movement  would  cause  many 
portions  of  a  littoral  sea-bottom  to  be  brought  up  to  the  height  most 
favourable  for  the  preservation  of  its  slope  seaward,  and  the  accumula- 
tion of  sand-hills  beyond  the  new  line  of  shore  inland.  Another  effect 
would  be  the  conversion  of  many  arms  of  the  sea  into  lakes,  the  shal- 
lower depths  found  in  many  localities  at  the  outer  or  seaward  part  of 
such  inlets  of  the  sea  amid  the  land,  forming  a  low  barrier  between  the 
sea  and  the  more  inward  and  deeper  parts  now  separated  from  it.  In 
such  cases  the  newly-included  portion  of  the  sea  would  gradually  be- 
come less  saline  from  the  continued  supply  from  the  rivers  which  are 
generally  to  be  found  in  such  localities,  so  that,  finally,  a  fresh-water 
lake,  such,  for  example,  as  Loch  Ness,  in  Scotland,  might  still  preserve 
a  considerable  depth,  its  surplus  waters  finding  their  way  to  the  sea  by 
some  river.  To  illustrate  this,  let,  in  the  subjoined  plan  (fig.  180),  a,  a, 

Fig.  180. 


represent  some  arm  of  a  tidal  sea,  such  as  is  to  be  found  in  many  parts 
of  the  world,  and  b  a  submarine  bank,  in  part  formed  by  the  check 
given  to  on-shore  waves,  stirring  up  detritus  seaward,  in  part  by  drifts 
produced  by  prevalent  winds,  as  in  the  manner  previously  pointed  out 
(p.  82,  fig.  50),  and  in  part  also  from  some  check  given  to  the  outflow 
of  the  ebb  tide  carrying  detritus  brought  down  by  feeding  rivers,  £,  £, 
in  seasons  of  flood,  where  it  reached  the  general  coast  line.  Submarine 
bars  of  this  kind  are  far  from  uncommon.  Upon  the  elevation  of  such 
a  coast,  so  that  its  previous  line,  m,  m,  becomes  shifted  to  w,  n,  a  low 
piece  of  ground,  /,  /,  of  a  breadth  depending  upon  its  shallowness 
beneath  the  former  relative  sea  level,  and  its  general  slope,  it  might 
extend  to  a  considerable  distance  outwards,  the  surplus  river  waters  find- 
ing their  way  as  a  river,  r,  amid  the  new  low  ground,  to  the  sea  at  0,  o. 
Lakes  at  the  outskirts  of  mountainous  countries,  bounded  by  low  ground 
at  their  outlets,  this  low  ground  continuing  to  some  neighbouring  sea, 
would  often  appear  to  have  been  thus  produced.  In  like  manner  nume- 
rous rivers  of  considerable  size  would  have  their  lower  portions  con- 
verted into  lakes,  their  present  bars  (p.  102)  with  much  of  an  adjoining 


LAKES    ON    THE    OUTSKIRTS    OF    MOUNTAINS.  477 

shallow  sea-bottom  being  upraised,  so  that  the  river  formed  a  new 
channel  between  the  old  bar  and  the  new  coast  line,  where,  assuming 
conditions  to  be  still  similar,  a  new  bar  would  be  formed,  and  the  spread 
of  water  behind  the  old  bar  might  continue  as  a  kind  of  lake  until  filled 
by  detritus,  its  waters,  after  the  change,  becoming  gradually  fresh  from 
the  absence  of  the  daily  inflow  of  the  sea  upon  the  flood  tide.  These 
and  other  modifications  of  coasts  by  an  elevation  of  land,  some  on  the 
small  and  others  on  the  large  scale,  will  readily  be  seen  by  an  inspec- 
tion of  the  charts  of  various  parts  of  the  world,  whereby  it  will  be 
found  that  lakes  would  be  the  frequent  consequence  of  these  changes, 
especially  upon  mountainous  shores,  where  the  continuations  of  many 
valleys  are  beneath  the  sea  level,  and  where,  at  their  termination  sea- 
ward, the  bottoms  become  somewhat  raised,  forming  more  of  a  portion 
of  a  general  slope  in  connexion  with  the  adjoining  sea-bottom  than  with 
the  arm  of  the  sea  continued  inwards. 

The  production  of  the  lakes  on  the  outskirts  of  mountainous  districts, 
in  the  manner  last  mentioned,  would  often  seem  to  involve  the  necessity 
of  a  previous  submergence  of  a  portion  of  the  same  region  beneath  the 
sea  level,  the  arms  of  the  sea  being  mere  continuations  of  that  level 
amid  depressed  land.  When  such  a  submergence  happens — and  there 
can  be  little  doubt  that  it  has  often  done  so  during  the  lapse  of  geo- 
logical time — the  filling  up  of  the  submerged  portions  of  such  valleys 
will  be  modified  according  as  the  land  may  be  situated  in  a  tidal  or 
tideless  sea.  In  the  one  case  there  would  generally  be  estuaries  and 
their  results  (p.  101),  in  the  other  the  mere  discharge  of  detritus  out- 
wards, much  as  at  the  head  of  lakes,  due  allowance  being  made  for  the 
mode  in  which  river  waters,  bearing  detritus  in  mechanical  suspension, 
may  flow  over  the  sea  water  in  such  situations  (p.  89). 

We  have,  while  noticing  the  accumulation  of  beaches  (p.  83),  the 
condition  of  estuaries  (p.  85),  the  preservation  of  foot-prints  (p.  148), 
coral  reefs  and  islands  (pp.  207,  211),  distribution  of  erratic  blocks 
and  superficial  gravels  (pp.  262,  264,  267,  289),  ossiferous  caves  (p. 
306),  and  the  uplifting  of  the  subaqueous  parts  of  volcanoes  (p.  383), 
been  compelled  to  mention  some  of  the  effects  which  would  be  produced 
by  the  elevation  and  depression  of  land  above  or  beneath  the  sea,  and 
even  to  advert  to  the  material  changes  which  would  be  produced  by  the 
depression  of  the  Isthmus  of  Panama,  and  the  elevation  of  the  sea- 
bottom  between  the  north  coast  of  Australia  and  the  Malayan  penin- 
sula (p.  154).  The  effects  thus  caused  have  to  be  more  or  less  re- 
garded with  respect  to  the  mineral  and  fossiliferous  accumulations  of 
all  geological  periods  to  which  the  modifications  and  changes  now  in 
progress  on  the  earth's  surface  are  applicable. 

As  with  an  elevation  of  the  dry  land  above,  so  with  its  depression 
beneath  the  sea,  the  steepness  or  gently-sloping  character  of  the 


478   MIXTURE   OF   ORGANIC   REMAINS   OF   DIFFERENT    PERIODS 

mineral  mass  moved  has  to  be  duly  regarded.  While  amid  a  mountain- 
ous region  the  depression  of  the  land  for  about  200  or  300  feet  may 
merely  somewhat  more  intermingle  the  sea  with  the  land,  arms  of  the 
sea  extending  further  into  the  country,  the  same  depression  in  lower 
lands  may  cover  whole  districts,  the  tops  of  some  higher  grounds  only 
rising  as  scattered  islands  amid  a  wide-spread  sea.  The  effects  pro- 
duced in  one  region  would  form  no  measure  of  those  following  such  a 
depression  (in  a  geological  sense  of  a  very  minor  kind)  in  another.  The 
change  might,  indeed,  so  far  affect  a  mixed  region  of  mountains  and 
low  plains,  that  some  old  state  of  things  may  often,  to  a  certain  extent, 
be  reproduced,  the  mountains  forming  islands,  or  groups  of  islands,  in 
a  part  of  the  ocean,  and  so  that  ravages  on  their  flanks  from  heavy 
breaker  action  are  recommenced.  While,  in  the  one  case,  the  area 
occupied  by  terrestrial  life,  animal  and  vegetable,  was  comparatively 
little  circumscribed,  in  the  other,  large  tracts  would  be  laid  waste,  and 
many  a  plant  and  animal,  peculiar  to  the  low  districts,  might,  under 
certain  conditions,  be  entirely  swept  away. 

Whether  we  contemplate  the  submergence  of  a  large  area  of  dry 
land  much  intermingled  with  lakes,  such  as  Northern  America,  partly 
overspread  by  deserts,  such  as  portions  of  Africa  and  Asia,  or  under 
an  ordinary  condition  of  the  growth  of  trees  and  other  terrestrial 
plants,  and  an  adjusted  distribution  of  animal  life,  there  would  appear 
few  geological  changes  so  effective  in  bringing  deposits  marked  by  dis- 
similar organic  remains  into  contact,  than  such  submergences.  Even 
horizontal  or  nearly  horizontal  accumulations  may  be  thus  superim- 
posed, after  the  lapse  of  considerable  intervals  of  geological  time, 
should  one  sea-bottom  have  been  long  horizontally  raised  above  water 
until  a  change  in  the  relative  levels  of  sea  and  land  in  that  area  pro- 
duced the  conditions  for  its  submersion  and  subsequent  covering  by 
new  deposits.  Under  such  circumstances  it  may  require  some  caution 
on  the  part  of  the  observer  not  to  conclude  that  the  two  kinds  of  sea- 
bottom  have  succeeded  each  other  quietly  beneath  the  sea.  If  any  low 
region  be  regarded  with  reference  to  the  effects  which  might  be  pro- 
duced during  its  tranquil  submergence,  such,  for  example,  as  where 
wide  tracts  of  sand-hills  border  such  a  district,  it  will  be  obvious  that 
these  latter  would  soon  disappear  before  the  action  of  the  sea,  and  be 
readily  spread  over  the  low  grounds  inland  as  these  became  depressed. 
As  the  land  descended,  its  surface  would  be  acted  upon  by  the  sea,  the 
loose  and  lighter  parts  readily  taken  up  and  removed,  to  be  deposited 
elsewhere  in  fitting  situations  according  to  circumstances,  the  larger 
and  harder  parts  often,  as  it  were,  sifted  from  the  finer  and  lighter, 
and  occasionally  enveloped  by  new  detritus  not  far  distant  from  their 
places  of  first  accumulation.  When  a  geologist  considers  the  decom- 
position of  the  surface  of  ancient  and  upraised  sea  and  lake  bottoms, 


SOMETIMES  EFFECTED  BY  A  SUBMERGENCE  OF  LAND.  479 

forming  soils,  and  the  frequent  dispersion  of  their  organic  contents 
either  in  these  soils  or  subjacent  decomposed  rocks,  he  will  perceive 
that,  under  favourable  conditions,  these  remains  may  sometimes  be  pre- 
served with  little  injury,  and  be  mingled  with  those  of  the  animal  life 
introduced  over  the  old  land  surface  by  the  new  submergence  beneath 
the  sea.  The  lower  part  of  the  new  accumulations  and  the  upper  sur- 
face of  the  old  deposits  may  thus  become  mixed,  and  lead,  without  due 
care,  to  the  supposition  that  the  two  were  marked  by  a  passage  of  the 
organic  remains  found  in  the  one  into  the  other.  This  is  no  useless 
caution,  as  the  observer,  when  studying  the  effects  produced  during  the 
submergence  of  some  ancient  land,  will  have  occasion  to  remark. 
Some  good  examples  of  weathered  fossils  of  the  carboniferous  lime- 
stone, even  so  much  so  as  to  be  completely  detached,  may  be  seen  in 
the  dolomitic  or  rnagnesian  limestone  deposits  (of  the  new  red  sandstone 
series)  in  Somersetshire,  Gloucestershire,  and  Glamorganshire,  and  these 
might  readily,  without  due  care,  be  considered  as  organic  remains  of 
the  later  geological  time.  It  is  as  if,  after  abstracting  the  turf  or 
soil  covering  the  carboniferous  limestone  of  a  district,  and  the  quiet 
removal  of  the  intermingled  earth  in  place,  a  deposit  of  magnesio-cal- 
careous  matter  was  thrown  down  from  solution  amid  the  fossils  and 
fragments  of  the  older  rock.  The  fitting  of  deposits  of  this  kind  into 
the  inequalities  beneath  is  well  shown  in  the  district  to  which  allusion 
has  been  made,  and  may  be  illustrated  by  the  following  section  (fig. 
181),  seen  at  Pen  Park,  north  of  Bristol,  where  the  dolomitic  or  mag- 
Fig.  181. 


nesian  limestone,  6,  rests  upon  the  edges  of  upturned  beds  of  carbonife- 
rous limestone,  a,  a,  into  the  superficial  inequalities  and  interstices  of 
which  it  enters,  covering  up  blocks  of  the  same  rock,  <?,  reposing  on  the 
surface  before  the  deposit  of  the  newer  rock.  In  such  localities,  the 
weathered  portions,  including  fossils,  of  the  subjacent  rock  may  some- 
times be  found  penetrating  or  intermingled  with  the  subsequent  accu- 
mulations, occasionally  marking  a  state  of  much  tranquillity,  and  as  if 
an  overspreading  deposit  had  been  effected  on  an  old  surface  of  land 
which,  in  favourable  localities,  had  not  been  much  subjected  to  breaker 
action,  rounding  the  fragments  and  destroying  the  old  weathered  sur- 
face of  the  rock. 


480     VARIABLE    EFFECTS     FROM    THE    SUBMERGENCE    OF 

That  a  mixture  of  the  organic  remains  of  former  geological  times 
with  those  of  molluscs  and  other  marine  animals,  the  species  of  which 
at  present  exist  in  the  seas  adjoining,  is  now  taking  place,  a  walk  along 
many  a  coast  will  show,  shells  especially  being  seen  washed  out  of 
sands  and  clays  forming  the  cliffs,  and  being  mixed  with  those  now 
cast  on  shore.  We  are,  therefore,  well  prepared  to  expect  that  when, 
during  a  submergence  of  dry  land,  the  loose  surfaces  of  ground,  with 
distributed  organic  remains,  are  exposed  to  similar  action,  the  results 
will  be  the  same,  with  this  difference,  that  while,  on  an  exposed  coast, 
the  ancient  and  modern  organic  remains  may  often  be  all  ground  down 
together  into  one  common  mass,  in  a  submerging  land,  more  sheltered 
localities  may  frequently  present  themselves  where  the  ancient  organic 
remains  may  be  more  quietly  sifted  out  of  the  loose  earthy  matter  sur- 
rounding them,  and  be  intermingled  with  the  exuviae  of  animals,  the 
habits  of  which  lead  them  to  prefer  equally  tranquil  situations. 

Fully  to  appreciate  the  varied  geological  effects  which  may  be  pro- 
duced by  the  submergence  of  differently  circumstanced  dry  land,  it  may 
not  be  uninstructive  for  the  observer  to  consider  those  which  would  follow 
the  re- establishment  of  the  sea  over  the  many  thousand  square  miles 
now  occupied  by  the  great  desert  or  deserts  of  Northern  Africa,  Sahara, 
and  others.  Judging  from  such  observations  respecting  the  heights  of 
parts  of  these  deserts  as  appear  deserving  of  credit,  a  submergence  of 
the  kind  mentioned  as  probable  for  the  British  Islands  during  the  in- 
ferred cold  period  preceding  the  present  state  of  that  area,  namely, 
from  1200  to  1500  feet,  would  place  at  least  a  large  portion  of  them 
beneath  a  continuation  of  the  Atlantic.  As  the  sea  moved  inwards, 
according  to  its  level,  however  this  might  present  itself  with  respect  to 
the  variation  from  horizontality,  wholly  or  partially,  of  the  submerging 
land,  the  sifting  of  hard  and  coarser  parts  from  the  lighter  and  softer 
would  be  effected,  and  thus  the  remains  of  men,  camels,  and  the  ordi- 
nary desert  animals,  here  and  there  mingled  with  the  additions  to  the 
former  which  the  oases  produce,  might  be  mingled  with  those  of  the  marine 
animals  introduced  with  the  sea  as  it  advanced  over  the  land.  Should 
there  still  be  organic  remains  amid  the  sands  of  the  deserts,  entombed 
when  the  whole  had  previously  been  beneath  water,  these  also  might  be 
mixed  with  the  animal  exuviae  of  the  new  sea-bottom. 

When  we  consider  the  depression  of  land  occupied  by  many  and  per- 
haps great  lakes,  such  as  those  in  North  America,  the  amount  of  sub- 
mergence more  in  one  part  of  the  general  area  than  in  another  has  to 
be  duly  regarded ;  as  also  the  consequent  different  conditions  under 
which  these  bodies  of  fresh  water  may  be  placed.  While  the  progress 
of  depression  may  in  some  cases  be  such  that  the  outflowing  waters 
were  gradually  shortened  in  their  courses,  until  the  time  arrived  when 
the  sea  entered  into  the  lakes,  a  mere  overtopping  of  the  fresh-water 
basin  being  accomplished ;  in  others  the  unequal  tilting  of  the  ground 


I 

LAKGE  TRACTS  OF  THE  PRESENT  DRY  LAND.     481 

may  have  occurred  so  that  the  sea  was  introduced  and  covered  a  deeper 
portion  of  the  lake  basin  in  one  direction  than  in  another.  Inferring 
the  usual  mode  of  distribution  of  .matter  by  the  combination  of  wind- 
wave  action  beneath  the  sea  at  the  proper  depths,  and  breaker  action 
on  the  shores,  with  the  effects  of  tidal  streams  in  tidal  seas,  the  accu- 
mulations might  so  far  differ  under  these  conditions  that  while,  in  both 
instances,  the  animal  life  gradually  became  adjusted  to  the  sea,  the 
greater  part,  if  not  the  whole,  of  the  previous  deposits  in  the  simply 
overtopped  lake  might  be  preserved  and  be  covered  by  the  brackish 
water,  and  finally  by  the  marine  accumulations.  The  unequally-tilted 
lake  banks  might  permit  a  part  of  the  older  deposits  to  be  so  exposed 
to  breaker  action  that  they  were  partially  removed,  the  component 
mineral  matter  and  its  organic  contents  partially  also  rearranged  with 
the  new  accumulations.  If,  during  a  re-establishment  of  part  of  North 
America  beneath  the  sea,  it  so  occurred  that  lakes  Erie  and  Ontario 
were  depressed  more  rapidly  than  lakes  Huron,  Michigan,  and  Superior, 
the  sea  finally  overspreading  the  whole,  the  relative  positions  of  the 
lakes  to  the  direction  of  the  greatest  depression  would  much  influence 
the  results.  Lakes  Erie  and  Ontario  would  present  their  breadths  to 
the  movement,  while  lakes  Michigan  and  Huron  would  be  acted  upon 
in  their  lines  of  length,  Lake  Superior  presenting  a  more  complicated 
form.  Under  such  a  movement,  the  entrance  of  the  sea  would  neces- 
sarily depend  upon  the  varied  surface  and  levels  for  the  time  opposed 
to  it ;  but  it  may  readily  happen  that  while  lakes  Ontario  and  Erie 
were  beneath  the  sea,  and  Lake  Huron  brackish  water,  Lake  Superior 
might  continue  as  fresh  water,  the  contemporaneous  deposits  in  each 
containing  the  remains  of  animals  capable  of  living  in  the  various  kinds 
of  water  respectively,  such  of  the  original  lacustrine  creatures  remain- 
ing in  the  brackish  water  as  could  adjust  themselves  to  it,  mingled  with 
those  marine  animals  which  could  support  life  under  the  same  condi- 
tions, the  terrestrial  vegetation  drifted  into  all  the  deposits  being  of  the 
same  general  kind. 

While  the  remains  of  drifted  terrestrial  plants,  large  or  small,  may 
not  give  very  exact  information  as  to  the  area  occupied  by  dry  land, 
whence  they  have  been  derived,  since  they  could  have  floated  from  con- 
siderable distances  (p.  144),  according  to  the  currents  of  particular 
geological  times,*  where  these  remains  occur  either  in  their  places  of 
growth,  or  so  that  we  may  rightly  conclude  that  they  have  not  been 
removed  far  from  them,  they  become  important.  Those  deposits  of 
vegetable  matter  interstratified  with  shales,  sandstones,  and  conglome- 
rates, which  occur  in  a  particular  portion  of  the  geological  series  of 

*  The  Gulf  Stream,  as  before  pointed  out,  is  an  excellent  example  of  a  body  of  water 
capable  of  transporting  the  vegetable  products  of  the  tropics  to  the  temperate  regions  of 
the  north  across  an  ocean. 


482  STEMS    OF    PLANTS    IN    THEIR    POSITIONS    OF 

accumulations  in  Europe  and  America,  and  to  which  the  term  coal  mea- 
sures has  been  assigned,  from  abundantly  furnishing  the  fuel  which  has 
become  so  important  to  the  progress  of  civilization,  afford  the  observer 
the  means  of  inferring  the  existence  of  land  in  particular  portions  of 
the  northern  hemisphere  at  that  time.  When  carefully  examined,  a 
large  proportion  of  the  coal  beds  have  been  found  in  the  British  Islands 
(and  the  evidence  would  also  appear  to  justify  similar  conclusions  in 
many  other  countries),  resting  upon  beds  immediately  beneath,  in  which 
the  roots  of  particular  plants  are  found  to  extend  in  a  manner  showing 
that  these  are  actually  in  their  places  of  growth,  as  respects  the  beds  of 
mineral  matter  containing  them.  These  roots  were  at  one  time  con- 
sidered as  separate  plants  (Stigmaria\  but  now,  from  the  researches  of 
Mr.  Binney  and  other  geologists,  it  seems  established  that  they  belong 
to  other  plants  (Sigillaria,  if  not  also  to  other  genera).  With  this 
advance  of  knowledge,  we  find  that  great  sheets  of  vegetable  matter 
were  based  upon  a  mud  or  silt,  in  which  the  amount  of  arenaceous 
matter  varied  considerably  in  different  situations,  even  in  the  prolonga- 
tion of  the  same  bed,  and  that  into  this  mud  or  silt  the  roots  of  at  least 
some  of  the  plants  of  the  time  and  locality  spread  as  in  ground  for 
which  they  were  suited. 

Upon  still  further  investigation,  it  has  been  found  that  roots  of  this 
character  are  to  be  seen  attached  to  stems  of  plants  still  vertical,  or 
nearly  so,  to  the  beds  of  shale  or  sandstone  (formerly  mud,  silt,  or 
sand),  in  which  they  are  enclosed.  Though  the  attachment  of  such 
roots  may  be  rarely  seen,  the  examples  of  vertical  stems  of  plants, 
apparently  in  their  places  of  growth,  are  sufficiently  common,  so  much 
so  that  if  certain  parts  of  the  coal  measures  of  the  British  Islands  could 
have  the  detrital  matter  removed,  various  and  extensive  areas  would  be 
found  covered  by  the  stumps  of  plants  in  such  positions.  These  stumps 
are  so  numerous  in  the  ordinary  detrital  deposits  reposing  on  some  coal 
beds,  that  they  become  dangerous  in  the  collieries  (unless  great  care  be 
taken  in  the  works),  from  being  merely  sustained  aloft  by  the  coaly 
matter  representing  the  former  outer  portion  of  the  plants,  so  that  when 
this  is  insufficient  to  retain  them,  they  fall  on  the  heads  of  the  miners. 
The  following  sketch  (fig.  182),  at  Cwm  Llech,  towards  the  head  of  the 
Swansea  valley,  Glamorganshire,*  may  serve  to  illustrate  the  manner 
in  which  these  plants  may  sometimes  be  exhibited,  in  quarries  or  natural 
cliffs,  rising  amid  the  beds  which  have  enveloped  them  in  their  places  of 
growth.  The  largest  of  the  two  stems  was  5 J  feet  in  circumference. 
They  merely  formed  a  part  of  a  surface  more  or  less  covered  by  stems 
of  this  kind,  as  others  were  to  be  seen  in  similar  positions  in  the  same 

*  Made  by  Mr.  Logan,  by  -whom  and  the  author  the  locality  was  carefully  examined. 
The  stems  were  subsequently  removed  to  the  Royal  Institution  of  South  "Wales,  at 
Swansea,  where  they  now  are. 


» 
GROWTH    IN    THE    COAL    MEASURES    OF    ENGLAND.       483 

bed  of  rock  higher  up  in  the  same  valley.  Upon  uncovering  a  shale 
beneath  the  sandstone,  in  which  these  plants  (Sigillarice)  stood,  an 
abundance  of  fern  leaves,  and  fragments  of  other  plants,  commonly 

Fig.  182. 


seen  in  these  deposits,  were  found  distributed  around  in  the  same  man- 
ner as  leaves  and  other  parts  of  plants  may  be  dispersed  around  stems 
of  trees  in  muddy  places  at  the  present  day. 

It  sometimes  happens  that  the  vertical  stems  of  the  plants  rise  through 
different  kinds  of  beds,  the  component  parts  of  which  accumulated 
around  them,  while  the  vegetable  matter  still  held  together.  The 
following  (fig.  183)  is  an  example  of  this  kind,  as  it  was  exhibited  at 
the  Killingworth  Colliery,  Newcastle  district.  In  this  section  a  repre- 
sents the  high  main  coal  of  the  district,  b  argillo-bituminous  shale  (for- 
merly carbonaceous  mud),  c  blue  shale  (mud  or  clay),  d  compact  sand- 
stone (sand),  e  alternating  shales  and  sandstones  (beds  of  mud  and 
sand),  h  white  sandstone  (clean  sand),  i  micaceous  sandstone  (sand  with 
mica),  and  k  shale  (mud  or  clay).  In  such  cases  various  changes  were 
effected  in  the  kind  of  mineral  matter  transported  to  and  deposited 
amid  the  vegetation  there  standing.  Though  we  do  not  know  the  extent 
to  which  such  plants  may  have  been  covered  up  before  they  died,  an 
attentive  study  of  the  mode  in  which  the  mud,  silt,  or  sand  has  been 
accumulated  round  the  stems  often  shows  the  observer  that  the  water 
bearing  or  moving  the  detritus  was  very  shallow.  Around  the  stems  at 
Cwm  Llech  (fig.  182),  the  laminae  of  the  sandstone  were  so  arranged  as 
forcibly  to  suggest  that  they  represented  the  washing  up  of  sands 
around  the  plants  in  shallow  water  agitated  by  slight  waves.  Such  an 


484        FILLING    UP    OF    HOLLOW    VERTICAL    STEMS,    AND 

arrangement  may  frequently  be  seen,  as  also  occasionally,  when  the 
stems  are  carefully  uncovered,  an  adjustment  of  the  laminae  of  the 
original  sand  or  silt,  in  a  manner  pointing  to  the  passage  of  a  slight 


Fig.  183. 


current  of  water  by  them.  When  this  can  be  found,  the  direction 
whence  the  current  came  may  be  inferred  by  the  position  of  the  laminae 
marking  the  place  of  the  eddy,  behind  the  stems. 

From  the  manner  in  which  these  vertical  stems  are  so  frequently  ter- 
minated upwards,  it  would  appear  that  while,  for  a  time,  their  lower 
portions  continued  to  resist  the  pressure  both  of  the  water  in  which  they 
were  immersed,  and  the  gradually-accumulating  detritus  borne  or  drifted 
by  it,  their  tops  became  decayed,  and  were  removed,  so  that  finally 
sheets  of  detritus  uninterruptedly  spread  over  the  localities  where  such 
plants  may  have  grown.  We  seem,  indeed,  to  have  evidence  in  the 
manner  in  which  so  many  of  these  stems  have  been  filled  with  mud,  silt, 
sand,  and  the  remains  of  other  plants,  that  before  such  sheets  of  con- 
tinuous detritus  were  spread  over  their  tops,  they  were  hollow,  like  so 
many  open  and  vertical  tubes,  in  which,  when  overtopped  by  waters 
bearing  detrital  matter,  and  the  leaves  and  fragments  of  plants,  these 
were  deposited  in  the  same  way  that  sediment  and  the  remains  of  vege- 
tation are  accumulated  in  the  hollows  of  upright  and  decayed  or  broken 
stems  of  bamboos,  and  other  plants  on  the  side  of  rivers,  or  amid  low 
grounds,  during  and 'upon  the  subsidence  of  floods.  That  the  interior 
and  exterior  deposits,  in  and  around  the  vertical  stems  are  not  the 
same,  different  minor  layers  being  found  in  the  stems  not  corresponding 
with  those  outside,  may  often  be  seen,  as  shown  in  the  annexed  section 
(fig.  184),  where  a  stem,  a,  a,  covered  by  a  sandstone  bed,  #,  is  sur- 
rounded by  other  sandstones,  c,  c,  c,  interstratified  with  shales,  d,  d, 


MIXTURE    OF    PROSTRATE    PLANTS    WITH    THEM.         485 

their  lines  of  deposit  abutting  against  the  stem,  the  only  remains  of 
which  are  usually  formed  of  coal  from  half  an  inch  to  two  inches  in 
thickness,  according  to  the  size  of  the  plant,  in  the  inside  of  which 

Fig.  184. 


other  layers,  e,  e,  of  shale  and  sandstone,  with  or  without  leaves  of  fern 
or  other  plants,  occur  arranged  in  a  manner  showing  that  they  were 
accumulated  independently  of  those  outside. 

Strewed  amid  the  same  accumulations  (those  of  the  coal  measures), 
prostrate  stems,  sometimes  measuring  thirty  feet  in  length,  and  of  pro- 
portionate breadth,  considered  by  botanists  to  be  of  the  same  and  simi- 
lar genera,  and  frequently  even  species  as  those  found  vertical,  would 
often  appear  to  show  that  they  have  not  undergone  violent  transport  in 
waters,  being  so  little,  if  at  all,  injured.  Indeed,  occurring,  as  they 
sometimes  do,  among  the  stumps  of  stems,  these  apparently  in  the  posi- 
tions in  which  they  grew,  they  far  more  resemble  those  prostrate  trees 
found  amid  the  stumps  of  the  rooted  trees  in  the  "  submarine  or  sunk 
forests"  (p.  434).  In  some  collieries  an  observer  may,  as  it  were,  see 
beneath  such  an  accumulation  of  plants  in  muddy  ground,  the  ends  of 
the  upright  stumps,  like  so  many  irregular  rings,  scattered  over  head, 
the  long  prostrate  stems  strewed  among  them,  and  a  multitude  of  ferns 
of  various  kinds,  Lepidodendra,  and  other  plants  matted  together,  the 
whole  presenting  the  appearance  of  a  growth  of  plants  in  soft  or  wet 
ground,  if  not  shallow  water,  mud  mingled  with  various  portions  of 
them.  Often  the  plants  appear  to  have  partly  grown  in  the  same 
locality,  and  partly  to  have  been  drifted  into  it,  sometimes  from  an 
adjoining  situation,  at  others  from  more  distant  places. 

While  areas  of  fair  size  are  known  by  colliery  workings  to  have  had 
numbers  'of  vertical  stems  tranquilly  covered  over  by  detrital  matter  on 
a  particular  geological  plane,  so  that  a  forest  of  this  kind  of  vegetation 
has  been  contemporaneously  entombed,  it  sometimes  occurs  that  there 
is  good  evidence  of  similar  conditions  having  produced  similar  results 
more  than  once  over  the  same  area.  Of  the  facts  brought  to  light  on 
this  head,  though  it  may  be  well  known  in  many  coal  districts  that  ver- 
tical stems  of  plants  are  found  at  more  than  one  geological  level,  the 
occurrence  of  one  series  of  vertical  stems  above  others  seems  to  have 
been  hitherto,  in  no  artificial  or  natural  sections,  better  exhibited  than 


486       GROWTH    OP    TERRESTRIAL    PLANTS    IN    SUCCESSIVE 


Fig.  185. 


in  the  coal  districts  of  Nova  Scotia  and  Cape  Breton,  where  several  of 
these  planes  of  vegetation,  the  stems  of  plants  still  standing  in  their 
places  of  growth,  are  seen  above  each  other.  Sir  Charles  Lyell  de- 
scribes ten  forests  of  this  kind,  as  occurring  above  each  other,  in  the 
cliffs  between  Minudie  and  the  South  Joggins,  at  the  head  of  the  Bay 
of  Fundy.  The  thickness  of  the  mass  of  beds  containing  the  upright 
stems  is  estimated  at  about  2,500  feet,  and  the  usual  height  of  the  trees 
is  from  six  to  eight  feet,  but  one  was  seen  apparently  25  feet  high  and 

four  feet  in  diameter,  with  a  conside- 
rable bulge  at  the  base.  All  these 
stems  appeared  to  be  of  the  same 
species.*  We  are  indebted  also  to 
Mr.  Logan  for  a  very  detailed  account 
of  these  coal  measures.  In  his  de- 
scription of  the  Sydney  coal  field,  Is- 
land of  Cape  Breton,f  Mr.  Richard 
Brown  notices  many  upright  stems  of 
plants  in  different  beds.  Among  the 
sections  given,  the  annexed  (fig.  185), 
will  be  useful,  as  showing  this  occur- 
rence of  many  vertical  stems  above 
each  other.J  In  it,  a  represents  sand- 
stones, b  shales,  c  coal,  and  d  the  beds, 
usually  argillo-arenaceous,  in  which 
the  roots  (Stigmarid)  are  in  their  posi- 
tions of  growth.  The  total  thickness 
of  the  deposits  amounts  to  92  feet,  and 
in  it  occur  four  planes  of  upright  stems, 
the  second  showing  different  levels  of 
growth  in  it,  and  six  ancient  soils,  sur- 
mounted by  as  many  seams  or  beds  of 
coal  of  very  different  depths,  the  most 
considerable  being  six  feet,  and  the  least  seam,  one  of  mere  carbo- 
naceous matter,  one  half  inch  thick. 

*  Lyell,  «  Travels  in  North  America,"  vol.  ii.  pp.  179-188. 

f  Brown,  "  Section  of  the  Lower  Coal  Measures  of  the  Sydney  Coal  Field,  in  the  Island 
of  Cape  Breton"  (Quarterly  Journal  of  the  Geological  Society  of  London,  vol.  vi.  p.  115). 
After  adverting  to  the  descriptions  of  the  coal  measures  of  Novia  Scotia  by  Sir  Charles 
Lyell  (Travels,  &c.),  and  by  Mr.  Logan  (Section  of  the  Nova  Scotia  Coal  Measures  at 
the  Joggins),  Mr.  Brown  estimates  the  productive  coal  measures  of  Cape  Breton  at 
more  than  10,000  feet  in  thickness.  The  Sydney  portion,  described  in  this  communica- 
tion, was,  by  measurement,  1,860  feet  thick.  The  dip  is  mentioned  as  at  an  angle  of  7°. 

J  In  this  section  the  beds  are  reduced  to  horizontality,  and  are  on  a  proportional 
scale,  the  relative  thickness  of  the  beds  being  taken  from  the  detailed  description  of 
them  by  Mr.  Richard  Brown  (Journal  of  the  Geological  Society,  vol.  vi.  p.  120). 


PLANES    IN    THE    COAL    MEASURES.  487 

It  will  no  doubt  at  once  suggest  itself  to  the  observer  that  such  accu- 
mulations of  mud,  silt,  sand,  and  sometimes  gravel,  intermingled  with 
layers  of  fossil  vegetation,  these  layers  based  upon  a  soil,  probably 
moist  or  wet,  in  which  the  roots  of  certain  plants  freely  grew,  while 
vertical  stems  occurred,  as  much  sometimes  as  15  or  20  feet  high,  and 
two  to  four  feet  in  diameter,  even  planes  of  these  old  forests  being  found 
above  each  other  in  limited  sections,  must  have  been  gradually  sub- 
merged, so  that,  at  intervals,  the  soil  was  sufficiently  exposed  to,  or 
near  the  atmosphere,  that  the  plants  entombed  amid  them  could  come 
under  their  proper  conditions  of  growth.  A  trough  or  other  cavity,  or 
slightly-inclined  plane  of  shore,  gradually  filled  up  to  the  level  of  the 
atmosphere,  would  only  give  one  layer  of  vegetation,  whereas,  in  some 
coal  districts,  where  the  seams  of  coal  are  reckoned  with  the  soils  on 
and  in  which  their  constituent  plants  grew,  50  or  more  intervals  for 
growth  may  have  to  be  accounted  for.  A  submergence  of  the  ground 
on  which  the  plants  flourished,  so  that  at  times  the  mud,  silt,  or  sand  of 
the  time  accumulated  at  a  greater  rate  than  this  submergence  could 
keep  them  beneath  the  level  of  water,  or  during  which,  though  the 
descent  of  the  land  may  have  been,  as  a  whole,  constant,  there  were 
minor  amounts  of  movement,  by  which,  after  a  subaqueous  area  had 
been  filled  up  to  the  atmosphere,  there  were  pauses  when  the  plants 
could  grow,  would  alike  appear  to  explain  the  facts  observed.  The 
section  of  the  1,860  feet  in  which  the  upright  stems  of  the  Sydney  beds 
(Cape  Breton)  occur,  shows  that  there  were  more  than  40  periods  in 
the  general  descent  of  the  mass  when  there  were  soils  in  which  the 
roots  (Stigmaria)  of  the  plants  of  the  time  and  locality  found  their 
needful  conditions  for  growth,  those  for  the  accumulation  of  the  vege- 
table matter  above  them  having  varied  materially.*  When  we  turn  to 

*  The  detail  of  the  general  mass  is  thus  summed  up  by  Mr.  Brown : — 

Feet.    In. 

Arenaceous  and  argillaceous  shales        .         .         .         .  1,127     3 

Bituminous  shales .  26     5 

Carbonaceous  shales       .......  33 

Sandstones 562     0 

Conglomerate 08 

Limestone      .........  3  11 

Coal •     .    .         .         .         .  37     0 

Underclays 99     6 


Total     .         .         1,860     0 


From  this  it  would  appear,  that  while  the  calcareous  matter  (limestone),  gravel  (con- 
glomerate), and  mud-mingled  organic  matter  (bituminous  and  carbonaceous  shale), 
were  of  little  importance,  the  mass  was  composed  of  silt  and  mud  (arenaceous  and 
argillaceous  shales),  and  of  sand  (sandstone),  the  former  double  the  thickness  of  the 
latter.  The  more  pure  vegetable  matter  (coal)  amounts  to  about  y\)th  part,  and  the 
soils  (underclays)  to  somewhat  less  than  y^th  part. 


488         THICKNESS    OF    SOUTH    WALES    COAL    MEASURES. 

the  sections  of  the  European  coal  fields  of  this  kind,  similar  evidence 
presents  itself.*  In  the  section  of  the  Bristol  coal  measures  between 
the  Avon  and  Cromhall  Heath,  there  were  no  less  than  50  periods 
during  which  the  conditions  for  soils  obtained,  and  roots  (Stigmaria) 
were  freely  developed  in  them,  these  soils  topped  by  a  growth  and  accu- 
mulation of  plants,  apparently  requiring  contact  with  the  atmosphere 
for  their  existence.  The  general  thickness  of  that  series  is  about  5,000 
feet,  and  it  is  based  upon  an  accumulation  chiefly  sandy,  about  1,200 
feet  thick.  The  Glamorganshire  coal  field  gives  a  still  greater  deposit 
of  mud,  silt,  sand,  and  gravel,  intermingled  with  soils  in  which  roots  of 
some,  at  least,  of  the  plants  of  the  time  spread  out  freely,  most  fre- 
quently, though  not  always,  covered  by  beds  or  seams  of  coal,  the 
thickness  of  which  necessarily  depended  upon  the  duration  of  the  con- 
ditions needful  for  the  growth  and  accumulation  of  their  component 
plants.  The  mass  of  these  various  beds  in  the  neighbourhood  of  Swan- 
sea may  be  estimated  at  about  11,000  feet ;  so  that  if  accumulated  by 
subsidence,  horizontal  beds  piled  on  each  other,  it  would  have  to  be 
inferred  that  in  this  part  of  the  earth's  surface,  and  at  that  geological 
time,  there  had  been  a  somewhat  tranquil  descent  of  mineral  deposits, 
sometimes  capable  of  supporting  the  growth  of  plants  requiring  contact 
with  the  atmosphere,  but  most  commonly  beneath  water,  for  a  depth  by 
which  the  first-formed  deposits  became  lowered  more  than  two  miles 
from  their  original  position.  It  may  be  inferred  that  this  thickness  is 
not  really  that  of  the  general  mass,  as  the  component  beds  might  have 
been  accumulated  one  against  each  other,  as  happens  in  single  sand- 
stone and  conglomerate  beds  (figs.  38,  57),  and  as  no  doubt  has  more 
often  to  be  taken  into  account  than  it  has  been,  in  the  calculations  of 
thickness.  It  may,  however,  be  remarked,  that  in  these  coal  deposits, 
where  planes  of  vegetation  of  a  peculiar  kind  seem  so  frequently  to 
have  been  based  on  very  soft  soils,  and  the  whole  has  been  so  inter- 
mingled with  continuous  accumulations  of  mud,  that  the  general  sections 
appear  often  to  point  to  great  thickness,  more  particularly  when  the 
component  beds  are,  after  dipping  downwards,  found  rising  with  similar 
characters  at  a  considerable  distance,  though,  no  doubt,  the  unevenness 
in  many  of  the  deposits  should  be  well  considered,  and  the  probable 
value  of  the  general  decrease  of  the  whole  thickness  from  such  causes 
be  duly  estimated. 

Though  the  fine  mud  of  the  time  (now  argillaceous  shales),  gives 
little  information  as  to  deep  or  shallow  water  in  which  it  may  have  been 
deposited  from  mechanical  suspension,  the  sandstones  of  the  coal  mea- 

*  See  the  detail  of  the  coal  fields  of  South  Wales,  Monmouthshire,  and  Gloucestershire, 
(Vertical  Sections  of  the  Geological  Survey  of  Great  Britain,  Sheets  1-11),  and  descrip- 
tions of  portions  of  the  same  districts  (Memoirs  of  the  Geological  Survey  of  Great 
Britain,  vol.  i.  pp.  161-212). 


FALSE     BEDDING    IN    COAL-MEASURE    SANDSTONES. 


489 


sures  very  frequently  show  that  they  have  been  far  more  the  result  of 
sands  drifted  along  the  bottom  of  moving  water,  than  of  having  been 
mechanically  suspended  in  it.  Indeed,  the  accumulation  of  the  sands 
is  much  that  which  would  be  expected  from  a  pushing  forward  of  the 
bottom  detritus  into  a  shallow  depression,  where  the  conditions  may 
have  been  so  changed  by  alteration  of  levels  that  the  sand  of  a  higher 
situation,  and  nearer  its  source  of  supply,  was  readily  transported  into 
it.  Sections  of  the  subjoined  kind  (fig.  186)  are  of  the  commonest 

Fig.  186. 


occurrence  in  many  parts  of  the  British  coal  measures,  and  they  would 
appear  not  less  common  in  the  great  coal  deposits  of  North  America 
and  parts  of  Europe,  the  geological  age  of  which  has  been  considered 
somewhat  equivalent.  By  careful  removal  of  the  upper  surfaces  of  these 
beds,  the  overlaps  of  the  differently-drifted  laminae  may  be  seen,  and 
occasionally  still  better  in  coast  exposures.  The  following  (fig.  187)  is 
a  sketch*  of  the  upper  surface  of  a  bed  of  sandstone  exposed  on  the 
coast  near  Nolton  Haven,  Pembrokeshire,  showing  the  diffent  margins 
of  the  sand,  as  its  various  drifts  proceeded. 

Fig.  187. 


An  observer  having  thus  obtained  evidence  of  the  apparent  growth 
and  accumulation  of  terrestrial  plants  in  place,  and  the  rooting  of  at 
least  some  of  them  in  soils  beneath  of  such  a  character  that  fine  rootlets 

*  By  Professor  John  Phillips,  when  examining  that  part  of  South  Wales  with  the 
author. 


490      DRIFTS    OF    MATTED    PLANTS    IN    COAL    MEASURES. 

could  spread  freely  amid  their  parts,  has  to  look  carefully  into  the 
species  of  these  and  other  plants  entombed  in  the  general  mass,  endea- 
vouring to  see  if  there  may  not  be  some  drifted  amid  the  mud,  silt,  and 
sands,  and  even  included  among  the  coal  itself,  which  may  differ  from 
those  inferred  to  have  grown  on  the  spot.  There  would  appear  much 
to  accomplish  on  this  head,  at  the  same  time,  however,  it  seems  pro- 
bable that  while  some  plants  have  thriven  in  the  planes  of  vegetable 
matter  now  converted  into  coal,  others,  even  trees,  have  been  borne 
into  the  general  mass  of  vegetation,  by  water  transporting  them,  as 
many  a  river  now  does.  Matted  masses  of  plants  are  often  discovered 
among  the  sandstones,  as  if  drifted  by  some  stream,  "transporting  such 
plants  on  its  surface,  while  it  pushed  onwards  the  sands  beneath  it, 
streaks  of  such  intermingled  vegetation  sometimes  extending  many 
yards  in  length,  and  occurring  amid  sandstones,  the  component  sands 
of  which  have  been  thus  accumulated.  The  following  is  a  sketch  (fig. 
188)  of  the  upper  surface  of  part  of  one  of  these  vegetable  drifts  at 
Pembrey,  Caermarthenshire,  in  which  multitudes  of  the  stems  of  Sigil- 
larice  and  Lepidodendra,  chiefly  the  former,  and  now  converted  into 
coal,  are  crossed  and  matted  together  in  all  directions. 

Fig.  188. 


These  drifts  of  plants,  now  forming  streaks  of  coaly  matter  in  the 
sandstones  or  shales  including  them,  are  sufficient  to  show  that  though 
numerous  coal  beds  may  be  the  result  of  the  growth  of  a  peculiar  vege- 
tation in  place,  the  roots  of  which  required  and  penetrated  a  suitable 
soil  beneath,  it  might  so  happen  that  extensive  and  deep  accumulation 
of  drifted  plants  may  wholly  form  coal  beds  under  favourable  circum- 
stances, so  that  an  observer,  while  investigating  coal  deposits,  should 
carefully  weigh  any  evidence  of  this  kind,  as  well  as  that  pointing  to 
the  growth  of  plants  in  the  situations  where  their  remains  now  constitute 
coal.  The  two  modes  of  accumulation  are  by  no  means  incompatible 


EXTENT  OF  COAL  BEDS.  491 


with  each  other.  On  the  contrary,  they  may  be  often  intermingled, 
sometimes  conditions  prevailing  more,  or  even  entirely,  in  favour  of  one 
instead  of  the  other.  At  the  same  time  it  may  be  remarked  that,  as 
careful  investigations  have  proceeded,  the  evidence  of  the  growth  in 
place  of  the  mass  of  plants  now  constituting  extensive  coal  beds,  during 
the  time  when  the  chief  coal  accumulations  of  Europe  and  America 
were  effected,  has  been  gaining  ground,  inasmuch  as  the  soils  beneath 
most  of  the  coal  beds  and  containing  roots  (Stigmarid)  have  been  very 
commonly  found.* 

An  observer  will  not  long  have  been  engaged  in  the  examination  of 
extensive  coal  districts  without  usually  finding  that,  while  certain  beds 
of  coal  can  be  traced  outcropping  for  long  distances,  and  found  when 
sunk  far  beneath  the  surface  at  various  depths,  according  to  circum- 
stances, others  are  more  local,  mere  patches,  as  it  were,  amid  sheets 
of  vegetable  matter  far  more  persistent  over  wider  areas.  In  like 
manner,  some  of  the  former  mud,  silt,  or  sands,  accumulated  at  the 
same  time,  present  a  more  common  character,  scattered  over  extensive 
districts,  than  others,  the  muds  usually,  as  might  be  expected  from 
their  component  parts  having  been  diffused  in  a  fine  state  of  mechanical 
suspension  in  water,  being  the  most  persistent.  Taking  the  chief 
sheets  of  coal  as  guides,  duly  weighing  the  kind  and  amount  of  distribu- 
tion of  the  accompanying  ancient  muds,  silts,  sands,  and  gravels,  and 
reducing  the  section  and  plan,  so  that  all  embarrassments  of  contorted 
or  simply  tilted  beds,  with  any  fractures  or  dislocations  which  the 
whole  accumulation  may  have  sustained,  be  removed,  it  will  be  seen 
how  far  these  sheets  of  interstratified  matter  may  extend  in  a  manner 
requiring  an  even,  or  nearly  even  surface,  over  a  wide  space.  To 
accomplish  such  an  object,  it  will  be  obvious  that  an  observer  should 
free  himself  from  mere  local  variations,  and  attend  to  the  evidence 
presented  on  the  large  scale.  Thus  it  may  be  required  that  all  the 
coal  districts  of  Great  Britain  and  Ireland,  whether  remaining  as 
patches,  reposing  on  older  rocks,  or  simply  exposed  by  the  action  of 
denuding  causes,  which  have  removed  some  covering  of  subsequent 
deposits,  should  be  regarded  as  a  whole,  and  with  reference  to  any 
portion  of  dry  land  of  which  they  may  have  constituted  an  addition, 
and  from  which  the  needful  supply  of  mud,  silt,  sands,  or  gravel,  now 

*  These  soils,  though  far  from  having  been  acknowledged  as  such,  have  long  been 
known,  and  employed  as  guides  by  the  working  colliers,  whose  experience  taught  them 
their  frequent  occurrence  beneath  beds  of  coal,  the  more  especially  where  they  consti- 
tute, as  they  frequently  do,  excellent  materials  for  the  fire-bricks  so  often  required  in 
our  coal  districts,  for  the  different  metallurgical  and  other  uses  for  which  that  fuel  is 
employed.  The  name  given  to  these  ancient  soils  varies  in  different  districts — underclay, 
bottomstone,  and  undercliff,  are  not  uncommon  names  in  South  AY  ales  and  the  west  of 
England.  The  ganister  of  Yorkshire  and  Derbyshire  is  a  bed  or  beds  of  this  kind. 
Though  so  long  known  to  the  coal  miner,  they  have  been  rarely  noticed  until  lately  in 
colliery  sections. 


492  CHANNELS  ERODED  IN  COAL  BEDS,  FOREST  OF  DEAN. 

forming  its  accompanying  beds  of  shale,  argillaceous  and  arenaceous, 
sandstone  and  conglomerate,  were  derived. 

"With  regard  to  the  sheets  of  vegetable  matter,  now  constituting  coal 
beds,  they  sometimes  present  traces  of  water  action  on  their  surfaces, 
much  reminding  us  of  the  erosion  to  be  seen  upon  extensive  areas  of 
bog,  channels  being  cut  out  by  drainage  and  running  waters.  Sands 
have  been  sometimes  drifted  above  such  sheets  of  vegetable  matter, 
before  they  became  consolidated,  removing  mud,  or  even  sands,  first 
covering  them,  as  in  the  following  section  (fig.  189) — 

Fig.  189. 


where  d  is  a  coal  bed  reposing  on  an  ancient  soil  0,  full  of  roots  (Stig- 
maria\  and  c,  mud  (shale)  first  covering  the  vegetable  matter  (coal), 
but  which  was  subsequently  cut  into  by  the  water  drifting  the  sand 
(sandstone)  5,  a  deposit  covered  subsequently  by  mud  (shale)  a.  In 
this  manner  many  a  portion  of  the  bed  once  resting  on  coal  may  be 
found  swept  away  in  parts,  even  to  the  removal  of  portions  of  the  coal 
beds  themselves.  The  Forest  of  Dean  presents  an  excellent  example 
of  channels  cut  in  the  vegetable  matter  (now  forming  coal)  of  a  par- 
ticular portion  of  the  coal  measures  there  seen.  The  chief  channel 
represented  in  the  annexed  plan  (a,  5,  fig.  190),  has  long  been  known 
to  the  colliers  of  the  district  as  the  "  Horse."  Mr.  Buddie  very  care- 
fully examined  the  circumstances  connected  with  the  "Horse"  and  its 
tributaries  (<?,  <?,  c\  known  as  the  "Lows,"  whence  it  would  appear 


that  when  the  vegetation  was  in  an  easily  removable  state,  like  that  of 
some  bogs,  drainage  water  had  cut  out  a  main  and  subsidiary  channels, 


LAPSE    OF    TIME    DURING    DEPOSIT    OF    COAL.  493 

into  which  a  subsequent  deposit  of  sand  was  thrown  down,  covering 
over  the  whole  surface,  as  any  sand  deposit  might  now  do  a  great  area 
of  bog  if  submerged.* 

As  proving  that  the  unequal  action  of  water  was  not  confined  to  that 
on  the  surfaces  of  the  sheets  of  vegetable  matter,  it  is  needful  to 
remark  that  careful  observation  will  frequently  show  this  to  have  hap- 
pened with  other  portions  of  the  coal  measures.  The  following  section 
(fig.  191),  observed  on  a  cliff,  composed  of  these  rocks,  between  Little 

Fig.  191. 


Haven  and  Gouldtrop  Road,  Pembrokeshire,  may  serve  to  illustrate  this 
circumstance.  Herein  a  deposit  of  mud  (shale),  a,  #,  seems  to  have 
been  cut  into  by  a  furrow  at  5,  extending  to  <;,  the  water  which  made  it 
bearing  in  sand,  and  mud  being  again  accumulated  over  the  sand  at  d. 
A  sweep  of  the  surface  appears  now  to  have  occurred,  and  on  the  side 
e  sands  were  thrown  down  from  mechanical  suspension  (the  component 
layers  being  quite  flat,  and  unmarked  by  diagonal  drifting),  into  a 
cavity  formed  in  that  direction,  by  which  the  previous  mud  deposit, 
a  a,  was  worn  away.  Circumstances  connected  with  the  local  mode  of 
deposit  then  changed,  and  mud,  //,  was  again  spread  over  the  surface 
of  the  first  accumulation,  its  modifications,  and  the  deposits  which  fol- 
lowed those  modifications. 

While  adverting  to  various  changes  produced  by  the  removal  and 
deposit  of  the  mineral  matter  of  coal-bearing  deposits,  it  may  be  de- 
sirable to  notice  the  evidence  often  afforded  by  the  coal  measures  as  to 
the  lapse  of  time  during  which  their  accumulation  was  effected.  The 
various  growths  of  plants  upon  different  soils,  and  the  general  thick- 
ness of  the  mass,  may,  no  doubt,  be  taken  as  evidence  of  a  long  lapse 
of  time,  though  the  rapidity  of  the  growth  of  such  plants  as  are  found 
entombed  in  these  beds  may  have  been  considerable ;  the  sand  and  mud 
deposits  may  also  have  been  somewhat  readily  effected,  and,  from  a 
rapid  mode  of  accumulation,  the  soils  (underclays)  may  also  have  been 
soon  formed.  When,  however,  pebbles  and  small  grains  of  coal  itself, 

*  The  "Horse"  has  been  followed  in  the  working  of  the  coal  bed  in  which  it  occurs 
(that  named  the  Coleford  High  Delf)  for  about  two  miles,  and  it  has  been  found  to  vary 
in  breadth  from  170  to  340  yards.  Quartz  pebbles  are  observed  in  some  portions  of 
the  sandstone  covering  up  the  "Horse"  and  the  "Lows,"  as  also  fragments  of  coal 
and  ironstone. — Buddie,  "  Geological  Transactions,"  vol.  vi. 


494     PEBBLES  OF  COAL  IN  COAL  ACCUMULATIONS. 

are  discovered  amid  the  sand-drifts  and  deposits  of  the  period,  we 
seem  to  advance  somewhat  further  in  the  evidence  of  a  considerable 
lapse  of  time.  We  certainly  do  not  know  that  required,  under  fitting 
conditions,  for  converting  the  vegetation  of  the  kind  and  period  into 
the  coal,  so  that  beds  of  it,  partially  broken  up,  may  be  used  as  a  por- 
tion of  the  higher  deposits  of  the  general  mass.  Herein  there  may  be 
somewhat  of  a  difficulty.  Still,  viewing  the  subject  generally,  and 
with  due  reference  to  the  action  of  running  water  on  land,  or  breaker 
action  on  the  shores  of  waters,  also  required,  no  little  lapse  of  time 
would  appear  needed  for  the  changes  in  the  vegetable  matter,  its  re- 
moval in  part,  and  its  redeposit.  It  sometimes  happens  in  certain  coal- 
measure  districts,  that  the  ironstones  also  of  previously-formed  strata 
have  in  like  manner  been  broken  up,  and  pebbles  of  them  drifted  into 
beds  amid  other  detrital  deposits.  Whatever  may  be  the  time  required, 
there  has  been  sufficient  for  the  production  of  the  coal,  the  consolida- 
tion of  the  ironstone,  the  breaking  up  of  both,  and  their  distribution 
in  higher  portions  of  a  series  of  generally  similar  accumulations.  When 
sufficiently  large,  the  pebbles  of  coal  (and  they  are  sometimes  discovered 
two  or  three  inches  in  diameter)  often  exhibit  the  jointed  or  cleavage 
structure*  of  the  beds  whence  they  were  derived,  their  planes  of  cleavage 
taking  various  directions  in  the  coal-pebble  beds  of  which  they  now 
form  parts,  while  the  cleavage  of  the  outside  portions  of  the  stems  of 
Sigillaria,  occasionally  drifted  with  them,  and  converted  into  coal,  have 
a  constant  direction  in  the  same  beds.  Moreover,  rounded  portions  of 
coal  of  a  distinct  character,  and  known  in  lower  portions  of  the  general 
deposits,  have  been  found  higher  in  the  series,  and  little  doubt  can 
exist  that  at  the  time  they  were  detached,  they  had  undergone  the 
same  order  of  change  as  their  parent  beds,  and  that,  even  if  these  have 
been  still  further  modified,  the  same  modification  from  similarity  of 
structure  had  extended,  under  the  same  general  influence  to  which  the 
whole  mass  of  these  deposits  has  been  exposed,  to  these  pebbles  also. 
Certain  beds,  well  exhibited  amid  the  quarries  of  the  Town  Hill,  Swan- 
sea, are  highly  illustrative  of  the  pell-mell  drift  of  such  coal  pebbles 
with  stems  of  Sigillaria,  the  latter  showing  the  forms  of  many  a  coal 
pebble  beneath,  the  plants  having  conformed  in  a  soft  state  to  the  hard 
pebbles  of  the  coal,  itself  a  substance  probably  derived  from  plants  of 
the  same  genus,  and  often  also  of  the  same  species  as  the  stems,  inter- 
mingled and  entangled  in  the  common  drift. 

The  necessity  of  land  for  the  sufficient  supply  of  the  detrital  matter 
of  the  "  coal  measures"  would  appear  a  somewhat  needful  condition 
carefully  to  be  borne  in  mind,  since  the  mass  of  the  coal  measures  of 
the  British  Islands  would  require  its  contents  to  be  measured  by  no 
small  amount  of  cubic  miles  of  mineral  matter,  worn  away  from  some 
other  position  which  its  parent  rocks,  even  themselves,  perhaps,  detrital, 


MARINE    REMAINS    IN    PART    OF    THE    COAL    MEASURES.      495 

may  have  occupied  at  a  distance  whence  they  could  have  been  moved. 
An  observer  has  next  to  inquire  how  far  the  removal  of  this  large 
amount  of  detritus  has  been  accomplished  by  breaker  action,  or  by 
other  means,  for  distribution  at  the  bottom  of  water.  Here  the  great 
sheets  of  vegetation,  based  upon  old  soils  in  many  situations,  and  often 
so  frequently  repeated,  afford  him  important  aid,  inasmuch  as  they  are 
not  composed  of  marine  plants,  neither  are  the  numerous  upright  stems, 
in  their  places  of  growth,  marine.  Over  some  wide  spaces,  and  through 
considerable  thicknesses  of  deposits,  no  trace  of  a  sea-bottom  is  found, 
though  the  remains  of  molluscs,  inferred  to  be  forms  similar  to  those 
now  detected  in  rivers  or  fresh-water  lakes,  have  been  discovered. 
While  this  may  be  true  in  many  districts,  and  through  considerable 
thicknesses,  it  is  not  so  as  a  whole,  even  for  the  comparatively  limited 
area  of  the  British  Islands,  for  here  and  there  the  forms  of  marine 
molluscs  are  discovered  amid  the  other  deposits.  Proceeding  from 
south  to  north  over  this  area,  it  is  found  that  the  remains  of  other 
marine  animals,  as  well  as  molluscs,  are  entombed  in  beds  interstratified 
with  the  coal  deposits,  even  somewhat  thick  limestones  affording  evidence 
of  the  presence  of  the  sea  for  a  time  sufficient  for  the  growth  and  con- 
tinued increase  of  different  marine  creatures  at  intervals  between  the 
conditions  of  the  ordinary  kind  obtaining  in  these  coal  deposits.*  Duly 
flattening  out  all  the  present  inequalities  of  the  British  coal  districts, 
and  reducing  the  whole  towards  horizontality,  several  thousand  square 
miles  of  tolerably  even  ground  would  appear  to  present  themselves, 
much  reminding  an  observer  of  some  great  delta,  such  as  those  of  the 
Ganges,  the  Quorra,  or  the  Mississippi,  in  a  state  of  descent  as  regards 
the  level  of  the  ocean,  in  such  a  manner  that,  as  the  land  was  depressed, 
and  the  fall  and  velocity  of  some  great  river  or  rivers  for  the  time 
increased,  detritus  was  borne  readily  onwards  over  sinking  sheets  of 
vegetation. 

That  some  sheets  of  vegetation  should  be  more  extensive  than  others 
could  scarcely  otherwise  than  happen  under  such  conditions ;  or  that 
occasionally  also  the  sea  waters  became  introduced,  should  there  be  any 
partial  subsidence  so  great  that  these  waters  entered  areas  of  different 

*  Except  in  some  rare  and  higher  part  of  the  carboniferous  limestone  series,  even 
small  coal-seams  cannot  be  traced  in  that  rock  in  Southwestern  England  and  South 
Wales.  At  the  same  time  the  mass  of  the  coal  measures  of  the  same  district,  notwith- 
standing its  great  thickness,  exhibits  no  admixture  of  marine  remains  with  those  of 
terrestrial  vegetation  and  of  the  molluscs  possessing  forms  resembling  those  now 
inhabiting  fresh  waters.  The  same  general  conditions  appear  to  have  reached  as  far 
north,  in  the  British  Islands,  as  Northern  Wales  and  Derbyshire.  Still  further  north, 
however,  coal  beds  become  more  intermingled  with  the  mass  of  supporting  calcareous 
deposits  (mountain  or  carboniferous  limestones),  so  that  the  latter  include  among  them 
shales,  sandstones,  and  coal ;  thus  showing  that,  in  the  northern  portion  of  this  area, 
the  conditions  for  the  growth  and  entombment  of  this  kind  of  vegetation  commenced  at 
an  earlier  geological  period  than  in  the  southern. 


496  GRADUAL    SUBSIDENCE    OF    DELTA    LANDS. 

dimensions,  while  lakes  of  fresh  water  were  tenanted  by  suitable  inhabi- 
tants, and  even  limestones  were  formed,  embedding  their  remains. 
That  the  general  conditions  should  be  introduced  earlier  at  one  portion 
of  a  given  area  than  another,  might  be  anticipated,  if  some  general  sea- 
bottom,  preceding  any  extension  of  a  delta  or  accumulation  of  that 
order  had  been  sufficiently  raised  either  by  the  amount  of  deposits 
thrown  down  upon  it,  or  by  general  movements  in  the  mass  of  such  sea- 
bottom,  and  adjoining  dry  land,  so  that  the  vegetation  of  the  low  flat 
grounds  of  the  time  could  flourish.  To  whatever  extent  this  or  any 
other  view  of  a  similar  kind  may  assist  observation  with  respect  to  the 
general  circumstances  connected  with  these  coal  deposits,  the  geolo- 
gist, in  search  of  evidence  of  dry  lands  in  certain  portions  of  the 
earth's  surface  at  given  geological  times,  should  carefully  attend  to  any 
which  may  present  itself  in  favour  of  terrestrial  plants  having  grown  at 
or  near  the  place  where  their  remains  are  now  discovered.  It  will  rea- 
dily be  inferred  that  circumstances  may  have  occurred  at  different 
geological  dates,  in  fitting  situations  under  which  vegetation  may  have 
been  entombed,  producing  layers  of  carbonaceous  matter  in  different 
conditions  of  change,  so  that  anthracite,  bituminous  coals,  or  lignite 
may  now  occur  among  the  mud,  silt,  sand,  and  gravel,  accumulated  at 
those  different  dates.  This  is  now  well  understood ;  and  the  deposits 
to  which  the  term  "coal  measures"  has  been  especially  assigned  in 
Europe  and  North  America,  have  only  been  selected  for  notice,  because 
of  easy  access  in  several  parts  of  those  continents.  Coal  deposits  of 
importance  are  now  well  known  in  Asia,  Australia,  and  some  other 
regions.  How  far  there  may  be  proof  of  the  growth,  in  place,  of  the 
plants  which  have  furnished  the  materials  for  the  carbonaceous  portions 
of  these  accumulations,  becomes  a  matter  of  no  slight  geological  interest, 
as  supplying  information  not  only  of  the  dry  land  of  the  relative  time 
which  the  general  evidence  may  lead  us  to  infer  most  probable,  but  also 
of  the  kind  of  vegetation  which,  under  certain  conditions,  flourished  at 
such  times  in  given  regions. 

To  return  to  the  comparatively  limited  area  of  the  British  Islands  for 
the  purpose  of  again  illustrating  how  much  may  sometimes,  under  favour- 
able circumstances,  be  observed  in  minor  portions  of  the  earth's  surface, 
we  find  two  other  instances  at  different  geological  dates  ;  one,  during 
the  accumulation  of  the  group  of  beds  known  as  the  oolitic  series,  and 
the  other,  at  the  close  of  its  deposit,  when  vertical  stems  so  occur  that 
we  have  further  evidence  of  plants  entombed  in  their  places  of  growth. 
The  coal  beds  of  the  oolitic  series  in  Yorkshire  have  been  long  known  as 
occurring  on  a  "  geological  horizon,"  to  adopt  the  term  of  Humboldt,  with 
limestones,  and  clays,  replete  with  marine  organic  remains,  on  the  south 
of  England ;  and  Sir  Roderick  Murchison  pointed  out,  in  1832,  that  the 
vertical  stems  of  the  Equisetum  columnare,  apparently  in  the  positions 


FOSSIL    TREES    AND    ANCIENT    SOILS,    PORTLAND.        497 

in  which  they  grew,  were  not  only  found  in  the  shale  and  sandstone  of 
these  deposits  on  the  coast,  but  also  at  a  distance  of  40  miles  on  the 
northwestern  escarpment  of  the  Yorkshire  moorland,  pointing  to  the 
submergence  of  many  square  miles  of  ground  in  such  a  manner  that  the 
plants  were  quietly  entombed  in  the  mud  or  sand  accumulating  round 
them.* 

The  Island  of  Portland,  on  the  coast  of  Dorsetshire,  also  affords  evi- 
dence of  trees  in  place,  some  standing  as  they  grew,  with  the  soil  pre- 
served on  which  they  spread  their  roots.  These  soils  have  long  been 
known  by  the  quarrymen  of  the  island  as  the  "dirt-beds."f  While 
some  trees  are  rooted  in  their  ancient  soils,  others  are  prostrate,  in  the 
manner  represented  in  the  following  section  (fig.  192) ;  one  much 
reminds  us  of  the  "submarine  or  sunk  forests"  (fig.  152,  p.  434)  so 
frequent  on  the  shores  of  Western  Europe.  In  this  section^  the  erect 

Fig.  192. 


and  prostrate  remains  of  trees,  among  which  occur  those  of  cycadeous 
plants,  with  the  soil  of  the  period  (a,  5),  repose  on  a  calcareous  rock  (c,  c), 
containing  the  remains  of  fresh-water  animals,  and  resting  upon  the 
marine  oolitic  limestones  (d,  d\  commonly  known  as  the  Portland  oolite. 
Above  the  remains  of  the  trees  and  cycadeous  plants  there  are  other 
calcareous  deposits  (e,  e),  also  containing  animal  remains,  pointing  to 
accumulation  in  fresh  waters,  and  known  as  the  Purbeck  beds,  from 
being  well  exhibited  at  that  locality,  on  the  coast  eastward  from 
Portland. 

Thus  the  vegetation  and  the  soil  upon  which  it  flourished  are  included 
in  an  accumulation  effected  in  fresh  water,  implying  that  dry  land 
existed  somewhere  in  the  vicinity  anterior  to  the  growth  of  the  trees. 
From  an  attentive  examination  of  the  district,§  Professor  E.  Forbes 

*  Murchison,  "Proceedings  of  the  Geological  Society,"  vol.  i.  p.  391. 

f  These  beds  were  first  described  by  Mr.  Webster,  "  Geol.  Trans.,"  vol.  ii.  p.  41. 

|  As  many  as  three  of  these  "dirt-beds"  have  been  noticed  in  some  parts  of  this 
series  of  deposits  in  Portland — different  remains  of  successive  soils,  perhaps  not  always 
of  exactly  the  same  equal  date,  though  representing  general  conditions  of  the  time. 
Only  one  of  such  "  dirt-beds"  is  represented  in  the  section,  for  more  clear  illustration 
of  the  general  circumstances  under  consideration. 

%  The  ancient  soil,  with  its  trees,  some  prostrate,  and  others  in  their  place  of  growth, 
is  not  confined  to^the  Isle  of  Portland.  It  may  be  also  well  seen  amid  beds  of  the  Pur- 
beck  series,  in  the  east  cliff  of  Lulworth  Cove,  a  few  miles  to  the  eastward.  With 

32 


498   CONDITIONS    UNDER    WHICH    THE    ANCIENT    SOILS    AND 

found  that  the  fresh-water  animals,  the  remains  of  which  occur  in  the 
lower  part  of  the  covering  beds,  were  not  changed  by  the  conditions 
permitting  the  production  of  the  "  dirt-bed,"  and  the  growth  of  the 
plants,  being  the  same  as  in  the  calcareous  beds  immediately  beneath. 
He  found,  moreover,  that  there  had  been  three  successions  of  species  in 
the  Purbeck  deposits.  As  to  the  general  character  of  those  beds,  the 
Professor  ascertained  that  while  the  higher  and  lower  accumulations 
bear  evidence  (from  their  organic  contents)  of  having  been  deposited  in 
fresh  waters,  the  central  portion  points  to  alternations  of  fresh  water, 
brackish  water,  and  sea.  Altogether  a  highly  interesting  series  of  facts, 
showing  a  disappearance  of  the  sea,  and  the  formation  of  dry  land,  by 
which  animals  inhabiting  fresh  water  could  obtain  the  conditions  for 
their  existence,  the  actual  evidence  of  this  dry  land  in  particular  por- 
tions of  the  area,  and  the  continuance  of  the  fresh  water  accumulations 
by  some  change,  during  which,  while  the  soil  or  soils  became  submerged 
beneath  the  fresh  water,  the  sea  was  not  admitted.  A  time  came,  how- 
ever, when  the  sea  was  let  in,  brackish  water  also  occurring ;  but  this 
did  not  last,  for  we  find  again  fresh-water  deposits  above  these  deposits. 
Professor  E.  Forbes  mentions,  that  so  far  as  the  remains  of  the  inverte- 
brate animals  extend,  it  would  be  impossible,  without  the  evidence  to  be 
obtained  from  superposition  of  other  accumulations,  to  say  whether  the 
fresh-water  deposits  belonged  to  the  oolitic,  cretaceous,  or  tertiary 
series  of  rocks.*  Referring  back  to  the  time  (p.  464)  when  a  depres- 
sion of  the  lands  then  above  water  in  the  area  of  Southern  England 
was  in  progress,  so  that  the  lower  part  of  the  oolitic  series  of  deposits 
(various  limestones,  sometimes  oolitic,  f  sands,  and  clays),  spread  over 
the  submerged  rocks,  the  animals  of  the  period  even  boring  into  them 
under  favourable  conditions  (p.  469),  the  depression  apparently  ceased 
not  long  after  that  geological  date.  Whether  the  sea-bottom  and  adja- 
cent lands  then  took  a  contrary  movement,  rising  gradually,  so  that  the 
area  occupied  by  sea  was  diminished,  and  the  shores  extended,  or  that, 
remaining  stationary,  the  detrital  and  animal  accumulations  so  filled  up 

regard  to  the  further  extension  of  these  conditions  at  that  geological  time,  it  should  be 
observed,  that  Dr.  Fitton  mentions  an  earthy  bed  in  the  same  geological  position  in 
Buckinghamshire  and  the  Vale  of  Wardour,  as  also  in  the  cliffs  of  the  Boulonnais. 
Silicified  wood  is  found  in  a  bituminous  bed  from  Boulogne  to  Cap  Gris-nez  ("Geological 
Sketch  of  the  Vicinity  of  Hastings,"  1833,  p.  76).  A  "  dirt-bed"  is  noticed  by  Dr. 
Buckland  as  occurring,  in  its  geological  place,  near  Thame,  in  Oxfordshire ;  and  Dr. 
Mantell  mentions  one  as  found  at  Swindon,  Wiltshire,  on  the  top  of  the  Portland  beds, 
fossil  coniferous  wood  being  seen  in  abundance,  with  a  few  examples  of  Mantellia. 
"Wonders  of  Geology,"  6th  edit.,  vol.  i.  p.  390. 

*  Among  other  important  observations,  Professor  E.  Forbes  found  that  although  a 
bed  of  oysters  (Ostrea  distorta),  occurs  as  the  most  conspicuous  feature  of  the  middle 
division  of  the  Purbeck  beds,  that  the  fresh-water  fauna  of  the  time  was  not  interrupted. 

f  The  calcareous  grains  so  united  together  as  to  resemble  the  roe  of  some  fishes, 
whence  also  the  name  roe-stone  for  this  description  of  rock. 


GROWTH  OF  TREES  WERE  PRODUCED  AT  PORTLAND.  499 

the  seas  around  that  the  shores  were  thrown  back,  or  that  both  these 
causes  were  in  operation,  it  would  appear  that  the  remainder  of  the 
limestones,  sands,  and  clays  of  the  oolitic  series,  with  their  animal 
remains,  was  formed  within  a  gradually-diminishing  area,  as  far  as  that 
of  the  British  Islands  was  concerned,  so  that  finally,  in  a  particular 
portion  of  it,  the  conditions  prevailed  which  produced  the  results 
observed  in  Dorsetshire,  and  by  which  the  existence  of  dry  land  in  par- 
ticular spots  is  proved,  the  remains  of  trees  being  found  rooted  in  the 
soil  in  which  they  grew. 

The  change  from  sea  to  dry  land  conditions  would  appear  to  have 
further  continued,  for  upon  these  lower  (Purbeck)  accumulations  marked 
by  the  remains  of  fresh-water  animals,  a  very  considerable  depth  of  de- 
posits is  found,  pointing  to  the  presence  of  some  large  river  or  body  of 
fresh  water  in  the  area  of  Southeastern  England.  These  accumulations, 
with  the  Purbeck  beds,  are  now  commonly  known  as  the  Wealden  series, 
a  name  derived  from  the  beds  of  that  geological  time  found  in  the  Weald 
of  Sussex,  for  our  first  knowledge  and  numerous  subsequent  illustrations 
of  which  we  are  indebted  to  Dr.  Mantell.*  These  beds,  consisting  of 
ancient  mud,  sands,  and  calcareous  accumulations,  are  not  only  marked 
by  the  remains  of  fresh-water  molluscs,  but  also  contain  those  of  remark- 
able reptiles  (Iguanodon,  &c.),  of  gigantic  size,f  and  of  the  terrestrial 
plants  growing  in  the  banks  of,  or  swept  down  by  a  river,  the  matter 
borne  in  mechanical  suspension  in  it  covering  the  whole  up,  as  fitting 
circumstances  for  the  deposits  occurred.  That  an  elevation  of  a  mass 
of  land,  and  its  adjoining  sea-bottom  might  first  produce  variable  mix- 
tures of  lakes  and  minor  estuaries,  and,  finally,  some  larger  rivers,  will 
readily  be  seen,  by  considering  the  effects  which  would  be  produced  by 
an  elevation  which  should  extend  the  coast  line  of  the  British  Islands 
and  the  continent  of  Europe  from  Norway  to  the  Pyrenees  (figs.  65  and 
99),  so  that  the  present  drainage  of  Western  Europe,  from  Ushant  to 
Norway,  and  from  the  Land's  End,  by  the  east  coast  of  Great  Britain, 
to  the  north  of  Scotland,  should  be  thrown  into  two  chief  drainage  de- 
pressions, divided  at  the  Straits  of  Dover,  or  thereabouts.  At  first,  as 
the  sea-bottom  gradually  rose,  there  would  be  many  minor  admixtures 
of  estuaries  and  of  bodies  of  water  subsequently  rendered  fresh,  until, 

*  The  Tilgate  beds  were  described  by  Dr.  Mantell  in  1822,  in  his  "  Fossils  of  the 
South  Downs,"  and  the  same  year  he  communicated  the  joint  observations  of  Sir 
Charles  Lyell  and  himself  as  to  the  extension  of  these  beds  over  the  Weald.  The 
observer  will  find  an  excellent  summary  of  the  Wealden  series,  as  known  in  England, 
and  on  the  continent  of  Europe,  in  Dr.  MantelPs  "  Wonders  of  Geology,"  6th  edition, 
vol.  i.  pp.  360-449.  He  should  also  consult  the  works  of  Dr.  Fitton  on  the  lower  part 
of  the  cretaceous  series  (green  sand,  &c.),  contained  in  the  "Geological  Transactions 
and  Proceedings,"  and  he  will  find  much  instruction  in  his  "Guide  to  the  Geology  of 
Hastings." 

f  For  the  knowledge  of  these,  also,  geologists  are  indebted  to  the  labours  of  Dr. 
Mantell. 


500  EAISED    SEA-BOTTOM    ROUND    BRITISH    ISLES. 

finally,  all  the  rivers  draining  into  the  Baltic,  with  those  now  finding 
their  way  into  the  North  Sea  (Elbe,  Weser,  Ems,  Rhine),  would  have 
to  flow  outwards,  more  or  less  uniting  at  different  distances,  together 
with  the  drainage  of  the  new  area  of  dry  land,  into  the  Atlantic,  be- 
tween the  Shetland  Isles  and  Norway,  perhaps  somewhat  about  the  sub- 
marine gulf  stretching  down  southerly  between  them  (fig.  65).  While 
this  happened  on  the  north,  all  the  rivers  in  the  English  Channel  would 
be  more  or  less  united,  and  flow  out  into  the  Atlantic  by  the  greatest 
depression  between  the  Land's  End  and  Ushant,  the  drainage  waters  of 
the  new  dry  land  being  also  added  to  them.  In  both  cases  marine  de- 
posits would  be  succeeded  at  first  by  many  intermingled  estuary  arid 
fresh-water  accumulations  of  various  extent,  and,  finally,  by  those  mark- 
ing at  the  mouth  of  the  English  Channel,  and  between  the  Shetland 
Isles  and  Norway,  the  presence  of  far  greater  rivers  than  those  which 
now  discharge  their  waters  into  any  of  the  seas  bounding  Western 
Europe  from  Norway  to  the  Pyrenees.  While  the  Loire  and  the  Ga- 
ronne might  readily  extend  their  courses  without  union  over  the  new 
dry  land,  a  portion  of  the  Bay  of  Biscay,  more  complication  would  arise 
amid  the  rivers  of  the  west  part  of  Great  Britain  and  around  Ireland. 
Looking,  however,  to  the  charts,  there  would  be  a  tendency  to  gather 
waters  together  into  great  rivers  outwards  between  Northern  Ireland 
and  Scotland,  and  between  Southern  Ireland  and  the  Land's  End. 

While  thus  so  far  advanced  upon  the  changes  which  have  occurred 
with  regard  to  the  presence  and  disappearance  of  dry  land  in  so  limited 
an  area  as  that  which  has  been  noticed,  it  may  not  be  undesirable  to 
advert  to  the  great  change  which  subsequently  converted  a  very  ex- 
tended portion  of  the  same  part  of  the  earth's  surface  again  into  a 
sea-bottom,  upon  which  a  considerable  thickness  of  mud  and  sands 
(green-sands  and  gault),  with  a  thick  covering  of  calcareous  matter 
(chalk,)  was  accumulated.  This  was  apparently  accomplished  by  a 
somewhat  gradual  depression  of  a  sea-bottom  making  way  for  the 
detritus  borne  to,  and  over  it,  in  addition  to  so  much  of  the  volume  of 
deposit  as  was  due  solely  to  the  accumulation  of  the  hard  parts  of 
marine  animals,  for  the  evidence  is  in  favour  of  a  greater  general  area 
being  gradually  covered,  as  this  portion  of  geological  time  advanced,  so 
that  the  higher  beds  overlapped  or  overspread  the  lower,  the  upper 
members  of  this  series  of  deposits  (the  cretaceous),  thus  reaching 
beyond  the  lower  in  Northern  and  in  Southwestern  England.  Again 
conditions  changed  over  the  same  area,  and  in  the  supra-cretaceous  or 
tertiary  time  we  find  deposits  according  with  such  altered  circum- 
stances, and  showing  that  dry  land  was  then  intermingled  with  sea ; 
that  there  were  estuaries  and  fresh-water  lakes ;  and,  moreover,  that 
there  were  oscillations  of  the  land  and  sea-bottom,  producing  submer- 
gence beneath  and  emergence  above  the  level  of  the  adjacent  ocean. 


CRACKED    SURFACES    OF    DEPOSITS.  501 

These  oscillations  and  their  consequences  have  been,  as  we  have  seen 
(p.  432),  continued  up  to  the  present  adjustments  of  land  and  water, 
when  we  have  atmospheric  influences  and  the  sea  wearing  away  the 
former,  the  matter  thus  removed  variably  dispersed  along  the  shores 
and  over  the  adjacent  sea-bottom,  no  doubt  entombing  a  mass  of  the 
remains  of  the  vegetable  and  animal  life  of  the  time  and  area — the 
whole,  with  the  dry  land  and  its  lakes,  rivers,  and  estuaries,  ready  to 
be  elevated  above,  or  depressed  beneath  the  ocean  level,  as  has  hap- 
pened over  the  same  area  at  previous  geological  times. 

The  footprints  of  animals  and  cracked  surfaces  of  beds  also  afford 
the  observer  the  means  of  judging  of  the  presence  of  dry  land  at  par- 
ticular times.     These  have  of  late  received  their  well-deserved  share 
of  attention.     Although,  as  in  the  plan  beneath  (fig.  193),  when  un- 
rig. 193. 


covering  a  clay  or  shale  bed,  he  detects  a  splitting  of  parts  corre- 
sponding with  that  seen  upon  the  drying  of  any  mud  or  clay  surface 
exposed  to  the  sun  and  air,  he  would  be  led  to  infer  the  contact  of  the 
atmosphere  with  such  a  surface,  and  the  consequent  presence  of  land, 
so  as  at  least  to  permit  a  space  to  be  exposed  for  a  time  sufficient  to 
produce  this  amount  of  desiccation ;  such,  for  example,  as  on  somewhat 
flat  shores  upon  which  there  were  great  differences  in  the  spring  and 
neap  tides  (p.  103),  the  evidence  becomes  more  perfect,  by  the  addition 
of  the  well-marked  footprints  of  animals.  Such  footprints  have  now 
been  found  in  various  parts  of  the  world — Europe,  Asia,  and  America 
— with  and  without  the  evidences  of  the  cracks  pointing  to  exposure  of 
the  atmosphere,  and  are  highly  important,  as  showing  the  tread  of 
animals  on  shores  or  in  waters  so  shallow  and  tranquil,  that  creatures 
breathing  in  the  air  and  walking  on  soft  ground  left  the  prints  of  their 
footsteps  uninjured  behind  them.  The  following  sketch  (fig.  194)  is 
taken  from  the  figure  by  Dr.  Sickler,  of  footprints  in  the  red  sand- 
stone quarry  at  Hessberg,  near  Hildburghausen,  Saxony,*  and  well 

*  These  footprints  appear  to  have  attracted  attention  at  Hessberg,  about  1833  or 
1834,  when  they  were  described  by  Dr.  Hohnbaum  and  Professor  Kaup,  the  latter  of 
whom  gave  the  animals  considered  to  have  formed  them  the  name  of  Chirotherium.  Dr. 
Sickler  published  a  further  account  of  them  in  a  letter  to  Blumenbach  in  1834.  Prior 
to  this  discovery  (1828),  Dr.  Duncan  gave  an  account  (Transactions  of  the  Royal 
Society  of  Edinburgh,  vol.  xi.)  of  similar  footsteps  found  in  the  new  red  sandstones  of 


502 


FOOTPRINTS    OF    AIR-BREATHING    ANIMALS 


illustrates  both  such  impressions  and  cracks  from  desiccation.     While 
these  footprints  have  been  considered  as  those  of  reptiles,  some  of 


Fig.  194. 


gigantic  Batrachians,  others  have  been  discovered  of  forms  from  which 
they  have  been  attributed  to  birds  of  different  species  and  sizes.     To 


Fig.  195. 


these  Professor  Hitchcock  long  since  called  attention  as  occurring  in  a 
red  sandstone  series  in  the  valley  of  the  Connecticut,  United  States.* 

Corn  Cockle  Muir,  Dumfriesshire,  and  in  1834  Dr.  Duncan  informed  Dr.  Buckland 
(Bridgewater  Treatise,  vol.  i.  p.  269)  that  like  impressions  had  been  found  in  the  same 
series  of  deposits,  10  miles  from  the  former  locality,  and  2  miles  from  the  town  of 
Dumfries. 

*  Professor  Hitchcock  described  these  footprints  under  the  name  of  Ornithichnidx,  in 
the  American  Journal  of  Science,  vol.  xxix.,  1836,  and  also  in  his  Report  on  the 
Geology  of  Massachusetts.  Sir  Charles  Lyell  also  gives  an  account  of  them  in  his 
Travels  in  North  America,  chap.  12.  The  footprints  are  of  various  sizes,  some  not 
longer  than  those  of  our  common  sanderlings,  while  others  exceed  that  of  the  ostrich, 
measuring  16  inches  in  length,  exclusive  of  the  largest  claw,  two  inches  long.  Dr. 
Buckland,  remarking  on  the  dimensions  of  this  supposed  bird,  observes  (Bridgewater 
Treatise,  vol.  ii.  p.  40),  that  "in  the  African  ostrich,  which  weighs  100  Ibs.,  and  is  nine 
feet  high,  the  length  of  the  leg  is  about  four  feet,  and  that  of  the  foot  ten  inches." 


AND    RAIN-MARKS    ON    THE    SURFACES    OF    ROCKS.        503 

The  preceding  sketch  (fig.  195)  is  taken  from  among  the  illustrations 
given  by  the  Professor. 

With  regard  to  these  impressions  being  those  of  birds,  Professor  Owen 
points  out  that,  taken  by  themselves,  they  "  are  insufficient  to  support 
the  inference  of  the  progression  of  the  highly-developed  organization  of 
birds  of  flight  by  the  creatures  which  have  left  them."* 

The  footsteps  attributed  to  reptiles  have,  in  part,  been  assigned  as 
probable  to  the  Labyrinthodon^  whose  bones  have  been  discovered  in 
the  same  series  of  deposits.  As  still  further  showing  contact  of  the  air 
with  mud  or  sand  where  these  or  other  animals  have  left  the  imprints 
of  their  feet,  marks  in  the  same  as  well  as  other  surfaces  of  associ- 
ated beds  have  been  discovered,  strongly  resembling  those  left  on  clay 
or  sand  by  a  heavy  fall  of  rain,  such  as  may  often  be  observed  on  coasts 
when  the  tide  is  out.J  These  various  impressions  have  usually  been 
made  upon  layers  of  clay  or  mud,  sand  having  been  tranquilly  accumu- 
lated over  the  hardened  surface  retaining  the  footprints  and  other  marks. 
As  the  resulting  marl,  clay,  or  shale  is  frequently  broken  by  the  removal 
of  the  sandstone  bed  covering  it,  the  "lower  surface  of  the  latter  usually 
reveals  the  condition  of  the  upper  surface  of  the  former  before  it  was 
overspread  by  the  sand.  At  the  same  time  we  have  seen  impressions 
on  the  upper  surfaces  of  sandstones  themselves,  which,  though  not  so 
well  defined,  resemble  footprints  on  sand  subsequently  and  quietly 
covered  over  by  mud.§ 

Of  whatever  animals  the  footprints  may  have  been,  with  the  cracks 
from  the  exposure  of  surfaces  of  mud  and  clay  to  desiccation  in  the  air, 
and  the  marks  resembling  the  rain-drops — for  these,  however  singular 
they  may  appear,  are  not  to  be  neglected — they  show  us  that,  during 
the  deposits  of  the  layers  or  beds  of  sand,  silt,  or  mud  in  which  they 
occur,  dry  land  was  there  at  hand  also,  and  that  the  beds  themselves 
may  have  formed  part  of  its  shores,  as  those  in  the  Bay  of  Fundy,||  in  the 

*  "The  Rhyncosaur,"  continues  the  Professor,  "  and  the  biped  Pterodactyles,  already 
warn  us  how  nearly  the  ornithic  type  may  be  approached  without  the  essential  character 
of  the  Saurian  being  lost ;  and  by  the  Chirotherian  Ichnolites,  we  learn  how  closely  an 
animal,  in  all  probability  a  Batrachian,  may  resemble  a  pedimanous  mammal  in  the  form 
of  its  footprints."  British  Association  Reports,  1841,  p.  203. 

f  The  Batrachian,  alluded  to  by  Professor  Owen  in  the  previous  note. 

J  An  illustrative  figure  of  the  impression  of  rain-drops  upon  the  same  slab  with  that 
of  a  biped,  from  the  red  sandstone  series  of  Massachusetts,  is  given  by  Dr.  Mantell,  in 
his  Wonders  of  Geology,  vol.  ii.  p.  556. 

$  The  footprints  noticed  in  the  text  as  discovered  in  Asia,  were  found  impressed  upon 
red  sandstone  in  India,  by  Lieut.  Pratt. 

||  Sir  Charles  Lyell  has  figured  the  recent  footprints  of  the  sandpiper  on  the  shores 
of  the  Bay  of  Fundy,  in  his  "  Travels  in  North  America,"  vol.  ii.  pi.  vii.,  and  has  pre- 
sented specimens  illustrative  of  the  preservation  of  these  footprints  in  different  layers, 
deposited  in  succession,  to  the  British  Museum,  and  to  the  collections  of  the  Museum  of 
Practical  Geology. 


504  ELEVATION    OR    DEPRESSION    OF    SEA-BOTTOM. 

Bristol  Channel,*  and  in  numerous  other  localities,  where  similar  and 
fitting  conditions  present  themselves,  now  do.  The  mere  piling  of  layer 
upon  layer  on  shores  of  this  kind  has  been  found  sufficient  to  preserve  such 
marks  (p.  148) ;  but  when  this  is  combined  with  a  quiet  submergence  of 
the  locality,  so  that  the  layers  of  deposit  are  little,  if  at  all,  broken  up, 
a  considerable  thickness  of  beds  marked  in  this  manner  may  be,  as  they 
apparently  have  been,  accumulated  in  succession,  until  finally  the  fitting 
conditions  cease,  and  the  preservation  of  such  impressions  can  no  longer 
be  effected. 

However  desirable  it  is  for  an  observer  thus  to  trace,  by  means  of 
beaches,  fresh  or  brackish  water  deposits,  the  footprints  of  animals  on 
shores  and  the  remains  of  plants  rooted  in  their  places  of  growth,  the 
presence  of  dry  land  on  different  parts  of  the  earth's  surface  (for  the 
circumstances  which  have  been  noticed  by  way  of  illustration  are  appli- 
cable, with  certain  modifications,  to  many  other  regions),  in  some  dis- 
tricts he  finds  himself  so  completely  surrounded  by  ancient  sea-bottoms, 
piled  up  in  various  modes  in  succession,  that  he  cannot  avail  himself  of 
the  aid  which  this  knowledge  of  the  probable  position  of  the  dry  lands 
of  given  geological  times  may  afford  him.  Although  aware  that  the 
wearing  away  of  the  mineral  masses  forming  dry  land,  furnished,  with 
the  stirring  up  of  sediment  from  shallow  depths  by  wave  action,  the 
materials  for  the  detrital  accumulations  he  may  have  before  him,  and 
which  may  alone  contain  the  remains  of  marine  life,  should  the  arrange- 
ment of  their  inorganic  component  parts  merely  point  to  a  deposit  from 
mechanical  suspension  in  water,  he  might  still  be  at  a  loss  as  to  the 
direction  or  character  of  the  dry  land  of  the  time.  A  study  of  the 
charts  of  many  different  regions  will  show  that  mud  is  found  as  well 
near  coasts  as  remote  from  them,  according  as  the  required  tranquillity 
for  deposit  and  subsequent  rest  may  prevail,  though  as  a  whole  wind- 
wave  action  upon  sea-bottoms  at  depths  where  it  can  have  influence 
tends  so  to  shift  those  bottoms  as  to  remove  muddy  sediment  further 
away  from  land  than  sand. 

When  all  the  modes  of  distributing  detrital  matter  above-mentioned, 
as  now  in  progress  in  tidal  or  tideless  seas  (pp.  89,  101),  are  combined 
with  movements  of  dry  land  and  sea-bottoms,  sometimes  upwards,  at 
others  in  the  contrary  direction,  it  is  evident  that,  in  addition  to  the 
consequences  of  such  movements  on  coasts  and  sea-bottoms  adjoining 
them,  it  might  often  happen  that  considerable  areas  may  be  elevated  or 
depressed  in  the  sea  itself  without  rising  above  its  surface  into  the 
atmosphere.  Mere  points  constituting  their  higher  portions  may  now 
and  then  be  protruded  and  be  acted  upon  by  breakers  and  atmo- 

*  We  have  frequently  collected  good  examples  of  footprints  of  different  kinds  pre- 
served in  the  muddy  banks  of  this  Channel,  left  dry  and  hardened  in  hot  summer 
weather,  on  the  wide  spaces  between  the  lines  of  neap  and  spring  tides. 


CHARACTER  OP  THE  SURFACES  OF  ROCKS.      505 

spheric  influences,  the  detritus  thence  arising  being  scattered  around, 
and  arranged  by  tidal  streams,  or  transported,  especially  the  finer 
matter,  in  a  broader  and  more  distant  manner  by  ocean  currents,  still 
able  to  force  their  way  amidst  these  minor  obstacles  to  their  courses. 
The  floor  of  the  ocean  is  not  yet  so  well  known  as  probably  it  will  be  at 
some  future  time,  when  systematic  researches  in  this  direction  may  be 
deemed  important  by  maritime  nations.  The  depths,  nevertheless,  of 
certain  points  have  been  ascertained,  more  especially  of  late  years,  suf- 
ficient to  render  it  probable  that  very  important  aid  to  geological  infe- 
rences would  be  obtained  by  more  extended  information  on  this  head. 

While,  on  the  one  hand,  the  distribution  of  detritus  outwards  by  the 
great  rivers  of  the 'world,  draining  large  portions  of  continents  and 
pushing  forward  their  deltas,  has  to  be  well  borne  in  mind,  on  the  other, 
such  changes  as  shall  raise  a  mass  of  sea-bottom,  scattered  higher 
portions  of  which  may  or  may  not  now  rise  into  the  atmosphere,  should 
receive  their  due  attention.  If  the  extent  of  sea-bottom,  above  which 
various  points  rise  and  form  the  multitude  of  isles  and  islets  of  the  Poly- 
nesian groups  in  the  Pacific,  were  to  be  gradually  elevated  so  as  to  con- 
stitute some  great  continent  of  dry  land,  no  great  deltas  would  be  raised 
— at  least  none  now  in  progress — whatever  former  conditions  of  that 
part  of  the  earth's  surface  may  have  produced ;  and  it  would  only  be  by 
degrees  that  the  drainage  of  the  new  land  formed  rivers,  these  uniting 
into  larger  streams  as  the  dry  land  became  extended,  some  perhaps, 
finally,  of  the  magnitude  and  importance  of  the  present  great  rivers  of 
the  world.* 

Although  detrital  matter  deposited  from  mechanical  suspension  in 
water,  and  arranged  in  layers  and  beds,  may  not,  from  the  structure  of 
the  interior  portions  of  the  layers  or  beds  themselves,  present  much 
information  as  to  the  depths  of  the  water  beneath  which  they  have  been 
accumulated,  while  they  may,  as  they  often  do,  exhibit  the  proof  of  a 
multitude  of  very  thin  layers  having  been  thrown  down  above  each  other 
(as  many,  perhaps,  as  twenty  or  thirty  of  these  in  one  inch  of  depth), 
their  surfaces  often  aid  most  materially  in  affording  valuable  information 
on  this  head.  It  frequently  happens  that  the  under  surfaces  may  be 
useful  as  well  as  the  upper,  inasmuch  as  they  often  give  the  imprint  of 
the  former  condition  of  the  surface  of  layers  or  beds  which  they  cover, 

*  If  the  observer  will  follow  out  this  supposed  uprise  of  the  area  in  question,  he  will 
find  numerous  subjects  of  interest  connected  with  it,  which,  though  many  may  be  suffi- 
ciently obvious,  such  as  the  mode  of  occurrence  of  the  coral  accumulations  now  in  pro- 
gress, their  modifications  as  the  dryland  became  extended,  the  effects  of  tides  and  altered 
courses  of  ocean  currents  during  the  change,  the  modified  distribution  of  animal  and 
vegetable  life  on  the  land  and  in  the  seas  adjoining,  the  chances  of  salt  or  fresh  water 
lakes,  mediterranean  seas,  or  the  like,  are  yet,  collectively,  of  importance  to  be  well 
borne  in  mind  while  he  may  be  occupied  upon  the  geological  effects  which  would 
thence  arise. 


506  FRICTION-MARKS    ON    ROCK    SURFACES. 

the  materials  of  which  were  of  a  perishable  kind  when  raised  into  situ- 
ations where  the  percolation  of  water  either  softened  or  even  removed 
them.  Thus  the  upper  surfaces  of  shales,  or  hard  clays,  may  be  con- 
verted into  mud  or  soft  clay,  in  which  all  traces  of  their  original  state 
are  lost,  while  some  sandstones  above  them,  the  consolidated  sand  which 
covered  over  the  impressions  left  in  these  surfaces  of  clay  or  hard  mud, 
preserve  reversed  impressions  of  the  state  of  the  old  sea-bottom  before 
it  was  covered  up.  Under  the  conditions  which  so  frequently  present 
themselves,  while  alternating  or  intermingled  beds  of  shales,  clays,  and 
sandstones  are  under  examination,  and  occasionally,  also,  limestones, 
and  it  is  considered  desirable,  if  possible,  to  trace  the  state  of  the  upper 
surfaces  of  the  mud  or  clay  before  they  were  covered  up,  the  under  sur- 
faces of  the  present  hard  beds  above  them  should  be  carefully  studied. 
The  search  will  frequently  reward  the  observer  with  an  excellent  picture 
of  such  old  surfaces  of  sea-bottoms,  with  their  various  markings,  even  to 
the  impressions  left  by  the  crawlings  or  way-tracks  of  the  molluscs  of  the 
time.  There  is  a  class  of  surface  conditions  on  consolidated  layers  of 
sand  and  silt  (sandstone  and  arenaceous  shale),  to  which  the  term  ripple- 
mark  has  been  applied,  from  a  supposed  resemblance  to  the  ripple  produced 
by  light  winds  on  water,  or  the  condition  of  many  tracts  of  sand  on  the 
retreat  of  the  tide,  that  would  afford  most  valuable  information  as  to  the 
depths  at  which  the  layers  or  beds  were  situated  beneath  water  when 
any  such  markings  were  produced,  were  it  not  that  such  kinds  of  surface 
might  frequently  arise  from  similar  conditions  at  different  depths.  We 
have  previously  mentioned  (p.  113),  the  friction  of  streams  or  cur- 
rents of  water  on  sandy  surfaces  beneath  them,  ridging  and  furrowing 
the  yielding  matter.  Such  may  be  often  seen  on  the  surfaces  of  sand- 
stone beds,  the  ridges  and  furrows  well  preserved,  as  beneath  (fig.  196), 
so  that  by  carefully  studying  the  steep  sides  of  the  ridges,  the  direction 
taken  by  the  moving  water  at  the  time  may  be  determined.  In  this  case 

Fig.  196. 


it  is  assumed  that  a  section  taken  across  at  a  b  would  give  that  shown 
by  c  d,  one  pointing  to  the  course  of  the  moving  water  from  a  to  b.  If 
we  were  sure  of  the  depths  at  which  existing  ocean  currents  swept  sands 
at  the  sea-bottoms  beneath  them,  producing  surfaces  of  this  kind,  some 
guide  would  be  obtained  to  the  range  of  depths,  from  a  few  feet  down- 


RIDGED    AND    FURROWED    SURFACES    OF    ROCKS.  507 

wards,  at  which,  only  measuring  by  the  amount  of  force  now  in  action, 
these  effects  could  follow.  Herein,  however,  there  is  much  uncertainty. 
From  the  experiment  of  Sir  Edward  Belcher,  off  the  west  coast  of  Africa 
(lat.  15°  27'  9"  N.,  and  long.  17°  31'  50"  W.),  it  would  appear  that  a 
current  there  found  moved  with  nearly  the  same  velocity  (0'75  nautical 
miles  per  hour)  at  the  depth  of  240  feet  (40  fathoms)  as  at  the  surface. 
When  we  regard  the  great  ocean  currents  of  the  world,  with  the  probable 
masses  of  water  put  into  movement  in  given  directions  at  the  same  time, 
it  may  not  be  improbable  that  comparatively  considerable  depths  are 
exposed  to  conditions  where  the  ridging  and  furrowing  of  sand  and  silt 
sea-bottoms  may  be  produced.  The  observer  has  also  to  recollect  that 
as  large  surfaces  of  sea-bottoms  may  be  raised  or  depressed,  from  some 
of  the  more  general  movements  of  the  solid  parts  of  the  earth's  surface, 
very  considerable  areas  could  be  brought  up  to  the  action  of  ocean  cur- 
rents, or  removed  beneath  their  influence. 

Upon  carefully  studying  the  surfaces  of  great  banks  and  flat  tracts 
of  sand  which  are  somewhat  suddenly  drained  by  a  retiring  tide,  so 
that  they  were  not  much  altered  by  the  action  of  the  small  waves  or 
heavy  breakers  of  the  time,  as  the  case  may  be,  the  geologist  will  fre- 
quently find,  as  already  noticed  (p.  113),  a  mixed  adjustment  of  inequali- 
ties, partly  due  to  the  movement  of  the  waves  before  the  superincumbent 
water  passed  away,  and  in  part  to  the  friction  of  this  water  draining  off 
the  banks  and  sandy  flats.  These  ridged  and  furrowed  surfaces  are 
occasionally  somewhat  extensive  when  the  sea  deserts  a  considerable 
area  in  a  short  time,  so  that  friction  is  produced  rather  suddenly  in 
some  general  direction.  This  will  often  happen  when  there  may  be  a 
heavy  sea  on  shore,  as  the  great  waves  break  at  a  proportionate  dis- 
tance outwards  upon  the  shallows  during  the  progress  of  the  ebb-tide, 
minor  action  only  taking  place  nearer  the  coast,  where  the  great  body 
moving  outwards,  the  ridging  and  furrowing  by  friction  on  the  sands 
may  point  to  the  chief  movement,  with  the  sharp  escarpment  of  the 
furrows  often  seaward,  though  the  wash  of  the  breakers  would  tend  to 
drive  sand  before  them  while  rushing  on  shore. 

Where,  as  on  many  great  banks  dry  at  low  tides  at  the  mouths  of 
estuaries,  there  may  be  a  complication  of  surface  arising  from  the  wave 
movements  anterior  to  the  removal  of  the  sea  from  above  them  and 
from  the  friction  of  waters  left  to  drain  off  them,  the  observer  will 
remark,  as  might  be  anticipated,  that  much  will  depend  upon  the  state 
of  the  weather  and  tides  of  the  time.  Calms  would  leave  friction- 
markings  such  as  might  arise  from  the  movement  of  a  stream  of  water 
over  a  sand-bank  before  it  was  left  by  the  tide,  more  than  gales  of  wind, 
since  the  wash  of  the  breakers,  as  its  action  was  felt,  would  pass  over 
and  tend  to  obliterate  the  ridges  and  furrows  due  simply  to  the  stream 
of  tide.  The  more  sudden  retreat  of  the  sea  during  the  chief  spring- 


508  RIDGED    AND    FURROWED    SURFACES    OF    ROCKS. 

tides,  from  the  same  depths,  would  tend  also  to  leave  the  surface  of  a 
sand-bank  more  marked  by  any  furrowing  from  the  previous  flow  of  a 
stream  of  tide  over  it,  other  circumstances  being  equal,  than  a  neap- 
tide,  during  the  descent  of  which,  wave-action  might  be  continued  for  a 
longer  time  after  the  stream  of  tide  ceased  to  be  felt  on  the  surface  of 
the  bank. 

The  surfaces  of  some  layers  and  beds  of  rock  so  resemble  those 
which  are  seen  in  the  last-mentioned  situations,  particularly  when  suffi- 
ciently large  portions  of  them  are  exposed,  either  on  coasts  or  amid 
highly-inclined  strata  in  mountainous  regions,  even  to  the  apparent 
minor  drainage  of  waters  off  sand-banks,  that  the  inference  of  these 
surfaces  having  been  produced  on  or  near  tidal  coasts  (p.  113)  some- 
what forces  itself  upon  an  observer.  At  the  same  time  he  will  have 
properly  to  weigh  the  probable  effects  due  to  wind-  waves  on  sea-bottoms 
at  different  depths  beneath  (p.  112),  and  the  power  thus  brought  into 
action  of  disturbing  such  bottoms,  occasionally  sifting  their  constituent 
parts,  so  that  a  tranquilly-formed  deposit  of  mud  may  cover  an  un- 
equally-disposed surface  of  sand,  produced  while  the  agitation  of  the 
sea  continued.  Many  surfaces  of  rocks  strongly  remind  us  of  loose 
matter  thus  moved  about  by  the  to-and-fro  action  of  an  agitated  sea 
above,  in  the  same  manner  as  sand  may  be  readily  acted  upon  by 
agitating  water  above  it  in  conveniently-formed  vessels  of  sufficient 
dimensions.  Such  approximations  to  the  ridges  and  furrows  of  friction 
upon  sands  and  silts  in  one  given  direction  should  be  well  distinguished 
from  the  latter.  These  sections,  instead  of  being  as  above  represented 
(fig.  196),  are  usually  more  undulating  or  even-sided,  the  surfaces  vary- 
ing from  obscure  ranges  of  depressions,  a,  5,  (fig.  197)  and  those  some- 

pig.  197. 


TSPT/TTTpr-!^ 

what  resembling  the  sharp  ridges  and  furrows  of  current  or  stream 
action,  c,  to  unequally-distributed  and  variably-formed  elevations  and 
depressions  (fig.  198),  which  require  also  to  be  well  separated  from  con- 
cretions, to  be  noticed  hereafter,  and  which  sufficiently  juxtaposed  may 
present  a  somewhat  similar  appearance. 

With  regard  to  the  surfaces  of  sea-bottoms,  now  consolidated  into 
hard  layers  and  beds  of  rock,  attention  should  be  paid  to  the  probable 
modifications  of  them,  even  at  great  depths,  by  the  passage  of  earth- 
quake movements,  shaking  these  surfaces  in  contact  with  the  superin- 
cumbent water.  In  some  regions,  such  movements  can  scarcely  be 
otherwise  than  frequent,  the  force  employed  being  sometimes  so  con- 


EFFECT    OF    EARTHQUAKES    ON    SEA-BOTTOMS.  509 

siderable,  and  its  application  repeated  in  such  quick  succession,  that  the 
finer  sediment  may  be  shaken  up  into  a  mechanical  suspension,  whence 

Fig.  198. 


it  would  require  some  lapse  of  time  again  to  settle  and  cover  over  the 
heavier  bodies,  taking  superficial  arrangements  according  to  the  vibra- 
tions produced  by  the  earthquake,  the  kind  of  substances  acted  upon, 
and  their  mode  of  previous  distribution.  In  cases  of  fissures  produced 
beneath  the  sea,  as  on  land,  during  earthquakes,  the  consequent  distur- 
bance of  adjoining  sea-bottoms  has  also  to  be  regarded.  Thus  the 
effects  of  the  transmission  of  earthquake  vibrations  both  on  the  large 
and  minor  scales,  those  of  the  great  sea-wave,  and  of  .the  smaller 
movements,  produced  by  the  contact  of  the  sea-bottom  and  water  above 
it,  the  earthquake  vibration  travelling  faster  through  the  former  than 
the  latter,  have  also  to  be  borne  in  mind  when  the  surfaces  of  sea-bot- 
toms of  even  the  oldest  geological  times  are  under  consideration,  and 
the  geologist  is  endeavouring  to  deduce  from  them  the  probable  depths 
of  water  beneath  which  they  took  the  forms  presented  to  his  attention. 
Submarine  areas  thus  disturbed,  and  the  surfaces  of  the  sea-bottoms 
moved,  could  scarcely  often  be  otherwise  than  considerable,  the  effects, 
no  doubt,  modified  by  relative  depths  of  the  water,  the  facility  with 
which  the  vibrations  may  be  transmitted  through  the  various  support- 
ing bodies,  and  the  like.  Ridges  and  furrows  may  be  raised  in  certain 
localities  by  the  onward  courses  of  chief  sea-waves  in  the  shallower 
waters,  and  not  be  again  wholly  obliterated,  though  often  modified  in 
form  before  they  were  finally  covered  up  and  secured  in  shape  until 
constituting  a  portion  of  hard  rock. 

While  there  may  often  be  much  uncertainty  as  to  the  depths  at  which 
the  component  parts  of  layers  and  beds  of  rock,  even  with  ridges  and 
furrows  on  their  surfaces,  have  been  thrown  down  from  the  waters  in 
which  they  have  been  previously  held  in  mechanical  suspension,  when 
unaided  by  other  evidence,  the  arrangement  of  parts  resulting  from 
the  pushing  of  detrital  matter  forward  on  the  bottom  often  seems  to 
point  to  somewhat  shallow  waters.  In  this  case,  again,  as  the  depth  is 
uncertain  to  which  currents  may  act  on  sea-bottoms,  these  unequal,  like 
those  at  the  edge  of  the  soundings  of  1200  feet  (200  fathoms),  from 
Spain  round  the  British  Islands  to  Norway  (p.  446),  so  that  sedimen- 
tary matter  derived  from  adjacent  lands  is  transported  and  pushed 


510  DIAGONAL    ARRANGEMENT    OF    THE    MINOR 

along  the  bottom  into  the  hollows,  the  like  effects  may  be  produced  at 
far  greater  depths  than  is  usually  inferred.  Supposing  an  ocean  cur- 
rent or  tidal  stream  so  to  act  as  to  push  forward  detrital  substances 
from  some  land  affording  the  required  amount  of  increase  to  the  general 
mass  of  previous  accumulations,  much  in  the  same  manner  as  that  to 
which  Mr.  Austen  has  called  attention,*  so  that  after  spreading  over  a 
somewhat  level  sea-bottom,  the  general  increase  had  to  be  provided  for 
still  further  outwards  over  uneven  ground,  the  matter  thus  shoved  on 
would  have  to  fall  over  into  deeper  waters,  and  arrange  itself  much  as 
on  the  outskirts  of  rivers  delivering  their  detritus  into  deep  and  tideless 
seas  or  other  still  waters  (p.  73).  In  this  manner,  even  sandy  beds, 
affording  sections  of  the  component  layers  arranged  diagonally  to  their 
upper  and  under  surfaces,  might,  as  before  mentioned  (p.  92),  extend 
over  large  and  flat  accumulations  of  mud,  thrown  down  from  mechanical 
suspension. 

Diagonal  arrangements  of  the  minor  parts,  resulting  from  this  push- 
ing action  along  the  bottom,  are  very  common  in  many  sandstones,  as 
well  as  those  which,  from  their  occasional  organic  contents,  leave  little 
room  to  doubt  were  formed  beneath  the  sea,  as  in  those  so  frequent  in 
many  parts  of  the  coal-measure  accumulations  (p.  489).  These  arrange- 
ments are  sometimes  diversified  in  a  way  to  show,  that  while  some  of 
the  sandy  matter  has  thus  been  forced  or  brushed  onwards  on  the  bot- 
tom, the  same  kinds  of  sand  were,  at  other  times,  thrown  down  in  hori- 
zontal layers,  more  pointing  to  deposit  from  mechanical  suspension. 
Instances  of  this  kind  are  not  rare.  The  following  section  (fig.  199)  of 

Fig.  199. 


the  arenaceous  beds,  forming  a  kind  of  passage  from  the  old  red  sand- 
stone in  parts  of  Ireland  to  the  lower  and  usually  shaly  beds  of  the 
carboniferous  limestone  (the  yellow  sandstone  series  of  Mr.  Griffith), 
may  be  found  useful,  f 

*  Austen,  on  the  Valley  of  the  English  Channel;  Journal  of  the  Geological  Society 
of  London,  vol.  vi. 

f  The  section  was  obtained  at  Clonea  Bay,  County  Waterford,  an  interesting  locality 
for  the  study  of  the  upper  part  of  the  old  red  sandstone  series  and  the  lower  part  of 
the  carboniferous  limestone,  more  especially  when  taken  in  connexion  with  the  develop- 
ment of  equivalent  accumulations  at  the  Hook  Point,  County  Wexford,  on  the  eastward, 
and  the  country  near  Cork,  and  extending  thence  by  Cape  Clear  to  Bantry  Bay.  The 
whole  is  highly  illustrative  of  contemporaneous  accumulations  of  this  geological  date, 
modified  by  the  conditions  under  which  they  have  been  formed,  such  as  varieties  of  the 
sedimentary  matter  carried,  pushed  forward,  or  thrown  down,  according  to  distance 
from  its  supply,  and  different  depths  of  water. 


PARTS  OF  BEDS  AMONG  DETRITAL  ROCKS. 


511 


In  this  section,  forming  only  a  portion  of  a  far  more  considerable 
thickness  and  extent  of  beds,  exhibiting  general  evidence  of  the  like 
kind,  a  horizontal  deposit  of  sand  (e\  probably  from  mechanical  suspen- 
sion, is  covered  by  a  silt  (d\  apparently  also  accumulated  in  the  same 
manner.  To  this  layer  succeed  two  beds  (c,  5),  pointing  to  an  accumu- 
lation from  sands  pushed  or  brushed  along  the  bottom,  there  having 
been  a  sufficient  pause  to  make  a  surface  between  them.  This  condition 
changed,  and  horizontal  layers  (a)  were  again  formed. 

The  following  section  (fig.  200)  will  serve  to  show  that  the  like  un- 

Fig.  200. 


equal  distribution  of  component  parts,  even  extending  to  gravel  drifts 
amid  sandy  and  muddy  sediment,  is  to  be  found  among  still  older 
fossiliferous  deposits,  being  one  among  many  others  to  be  seen  on  the 
ascent  of  the  Glydyr  Vawr,  on  the  northeast  of  Snowdon,  where  the 
lower  Silurian  rocks  are  much  mingled  with  volcanic  accumulations  of 
that  geological  time.  Among  some  rocks,  the  exposed  surfaces  as  well 
as  sections  point  so  much  to  the  shifting  of  minor  streams  or  currents, 
sufficient  to  carry  forward  pebbles  of  fair  size,  the  general  accumula- 
tions pointing  to  repeated  action  of  this  kind,  that,  looking  at  the  forces 

Fig.  201. 


of  existing  currents,  these  deposits  would  generally  seem  referable  to 
shallow  waters.      The  preceding  section  (fig.   201)  of  old  red  sand- 


512    MODE  OF  OCCURRENCE  OF  ORGANIC  REMAINS. 

stone  at  Ross,  Herefordshire,*  of  a  kind  common  to  much  of  the  same 
series  of  deposits  in  that  and  adjoining  districts,  will  illustrate  this 
mode  of  occurrence. 

When  the  disturbing  power  of  wind-wave  action  upon  sea-bottoms,  to 
whatever  depth  that  power  may  sometimes  extend,  as  also  the  modifica- 
tion of  surfaces  which  may  be  produced  during  earthquakes,  are  re- 
garded, as  also  any  greater  vibrations  of  the  sea-bottom,  should  larger 
masses  of  water  be  thrown  into  movement  by  forces  of  a  similar  kind, 
but  of  far  greater  intensity  than  anything  known  as  an  earthquake,  it 
will  be  obvious  that  tranquil  alterations  of  the  depths  at  which  the  sea- 
bottom  of  any  geological  time  may  be  submerged,  would  produce  modi- 
fying effects  of  a  marked  kind.  Surface  beds  which  have  been  accumu- 
lated in  one  manner,  may  be  remodelled  in  another.  For  example, 
diagonally-arranged  portions  of  unconsolidated  beds  may  be  worked 
backwards  and  forwards  when  exposed  to  the  to-and-fro  motion  of  water 
disturbed  by  the  winds  above,  or  by  the  tides  brought  into  action,  so 
that  their  streams  are  rendered  more  or  less  sweeping  by  intermixture 
with  shallow  depths  and  the  unequal  configuration  of  adjoining  lands. 
Though  these  causes  may  only  modify  the  surfaces  for  the  time  being, 
a  repetition  of  them,  with  oscillations  in  the  movement  of  the  sea-bot- 
toms, would  often  produce  complicated  effects,  so  far  as  the  original 
mode  of  deposit  of  any  beds  may,  in  part,  be  subsequently  altered; 
even  the  organic  remains  contained  amid  the  detritus  being  sifted  and 
rearranged  without  much  injury. 

It  is  when  the  structure  of  the  beds  of  detrital  rocks,  and  the  forms 
of  their  surfaces  are  viewed  in  connexion  with  any  organic  remains  they 
may  contain,  that  the  observer  has  increased  opportunities  of  inferring 
the  depth  of  water  beneath  which  the  layers  or  beds  have  acquired  the 
general  characters  they  now  present.  With  respect  to  the  mode  in 
which  organic  remains  generally  may  be  entombed  beneath  fresh 
waters  or  the  sea,  whether  the  latter  be  tidal  or  tideless,  we  would  refer 
to  the  previous  remarks  on  this  subject  (pp.  132-215).  Amid  the 
detrital  matter,  of  whatever  kind  this  may  be,  piled  up  in  successive 
layers  or  beds,  every  variety  of  manner  in  which  organic  remains  have 
been  enveloped  by  it  occasionally  presents  itself.  While,  on  the  one 
hand,  we  see  the  shells  of  molluscs  precisely  in  the  positions  in  which 
these  animals  buried  themselves  in  the  mud,  silt,  or  sand,  of  the  time, 
according  to  their  habits ;  at  others,  we  find  the  fragments  of  shells  or 
corals  in  multitudes,  dealt  with  and  arranged  like  ordinary  mineral 
substances,  precisely  as  may  often  be  found  at  the  present  day,  and 
especially  amid  coral  accumulations  on  the  large  scale,  such  as  among 
the  Great  Barrier  Reefs  of  Eastern  Australia. 

*  Part  of  a  more  extended  section  by  Captain  James,  R.  E. ;  Memoirs  of  the  Geolo- 
gical Survey,  vol.  i.  pi.  8. 


MODE  OF  OCCURRENCE  OF  ORGANIC  REMAINS.    513 

The  occurrence  of  organic  remains  in  the  situations  where  the  ani- 
mals lived  and  died,  affords  direct  proof  that  the  fluviatile,  lacustrine, 
estuary,  or  sea-bottoms,  thus  containing  these  remains,  have  not  been 
broken  up  and  rearranged,  but  that,  independently  of  consolidation  or 
certain  other  modifications  of  structure,  they  exhibit  plans  and  sections 
of  the  fresh  or  brackish  water,  or  sea-bottom  of  a  particular  geological 
time.  Careful  search  shows  that  this  manner  of  entombment  is  by  no 
means  so  rare  as  might  once  have  been  considered.  The  occurrence  of 
the  remains  of  boring  molluscs  in  the  holes  formed  by  them  in  rocks, 
has  been  already  noticed,  as  resembling  those  of  any  Pholas  in  lime- 
stones of  the  present  day  on  the  British  coasts  (fig.  176) ;  and  it  has 
been  also  stated,  that  during  calcareous  deposits  of  the  same  date  (in- 
ferior oolite)  several  beds  in  succession  were  drilled  at  their  surfaces  by 
the  same  species,  the  shells  still  in  the  holes  made  by  their  animals 
(p.  470).  With  respect  to  molluscs  piercing  mud,  silt,  or  sand,  we  may 
point  to  the  observations  of  Mr.  Prestwich,  as  to  the  shells  of  Panopcea, 
found  abundantly  in  the  vertical  position  common  to  the  habits  of  the 
existing  species,  in  the  beds  of  the  London  clay  at  Clarendon  Hill,  and 
Panopcea,  Pholadomya,  and  Pinna,  at  Cuffnell ;  as  also  to  those  of 
Dr.  Fitton,  on  a  similar  mode  of  preservation  of  the  shells  of  Panopcea 
and  Pinna,  in  the  lower  green  sand  of  Southern  England.*  In  cases  of 
this  kind,  it  certainly  is  not  always  clear  that  the  animals,  thus  in  the 
positions  which  their  habits  required,  were  suddenly  destroyed  by  any 
physical  change  in  the  water  or  the  kind  of  sediment  deposited  above 
them,  though  this  may  be  surmised,  since  in  all  beds  containing  bur- 
rowing molluscs,  their  shells  may  be  found  in  the  positions  where  they 
died  under  ordinary  circumstances.  Be  this,  however,  as  it  may,  it 
proves  that  these  animals  of  the  time  lived  and  died  in  the  mudr 
silt,  or  sand,  now  perhaps  beds  of  hard  rock,  in  which  their  remains  are 
found. 

Many  shells  of  molluscs  so  occur  that  even  the  direction  of  the  stream 
or  current  which  drifted  them  according  to  their  weights,  volumes,  and 
forms,  may  be  inferred,  having  been,  in  all  probability,  empty  shells  at 
the  time,  and  the  same  with  the  exuviae  of  other  fresh-water  and  marine 
animals.  Sometimes,  as  beneath  (fig.  202),  whole  and  broken  shells 
are  found  drifted  along  the  bottom  with  intervals  of  repose,  during 
which  mud  was  alone  thrown  down. 

With  regard  to  the  destruction  of  marine  animals  in  place,  that  in 
volcanic  regions,  certain  gases,  such  as  carbonic  acid,  sulphuretted 
hydrogen  and  others  (p.  322),  when  suddenly  discharged  into  waters 
through  subaqueous  fissures  or  volcanic  vents,  should  destroy  the  ani- 
mals to  which  they  find  access,  would  be  expected  at  all  geological 
times  as  well  as  at  present.  In  like  manner,  subaqueous  fissures  formed! 

*  Journal  of  the  Geological  Society  of  London,  vol.  i. 
33 


514    MODE  OF  OCCURRENCE  OF  ORGANIC  REMAINS. 

at  all  periods  during  earthquakes,  and  from  which  gases  have  been 
evolved,  destructive  of  animal  life,  would  be  inferred  to  have  been 


Fig.  202. 


a,  a,  a,  beds  formed  of  diagonal  layers,  composed  of  broken  shells,  fish-teeth,  pieces 
of  wood,  and  oolitic  grains,  sometimes  mere  rounded  pieces  of  shells,  the  various  sub- 
stances lying  in  the  planes  of  the  diagonal  layers,  and  presenting  every  appearance  of 
having  been  shoved  or  pushed  over  the  more  horizontal  surfaces  formed  during  the 
intervals  between  the  mud  deposits,  b,  b,  b,  b.* 

always  followed  by  the  same  results.  So  also  with  the  heat  communi- 
cated to  waters  during  submarine  volcanic  eruptions,  or  when  fissures, 
formed  during  earthquakes,  reached  the  depth  of  very  considerable 
temperatures.  With  regard  to  waters  impregnated  with  deleterious 
gases,  so  long  as  these  remained  sufficiently  disseminated  in  them,  pre- 
daceous  animals  not  included  in  the  areas  so  affected,  would  be  pre- 
vented from  entering  in  order  to  feed  upon  the  multitudes  of  fresh-water 
or  marine  animals  which  may  have  been  killed,  until  their  remains  were 
covered  over  by  fine  sedimentary  matter ;  or,  being  burrowing  creatures 
amid  mud,  silt,  or  sand,  until  the  sedimentary  matter  was  so  adjusted 
around  them,  with  probably  also  a  certain  decomposition  of  the  softer 
parts,  as  to  be  no  longer  desirable  food,  if  even  they  were  attainable. 

Multitudes  of  fossil  fish  are  sometimes  so  found  in  rocks,  that  their 
sudden  destruction,  with  the  preservation  of  their  bodies  from  predaceous 
and  scavenger  creatures,  seems  needful  in  order  to  account  for  their 
mode  of  occurrence,  it  appearing  also  necessary  that  their  entombment 
in  the  containing  substances  was  sufficiently  rapid,  subsequently  to  their 
death,  to  prevent  the  distribution  of  the  various  harder  parts  of  their 
bodies  after  decomposition.  In  all  cases  where  volcanic  action  can  be 
inferred  at  various  geological  times,  at  or  near  the  localities  where  the 

*  This  section  was  taken  at  a  quarry  of  Forest  marble,  part  of  the  oolitic  series,  at 
the  Butts,  Frome,  Somersetshire.  The  Bath  oolite,  into  which  this  part  of  the  oolitic 
series  graduates,  as  may  be  well  seen  in  Somersetshire,  is  often,  in  some  of  its  beds, 
nothing  else  than  a  modification  of  the  same  thing,  the  rounded  grains  of  shells  and 
corals,  mixed  with  those  of  the  true  oolite  (having  concentric  coatings  of  calcareous 
matter),  being  drifted  in  a  similar  manner.  Broken  shells,  fish-teeth,  and  other  organic 
remains  are  seen  in  the  sections  of  the  same  neighbourhood,  occurring  as  streaks  in 
clay,  conditions  from  time  to  time  having  occurred,  during  which  the  deposit  of  the 
mass  of  mud  of  the  beds  termed  Fullers'  earth,  was  locally  interrupted  by  these  shell 
drifts. 


MODE    OF    OCCURRENCE    OF    ORGANIC    REMAINS.         515 

observer  may  have  aqueous  deposits  under  examination,  and  which  pre- 
sent the  remains  of  animals  in  a  condition  showing  that  whole  creatures 
have  been  preserved  without  injury  to  the  arrangement  of  their  harder 
parts,  the  observer  will  do  well  to  recollect  the  modes  of  entombment 
which  may  now  be  in  progress  in  similar  regions  of  the  present  day. 
He  will  thus  see  organic  remains  among  the  volcanic  ashes  of  different 
geological  times,  even  amid  the  old  accumulations  of  the  Silurian 
deposits  (Ireland,  Wales),  and  in  such  positions  as  very  forcibly  to 
remind  him  of  the  causes  of  destruction  and  preservation  which  he  finds, 
or  can  fairly  infer  are  now  in  action. 

Independently  of  any  sudden  destruction  and  entombment  of  animal 
life  in  connexion  with  volcanic  eruptions  or  earthquake  movements,  the 
study  of  the  old  fresh-water  and  sea-bottoms  presents  us  with  the  occur- 
rence of  animal  remains  so  preserved,  and  amid  such  substances  that 
the  sudden  influx  of  waters  charged  with  much  fine  matter  in  mechanical 
suspension  may  have  destroyed  multitudes  of  aqueous  animals  in  some 
given  area.  At  least,  their  remains  are  so  entangled  amid  this  matter 
as  to  lead  to  this  inference.  That  fixed  creatures  or  others  of  slow 
movements  could  thus  readily  be  overwhelmed,  would  be  expected  under 
such  conditions  at  all  geological  periods.  When,  for  example,  in  the 
vicinity  of  Bradford,  the  Apiocrinites  of  that  locality  is  found  rooted 
upon  a  subjacent  calcareous  bed  (one  of  the  oolitic  series)  and  en- 
tangled in  a  seam  of  clay,  its  parts  sometimes  beautifully  preserved,  it 
may  be  inferred  that  it  was  destroyed  by  an  influx  of  mud  from  which 
it  could  not  escape.  In  like  manner  also,  the  preservation  of  long  un- 
injured stems  of  various  encrinites  found  amid  the  Silurian  and  other 
older  deposits,  on  the  surfaces  of  limestone  and  other  rocks,  and  having 
had  a  covering  of  fine  sediment,  would  appear  to  be  explained.  Some- 
times, as  in  the  lias  of  Golden  Cope,  near  Lyme  Regis,  multitudes  of 
belemnites,  some  with  even  the  ink-bag  of  these  molluscs  preserved,  so 
form  a  seam  of  organic  remains,  that  the  observer  is  led  to  infer  a 
sudden  destruction  of  thousands  of  them  over  a  moderate  area.  Am- 
monites are  also  sometimes  found  in  great  numbers,  distributed  in  a 
depth  of  only  a  few  inches,  over  areas  of  a  square  mile  or  more,  as  if 
suddenly  destroyed.  The  beautiful  bed  of  myriads  of  ammonites  occur- 
ring amid  the  lias  of  Marston  Magna,  Somerset,  was  a  good  case  of  this 
kind.  It  sometimes  happens  that  the  shells  of  molluscs  show  that  when 
their  animals  were  entombed,  the  space  occupied  by  their  bodies  pre- 
vented the  entrance  of  the  sediment  which  enveloped  them.  The 
following  section  (fig.  203)  of  an  ammonite  (lias,  Lyme  Regis)  may  be 
taken  as  an  example  of  this  mode  of  occurrence.  All  the  chambers  of 
the  ammonite  are  filled  by  carbonate  of  lime,  infiltrated  into  their 
hollows,  beyond  which  there  is  a  space  apparently  occupied  by  the 
animal  when  overwhelmed  by  the  surrounding  calcareous  mud,  now 


516        MODE    OF    OCCURRENCE    OF    ORGANIC    REMAINS. 

argillaceous  limestone  ;  this  space  is  terminated  outwards  by  sedimentary 
matter  (a)  which  entered  so  much  of  the  shell  as  the  retreat  of  the 
animal  permitted.  In  this  case  the  intruding  sediment  has  become 

Fig.  203. 


highly  impregnated  with  dark-coloured  matter,  as  if  effected  by  the 
decomposition  of  the  animal  within.  Such  deposits  as  clay  and  argil- 
laceous limestones,  the  latter  especially,  from  the  usual  consolidation, 
without  much  pressure,  of  the  matter  around  the  organic  remains,  are 
very  favourable  for  observations  of  this  kind,  numerous  shells  of  mol- 
luscs appearing  to  show  that  their  animals  may  have  been  in  them  at 
the  time  of  their  entombment.  In  such  researches  attention  should  be 
paid  to  the  positions  of  the  shells  in  the  beds,  and  the  forms  of  their 
interior  cavities,  so  that  the  entrance  of  sediment  might  be  prevented 
by  such  positions  and  forms.  Multitudes  of  examples  are  found  in 
certain  areas  and  deposits  where  the  presence  of  the  animals  in  their 
shells  would  seem  required.  When  we  consider  the  probable  Voracity 
of  numerous  creatures  in  fresh  and  sea  waters,  and  the  multitudes  of 
scavenger  animals  consuming  decayed  animal  matters  at  all  geological 
times,  the  discovery  of  certain  aqueous  reptiles  preserved  entire  amid 
rocks,  even  with  the  contents  of  their  intestines  preserved,  leads  us  to 
infer  that  their  entombment,  if  not  also  their  death,  was  sudden.  And 
this  appears  the  more  probable  when  we  find,  as  often  happens,  that  in 
the  same  deposits  the  same  kinds  of  aqueous  reptiles  are  dismembered, 
as  if  by  predaceous  animals  feeding  upon  them.  While,  at  times,  in  the 
lias  of  Western  England,  the  skeletons  of  Icthyosauri  and  Plesiosauri 
are  so  well  preserved  that  all,  or  nearly  all,  the  bones  are  in  their  proper 
relative  situations;  even  their  skins  preserved,  and  the  contents  of 
their  intestines,  at  the  time  of  death,  in  their  right  places ;  at  others, 
the  bones  of  these  reptiles  are  dispersed,  though  not  always  far  re- 
moved from  the  place  where  the  animals  died.  In  fact,  the  appearances 
presented  are  precisely  those  of  decomposition  having  been  so  far 
advanced  that  the  scavenger  animals  could  feed  upon  the  carcases,  and 
drag  the  bones  short  distances,  so  as  somewhat  to  scatter  them. 

Every  mode  of  the  occurrence  of  organic  remains  should  be  carefully 
considered,  and  viewed  with  reference  not  only  to  the  district,  as  regards 


DISTRIBUTION    OF    ORGANIC    REMAINS.  517 

the  depths  of  water,  and  the  probable  form  of  any  neighbouring  land, 
but  also  as  to  the  general  distribution  of  marine  life  at  equivalent  geo- 
logical times  over  much  more  extended  areas.  The  endeavour  to  obtain 
a  general  view  of  the  distribution  of  life  over  great  surfaces  at  given 
geological  times,  as  well  as  of  the  deposits  effected  during  those  lapses 
of  them  to  which  given  names  have  been  assigned,  would  appear  espe- 
cially needful.  Experience  has  taught  geologists  that  many  a  genus  of 
marine  animals,  the  remains  of  which  were  at  first  found  only  in  par- 
ticular beds  of  various  districts,  have  been  discovered  in  the  deposits, 
both  of  more  ancient  and  more  modern  periods ;  as  also  that  as  regards 
species,  these  will  be  observed  in  certain  districts  to  have  a  wider  range 
than  in  others,  through  a  section  of  consecutive  sea-bottoms. 

It  would  seem  essential  that  an  observer  should  well  weigh  the  evi- 
dence of  the  distribution  of  the  animal  and  vegetable  life  of  different 
geological  times,  as  exhibited  by  organic  remains,  with  reference  to  the 
probable  distribution  of  land  and  water  of  those  times,  and  the  conse- 
quent variation  of  depths  of  seas,  kinds  of  bottom,  forms  of  coasts,  dis- 
charge of  rivers  into  the  sea,  fresh-water  accumulations,  and  the  like. 
He  should  refer  to  the  depths  at  which  animal  and  vegetable  life  is  now 
known  to  exist  in  the  sea  (p.  162),  with  the  forms  and  kinds  of  both 
found  under  the  different  conditions  of  heat,  light,  and  shelter  from  vio- 
lent movements.  He  can  scarcely  neglect  the  views  of  naturalists,  as 
to  the  distribution  of  existing  animal  and  vegetable  life,  over  the  surface 
of  the  globe ;  the  spread  of  the  different  kinds  under  the  circumstances 
fitted  for  each  respectively ;  the  overpowering,  as  it  were,  of  some  by 
others,  the  centres  or  localities  whence  species  are  inferred,  under  favour- 
able circumstances,  to  have  been  diffused,  and  the  representatives  of 
different  species  in  different  localities.*  The  various  supposed  equiva- 
lent accumulations,  chiefly  sea-bottoms,  have  to  be  carefully  dissected  to 
ascertain  the  probable  conditions  under  which  the  remains  of  life  entombed 
in  them  have  been  gathered  into  the  situations  where  they  are  now  dis- 
covered, and  the  life  itself  was  then  adjusted.  At  all  geological  times 
when  waters  existed,  they  would  arrange  themselves  according  to  the 
laws  now  governing  their  position  as  to  temperature,  and  they  would 
possess  the  same  properties  with  respect  to  light  and  pressure.f  All 

*  As  regards  works  on  the  distribution  of  animal  and  vegetable  life,  the  observer  may 
conveniently  consult  the  text  and  maps  of  Johnston's  "Physical  Atlas."  For  the  geo- 
graphical distribution  of  plants,  reference  can  be  made  to  the  works  of  Humboldt  and 
Shouw,  and  the  Reports  by  Griesbach  (translated  by  the  Ray  Society).  The  distribu- 
tion of  fishes,  a  subject  of  considerable  geological  interest,  has  received  much  attention 
from  Sir  John  Richardson  in  his  "  Fauna  Boreali- Americana,"  and  British  Association 
Reports. 

•}•  Assuming  that  the  saline  contents  and  their  proportion  to  the  waters  have  not  been 
materially  different  during  the  lapse  of  time,  since  animals  existed  in  the  seas  and  fresh 
waters  of  the  world.  As  respects  the  adjustment  of  marine  animals  to  light,  the  eyes 
of  trilobites,  crustaceans  found  among  the  oldest  fossiliferous  deposits,  have  often  been 


518  DISTRIBUTION    OF    ORGANIC    REMAINS. 

masses  of  water  would  also  tend  to  be  moved,  as  now,  by  the  great 
causes  of  ocean  currents  and  tidal  streams,  however  modified  these  may 
have  been  by  the  manner  in  which  dry  land  presented  itself  amid  the 
ocean,  at  any  particular  geological  period. 

•  At  the  same  time  that  all  due  attention  is  paid  to  these  circumstances, 
it  becomes  also  necessary  to  bear  well  in  mind  the  modifications  and 
changes  which  would  arise  from  the  movements  of  the  crust  of  the  earth 
elevating  or  depressing  mineral  masses,  so  that  sometimes  they  were 
above  the  sea  level,  sometimes  beneath  it.  To  advert  again  to  the 
change  produced  by  the  submergence  of  the  Isthmus  of  Panama,  and 
the  junction  of  the  Atlantic  and  Pacific  Oceans,  the  land  descending  to 
the  moderate  (geological)  depth  of  1,000  feet,  relatively  to  these  oceans. 
By  recent  observations  it  would  appear,  that  the  summit  level  (named 
Baldwin's)  is  299  feet  above  the  sea,  so  that  when  the  depression  had 
continued  to  600  feet,  there  would  be  a  channel  above  this  height  deeper 
than  between  Dover  and  Calais  ;  and  when  the  submersion  to  1,000  feet 
had  been  completed,  one  deeper  than  any  part  of  the  North  Sea,  or  the 
channels  between  Great  Britain  and  Ireland,  or  these  islands  and 
France,  one  nearly  corresponding  with  the  line  of  100  fathoms,  extend- 
ing from  Spain,  outside  the  British  Islands,  to  Norway  (fig.  65). 

By  comparing  a  map  of  the  Americas,  with  the  land  which  would  be 
under  the  ocean,  if  this  movement  of  depression  were  carried  out,  gra- 
dually diminishing  no  further  than  20°  of  latitude  on  each  side  of  the 
isthmus,  the  great  modification  likely  to  arise  from  the  free  passage  of 
the  waters  of  the  Atlantic  into  those  of  the  Pacific,  and  the  difference 
of  the  surface  of  dry  land  will  be  obvious.*  It  is  by  carefully  con- 
sidering a  few  areas  of  the  present  dry  land  in  this  manner,  with  regard 
to  the  effects  of  depression  or  elevation,  as  the  case  may  require,  that 
the  observer  will  readily  perceive  how  needful  it  is  for  him,  when  endea- 
vouring to  trace  the  distribution  of  the  life  of  any  particular  geological 
time,  well  to  weigh  the  consequences  of  such  changes  ;  whether,  on  the 
one  hand,  they  permit  a  mingling  of  species  previously  separated,  or 
separate  some  given  area,  distinguished  by  the  presence  of  some  marked 
species  into  two  parts,  one  or  both  of  which  were  subsequently  subjected 
to  different  conditions. 

Inasmuch  as  we  find  marine  animal  life  adjusted  to  certain  conditions, 
among  which,  from  the  labours  of  Professor  Edward  Forbes,  and  other 
naturalists,  depths  of  water  may  be  considered,  all  other  circumstances 

pointed  out  as  satisfactory  proof.  Valuable  remarks  on  this  head  will  be  found  in  Dr. 
Buckland's  Bridgewater  Treatise,  vol.  i.  p.  896. 

*  With  regard  to  the  differences  in  the  levels  of  the  Pacific  and  Atlantic  on  the  shores 
of  the  Isthmus  of  Panama,  the  researches  of  Mr.  Lloyd  would  give  a  higher  relative 
level  to  the  former,  to  the  amount  of  3-52  feet.  High  water  mark  at  Panama  is  stated 
to  be  18-55  feet  above  that  of  the  Gulf  of  Mexico  at  Chagres  ;  while  it  is  only  6-51  lower 
at  low  water  on  the  Pacific  side. — Philosophical  Transactions,  1830. 


DISTRIBUTION    OF    ORGANIC    REMAINS.  519 

being  the  same,  to  have  an  important  influence;  reasoning  from  the 
known  to  the  unknown,  we  should  expect  an  adjustment  of  a  similar 
kind  to  have  extended  back  to  the  earliest  state  of  the  earth's  surface, 
when  water,  fitted  for  life,  washed  the  shores  of  continents  and  islands. 
Even  under  the  hypothesis  of  a  heat  of  the  earth's  solid  crust  at  former 
times,  sufficient  to  keep  the  waters  dispersed  as  oceans  and  seas  above 
it,  at  equal  temperatures  at  certain  depths,  independently  of  solar  heat, 
littoral,  shallow  and  deep  water  conditions  would  be  expected  to  have 
had  their  influence,  more  particularly  when  combined  with  differences 
in  sea-bottoms,  and  position  as  to  shelter  from  wind-wave  action,  tidal 
streams,  or  ocean  currents.  At  all  events,  it  would  appear  most  desirable 
that  the  observer,  having  before  him  the  advantage  of  the  sea-bottoms 
of  different  geological  times,  with  organic  remains  variously  distributed 
among  them,  should  endeavour  to  trace  out  differences  and  resemblances 
of  this  kind,  carefully  considering  the  evidence  afforded  by  the  physical 
structure  of  the  fossiliferous  rocks  in  connexion  with  that  presented  by 
the  contained  organic  remains.  It  may  be  that  certain  forms  of  the 
shells  of  molluscs,  for  example,  are  deceptive,  so  that  the  palaeontolo- 
gist may  not  always  reason  safely  when  referring  some  to  animals  simi- 
lar to  those  now  living  near  shores  or  in  shallow  or  deep  waters ;  and 
that  these  last  may  be  found  to  vary  at  the  present  day  more  than  is  now 
known ;  still  the  investigation  can  scarcely  but  be  productive  of  an  ap- 
proximation to  the  knowledge  sought,  the  general  evidence,  be  it  what 
it  might,  pointing  out  those  modes  of  occurrence  which  may  be  ultimately 
seen  to  be  somewhat  constant :  while  others,  though  they  present  them- 
selves in  a  more  uncertain  manner,  may  yet  be  important  as  regards  the 
general  subject. 

As  the  researches  of  naturalists  show  that  whether  we  rise  high  into 
the  atmosphere,  or  descend  deep  into  the  sea,  the  conditions  for  the 
existence  of  life,  under  various  adjustments  and  modifications,  terminate ; 
it  follows  that  the  great  mutability  of  the  earth's  surface,  as  respects 
both  conditions,  could  scarcely  fail  to  produce  great  changes  in  that  life, 
independently  of  those  made  inherent  to  it  as  created.  The  separation 
of  great  areas  of  dry  land  into  minor  portions  has  been  above  mentioned, 
as  producing  even  the  extinction  of  certain  kinds  of  terrestrial  life,  while 
at  others  it  may  have  preserved  parts  of  it  and  mingled  some  together. 
Upon  the  descent  of  a  continent  beneath  the  sea  (and  the  researches  of 
the  geologist  teach  him  the  necessity  of  such  submersions,  as  well  as 
that  the  dry  lands  for  the  time  have  been  chiefly  raised  from  beneath 
seas  into  the  atmosphere),  any  terrestrial  life  peculiar  to  it  would  be 
destroyed,  though  evidence  of  its  existence  might  be  preserved  amid 
mineral  matter  where  circumstances  permitted.  In  like  manner  when, 
upon  submergence,  shores  ceased  to  present  themselves,  the  littoral 
marine  animals,  previously  inhabiting  them  and  moving  to  the  coasts  as 


520  EFFECT    OF    THE    RISE    AND    FALL     OF    LAND 

these  retreated  upon  the  descent  of  the  main  mass  of  land,  would  be 
expected  also  to  have  disappeared,  unless  able  wholly  or  in  part  to  have 
adjusted  themselves  to  the  new  conditions.  When,  however,  zone  after 
zone  of  the  marine  vegetation  disappeared  as  the  circumstances  fitted 
for  its  growth  ceased,  the  animals  which  fed  upon  the  plants  would 
perish,  and  with  them  those  which  lived  upon  the  vegetable  eaters,  unless 
they  could  escape  to  other  localities  where  food  of  the  same  kind,  or  of 
others  which  they  could  substitute  for  it,  was  to  be  found,  and  was 
sufficient  for  them.  If,  in  the  annexed  section  (fig.  204),  a  b  represents 


7'  _-<?^\\\\^XN^^\\^  ~~  '-,          ~ 1 


the  level  of  the  sea,  remaining  constant,  or  nearly  so,  and  c  v  d  the  out- 
line of  any  mass  of  land,  partly  in  the  atmosphere  and  partly  beneath 
the  sea,  and  0,  0,  0,  0,  the  depth  at  which  marine  plants  supporting  the 
life  of  a  certain  portion  of  the  marine  fauna  grew,  the  littoral  portion  of 
that  life  would  be  shifted  to  x  #',  upon  a  submergence  of  the  land  to  e, 
f,  and  at  the  same  time  a  portion  of  the  sea-bottom  inhabited  by  animals 
at  greater  depths  would  be  brought  lower  down,  so  that  these  would 
probably  also  move  over  the  ground  of  others  previously  adjusted  to 
minor  depths.  Submergence  continuing,  when  it  reached  the  line  g,  A, 
the  shores  would  still  further  be  shifted  to  y,  y ',  with  the  same  general 
consequences  as  before,  and  so  also  with  the  submergence  to  i,  k.  When 
it  reached  I,  m,  the  whole  of  the  land,  previously  above  water,  would  be 
beneath  it,  and  littoral  life  may  be  considered  to  have  disappeared  when 
it  reached  n,  p.  At  the  amount  of  submergence  represented  by  the 
line  8,  t,  the  whole  of  the  former  dry  land,  with  its  shores  and  any 
shallow  seas  adjoining,  would  be  beneath  the  depths  of  marine  vege- 
tation. In  this  section  the  probable  consequences  of  breaker  action  on 
the  descending  land,  tending  to  plane  it  off,  as  the  great  Banks  of  New- 
foundland may  have  been  land  to  a  certain  extent  levelled  out  during  a 
gradual  submergence,  have  not  been  included,  in  order  to  render  the 
illustration  simple.  During,  however,  such  a  submergence,  this  action 
has  to  be  well  borne  in  mind,  so  that  the  detritus  thence  arising,  distri- 
buted over  the  sunk  land,  and  entombing  the  remains  of  the  animal  life 
of  the  time,  with  its  variations,  according  to  circumstances,  those  of 
deep-water  creatures  ranging  over  those  of  shallow  water,  and  littoral 
species,  be  not  neglected. 

With  respect  to  this  covering  of  detrital  deposits  containing  the 
remains  of  littoral  species  by  others  entombing  those  species  which 


ON    THE    DISTRIBUTION    OF    ORGANIC    REMAINS.         521 

contemporaneously  inhabited  deeper  waters  adjoining,  the  following 
section  (fig.  205)  may  serve  to  show  the  manner  in  which  this  may  be, 
and  appears  to  have  been  accomplished,  during  the  submergence  of  land 

Fig.  205. 


m  I 

and  its  shores.  If  a,  5,  represent  the  level  of  the  sea,  and  <?,  df,  a  surface 
of  land  and  its  shore  which  has  been  gradually  depressed  beneath  it, 
e,  the  littoral  accumulations  when  k  was  the  coast,  /  and  #,  those  when 
the  sea  boundaries  were  at  I  and  m,  as  h  is  supposed  to  be  at  the  time 
of  the  section,  there  would  always  be  deeper  waters  outwards  in  the 
direction  a,  d.  Hence,  though  a  certain  thickness  of  deposits,  e,  /,  </,  h, 
variable  according  to  circumstances,  might  cover  the  surface  of  the 
descending  land,  entombing  the  remains  of  the  littoral  marine  animals, 
these  would  be  covered  in  the  direction  outwards,  and  as  the  land 
descended,  by  detrital  deposits  of  kinds  which  could  be  transported  to 
and  formed  there,  a  corresponding  series  of  marine  animal  remains 
intermingled  with  them,  differing  as  far  as  the  deeper  water  differed  from 
the  littoral  marine  life  of  the  time.  Thus  numerous  species  which  had 
been  really  contemporaneous  with  those  entombed  beneath  may  appear, 
in  certain  sections,  to  have  succeeded  them  as  creations  in  the  progress 
of  geological  time,  this  appearance  extending  even  to  the  remains  of 
those  living  in  the  deepest  waters  of  the  period  and  locality,  as  any  large 
mass  of  dry  land  became  submerged. 

With  respect  to  the  emergence  of  land,  should  this  be  gradual,  large 
areas  might  be  laid  dry,  presenting  sheets  of  sedimentary  matter  not 
contemporaneously  produced,  yet  containing  littoral  species  of  molluscs 
in  great  abundance,  these  species  being  of  the  same  kinds,  should  no 
change  have  been  effected  in  that  portion  of  the  animal  life  of  the 
locality  and  time  during  the  rise  of  the  land  and  sea-bottom.  If  the 
sea-bottom  around  the  British  Islands  were  gradually  raised,  so  that  the 
boundary  line  extended  to  not  more  than  100  fathoms  in  depth  (fig.  65, 
p.  114),  the  remains  of  littoral  molluscs  would  be  scattered  amid  the 
accumulations  of  the  time,  as  the  shores  became  extended,  covering  over 
those  of  other  and  contemporaneous  molluscs.  If  a  b,  in  the  following 


k       I    m 

section  (fig.  206),  represent  the  level  of  the  sea,  c  d  a  surface  of  rock, 
partly  above  the  sea  and  partly  beneath  it,  and  e  a  deposit  extending  to 


522  DISTRIBUTION    OF    ORGANIC    REMAINS    WITH 

r,  it  would  contain  the  remains  of  molluscs  inhabiting  the  different 
depths,  including  those  at  which  wind-wave  action  could  drive  them 
onwards  towards  the  coast.  If  the  land  be  now  raised,  so  that  the  rela- 
tive sea  level  is  represented  by  A,  A',  a  deposit  /,  extending  to  s,  would 
be  under  similar  conditions  as  that  previously  formed  and  extending  to 
r,  and  so  with  an  accumulation  g  extending  to  t.  Successive  beds  &,  2,  w, 
are  thus  produced,  probably  containing  the  remains  of  molluscs,  allowing 
the  mingling  of  many  by  the  action  of  the  waves  in  shallow  situations, 
and  corresponding  with  the  depths  h  h',  gg',  //',  ee',  so  that  other 
things  being  equal,  these  exuviae  are  similar  in  sections  of  the  detrital 
accumulations  which  do  not  correspond  with  the  general  planes  of  those 
deposits,  but  with  others  representing  their  littoral,  shallow,  or  deep- 
water  conditions,  as  the  case  may  be  of  succeeding  times. 

These  modifications,  from  the  causes  noticed,  have  to  be  well  consi- 
dered when  certain  organic  remains  are  viewed  as  characteristic,  as  it 
has  been  termed,  of  the  accumulations  of  a  particular  geological  time, 
those  to  which  some  name  may  have  been  assigned.  When  any  such 
are  found  more  in  abundance  in,  or  seem  confined  to,  the  deposits 
of  some  particular  area,  and  appear  to  be  the  exuviae  of  animals  which 
have  lived  at  or  near  the  localities  where  they  are  obtained,  the  kind  of 
bottom,  probable  depth  of  water,  and  proximity  to  or  distance  from  the 
dry  land  of  the  time  have  to  be  sought,  so  that  the  conditions  under 
which  the  creatures  themselves  flourished  may  be  duly  appreciated.  In 
such  researches  it  will  be  often  found  that  the  kind  of  bottom  appears 
to  have  materially  influenced  the  abundance  and  distribution  of  these 
particular  animals,  so  that,  when  a  change  was  effected  in  the  sedi- 
mentary matter  deposited,  they  moved  elsewhere,  even  returning  in  the 
same  abundance  as  before  to  the  same  area,  should  the  conditions  fitted 
for  them  have  been  re-established.  If,  in  the  following  plan  (fig.  207), 

Fig.  207. 


the  shaded  portions  represent  minor  areas  of  mud,  distributed  amid 
sands,  it  would  be  expected  that  the  creatures  whose  habits  induced  them 
to  prefer  the  one  to  the  other  would  keep  within  the  respective  varia- 
tions of  sea-bottoms,  so  that  if,  in  the  course  of  accumulation,  this 
bottom  became  modified,  sands  drifting  or  being  thrown  over  the  mud, 
or  the  latter  over  the  former,  the  animals  would  follow  the  modifications 
according  to  their  habits.  Thus  in  any  given  sections  of  these  sea- 


RESPECT    TO     DIFFERENT    KINDS    OF    SEA-BOTTOMS.      523 

bottoms  streaks  of  different  kinds  of  them  may  be  found  accompanied 
with  peculiar  organic  remains,  the  animals  from  which  they  were  derived 
merely  shifting  their  ground  as  circumstances  arose,  thus  introducing 
interlacings,  as  it  were,  of  different  kinds  of  sea-bottoms.  Looking  at  the 
conditions  which  at  the  present  time  appear  to  govern  the  existence  of 
marine  life  both  as  regards  the  relative  position  of  different  portions  of 
it  and  the  distribution  of  similar  animals,  very  great  care  seems  to  be 
required  in  assuming  particular  species  as  characteristic  of  particular 
geological  periods  without  reference  to  their  mode  of  occurrence  at  the 
time.  It  would  seem  very  needful  that  the  probable  habits  of  these 
species  should  be  well  considered,  so  that  proper  importance  should  be 
assigned  to  other  and  contemporaneous  species  whose  remains  may  be 
equally  of  value  in  continuous  or  contemporary  accumulations  formed 
under  modified  conditions  elsewhere.  Unless  this  be  done,  it  may  often 
happen  that  littoral  species,  very  characteristic  of  the  shores  of  a  par- 
ticular region,  will  be  uselessly  sought  for  amid  contemporaneous 
accumulations  in  the  deep  seas  of  other  regions,  while  not  a  trace  can 
be  found  of  deep-sea  species,  abundant  elsewhere  at  the  same  geological 
time,  amid  shallow  water  and  littoral  deposits. 

The  calcareous  and  fossiliferous  accumulations  of  different  dates  are 
frequently  of  so  mixed  a  character  as  to  require  much  care.  They  are 
often  mere  beds  of  organic  remains ;  these,  cemented  together  by  the 
carbonate  of  lime,  which,  after  the  deposit,  has  been  formed  at  the 
expense  of  the  organic  remains  themselves.  At  other  times,  however, 
they  have  been  clearly  produced  by  deposits  from  solutions  of  the 
bicarbonate  of  lime,  in  the  manner  previously  mentioned  (p.  128). 
Some  limestones  require  very  careful  examination  in  order  to  ascertain 
their  mode  of  formation.  Thus  it  has  been  observed  that  beds  pre- 
senting no  appearance  of  organic  remains  to  the  naked  eye,  may  yet  be 
found  to  be  almost  wholly  composed  of  them  when  the  microscope  is 
employed  and  due  precautions  taken.  In  this  manner  many  beds  of 
the  mountain  limestone  series  of  the  British  Islands  have  been  found 
replete  with  the  remains  of  life  where  none  were  at  first  suspected.  Even 
when  upon  exposure  to  atmospheric  influences  fossils  of  far  larger 
dimensions,  readily  visible  to  the  naked  eye,  and  extending  to  half  an 
inch  or  more  in  length  or  breadth,  are  found  in  fair  abundance,  it 
sometimes  occurs  that  the  ordinary  fracture  of  the  limestone  bed  may 
not  readily  show  them.  We  do  not  here  include  the  remains  of  encri- 
nites,  echinites,  and  some  other  fossils,  which,  from  their  rhomboidal 
fracture  a  little  practice  will  enable  an  observer  readily  to  distinguish ; 
but  others,  where  they  are  far  from  being  easily  detected.  The  most 
beautiful  shells  will  occasionally  thus  present  themselves  upon  searching 
a  weathered  surface,  not  a  trace  of  which  can  be  obtained  by  ordinary 
observation. 


524  INFUSORIAL    REMAINS. 

It  is  now  known  that  certain  beds,  as  well  siliceous,  calcareo-siliceous, 
as  calcareous,  are  made  up  almost  wholly  of  minute  organic  remains, 
far  too  small  to  be  seen  by  the  unassisted  eye.  For  our  great  progress 
in  this  order  of  investigation  geologists  are  indebted  to  M.  Ehrenberg, 
who  has  shown  how  much  infusorial  remains  are  diffused,  even  producing 
deposits  of  considerable  importance,  and  most  materially  adding  to  the 
volume  of  others.  Whether  or  not  some  of  these  microscopic  minute 
bodies  may  be  vegetable  instead  of  animal,  their  geological  importance 
remains  the  same,  if  indeed  it  be  not  increased  from  such  deposits,  alto- 
gether or  in  a  great  measure  composed  of  myriads  of  microscopic  orga- 
nisms, being  referable  to  both  animal  and  vegetable  life.* 

While  on  the  subject  of  deposits  chiefly  formed  of  organic  remains, 
the  probable  chemical  composition  of  these  remains,  when  first  intro- 
duced amid  the  accumulations  in  which  they  are  found,  should  not  be 
neglected.  In  this  manner  it  may  be  seen  that  the  magnesia,  so  much 
more  commonly  distributed  amid  limestones  than  has  often  been  in- 
ferred, may  sometimes  be  due  to  such  remains,  particularly  where  many 
corals  are  present. f  The  like  also  with  the  phosphates  of  lime,  silica, 
and  other  substances.  Whole  layers  may  be  formed  of  the  harder  parts 
of  infusoria,  so  that  when  these  are  siliceous,  they,  and  the  spiculse  of 
many  sponges,  may  serve  to  diffuse  no  small  amount  of  silica  amid 
deposits  of  a  different  character. 

By  careful  investigation  of  the  conditions  under  which  the  remains 
of  various  fresh-water  or  marine  animals  may  be  found  in  rocks,  the 
deposit  of  which  by  means  of  water  is  evident,  and  also  by  well-directed 
attention  to  the  mode  in  which  the  remains  of  terrestrial  life,  not  for- 
getting those  of  insects,J  may  have  become  intermingled  with  them,  the 
observer  will  frequently  find  himself  most  materially  aided  in  a  know- 
ledge of  the  probable  physical  geography  of  different  areas,  often  con- 
siderable, at  given  geological  times.  With  this  knowledge  and  a  due 
regard  to  the  varied  distribution  of  the  life  of  the  time,  and  the  abun- 
dance and  kind  of  mineral  matter  deposited  at  the  same  period,  he  may 
be  enabled  to  trace  the  changes  and  modifications  which  have  taken 
place  contemporaneously  in  the  rivers  or  lakes,  amid  the  lands,  or  in  the 

*  As  to  some  of  these  supposed  infusoria  being  vegetable,  see  note,  p.  245. " 
t  In  some  investigations  undertaken  by  Mr.  Maule  at  the  Museum  of  Practical  Geo- 
logy, for  the  purpose  of  tracing  the  various  changes  which  organic  remains  may  have 
undergone  under  different  conditions  of  entombment,  he  found  magnesia,  even  to  the 
extent  of  6  and  7  per  cent.,  in  some  recent  corals. 

J  In  countries,  and  especially  in  tropical  islands,  such  as  the  West  Indies,  where  the 
off-shore  or  land  winds  are  at  times  somewhat  strong,  multitudes  of  insects  are  often 
borne  out  to  sea,  where,  though  the  greater  proportion  may  become  the  food  of  marine 
creatures,  some  fall  in  situations  to  be  entombed  amid  mud,  silt,  or  sand.  Those  accus- 
tomed to  pass  along  such  coasts  are  familiar  with  this  fact.  Our  own  coasts  in  summer 
weather  present  many  instances  of  insects  surprised  and  drawn  off  coasts  seaward  by 
the  sudden  setting  in  of  the  land  wind  in  the  evening. 


CHEMICAL    COMPOSITION    OF    ORGANIC    REMAINS.         525 

seas,  at  different  times  in  such  portions  of  the  earth's  surface.  Re- 
garding that  surface  as  a  whole,  it  is  difficult  to  conceive  that  the 
distribution  of  life,  allowing  for  great  changes  in  that  distribution  during 
the  lapse  of  time,  could  not  have  been  adjusted  to  conditions  as  they 
successively  arose,  and  which  modified  it  more  in  one  locality  than 
another,  so  that  great  care  seems  required  properly  to  separate  the 
local  from  the  general  effects  produced  at  assumed  equal  periods,  or 
during  a  long  succession  of  them.  Modern  investigations,  while  they, 
on  the  one  hand,  lead  us  to  infer  many  great  changes  in  animal  and 
vegetable  life  during  the  accumulation  of  the  various  deposits  in  which 
its  remains  have  been  preserved,*  teach  us,  on  the  other,  that  forms 
once  supposed  only  confined  to  the  more  modern  accumulations  have 
existed  in  far  more  remote  times. f  While  it  is  probable  that  the  evidence 
of  great  changes  having  taken  place  during  the  lapse  of  geological 

*  Referring  to  various  general  works  containing  lists  of  the  remains  of  animal  and 
vegetable  life  considered  characteristic  of  the  different  deposits  which  it  has  been 
thought  convenient  to  separate  and  class  under  particular  names,  it  is  only  required  to 
point  to  such  animals  as  the  trilobites,  among  the  more  ancient  accumulations,  and  to 
the  ammonites  of  the  middle  portion  of  the  fossiliferous  series,  to  show  that  certain 
marine  creatures  which  have  now  ceased  to  exist  once  swarmed  in  particular  areas  at 
given  times,  and  have  not  lived  after  those  times.  No  doubt  the  preservation  of  the 
parts  of  many  terrestrial  animals  requires  a  combination  of  favourable  circumstances, 
so  that  no  great  surprise  is  to  be  experienced  when  we  obtain  few  traces  of  such  animals 
amid  the  contents  of  the  old  sea-bottoms  usually  presented  to  our  examination.  The 
remains  of  the  marsupial  mammal  (Phascolotherium  Bucklandi,  Owen)  and  of  the  insecti- 
vorous mammals  (Amphitherium  Prevostii  and  Am.  Broderipii,  Owen)  in  the  Stonesfield 
slate  (oolitic  series),  near  Oxford,  are  sufficient  to  introduce  caution  into  general 
reasoning  as  to  the  existence  or  non-existence  of  terrestrial  mammals  at  different  geo- 
logical times.  Speaking  of  the  conditions  under  which  these  remains  occur,  Dr.  Buck- 
land  remarks  (Bridgewater  Treatise,  vol.  i.  p.  121),  that  "at  this  place  (Stonesfield)  a 
single  bed  of  calcareous  and  sandy  slate,  not  six  feet  thick,  contains  an  admixture  of 
terrestrial  animals  and  plants  with  shells  which  are  decidedly  marine ;  the  bones  of 
Didelphis  (Amphitherium  and  Phascolotherium],  Megalosaurus  (a  great  saurian  40  or  50 
feet  long,  partaking,  according  toCuvier,  of  the  structure  of  the  monitor  and  crocodile), 
and  Pterodactyle  (a  flying  saurian)  are  so  mixed  with  ammonites,  nautili,  belemnites, 
and  many  other  species  of  marine  shells,  that  there  can  be  little  doubt  of  this  forma- 
tion having  been  deposited  at  the  bottom  of  a  sea  not  far  distant  from  some  ancient 
shore."  With  respect  to  the  wing-covers  of  insects  found  in  the  same  deposit,  Dr.  Buck- 
land  remarks  (Bridgewater  Treatise,  vol.  i.  p.  411),  that  they  are  all  coleopterous, 
"and  in  the  opinion  of  Mr.  Curtis,  many  of  them  approach  nearly  to  the  JSuprestis,  a 
genus  now  most  abundant  in  warm  latitudes." 

f  As  regards  the  forms  of  molluscs,  the  genera  Avicula,  Modiola,  Terebratula,  Lingula, 
and  Orbicula  are  found  from  the  Silurian  rocks  upwards  to  the  present  day.  The  like 
with  Turbo,  as  a  restricted  genus,  and  also  with  Nautilus,  with  slight  variations  in  form. 
With  respect  to  those  remarkable  and  beautiful  animals  the  star-fishes,  Professor  Ed- 
ward Forbes  states,  that  species  of  the  genus  Uraster  are  found  in  the  Silurian  rocks 
closely  resembling  the  existing  northern  forms  (Decade  I.,  "  Memoirs  of  the  Geological 
Survey"),  and  that  in  the  lias,  Uraster  Gaveyi  (Decade  III.)  is  only  critically  to  be  dis- 
tinguished from  the  common  Uraster  rubens,  now  inhabiting  the  British  seas.  According 
also  to  the  Professor,  the  Terebratula  striatula,  of  the  cretaceous  series,  cannot  be  dis- 
tinguished specifically  from  the  Terebratula  caput-serpentis  of  the  same  seas. 


526         SIMPLE    SUBSTANCES    FORMING    IGNEOUS    ROCKS. 

time  in  the  vegetation  and  animals  which  have  existed  on  the  earth's 
surface  will  be  only  confirmed  by  extended  research,  it  seems  equally 
probable  that  investigations  carried  out  with  proper  regard  to  the 
varying  physical  geography  of  different  geological  periods  will  show 
the  necessity  of  tracing  the  probable  causes  productive  of  new  adjust- 
ments of  lands  and  waters  at  those  different  times,  and  of  studying  the 
distribution  of  the  life*  of  such  times  in  accordance  with  those  laws 
which  appear  to  govern  that  distribution  at  the  present  time,  not  forget, 
ting,  however,  those  conditions  which  would  follow  a  gradual  decrease  in 
the  heat  of  the  earth,  should  it  eventually  be  found  that  a  temperature 
more  equal  over  the  earth's  surface  than  that  afforded  by  the  sun  would 
appear  required  for  the  distribution  of  vegetable  and  animal  life  in  the 
earlier  periods  of  its  existence  on  our  planet. 

Igneous  products  of  earlier  date  than  those  of  modern  volcanoes. — 
As  has  been  previously  remarked,  the  distinction  between  the  products 
of  active  and  extinct  volcanoes  is  rather  one  of  convenience  than  of 
fact,  and  the  same  may,  to  a  certain  extent,  be  also  observed  as  to  the 
differences  between  those  above  noticed  (pp.  817-400),  and  the  products 
about  to  be  mentioned.  By  arranging  igneous  products  according  to 
the  different  geological  dates  to  which  they  may  be  assigned,  the  ob- 
server has  the  means  of  studying  not  only  their  modes  of  occurrence,  but 
also  the  constancy  or  change  of  the  elementary  substances  entering 
into  their  composition  during  the  lapse  of  geological  time. 

The  igneous  rocks  known  to  us  by  their  appearance  on  the  surface  of 
the  globe,  have  been  found  sufficiently  well  distributed  to  be  available 
for  an  approximate  estimate  of  their  elementary  bodies.  Viewed  as  a 
whole,  they  are  chiefly  oxides  of  substances  commonly  considered  sim- 
ple, one  of  the  oxides,  that  of  silicon,  acting  as  an  acid,  and  combining 
with  a  large  portion  of  the  other  oxides.  Silicic  acid  (silica),  free  or 
combined,  may  be  seen  more  to  prevail  in  certain  rocks  than  in  others ; 
but  there  are  few  igneous  products  found  in  any  abundance,  which  do 
not  mainly  consist  of  silica,  or  the  silicates.  The  simple  substances, 

*  It  is  very  desirable,  in  the  enumeration  of  organic  remains  discovered  in  different 
beds  and  localities,  properly  to  represent  the  abundance  of  the  individuals  of  each 
species.  This  mode  of  investigation  has  received  careful  attention  during  the  progress 
of  the  Geological  Survey  of  the  United  Kingdom.  Without  due  precaution  of  this  kind, 
the  remains  of  a  single  individual  figures  as  prominently  as  those  of  many  hundreds, 
and  a  correct  view  of  the  correspondence  or  difference  between  the  various  portions  of 
contemporaneous  accumulations  as  to  the  life  entombed  in  them  becomes  much  im- 
peded. A  careful  study  of  the  comparative  numbers  of  individuals  often  shows  how 
much  some  species  of  marine  molluscs  have  preferred  one  kind  of  sea-bottom  to  an- 
other, while  others  seem  to  have  nourished  equally  well  through  varied  changes  in  the 
sea-bottoms.  It  is  well  to  bear  in  mind  that  the  researches  of  naturalists  teach  us 
that  many  an  area  is  now  little,  if  at  all,  tenanted  by  marine  molluscs,  such  areas  being 
unsuited  to  their  habits,  while  others  adjoining  them  may  be  covered  by  multitudes  of 
various  molluscs. 


VOLCANIC    PRODUCTS    AMID    THE    OLDER    ROCKS.  527 

with  silicon,  constituting  this  mass  of  matter,  whence  the  sedimentary 
deposits  have  been,  with  minor  exceptions,  more  or  less  directly  or  in- 
directly derived  during  the  lapse  of  time,  have  not  been  found  nu- 
merous. They  are  chiefly  aluminium,  potassium,  sodium,  calcium, 
magnesium,  iron,  and  manganese,  making  with  silicon  eight  substances, 
considered  elementary,  all  combined  with  another,  oxygen,  and  forming 
the  great  volume  of  the  igneous  rocks,  such  as  they  are  known  to  us. 
Of  other  elementary  substances  entering  into  their  composition  on  a 
minor  scale,  probably  sulphur,  boron,  lithia,  and  fluorine,  may  be 
regarded  as  the  principal  bodies,  with  the  addition  of  hydrogen,  so  far 
as  it  may  enter  into  the  composition  of  any  water  that  can  be  regarded 
as  a  real  component  part  of  these  rocks.  Numerous  other  simple  sub- 
stances, no  doubt,  may  be  detected  amid  these  products  in  different 
localities,  even  sufficiently  abundant  in  some  to  be  remarkable ;  but 
viewed  in  the  mass,  the  nine  elementary  substances  above  mentioned, 
with  the  four  others  in  a  minor  manner,  appear  to  constitute  the  great 
mass  of  the  igneous  rocks  of  all  ages. 

That  so  much  of  the  great  volume  of  these  rocks  should  consist  of 
the  combination  of  oxygen  with  a  few  simple  substances,  and  that  the 
union  of  oxygen  with  one  of  them  should  constitute  such  an  important 
compound  for  further  union  with  the  other  oxides,  are  in  themselves 
circumstances  of  no  slight  interest  to  an  observer  anxious  to  trace  some 
connexion  between  the  igneous  products  of  all  geological  periods  and 
the  substances  beneath  the  exterior  and  consolidated  portion  of  the 
earth  during  the  same  lapse  of  time.  We  .have  elsewhere*  estimated 
silica  as  constituting  45  per  cent,  of  the  mineral  crust  of  the  globe, 
hence  the  oxygen  contained  in  silica  alone  would  form  at  least  26  per 
cent,  of  that  crust. f  If  the  amount  of  oxygen  in  the  other  oxides  be 
included,  the  percentage  becomes  largely  increased ;  so  that  when  this 
substance  is  regarded  as  free  from  its  union  with  the  matter  forming 
rocks,  and  in  a  gaseous  form,  its  volume  becomes  enormous. J 

In  studying  these  rocks,  it  may  be  assumed  that  the  observer  would 
be  desirous*  of  ascertaining  how  far  there  may  be  evidence  of  igneous 
products  having  been  thrown  out  in  the  manner  of  those  ejected  from 
active  volcanoes  at  different  geological  times.  As  it  so  happens  that 
while  certain  portions  of  the  earth's  surface  appear  to  have  remained 
in  a  state  undisturbed  by  igneous  action  from  very  early  periods  to  the 
present  day,  other  portions  seem  frequently  to  have  been  subjected  to 
this  action  during  the  same  lapse  of  time,  all  regions,  however  interest- 

*  "  Researches  in  Theoretical  Geology,"  1834,  p.  8. 

f  According  to  Berzelius,  silica  is  a  compound  of  48-4  parts  silicon  and  51-6  parts  of 
oxygen. 

J  The  volume  of  oxygen  would  be  obviously  still  farther  augmented  by  the  addition 
of  that  contained  in  the  various  waters  on  the  surface  of  the  globe,  water  being  a  com- 
pound of  oxygen  and  hydrogen. 


528      OLDER   IGNEOUS   PRODUCTS   OF   THE   BRITISH   ISLANDS. 

ing  they  may  otherwise  be  geologically,  do  not  present  the  needful  con- 
ditions for  this  kind  of  investigation.  In  the  British  Islands,  presenting 
so  many  coast  and  other  natural  sections,  as  also  so  cut  and  pierced  by 
the  operations  of  the  miner  and  engineer,  it  fortunately  happens  that 
amid  the  older  fossiliferous  deposits,  there  is  evidence  of  igneous  pro- 
ducts having  been  contemporaneously  ejected.  Igneous  rocks  are  so 
entangled  with  detrital  accumulations  of  the  Silurian  series,  especially 
well  exhibited  in  Wales,  and  in  the  counties  of  Wicklow,  Wexford,  and 
Waterford,  on  the  opposite  shores  of  Ireland,  that  a  geologist  has 
excellent  opportunities  afforded  him  for  observation.  He  finds  that  the 
igneous  products,  thus  associated  with  these  old  fossiliferous  deposits, 
may  be  divided  into  those  which  have  occupied  their  relative  positions 
in  a  molten  form,  and  those  which  have  been  mingled  with  them  through 
the  agency  of  water,  with  also  certain  accumulations  which  may  have 
been  piled  up  in  a  mechanical  manner,  either  in  air  or  beneath  the  sur- 
face of  water. 

Having  in  view  the  manner  in  which  the  products  of  existing  volca- 
noes are  thrown  out  into  the  air  or  water,  and  are  commingled,  it  is 
desirable  that  the  geologist  should  endeavour  to  trace  any  differences 
or  resemblances  he  may  find  when  opportunities  of  the  kind  noticed 
present  themselves.  In  the  first  place,  he  does  not  possess  the  advan- 
tages of  the  surfaces  usually  presented  in  active  volcanic  districts,  or 
of  those,  such  as  in  France  (p.  394),  which  have  not  been  disturbed  by 
the  action  of  seas  upon  them,  but  finds  masses  of  mineral  matter,  of 
which  the  igneous  products  only  constitute  a  part,  thrown  out  of  the 
positions  in  which  they  were  originally  accumulated,  the  igneous  often 
bent  and  contorted  with  the  aqueous  deposits  with  which  they  are  asso- 
ciated. These  districts,  moreover,  are  often  the  mere  wrecks  of  the 
mud,  silt,  and  sand  of  former  sea-bottoms,  combined  with  the  igneous 
products,  large  portions  having  been  removed  by  denuding  causes,  so 
that  not  only  has  the  general  mass  been  squeezed,  bent,  contorted,  and 
sometimes  broken,  but  portions  of  it  (occasionally  to  be  measured  by 
cubic  miles),  entirely  removed.  Hence  no  slight  care  and  exact  research 
is  required  to  collect  the  needful  evidence,  so  that  all  the  parts  may, 
mentally,  be  again  restored  satisfactorily  to  their  places.  This  may 
often  nevertheless  be  sufficiently  accomplished. 

In  examining  the  igneous  products  associated  with  the  Silurian  rocks 
in  Wales  and  Ireland,  two  kinds  become  somewhat  prominent,  one  in 
which  the  matter  constituting  felspar  prevails,  another  in  which  that 
forming  hornblende  is  mingled  with  the  first,  to  an  equal  and  even 
greater  amount.  Those  accustomed  to  active  volcanic  regions  might  be 
disposed  to  see  in  this  circumstance  a  general  resemblance  to  trachytes 
and  dolerites  (p.  349)  therein  distinguished,  as  also  to  those  mixed  pro- 
ducts which  have  been  named  trachyte-dolerites.  Proceeding  still  further 


FOSSILS    AMID    OLD    IGNEOUS     PRODUCTS.  529 

in  the  inquiry,  it  will  be  found  that  certain  of  these  old  products  are 
mingled  mechanically  with  substances  that  have  once  formed  ordinary 
mud,  silt,  sand,  and  even  conglomerates,  reminding  us  of  the  mixture 
of  the  ashes  and  lapilli  thrown  out  of  existing  volcanoes,  and  intermixed 
with  the  detrital  accumulations  forming  under  the  fitting  conditions, 
around  or  near  many  active  igneous  vents  of  the  present  day.  Even 
lapilli  may  be  detected  amid  beds  which  are  composed  of  something 
more  than  the  igneous  substances  themselves.  These  appearances 
would  alone  lead  an  observer  to  consider  the  old  igneous  products  before 
him  with  reference  to  certain  of  the  results  of  modern  volcanic  action, 
and  he  would  probably  be  not  the  less  induced  to  take  this  course  when 
he  found,  as  in  such  districts  he  often  may,  organic  remains  amid  them, 
either  alone  or  mingled  with  common  detritus,  preserved  among  them 
precisely  as  in  volcanic  tuff  associated  with  the  common  mud,  silt,  and 
sand  deposits,  of  the  present  time.  He  will  sometimes  find  the  organic 
remains  arranged  in  seams,  as  amid  ordinary  detrital  accumulations, 
representing  in  like  manner  the  bottoms  of  ancient  seas  strewed  with 
the  harder  parts  of  molluscs,  trilobites,  and  other  marine  animals  of  the 
time. 

The  geologist  may  occasionally  discover  organic  remains,  thus  ar- 
ranged in  seams,  the  matter  of  the  shells  of  molluscs  still  preserved  in 
beds  of  hard  and  solid  rocks,  ringing  under  the  hammer,  and  at  first 
sight  appearing  as  if  they  had  flowed  in  a  molten  state.  Such  beds  of 
consolidated  igneous  matter,  arranged  in  water,  are  frequently  very 
deceptive,  requiring  no  slight  care  not  to  confound  them  with  the  rocks 
which  have  really  flowed  in  a  molten  state  amid  those  with  which  they 
are  often  associated.  Not  only  in  cases  where  such  beds  contain  organic 
remains,  but  also  where  no  trace  of  them  can  be  detected,  much  caution 
is  needed.  For  the  most  part  microscopic  observation  will  show  that 
they  are  composed  of  fragments  of  igneous  molten  products,  in  which 
the  component  parts  of  felspathicor  hornblendic  minerals  have  variously 
prevailed,  and  that  these  fragments  are  angular.  When  lapilli,  espe- 
cially those  having  the  aspect  of  pumice,  are  mingled  in  these  accumu- 
lations, there  is  usually  little  difficulty  in  determining  their  true  cha- 
racter, and  they  then  assume  the  appearance  of  those  resulting  from 
the  deposit  of  the  ashes  and  cinders  thrown  out  of  volcanic  vents  at  the 
present  day,  more  especially  of  such  as  have  been  formed  in  water  by 
the  fall  of  volcanic  ashes  and  cinders  in  it,  and  are  now  elevated  above 
it,  so  that  they  can  be  studied,  as  in  the  vicinity  of  Vesuvius,  Etna, 
and  some  other  active  volcanoes,  which  have  showered  ashes  and  cinders 
into  seas  adjoining  them,  a  change  of  relative  level  of  the  land  and 
sea  having  been  effected,  and  parts  of  former  sea-bottoms  having  been 
upraised. 

Those  who  have  devoted  much  close  attention  to  the  structure  of  the 

34 


530      VOLCANIC    TUFF    AND    CONGLOMERATES    AMONG     THE 

volcanic  tuffs  of  the  present  time  can  scarcely  fail  to  be  struck,  particu- 
larly when  they  are  regarded  on  the  large  scale,  with  the  resemblance 
of  many  of  the  accumulations  of  igneous  products  associated  with  the 
Silurian  rocks  of  Wales  and  Ireland  to  certain  of  those  tuffs,  especially 
to  those  such  as  pelagonite  (p.  364),  and  some  others  which  have  become 
consolidated  and  modified  in  appearance,  so  that  the  original  small 
grains  of  ashes  and  fragments  thrown  out  of  volcanoes  have  become  one 
general,  and,  at  first  sight,  almost  homogeneous  substance.  While  in 
many  localities  the  laminated  character  of  the  beds,  and  the  presence 
of  marine  organic  remains  occurring  in  the  same  manner  as  in  any 
other  detrital  and  associated  deposit,  point  to  their  accumulation  be- 
neath the  sea,  ashes,  and  sometimes  lapilli,  vomited  forth  from  the 
volcanoes  of  the  time  and  locality,  and  arranged  in  extensive  and  com- 
paratively thin  beds ;  at  others,  the  conglomerates  and  breccias  of 
igneous  rocks,  mingled  confusedly  with  ancient  volcanic  tuff,  the  whole 
interlaced  with  dykes  and  veins  of  felspathic  and  hornblendic  molten 
rocks  of  different  kinds,  remind  the  observer  of  a  confused  mixture  of 
substances  in  the  body  of  a  volcano  itself,  partly  subaerial  and  partly 
subaqueous,  the  general  mass  buried  up  by  other  accumulations  as  the 
volcanic  rocks  gradually  descended  beneath  them.  Of  the  natural 
sections  exposed  in  Wales  and  Ireland,  though  there  are  many  excellent 
opportunities  in  various  places,  the  most  instructive  is  probably  on  the 
coast  of  the  county  of  Waterford,  between  Tramore  and  Bally  voil  Head, 
a  distance  of  fifteen  miles.  Huge  masses  of  these  igneous  products  are 
there  found  in  great  variety,  and  molten  rocks  of  different  kinds  and 
shapes  will  be  seen  sending  out  veins,  and  cutting  as  well  the  ordinary 
detrital  deposits  formed  prior  to  these  outbursts,  as  the  igneous  sub- 
stances of  the  time.  Conglomerates  and  breccias  are  found  piled  in 
various  forms,  cemented  by  igneous  matter,  apparently  thrown  out  as 
ashes,  and  ancient  tuffs  formed  of  smaller  fragments  are  observed  in 
different  places,  while  examples  are  to  be  seen  of  deposits  of  various 
kinds  changed  in  aspect  and  character  where  molten  matter  has  burst 
in  among  them.  There  is  also  a  variety  of  minor,  but  collectively  im- 
portant, objects  of  interest  bearing  upon  the  igneous  products  and  their 
mode  of  accumulation  at  this  early  geological  period.  As  regards  the 
intrusion  of  molten  matter  amid  the  conglomerates  and  breccias,  the 
following  section  (fig.  208)  on  the  west  of  Kilfarrasy  Point  may  be 
found  illustrative,  others  of  equal  interest  being,  however,  sufficiently 
common. 

Such  districts  require  obviously  to  be  studied  on  the  large  scale. 
For  example,  the  section  exhibited  on  the  Waterford  coast,  excellent  as 
it  may  be,  would  scarcely  afford  the  needful  evidence,  taken  by  itself. 
It  would  be  necessary  to  consider  it  with  reference  to  the  mode  of 
occurrence  of  similar  accumulations  along  their  whole  range,  thence 


SILURIAN    DEPOSITS    OF    WALES    AND    IRELAND.         531 

northward  through  the  counties  of  Water  ford,  Wexford,  and  Wicklow. 
When  this  is  accomplished,  the  sections  afforded  on  the  coast  of  Water- 


Fig.  208. 


a,  a,  compact  igneous  rock,  in  which  the  substances  composing  felspar  prevail;  b,  b,  6, 
conglomerate  and  breccia  formed  of  various  portions  of  igneous  products,  chiefly  fel- 
spathic,  cemented  by  matter  resembling  that  of  volcanic  tuff. 

ford  are  seen  to  form  part  of  the  general  evidence  pointing  to  the  rela- 
tive age  of  the  igneous  accumulations  at  this  time ;  one  shown,  more- 
over, to  have  been  anterior  to  the  formation  of  the  old  red  sandstone  of 
the  south  of  Ireland,  inasmuch  as  these  igneous  rocks,  as  also  the  beds 
of  the  Silurian  series  with  which  they  are  associated,  were  disturbed, 
bent,  and  contorted  before  its  accumulation,  and  this  old  red  sandstone 
not  only  reposes  quietly  upon  the  disturbed  rocks,  but  also  contains 
worn  fragments  of  the  latter,  the  igneous  substances  included. 

The  geologist,  seeing  this  considerable  resemblance  to  the  products 
of  modern  volcanoes,  and  also  the  general  similarity  of  the  elementary 
substances  found  in  them,  as  far  as  researches  have  yet  extended*  (con- 
sidering both  igneous  products  in  their  masses),  would  be  prepared  to 
find  evidence  of  igneous  action  also  bearing  a  resemblance  to  that  of 
volcanoes  at  the  present  time  amid  any  accumulations  of  intermediate 
geological  date,  should  the  fitting  conditions  prevail.  For  evidence  of 
this  action  he  would  look  necessarily  in  very  different  regions ;  for  not 
only  is  it  required  that  there  should  have  been  igneous  products  of  this 
kind  at  all  geological  times  in  various  parts  of  the  earth's  surface, 
sometimes  in  one  locality,  sometimes  in  another,  but  also  that  in  the 
present  arrangement  of  land  and  seas  they  should  be  attainable  for 
observation,  even  when  it  may  have  so  happened  that  having  occurred 
in  some  area,  and  that  area  be  now  above  the  sea  level,  all  traces  of 
such  igneous  action  may  not  be  concealed  by  more  modern  and  totally 
dissimilar  accumulations.  In  this  research,  however,  the  geologist  may 
again  find  opportunities  in  the  British  Islands.  In  Devon  and  Corn- 

*  Investigations  are  now  in  progress  in  the  laboratory  of  the  Museum  of  Practical 
Geology  for  the  purpose  of  ascertaining  the  chemical  composition  of  the  igneous  rocks 
of  different  dates,  obtained  during  the  progress  of  the  Geological  Survey  of  the  United 
Kingdom. 


532     OLD    VOLCANIC    PRODUCTS    INTERMINGLED    WITH     THE 

wall  he  may  obtain  evidence  of  a  continuance  of  the  like  igneous  action 
at  a  subsequent  period,  amid  deposits,  some  of  which  may  be  referred 
to  the  date  of  the  old  red  sandstone  series  of  other  parts  of  the  British 
Islands,  while  some  are  more  modern,  and  others  perhaps  more  ancient. 
Amid  the  Devonian  and  Cornish  accumulations  of  this  date  he  will 
detect  beds  apparently  also  formed  of  the  volcanic  ashes  of  the  time, 
and  other  arrangements  of  igneous  matter,  som0rocks  evidently  poured 
forth  in  molten  masses,  and  breaking  through  ordinary  and  previously 
formed  deposits.  Among  numerous  localities  good  sections  are  afforded 
at  low  tide  on  the  Tamar,  near  Saltash,  showing  an  association  of  the 
Devonian  rocks,  molten  products,  and  other  accumulations  of  igneous 
origin.*  In  many  situations,  the  igneous  ash  of  the  time  graduates 
into  the  ordinary  detrital  matter  associated  with  it,  as  well  in  the  con- 
tinuation of  a  contemporaneous  deposit  as  in  successive  deposits,  in  the 
one  case  pointing  to  a  gradual  removal  from  the  source  of  supply,  such 
as  a  volcanic  vent ;  in  the  other,  to  an  unequal  supply  over  the  same 
area,  occasionally  intermittent,  so  that  common  deposits  were  effected 
on  a  sea-bottom  at  intervals.  Good  examples  of  these  kinds  of  igneous 
accumulations,  with  an  intermixture  of  solid  molten  matter,  some  of  the 
latter  showing  large  grained  compounds  of  felspar  and  hornblende,  are 
to  be  found  in  the  direction  of  Davidstow  and  St.  Cletha.  In  certain 
of  the  ash-beds  much  calcareous  matter  is  sometimes  found,  assisting  as 
a  cementing  substance.  They  are  so  calcareous  near  Grylls,  on  the 
south  of  Lesnewth,  that  attempts  have  been  made  to  burn  the  compound 
rock  for  lime. 

Upon  attentively  examining  the  composition  of  those  beds  of  igneous 
substances  which  are  arranged  amid  the  ordinary  deposits  of  the  time, 
it  is  found  to  vary  much  as  to  the  molten  products  associated  with  the 
general  mass  of  deposits.  While  some,  like  the  trachytic  tuffs  of 
modern  times,  are  chiefly  formed  of  the  component  parts  of  felspar, 
others  are  more  like  the  dolerite  tuffs,  and  contain  substances  usually 
found  in  augites  and  hornblendes,  while  others  again  partake  of  the 

*  As  we  have  elsewhere  mentioned  ("  Report  on  the  Geology  of  Cornwall,  Devon, 
and  West  Somerset,"  1839,  p.  63),  there  is  an  abundant  mixture  of  igneous  and  ordi- 
nary sedimentary  rocks  in  the  vicinity  of  Saltash  and  St.  Stephen,  and  thence  across 
the  Tamar  to  St.  Budeaux  on  the  east,  and  towards  St.  Urney  on  the  west,  and  in  the 
creeks  which  run  up  from  the  Lyhner  to  Manaton  Castle  and  St.  Urney.  The  schistose 
varieties  are  certainly  contemporaneous  with  the  associated  sedimentary  deposits,  while 
dykes  of  greenstone  and  other  compounds  of  hornblendic  and  felspathic  matter  are  seen 
to  cut  through  the  various  accumulations  "analogous  to  those  which  are  produced  in 
the  beds  of  ash,  and  filled  by  lava  on  the  flanks  of  volcanoes,  in  cases  where  the  latter 
are  partly  submarine  ;  traversing  shales,  clays,  and  other  aqueous  deposits,  as  well  as 
the  ash,  which  in  such  cases  may  readily  have  become  interstratified  among  them."  In 
the  continuation  of  the  beds  near  Saltash,  many  of  the  schistose  accumulations  of  ash 
so  graduate  into  the  common  kinds  of  deposit  of  mud  and  silt,  that  no  correct  distinctions 
can  be  drawn  between  them. 


DEVONIAN    ROCKS    OF    SOUTHWESTERN    ENGLAND.        533 

character  of  both.  Seeing  that,  like  the  ordinary  muds,  silts,  and 
sands  with  which  they  are  associated,  they  have  become  consolidated, 
and  like  them  also  have  been  exposed  to  the  passage  of  water  through 
them,  as  well  when  buried  deep  (by  depressions  of  the  general  area) 
beneath  their  present  levels,  as  when  exposed,  as  now,  to  atmospheric 
influences,  many  of  these  rocks  may  not  now  contain  all  the  substances 
originally  distributed  in  them,  while  they,  like  the  other  deposits  asso- 
ciated with  them,  may  have  received  additional  mineral  matter.  It  will 
readily  be  inferred  that  soluble  substances,  such  as  the  silicates  of  soda 
and  potash,  may  have  been  removed  during  the  long  lapse  of  geological 
time  during  which  they  may  have  been  exposed  to  modification  and 
change.  Though  there  is  this  difficulty,  much  may  yet  be  accomplished 
by  accurate  analyses  of  portions  carefully  selected. 

In  Derbyshire  the  observer  will  again  see  igneous  rocks  associated 
with  ordinary  deposits  ;  in  this  case  with  limestone,  known  as  the  car- 
boniferous or  mountain  limestone,  in  such  a  manner  that  their  relative 
geological  antiquity  can  be  ascertained.  Careful  investigation  shows 
that  in  that  area,  at  least,  and  probably  much  beyond  it  (beneath  a 
covering  of  the  sands,  shales,  and  coals,  known  as  the  millstone  grit 
and  coal  measures),  and  after  a  certain  amount  of  these  limestones  had 
been  accumulated,  there  had  been  an  outburst  and  overflow  of  molten 
rock,  irregularly  covering  over  portions  of  them.  And  further,  that 
after  this  partial  overflow,  the  limestone  deposit  still  continued,  proba- 
bly spreading  from  other  localities  where  the  conditions  for  its  accumu- 
lation had  continued  uninterruptedly.  Occasionally  water  action  upon 
the  igneous  products  may  be  inferred  prior  to  the  deposit  of  the  calca- 
reous beds  upon  them,  if  not  also  a  certain  amount  of  decomposition  of 
the  former,  the  limestone  immediately  covering  them  containing  frag- 
ments (some  apparently  water-worn),  and  a  mingling  of  the  subjacent 
rock,  such  as  might  be  expected  if  calcareous  matter  had  been  thrown 
down  upon  the  exposed  and  weathered  surfaces  of  the  igneous  rock.  In 
some  parts  of  the  district  another  outflow  of  the  same  kind  of  igneous 
rock  again  took  place,  and  was  again  covered  by  limestone  beds,  so  that 
in  such  portions  of  the  area,  two  irregularly-disposed  sheets  of  once 
molten  rock  are  included  among  the  mass  of  the  limestone  beds. 

The  following  section  (fig.  209)  of  part  of  this  district,*  by  Professor 
John  Phillips,  may  serve  to  illustrate  the  mode  of  occurrence  of  these 
beds  of  igneous  rock,  the  areas  of  which  do  not  coincide,  so  that  on§ 
outflow  did  not  exactly  cover  that  overspread  by  the  other.  In  this 
section,  a  a  are  the  igneous  rocks,  locally  known  as  toactbtonesrf  and  b  b 

*  A  reduced  portion  of  one  (No.  18)  of  the  horizontal  sections  of  the  Geological  Sur- 
vey of  Great  Britain. 

f  Professor  John  Phillips  suggests  that  this  name  is  a  corruption  of  the  German  word 
todtestein ;  rothe  todte  liegende  (red  dead,  or  unproductive  bed)  being  a  term  applied  by 


534  IGNEOUS    ROCKS    ASSOCIATED    WITH    THE 

the  limestones,  c  being  the  covering  beds  of  the  millstone  grit,  and  // 
faults. 

Fig.  209. 
Fin  Cop.  Bow  Cross. 


Natural  sections  (many  of  which  are  excellent)  and  mining  opera- 
tions show  that  as  regards  thickness  these  overflows  vary  considerably, 
so  much  so  as  to  aid  the  observer  in  forming  some  estimate  of  the  loca- 
lities whence  the  molten  matter,  when  ejected,  may  have  been  distributed 
around. 

Although  there  are  clays  amid  the  limestones  in  the  relative  positions 
of  the  igneous  rocks,  and  some  of  these  seem  clearly  little  else  than 
such  rocks  in  a  highly  decomposed  state,  retaining  the  arrangement  of 
their  component  mineral  substances,  as,  for  example,  at  the  isolated 
boss  of  limestone  at  Crich,  protruding  (at  a  distance  of  3J  miles  from 
the  main  mass)  from  the  squeezing  action  to  which  these  rocks  and  the 
coal  measures  above  them  have  been  subjected,  through  the  lower  part 
of  the  latter,  known  as  millstone  grit,  it  would  scarcely  be  safe  to  con- 
clude that  all  lying  nearly  in  the  same  general  geological  levels  were 
so,  inasmuch  as  some  of  them  may  be  underclays,  of  the  kind  found  in 
the  coal  measures  (p.  482).  Care  on  this  head  is  rendered  necessary 
by  finding  a  clay  of  this  description,  a  true  underclay,  supporting  a 
thin  bed  of  impure  coal  in  the  higher  part  of  the  limestone  series  near 
Matlock  Bath.* 

In  the  case  of  Derbyshire,  though  there  may  have  been  a  removal  of 
a  portion  of  the  igneous  beds  by  the  action  of  water  upon  their  exposed 
surfaces  (and  an  attentive  examination  of  the  upper  overflow  likewise 
shows  a  quiet  adjustment  of  the  limestone  beds  formed  upon  it),  no 
deposits  resembling  the  ash  and  lapilli  beds  above  mentioned  as  found 
in  Devon  and  Cornwall,  Wales  and  Ireland,  have  yet  been  detected. 
There  is  no  evidence  showing  an  accumulation  of  ash  and  cinders  in  the 
manner  of  subaerial  volcanoes.  If  there  had  been  such,  and  this  had 
been  attacked  by  breaker  action  and  currents,  the  geologist  would 
expect  to  find  some  portions  included  amid  the  limestone  beds,  and  such 

German  miners  to  the  unproductive  rocks  subjacent  to  the  copper-bearing  slate  of 
Mansfield  and  other  localities.  In  like  manner,  the  name  Jlarmaster,  given  to  those 
who  superintend  t^c  distribution  of  the  mines  and  collect  the  dues,  or  royalties,  has 
long  been  considered  a  corruption  of  Bergmeister. —  See  Pilkington's  "Derbyshire," 
1789,  p.  110. 

*  This  impure  bed  of  coal  was  cut  while  driving  the  tunnel  through  the  High  Tor, 
for  the  railway  running  by  Matlock  Bath,  and  is  to  be  well  seen,  dipping  rapidly,  with 
the  other  beds,  in  the  drift  cut  into  the  cavernous  mine,  part  of  which  is  shown  by  the 
name  of  the  Rutland  Cavern,  at  the  Heights  of  Abraham. 


CARBONIFEROUS  LIMESTONE  OF  DERBYSHIRE.     535 

have  not  been  detected.  It  may  readily  have  happened,  therefore,  that 
the  igneous  matter  was  thrown  out  in  a  molten  state,  without  any 
accompaniment  of  ash  and  cinders  ;  and  this  might  have  taken  place  as 
well  beneath  the  level  of  the  sea  as  above  it. 

Upon  examining  the  structure  of  the  igneous  rock,  it  is  found  to  be 
partly  solid,  and  confusedly  well  crystallized,  a  compound  of  felspar 
and  hornblende,  with,  sometimes,  sulphuret  of  iron.  It  is  partly  vesi- 
cular, in  some  localities  highly  so ;  the  vesicles,  as  usual,  filled  with 
mineral  matter  of  various  kinds,*  where  the  rock  has  remained  unaf- 
fected by  atmospheric  influences,  but  exhibiting  the  original  and  vesi- 
cular state  of  the  molten  rock  where  these  have  removed  the  foreign 
substances  in  them.  In  some  localities  the  scoriaceous  character  of  the 
rock  is  as  striking  as  amid  many  volcanic  regions  of  the  present  day. 
Like  more  modern  igneous  products,  also,  it  will  often  be  found  decom- 
posed in  a  spheroidal  form.  The  following  (fig.  210)  is  an  example  of 
this  decomposition  at  Diamond  Hill,  on  the  south  side  of  Millersdale, 
where  the  concretionary  structure  has  been  developed  somewhat  on  the 
minor  scale,  and  the  size  of  the  spheroidal  bodies  is  about  that  of  bomb- 
shells and  cannon-balls. 

Fig.  210. 


It  will  be  thus  seen  that  amid  the  older  fossiliferous  deposits,  igneous 
rocks  may  be  so  associated  as  to  give  the  relative  dates  of  their  ejection, 
even  in  such  a  manner  as  to  lead  to  the  inference  that  in  some  cases, 
there  have  been  subaerial  volcanic  vents  at  hand,  whence  molten  matter, 
cinders,  and  ashes  may  have  been  thrown  out,  as  in  the  present  day, 
the  elementary  substances  of  which  this  ejected  mineral  matter  is  com- 
posed, reminding  the  geologist  very  strongly  of  those  thrown  out  in  a 
similar  manner  in  modern  volcanoes.  As  has  been  stated  (p.  528),  it 
will  require  the  observer  to  readjust  in  his  mind  the  various  parts  of 
countries,  like  those  noticed  in  Cornwall  and  Devon,  Wales  and  Ireland, 
replacing  the  portions  now  removed  by  denudation,  properly  to  consider 
this  subject  with  reference  to  the  relative  times  when  the  various  igneous 
products  were  ejected  and  accumulated  amid  the  ordinary  sedimentary 
deposits  of  that  early  geological  time.  Let  the  following  section  (fig. 
211)  be  one  of  a  volcano,  so  situated  that  while  lava  currents  and 
dykes  of  molten  matter  (a  a  a)  were  thrown  out  and  up  in  the  usual 

*  Carbonate  of  lime,  as  might  be  expected,  is  a  very  common  substance  in  these 
vesicles. 


536 


RELATIVE  GEOLOGICAL  DATE  OF  THE 


manner,  and  became  mingled  with  subaerial  tuff  and  volcanic  breccias, 
b  b  b,  subaqueous  deposits  were  formed  near  and  over  these  products, 
mingling  volcanic  and  ordinary  detritus  in  the  same  or  associated  beds. 


Fig.  211. 


If  the  volcanic  action  ceased,  and  the  general  area  were  depressed 
so  that  new  and  ordinary  deposits,  d  d  c?,  were  effected,  and  the  whole 
was  merely  tilted,  not  complicating  the  subject  with  squeezing  and  con- 
tortion, and  some  new  surface  n,  s,  be  given  to  the  general  mass,  as 
shown  beneath  (fig.  212),  the  observer  will  at  once  perceive  that  the 


Fig.  212. 


mode  of  occurrence  of  the  igneous  rocks  amid  the  ordinary  deposits 
will  require  careful  consideration  and  study.  He  will  see  that  a  hasty 
investigation  is  not "  likely  to  afford  the  requisite  data,  and  that  pro- 
longed research  is  needed  for  very  exact  determinations,  though  he  may 
often  find  sufficient  in  a  short  time,  if  the  natural  or  artificial  sections 
be  favourable,  for  a  just  general  view  of  the  subject. 

When  igneous  products  are  not  associated  with  ordinary  fossiliferous 
deposits  in  the  manner  mentioned,  and  often,  unfortunately,  they  can- 
not be  so  favourably  studied,  a  geologist  may  still  obtain  certain  relative 
dates  by  their  mode  of  occurrence  on  the  great  scale.  Fortunately,  we 
may  again  take  the  British  Islands  for  illustration,  as  showing  how 
much  may  be  found  connected  with  the  subject  even  in  that  minor  area. 
When  the  granite  range  of  Wicklow  and  Wexford,  and  which  also 
includes  portions  of  adjacent  counties,  is  examined  with  reference  to 
the  rocks  in  contact  with  it,  it  is  seen  that  certain  Cambrian  and  Silu- 
rian rocks,  the  range  of  which  it  traverses  in  a  slanting  manner,  are 
upturned,  much  modified  in  their  mineral  structure,  when  in  contact 
with  the  granite,  and  often  much  broken  at  the  junction ;  even  huge 
masses  of  them  included  in  the  latter,  granite  filling  the  cavities  and 
fissures  thus  produced ;  so  that  little  doubt  is  left  that  these  rocks  were 
formed  prior  to  the  intrusion  of  such  granite.  Thus  far  the  observer 
merely  obtains  evidence  of  no  very  definite  kind  as  to  the  actual  period 
of  this  intrusion,  though  in  the  district  noticed  he  would  see  that  this 
kind  of  igneous  action  took  place  after  that  which  in  the  same  area  pro- 


WICKLOW    AND    WEXFORD    GKANITES.  537 

duced  an  out-throw  of  felspathic  and  hornblendic  products  as  above 
noticed  (p.  528).  He  only  discovers  that  the  one  set  of  igneous  pro- 
ducts has  been  uplifted  by  the  other.  Continuing  his  researches,  he 
sees  certain  conglomerates  of  the  old  red  sandstone  reposing  quietly 
upon  the  granite,  and,  when  this  happens,  containing  rounded  portions 
of  that  rock,  as  well  as  much  finer  detritus  from  it.  He  also  finds 
where  the  same  conglomerate  stretches  over  the  disturbed  older  rocks, 
with  their  included  igneous  products,  that  rounded  and  angular  frag- 
ments of  these  products  are  imbedded  in  it.  He  has  now  the  approxi- 
mate relative  date  of  the  granite  of  the  district,  so  far  that  it  rose  up 
after  that  portion  of  the  Silurian  series  was  formed  which  is  there  dis- 
turbed, and  prior  to  such  portion  of  the  old  red  sandstone  series  as  is 
represented  by  this  conglomerate.  We  will  suppose  that  he  has  ob- 
tained evidence  of  the  portion  of  the  Silurian  series  disturbed  being 
the  lower,  and  of  the  conglomerate  representing  some  higher  or  middle 
portion  of  the  old  red  sandstone  series,  as  found  developed  elsewhere  in 
the  British  Islands.  There  would  then,  no  doubt,  be  something  of  an 
interval  in  the  geological  series,  during  which  the  uprise  of  the  granit  e 
may  have  taken  place ;  nevertheless  the  observer  has,  by  the  means  em- 
ployed, arrived  at  a  certain  approximation  of  no  slight  value  as  to  the 
real  relative  date  of  its  protrusion. 

To  show  this  value,  it  is  only  needful  to  turn  to  Devon  and  Cornwall, 
where  at  such  a  comparatively  trifling  distance,  the  geologist  finds  a 
granite  of  much  the  same  general  character  protruding  through  the 
equivalents  of  those  accumulations  which  have  quietly  covered  the  Irish 
granite  mentioned,  after  its  consolidation,  the  disturbance  caused  by 
the  uprise  of  the  Devonian  and  Cornish  granite  extending  to  the  lower 
portion  of  the  coal  measures,  as  may  be  seen  around  the  northern  part 
of  Dartmoor,  where  veins  extend  from  the  granite  in  that  direction 
into  these  sedimentary  rocks,  in  the  same  manner  as  into  the  Silurian 
deposits  of  Wicklow  and  Wexford.  In  the  case  also  of  the  granites  of 
Cornwall  and  Devon,  it  becomes  necessary  to  seek  for  evidence  as  to 
any  deposits  so  occurring  as  to  show  the  geological  dates  between  which 
their  uprise  was  effected.  Throughout  the  greater  part  of  the  district, 
evidence  of  the  kind  required  is  not  to  be  found,  but  on  the  eastward 
of  Dartmoor,  and  of  the  continuation  of  the  deposits  which  have  been 
disturbed  at  the  time  these  granites  were  intruded,  the  observer  finds 
beds,  known  as  the  new  red  sandstone  series,  reposing  quietly  on  the 
disturbed  rocks,  the  lower  portion  of  them  containing  rounded  and 
angular  fragments  of  the  latter.  It  would  thus  appear  that  the  ap- 
proximative date  for  the  elevation  of  the  Cornish  and  Devonian  granites 
amid  the  accumulations  effected  up  to  that  time,  was  somewhere  between 
the  lower  part  of  the  coal  measure  series  (including  the  millstone  grit 


538  GRANITES    OP    CORNWALL    AND    DEVON. 

of  Central  England  in  that  series),  and  the  lower  portion  of  the  new  red 
sandstone  deposits. 

Thus  in  Southeastern  Ireland  and  Southwestern  England  there  is 
evidence  of  two  protrusions  of  granite  at  different  geological  periods, 
different  rocks  of  known  relative  ages  being  disturbed  on  the  one  hand 
and  unmoved  on  the  other,  so  that  approximative  dates  are  obtained  for 
both  protrusions.  If  in  the  annexed  section  (fig.  213)  a,  a,  be  a  mass 

Fig.  213. 


of  granite  thrust  upwards  through  sedimentary  beds  b  b,  sending  veins 
into  fractures  effected  in  them,  as  well  as  modifying  their  mineral  struc- 
ture at  the  junction,  and  c  be  an  accumulation  containing  rounded  or 
angular  fragments  of  a  and  6,  it  follows  that  the  relative  geological 
dates  of  b  and  c  being  known,  that  of  the  protrusion  #,  a,  would  be 
known  also  within  greater  or  less  limits,  as  the  formation  of  b  and  c  may 
be  separated  or  approximate  to  each  other  in  the  geological  series. 
This  would  be  the  case  of  Southeastern  Ireland.  In  that  of  Devon,  the 
disturbed  beds  b  b,  altered  as  before,  and  with  granitic  veins  a,  a,  in 
them,  would  be  covered  by  beds,  /,  reposing  quietly  on  them,  and  also 
containing  fragments  of  them,  with  here  and  there  igneous  rocks,  e,  in- 
terposed. 

Though  the  relative  dates  of  the  rise  of  molten  mineral  substances 
into  fissures  of  prior-formed  rocks,  such  portions  of  igneous  matter 
usually  known  as  dykes,  could  not  be  obtained  when  these  are  uncovered 
by  accumulations  of  which  the  position  in  the  geological  series  is  known ; 
as,  for  example,  if,  in  the  subjoined  section  (fig.  214),  a  and  b  be 

Fig.  214. 


dykes  of  any  igneous  rocks  cutting  through  some  sedimentary  deposit 
c  d,  and  these  be  uncovered  by  any  accumulation  of  ascertained  geolo- 
gical date,  the  exact  relative  time  when  the  cracks  were  effected  and 
the  molten  matter  rose  in  them,  would  remain  uncertain.  It  sometimes 
happens,  however,  that  some  evidence  as  to  relative  date  may  be 
obtained,  of  a  fair  approximative  kind,  even  with  respect  to  dykes  of  this 
character.  It  would  not  be  sufficient  that  they  cut  one  set  of  rocks, 
and  not  another,  in  some  given  district,  without  further  general  evi- 
dence, so  as  to  refer  them  with  certainty  to  a  particular  time,  anterior 
to  the  formation  of  the  beds  not  cut  by  them,  since  it  may  have  hap- 


UNCERTAIN    DATE    OF    SOME     IGNEOUS    DYKES. 


539 


pened  that  contemporaneous  causes  did  not  act  beyond  a  given  area, 
though  in  certain  of  these  cases  there  may  appear  much  to  support  an 
inference  to  that  effect.  For  example,  numerous  greenstone  dykes  are 
found  to  traverse  the  Cambrian  rocks  in  Merionethshire  and  Caernar- 
vonshire, while  these  are  not  observable  amid  certain  upper  Silurian 
deposits  in  Denbighshire  and  Flintshire,  and  contemporaneous  igneous 
rocks  are  associated  with  intermediate  accumulations  in  Caernarvon- 
shire, and  other  adjacent  counties.  It  might  hence  be  inferred  that, 
when  the  igneous  eruptions  producing  the  latter  were  effected,  fissures 
were  formed  in  the  still  more  ancient  deposits  (Cambrian),  and  molten 
matter  injected  into  them,  and  that  igneous  action  ceasing,  the  adjoin- 
ing higher  parts  of  the  Silurian  deposits  were  undisturbed  by  the  intru- 
sion of  any  igneous  matter.  It  is  far  from  improbable  that  this  infer- 
ence would,  in  a  great  measure,  be  correct ;  but  that  it  is  not  wholly  so, 
the  inspection  of  dykes  of  the  same  kind  traversing  various  parts  of 
Anglesea,  and  seen  to  cut  into  the  coal  measures  of  the  Menai  Straits, 
between  Bangor  and  the  great  suspension  bridge,  at  once  shows.  It 
may  readily  have  happened  that  igneous  matter  had  been  thrown  into 
fissures  formed  at  these  different  times  in  even  the  moderate  area  of 
Caernarvonshire  and  Anglesea,  and  hence  it  would  be  hazardous,  with- 
out other  evidence,  to  decide  upon  one  dyke  being  separable  in  geologi- 
cal time  from  another,  even  when  not  far  distant  from  each  other,  at 
the  same  time  that  many  probabilities  might  seem  to  exist  as  to  the 
relative  date  of  some  of  them. 

The  granitic  and  porphyry  dykes  in  Cornwall  and  Devon,  known 
locally  as  elvans,  may  be  taken  in  illustration  of  the  approximation  to 
relative  geological  dates  occasionally  attainable.  It  has  been  seen  that 
the  granites  of  that  district  were  upraised  posterior  to  the  deposit  of  the 
lower  part  of  the  coal  measures,  and  anterior  to  that  of  the  new  red 
sandstone  series.  Subsequently  to  the  protrusion  of  the  granite,  and 
to,  at  least,  its  partial  consolidation,  fissures  were  formed  traversing 
both  the  granites  and  the  various  disturbed  sedimentary  rocks  adjoining 

Fig.  215. 


them,  and  into  these  fissures  molten  matter  was  introduced,  as  shown 
previously  (fig.  7,  p.  40),  and  as  may  be  further  illustrated  by  the  pre- 


540      RANGE    OF    THE    GRANITIC    OR    PORPHYRY    DYKES, 


ceding  section  (fig.  215),  seen  on  the  cliffs  at  Trevellas  Cove,  near  St. 
Agnes,  where  an  elvan  a,  a,  cuts  through  the  slates,  5,  6,  and  is  tra- 
versed by  dislocations,/,/,  one  of  which  materially  shifts  the  rocks, 
and  thereby  displaces  the  elvan  dyke,  near  the  sea.  With  respect  to 
the  same  fissures  having  traversed  both  the  previously-consolidated  rocks 
and  the  granite,  the  following  map  (fig.  216)  of  part  of  the  mining  dis- 

Fig.  216. 


trict  of  Gwennap,  Cornwall,  may  be  useful,  a,  a,  being  the  granite,  <?,  <?, 
the  schistose  rocks  broken  through  by  it,  6,  6,  the  elvan  dykes,  and  s, 
greenstone.  The  fissures  v,  v,  v,  and  d,  d,  c?,  were  produced  at  different 
subsequent  periods,  some  of  them  variously  filled  by  the  ores  of  tin  and 
copper,  or  other  substances,  and  known  (locally)  as  lodes  and  cross 
courses. 

Upon  examining  the  composition  of  these  elvans,  they  are  found  to 
be  formed  of  matter  similar  to  that  of  the  granites  of  the  districts, 
usually  corresponding  with  any  modifications  observable  in  patches  of 
that  rock  exposed  nearest  on  the  surface.  Indeed,  they  seem  merely 
portions  of  the  same  general  matter  which  rose  in  fissures  formed  by 
the  cracking  of  the  adjacent  granite,  only  consolidated  on  its  higher 
parts,  such  cracks  also  extending  through  the  various  rocks  above  the 
granite.  The  relative  date  would  be  only  so  far  thus  obtained  as  to 
show  that  the  filling  of  the  fissures  was  posterior  to  the  intrusion  of  the 
main  masses  of  granite,  some  of  the  latter  rock,  in  its  molten  state, 


KNOWN    AS    ELVANS,    IN    CORNWALL    AND    DEVON.         541 

readily  rising  into  such  fissures,  formed  both  in  its  own  higher  parts, 
and  in  any  covering  rocks.* 

Proceeding  eastward,  from  the  Dartmoor  granite  to  the  boundary  of 
the  new  red  sandstone  series,  where  this  reposes  on  the  uneven  surfaces 
and  indentations  of  the  older  and  previously-disturbed  fossiliferous 
deposits  in  that  direction,  igneous  rocks  are  found  associated  with  its 
lowest  part  in  some  localities,  pointing  to  local  igneous  action,  while 
these  lowest  beds  were  accumulating.  Not  only  are  some  of  these  lower 
accumulations  so  entangled  with  the  igneous  rocks,  that  there  appears 
difficulty  in  not  considering  them  of  contemporaneous  production  as  a 
whole  ;f  but  there  would  also  appear  to  be  traces  of  subaerial  action. 
The  latter  seems  to  occur  near  Calverleigh,  where,  as  in  the  annexed 
section  (fig.  217),  a,  a,  represent  the  disturbed  beds  of  the  lower  coal 

Fig.  217. 
Calverleigh. 


measures,  at  part  of  an  ancient  gulf  amid  those  rocks  ;  5,  a  conglomerate 
wholly  composed  of  portions  of  these  subjacent  deposits,  cemented  by 
red  sandstone  and  argillo-arenaceous  matter,  without  any  fragments  of 
rocks  ;  c,  felspathic  porphyries,  and  more  compact  felspathic  rocks, 
some  scoriaceous ;  and  d,  conglomerates  and  sandstones,  fragments  of 
the  igneous  rocks,  and  others  of  a  similar  character,  being  contained  in 
the  conglomerates.  Along  the  range  of  the  igneous  rocks,  particularly 
on  the  north  of  them,  there  is  an  arenaceous  deposit,  here  and  there 
mingled  with  the  ordinary  sandstone,  which  bears  a  great  resemblance 
to  a  volcanic  product,  so  much  so  as  to  lead  to  the  inference  that  it  had 
been  ejected  in  the  manner  of  volcanic  ash,  and  that  falling  into  water, 
it  had  been  mingled  with  the  mud,  sand,  and  gravel,  adjoining  some 
volcanic  vent  of  the  time.  J 

*  Occasionally  fragments  have  been  detached  from  the  adjacent  rocks,  and  enveloped 
in  the  molten  matter  of  the  elvans.  That  at  Pentuan  is  among  the  best  examples  of 
this  circumstance.  This  elvan  is  a  fine-grained  compound  of  felspar  and  quartz,  with 
crystals  of  mica.  Fragments  of  the  slate  rocks  traversed  are  found  in  it.  Occasionally, 
though  rarely,  there  are  portions  of  quartz  which  appear  to  have  been  broken  off  some 
quartz  vein  in  the  slates,  and  thus  became,  like  the  other  fragments,  included  in  the 
molten  rock.  In  a  branch  of  the  Pentuan  elvan,  taking  a  course  alongshore  to  the  Black 
Head,  the  fragments  derived  from  the  adjoining  rocks  are  very  numerous,  decreasing 
in  abundance  from  the  sides  of  the  dyke  towards  its  central  part,  in  which  they  are 
rarely  detected. 

f  The  intimate  connexion  of  igneous  rocks  and  the  red  sandstone  series  at  Thorverton 
and  Silverton  was  pointed  out,  in  1821,  by  the  Rev.  J.  Conybeare,  "Annals  of  Philoso- 
phy," new  series,  vol.  ii.  p.  161. 

J  The  facts  in  this  locality  would  appear  to  show,  that  along  a  range  of  ancient  coast, 
of  a  date  corresponding  to  the  first  production  of  the  new  red  sandstone  series  of  Devon 


542  IGNEOUS    ROCKS    IN    THE    LOWER    PORTION    OF 

The  igneous  rocks  of  this  date  can  be  well  studied  at  the  base  of  the 
new  red  sandstone  series  from  Exeter  to  Haldon  Hill.  They  are  seen 
at  Pocombe  Hill,  resting  directly  on  the  edges  of  the  disturbed  and  sub- 
jacent coal  measures,  and  are  chiefly  formed  of  a  siliceo-felspathic  com- 
pound, with  occasional  though  not  numerous  vesicles.  These  igneous 
rocks  are  also  well  exhibited  between  Ide  and  Dunchidiock,  resting  on 
similar  accumulations.  Near  Western  Town,  the  intimate  connexion 
between  them  and  the  red  sandstone  and  conglomerates  can  be  seen. 
By  reference  to  geological  maps,  it  will  be  observed  that  the  igneous 
rocks  thus  associated  with  the  lower  portions  of  the  new  red  sandstone 
series  near  Exeter,  Crediton,  Thorverton,  Kellerton,  Silverton,  and  even 
near  Tiverton,  have  been  thrown  out  in  a  prolongation  of  the  general 
direction  of  the  granite  bosses  and  el  vans  extending  from  the  Scilly 
Islands  to  Dartmoor.  By  examining  their  component  parts,  they  are 
observed  to  be  formed  of  substances  corresponding  with  those  found  in 
these  granites  and  elvans.  While  many  of  them  present  a  porphyritic 
character,  others  are  more  homogeneous  in  structure,  and  sometimes 
vesicular.  Much  of  the  lower  new  red  conglomerates  and  breccias  in 
the  neighbourhood  of  these  igneous  rocks  is  composed  of  fragments 
derived  from  them,  so  that  these  fragments,  if  again  gathered  together, 
would  constitute  no  inconsiderable  mass.  Among  them  many  porphyries 
are  found,  as  well  containing  crystals  of  quartz  as  felspar.  Masses  of  the 
igneous  rocks  from  which  they  are  derived  are  not  often  observable, 
though  in  such  a  district  the  portions  visible  on  the  surface  afford  no 
measure  of  the  igneous  masses  which  may  be  buried  beneath  a  thick 
covering  of  detrital  matter.  It  is,  therefore,  important  to  observe  por- 
phyries in  place,  sometimes  only  containing  quartz  crystals ;  at  others, 
these  mingled  with  crystals  of  felspar,  associated  with  the  lower  part  of 
the  new  red  sandstone  series,  at  Ideston  and  Knole. 

Weighing  all  the  facts  thus  observable,  the  geologist  might  be  led  to 
infer  that  the  date  of  at  least  some  of  the  elvans  of  Cornwall  and  Devon, 
though  they  are  uncovered  by  deposits  affording  direct  means  for 
approximating  to  the  time  when  they  rose  in  the  fissures  where  they  are 
found,  might  not  very  materially  differ  from  the  commencement  of  those 
accumulations  which  constitute  the  lower  portion  of  the  new  red  sand- 
stone series  of  that  part  of  England,  granitic  matter  constituting  the 
base  of  the  various  rocks  ejected,  and  being  merely  modified  in  its  aspect 
according  to  the  varied  conditions  to  which  it  had  been  subjected.  So 

and  Somerset  (see  Maps  of  the  Geological  Survey,  Sheets  20,  21,  22),  there  was  (1)  a 
subaqueous  valley,  or  depression,  among  the  disturbed  coal  measures,  there  occurring, 
the  partial  abrasion  of  which  by  breakers  on  the  shores  adjoining  produced  (2)  the 
shingles,  and  other  detritus,  now  forming  a  conglomerate.  Subsequently  (3),  igneous 
products  were  accumulated,  probably  ejected  from  a  neighbouring  vent,  which,  with 
others  in  South  Devon,  were  then  in  action ;  and  finally,  a  partial  destruction  of  these 
rocks  affording  (4)  some  of  the  materials  for  a  conglomerate,  afterwards  formed. 


THE    NEW    RED    SANDSTONE    SERIES    IN    DEVON.          543 

much  denudation  has  taken  place  in  this  region  since  these  ancient 
igneous  rocks  were  ejected,  that  no  doubt  many  a  mass  showing  any 
connexion  which  once  existed  between  such  igneous  rocks  as  those  near 
Exeter  and  other  adjacent  parts  of  Devonshire  has  been  swept  away. 
As  illustrating  a  denudation  of  deposits  of  the  new  red  sandstone  series 
in  Devonshire,  so  that  a  portion  of  them  only  now  remains,  we  have 
already  noticed  the  Thurlestone  Rock  in  Bigbury  Bay  (fig.  47,  p.  79), 
a  detached  piece  of  a  small  patch  there  occurring.  Proceeding  still 
further  westward  to  Plymouth  Sound,  a  porphyritic  rock  of  the  same 
general  kind  as  those  which  are  found  near  Exeter,  is  seen  cutting 
through  the  Devonian  rocks  at  Cawsand,  and  on  the  coast  thence 
towards  Redding  Point,*  forming,  as  it  were,  a  sort  of  connecting  link 
between  the  elvans  more  eastward  and  the  igneous  rocks  above  noticed, 
and  appearing  to  constitute  the  denuded  remains  of  the  lower  part  of 
the  new  red  sandstone  series,  extending  with  an  admixture  of  igneous 
products  in  this  direction,  a  small  patch  still  remaining  of  the  old  con- 
tinuous deposit  at  Bigbury  Bay,  and  at  Slapton,  in  Start  Bay. 

With  respect  to  the  el  van  dykes  in  the  counties  of  Wicklow  and 
Wexford,  which  in  their  mode  of  occurrence  and  aspect  resemble  those 
of  Devon  and  Cornwall,  though  an  observer  does  not  appear  to  possess 
the  same  opportunities  of  inferring  their  relative  dates,  inasmuch  as 
igneous  rocks,  composed  of  similar  substances  with  these  elvans  have  not 
hitherto  been  detected  in  the  lower  part  of  the  old  red  sandstone  covering 
up  the  disturbed  rocks  in  which  the  fissures,  filled  by  them,  have  been 
effected ;  still,  as  the  old  red  sandstone  contains  portions  of  the  granite 
of  the  district,  and  is  uncut  by  the  elvans,  it  might  be  inferred  that  the 
date  of  these  elvans  was  not  only  posterior  to  the  granite,  but  also 
anterior  to  the  old  red  sandstone.  They  are  to  the  granites  of  this  part 
of  Ireland  what  the  elvans  of  Devon  and  Cornwall  are  to  the  granite  of 
that  part  of  England.  They  seem  the  result  of  cracks  from  the  cooling 
and  solidification  of  a  crust,  so  to  speak,  of  the  molten  mass  beneath, 
such  cracks  passing  through  superincumbent  rocks  adhering  to  this 
cooled  and  solidified  crust.  The  elvans  of  Wicklow  and  Wexford  can 
be  well  studied,  not  only  inland  but  on  the  coasts.  Good  examples  of 
their  mode  of  occurrence  at  the  latter  are  to  be  found  at  Seapark  Point, 
Wicklow. 

Of  the  two  classes  of  igneous  rocks  above  noticed,  the  one  chiefly 
differs  from  the  other  chemically,  in  the  presence,  in  part  of  one  class 
only,  of  a  larger  proportion  of  lime  and  magnesia,  these  sometimes 
replaced  by  oxide  of  iron.  This  difference  is  principally  confined,  as  a 

*  This  porphyritic  rock  is  a  compound  of  felspar  and  quartz,  containing  crystals  of 
mica,  and,  more  rarely,  of  felspar.  It  is  of  a  somewhat  earthy  character,  probably  from 
the  effects  of  decomposition.  The  colour  is  reddish,  as  a  mass,  mixed  occasionally  with 
spots  of  bluish  green. 


544  CHEMICAL    COMPOSITION    OF    IGNEOUS    ROCKS. 

whole,  to  that  portion  of  one  class  which  contains  the  mineral  named 
hornblende  in  which  the  silicates  of  lime  and  magnesia,  though  some- 
what variable  in  quantities,  form  marked  ingredients,  the  lime  alone 
amounting  to  from  10  to  15  per  cent,  of  that  mineral,  and  the  magnesia 
varying  from  15  to  25  per  cent.  Usually  in  these  rocks  the  protoxide 
of  iron  more  or  less  replaces  some  of  the  lime  or  magnesia  of  the  horn- 
blende. The  presence  of  hornblende,  when  in  proportions  extending 
even  to  Jth  or  Jd  of  the  mass,  renders  the  rock  in  which  it  thus  occurs 
far  more  fusible  than  the  compounds  of  felspar  and  silica,  or  of  felspar 
quartz,  and  mica,  a  difference  due  probably,  in  great  measure,  to  the 
silicate  of  lime  acting  as  a  flux. 

In  the  other  igneous  rocks,  those  which  have  been  ejected  in  a  molten 
state  (not  referring  to  those  which  have  been  noticed  under  the  head  of 
modern  volcanic  products),  and  in  the  first  place  confining  our  attention 
to  the  great  mass  of  them  composed  of  two  or  more  of  the  minerals 
named  quartz,  felspar  (whether  orthoclase  or  albite),  mica,  and  horn- 
blende, as  chief  and  prevailing  substances,  neither  in  the  compounds  of 
quartz  and  felspar,  nor  in  that  of  quartz,  mica,  and  felspar  (orthoclase 
or  albite),  is  there  the  same  amount  of  lime  as  when  hornblende  enters 
into  the  mass.  The  prevailing  mica  in  such  rocks  seems  to  be  that 
commonly  termed  potash-mica,  from  that  substance  being  a  marked 
ingredient  in  it.  In  this  mineral  the  lime  is  usually  in  very  small 
quantity,  commonly  under  1  per  cent.  In  the  lithia  and  magnesia 
micas  it  is  rare,  and,  when  found,  has  been  so  only  in  very  small  pro- 
portion. In  the  felspar,  also,  when  either  orthoclase  or  albite,  members 
of  this  family  apparently  much  distributed  amid  the  older  igneous 
rocks,  lime  has  only  been  detected  hitherto  in  small  quantities,  rarely 
in  proportions  equal  to  1  per  cent.*  In  compounds  wherein  labradorite 
is  found,  the  case  would  be  different,  since  this  is  a  felspar  in  which 
lime  usually  occurs  in  comparatively  large  proportions,  from  10  to  15 
per  cent.  Silicate  of  lime,  therefore,  would  appear  to  constitute  a 
marked  source  of  difference  between  the  igneous  rocks  with  and  with- 
out hornblende  and  labradorite.  With  respect  to  the  magnesia  in  many 
hornblendes,  this  also  would  be  a  substance  of  importance  when  com- 
pared with  compounds  of  quartz,  felspar  (either  orthoclase,  albite,  or 
labradorite),  and  mica,  unless  the  latter  were  magnesia  mica,  into  which 
this  substance  is  found  to  enter  in  proportions  varying  from  10  to  15 
per  cent.,  or  those  varieties  of  felspar,  which  have  been  referred  to 
orthoclase,  and  yet  contain  from  10  to  20  per  cent,  of  magnesia. 

*  Dr.  Abich  found  1-26  of  lime  in  the  orthoclase  in  the  trachyte  of  Pantellaria,  and 
2-06  in  the  basis  of  the  Drachenfels  trachyte.  The  orthoclase  of  the  older  igneous  rocks 
has  not  hitherto  afforded  any  proportion  of  this  kind,  though  at  the  same  time,  it  must 
be  confessed  that  the  igneous  rocks  of  that  date  have  not,  as  yet,  received  sufficient 
extended  examination  to  arrive  at  any  accurate  results  as  to  the  chemical  composition 
of  the  greater  masses. 


EFFECT    OF    SILICATE    OF    LIME    IN    IGNEOUS    ROCKS.      545 

As  the  trachytes  of  more  modern  geological  times  have  been  inferred 
to  be  some  modifications  of  granites  (p.  357),  the  observer  might  be  in- 
duced to  inquire  how  far  the  old  igneous  products  noticed  as  occurring 
like  certain  of  those  of  the  present  time  may,  in  like  manner,  have  been 
modifications  of  granitic  matter  beneath  them  ;  how  far,  in  fact,  certain 
of  the  molten  felspathic  rocks  of  the  British  Islands  associated  with  the 
older  fossiliferous  deposits  may  have  been  the  trachytes  of  those  times, 
and  have  been  derived  from  granitic  matter  below  them,  such  granitic 
matter  afterwards  upheaving  these  earlier  modifications  of  portions  of 
it,  when  geological  time  advanced  and  with  it  conditions  for  such  a 
movement.  With  the  hornblendic  compounds  there  would  be  the  same 
difficulty  as  with  the  modern  dolerites  and  lavas  of  that  class,  so  far  as 
the  silicate  of  lime  was  concerned,  though  in  both  cases,  supposing  sili- 
cate of  lime  to  form  a  marked  part  of  a  fused  mass,  that  it  should  be 
ready,  as  a  substance  fluxing  others,  to  be  thrown  upwards,  might  be 
anticipated  from  the  conduct  in  our  furnaces  of  the  slags  into  which 
silicate  of  lime  largely  enters. 

Respecting  the  compound  of  the  matter  of  felspar  and  an  additional 
quantity  of  silica  beyond  that  required  for  the  silicates  in  the  minerals 
of  that  family,  good  opportunities  are  often  afforded  for  studying  the 
variable  aspect  it  assumes  as  the  conditions  for  cooling  may  have  been 
favourable  or  otherwise  to  the  crystallization  of  the  felspar.  When 
cooled  so  that  the  crystallization  is  not  apparent,  the  compound  has  a 
homogeneous  aspect,  and  is  commonly  known  as  compact  felspar  ;  when 
confusedly  crystallized  and  silica  is  well  separated,  as  quartz,  from  the 
other  ingredients,  it  forms  one  of  those  binary  granitic  mixtures  some- 
times termed  granitello.  Occasionally  crystals  of  felspar  being  developed 
while  the  remainder  of  the  rock  retains  its  homogeneous  character,  a 
variety  of  hornstone  porphyry  is  produced.*  The  variable  aspect  of 
the  less  crystalline  varieties  may  be  seen  in  numerous  situations,  the 
complete  crystallization  not  so  frequently,  f  In  countries  in  which 
granitic  matter  has  upheaved  the  prior  superficial  accumulations  of  this 
class,  the  resemblance  of  some  kinds  of  products  is  sometimes  so  con- 
siderable as  occasionally  to  lead  to  much  ambiguity  respecting  their 
relative  dates. 

Keeping  for  more  easy  illustration  to  the  districts  mentioned,  though 
the  observer  might  be  exposed  to  some  difficulties  in  determining  the 
relative  age  of  some  of  the  igneous  products,  when  their  composition  is 

*  Of  a  columnar  mass  of  the  latter,  the  columns  in  part  somewhat  bent,  a  good  exam- 
ple may  be  seen  among  the  igneous  products  associated  with  the  Silurian  series  west  of 
.Knock  Mahon,  on  the  coast  of  Waterford. 

f  A  good  example  of  a  binary  compound  of  quartz  and  felspar  may  be  found  among 
the  igneous  rocks  amid  the  Cambrian  series,  close  to  the  town  of  Caernarvon,  on  the 
northward;  part  of  a  portion  of  molten  matter,  in  which  the  more  common  homogeneous 
mode  of  occurrence  of  the  silicates  of  the  felspar  combined  with  the  quartz,  prevails. 

35 


546  GRANITES    IN    SOUTHWESTERN    ENGLAND 

alone  regarded,  he  would  experience  none  when  he  compares,  the  manner 
in  which  those  contemporaneously  associated  amid  the  ordinary  sedi- 
mentary deposits  of  their  respective  times  occur  with  that  in  which  the 
granites  of  the  same  districts  are  found.  Whether  he  studies  the  granite 
of  Southwestern  England,  or  that  of  prior  elevation  in  Southeastern  Ire- 
land, he  finds  the  same  general  mode  of  occurrence,  one  very  different 
from  that  of  the  igneous  products  associated  with  the  Devonian  rocks  in 
one  district,  and  the  Silurian  rocks  in  the  other.  There  is  no  interstra- 
tification  and  contemporaneous  intermingling  of  parts,  but  on  the  con- 
trary evident  protrusion  in  mass,  and  a  subsequent  filling  of  fissures 
traversing  the  beds  of  pre-existing  deposits.  In  both  districts,  the 
granitic  protrusions  appear  the  accompaniments  of  great  contortions, 
foldings,  and  even  dislocations  of  prior  accumulations  of  all  kinds,  as  if 
amid  this  squeezing  and  new  adjustment  of  such  accumulations,  molten 
matter  beneath  rose  upwards  (there  being  sufficient  pressure  upon  it), 
and  occupied  areas  where  the  resistance  of  any  prior  superficial  covering 
was  insufficient  to  resist  this  intrusion. 

Upon  examining  the  boundaries  of  the  granitic  masses  observable  on 
the  surface,  the  amount  of  fractures  effected  around  them,  and  in  the 
various  rocks  adjoining,  is  found  to  be  considerable.  Indeed,  where 
opportunities  are  afforded  either  by  natural  exposures  or  artificial  sec- 
tions, they  are  seen  to  be  common.  Thus  independently  of  any  great 
movements  or  dislocations  of  prior-formed  rocks  of  all  kinds,  the  margins 
of  the  granitic  intrusions  are  themselves  marked  by  abundant  fractures 
on  a  minor  scale,  as  if  that  intrusion  had  itself  in  some  measure  been 
connected  with  their  production.  As  to  the  extent  of  the  fractures  into 
the  adjoining  and  prior-formed  rocks,  it  may  be  considered  as  somewhat 
insignificant  when  regarded  with  reference  to  their  mass  and  that  of  the 
granites.  In  the  range  of  the  Wicklow  and  Wexford  granite,  not  only 
are  these  cracks  found  abundantly,  but  evidence  is  also  afforded  of  huge 
detached  masses  of  detrital  rocks  being  apparently  embedded  in  the 
external  parts  of  the  same  granite.  This  can  be  well  studied  in  Glen- 
malure,  where  such  great  masses  seem  as  if  partly  contained  in  the 
granite,  having  floated  on  that  rock  when  in  a  molten  state,  like  great 
icebergs  in  the  sea,  and  like  them  also  in  part  submerged.  No  doubt 
this  may  be  only  appearance,  as  the  parts  connecting  these  masses  may 
have  been  removed  by  denudation.  At  the  same  time  when  sections 
are  made  of  the  whole  on  a  scale  equal  for  height  and  distance,  and  all 
the  foldings  of  the  older  rocks  are  considered,  a  great  breaking  up  of 
the  latter  seems  needed  to  account  for  the  mode  of  occurrence  of  all  the 
rocks.  No  doubt  that  much  of  both  the  older  rocks  and  the  granite  of 
Southeastern  Ireland  has  been  removed  by  denudation  effected  during  a 
long  lapse  of  geological  time,  often  by  abrasion  from  heavy  breaker 


AND    SOUTHEASTERN    IRELAND.  547 

action,  while  rising  above  or  descending  beneath  the  ocean  level;*  yet 
there  still  appears  to  have  been  disruption  of  the  prior-formed  Cambrian 
and  Silurian  rocks.  The  curve,  which  agrees  with  the  upraised  masses 
of  the  prior-formed  rocks,  and  fortunately  many  of  these  are  still  pre- 
served, showing  the  probable  extent  to  which  they  have  been  so  raised 
to  a  height  above  those  crumpled  and  folded  on  either  side,  is  of  the 
kind  represented  beneath  (fig.  218).  This  may  not  be  considerable, 
yet  it  seems  difficult  to  obtain  the  effects  produced  without  much  sepa- 
ration as  well  as  disruption  of  parts  of  the  older  rocks.  In  this  section, 
upon  the  same  scale  for  heights  and  distances,  a,  a,  is  the  intruded 
granite  <?,  c,  the  contorted  and  older  rocks  on«either  side,  altered  near 
the  granite,  and  5,  5,  6,  portions  of  them  uplifted,  a  larger  mass  form- 
ing the  summit  of  (L)  Lugnaquilla. 


Upon  examining  the  contents  of  the  cracks  in  the  prior-formed  rocks 
surrounding  the  granitic  masses,  they  are  found  filled  with  the  granite 
in  such  a  manner  as  to  show  the  comparative  liquidity  of  that  substance 
when  the  cracks  were  made  and  filled,  for  even  fine  threads  may  be 
occasionally  seen,  branching  out  of  the  main  cracks,  .with  granitic  matter 
in  them.  Though,  as  might  be  anticipated,  the  crystallization  of  this 
matter  is  modified  in  the  finer  fissures,  from  differences  of  the  rate  of 
cooling  alone,  the  contents  of  the  granitic  veins  generally  would  point 
to  long-sustained  heat  among  the  intruded  rocks,  the  whole  having  pro- 
bably required  a  considerable  lapse  of  time  for  solidification.  The  fol- 

*  It  is  not  a  little  interesting,  in  this  part  of  Ireland,  to  study  the  denudation  with 
reference  to  the  exposure  of  both  the  granite  and  altered  sedimentary  rocks  (for  they 
and  certain  associated  igneous  products  of  that  date  are  much  modified  and  altered,  as 
•will  be  hereafter  noticed)  to  the  same  degrading  forces.  The  granite  is  of  a  decom- 
posing kind,  while  the  altered  rocks  are,  for  the  most  part,  tough ;  hence  the  exposure 
of  both  to  the  same  abrading  force  has  caused  the  softer  substance  to  be  worn  away 
more  than  the  harder.  In  consequence,  the  tough  altered  rocks  have  been  the  means 
of  preserving  much  of  the  granite  beneath  them  from  removal.  Lugnaquilla,  the  highest 
of  the  range,  is  capped  by  these  altered  rocks,  now  chiefly  mica  slates ;  and  many  other 
examples  of  heights  and  flanks  of  mountains  thus  preserved  may  be  seen.  When  this 
denudation  is  also  studied  with  reference  to  an  Atlantic  exposure,  the  interest  is  not 
lessened,  inasmuch  as  the  western  flanks  of  the  mountains  point  to  more  abrasion  on 
that  side  than  on  the  east,  just  as  would  happen  from  the  destructive  influence  of 
Atlantic  breakers,  rolling  in,  as  now,  from  the  westward.  It  requires  very  little  imagi- 
nation, when  standing  upon  some  parts  of  this  range,  to  fill  up  the  lower  ground  with 
sea,  so  that  the  Atlantic  may  break  upon  the  cliffs  beneath,  facing  the  west.  In  the 
range  of  mountains  near  that  named  Blackstairs,  the  cliff  character  of  the  western 
flanks  is  very  marked. 


548 


GRANITE    VEINS. 


lowing  sketch  (fig.  219)  of  some  granitic  veins  at  Wicca  Cove,  or  Pool, 
near  Zennor,  Cornwall,  may  serve  to  illustrate  the  mode  of  occurrence 


Fig.  219. 


•    V,i  „       -        -; 


of  many  of  them,  and  the  annexed  section  (fig.  220)  will  show  their  con- 
nexion with  an  adjacent  mass  of  granite  behind  the  rocks  exposed  in 


Fig.  220. 


the  sketch  (219),  #,  a,  being  the  granitic  veins,  5,  5,  altered  slate,  and 
c,  the  main  mass  of  granite. 

The  west  coast  of  Cornwall,  exposing  the  junction  of  the  granite  of 
that  district  with  the  sedimentary  deposits  and  the  igneous  rocks  asso- 
ciated with  them,  offers  many  other  illustrative  instances,  as  at  Pendeen 
Cove,  Cape  Cornwall,  Tetterdu  Point,  Mousehole,  and  other  places. 
They  are  also  as  well  and  easily  seen  at  St.  Michael's  Mount.  The 
annexed  plan  (fig.  221,  p.  549),  exhibits  a  somewhat  complicated  frac- 
ture, the  shaded  parts  (a,  a,  a)  being  altered  slates,  and  the  dotted 
portion  granite,  the  mass  of  the  latter  occurring  on  the  side  6,  b. 
Looking  at  these  veins  as  a  whole,  it  would  often  appear  as  if  the  prior- 
formed  rocks  had  not  yielded  very  slowly  to  the  force  applied,  but  in  a 
comparatively  sudden  manner,  the  granitic  matter  being  driven  into 
the  cracks  formed  by  heavy  pressure  so  as  to  fill  up  the  fine  fissures.* 
There  often  also  seems  evidence  of  cracks  having  been  formed  after 
only  a  mere  comparative  film  of  the  main  mass  of  granite  had  been 
consolidated,  granitic  veins  similar  to  those  amid  the  prior-formed  rocks, 
and  clearly  merging  into  the  main  mass  of  granite  at  its  junction  with 

*  Portions  of  these  rocks  are  sometimes  found  completely  isolated  in  the  matter  of 
the  granitic  vein. 


GRANITE    VEINS. 


549 


those  rocks,  being  found  alike  to  traverse  a  certain  amount  of  the 
external  parts  of  the  granite  and  these  other  rocks.*     In  general  such 


Fig.  221. 
b 


veins  are  easily  to  be  distinguished  from  the  elvan  dykes  (the  result 
apparently  of  subsequent  action)  by  their  tortuous  courses,  and  by 
their  general  resemblance  to  those  first  formed  amid  the  older  rocks  at 
their  junction  with  the  granite,  f 

The  chemical  composition  of  granitic  masses  will  necessarily  engage 
the  attention  of  the  observer,  more  especially  when  he  considers  that 
so  much  of  the  detrital  deposits  of  all  ages  have  been  derived  from 
granitic  matter ;  indeed,  the  volume  thus  distributed  as  detrital  accu- 
mulations must  be. enormous.  As  has  been  seen,  the  elementary  sub- 
stances forming  the  chief  part  of  the  volume  of  this  rock  do. not  appear 
to  be  numerous.  For  certain  of  the  modifications  of  mineral  structure 
it  may  be  again  desirable  to  refer  to  the  portions  of  the  British  Islands 
already  noticed,  since  the  relative  ages  of  the  igneous  rocks  in  them 
are  so  well  shown.  Fundamentally,  the  constituents  of  the  granites  in 

*  Instances  of  this  kind  are  not  uncommon,  both  in  Southeastern  Ireland  and  South- 
western England.  They  are  well  exhibited  at  Killiney  Hill,  near  Dublin,  and  the  large 
masses  of  granite  brought  from  thence  for  the  harbour  at  Kingstown  often  show  them. 
They  are  also  to  be  well  seen  in  the  granite  of  the  Scilly  Islands,  and  the  exposed 
granites  of  the  Land's  End  coast,  as  at  Tol-Pedn-Penwith  and  Lamorna  Cove. 

•j-  In  examining  granitic  countries  it  is  very  needful  not  to  confound  the  filling  of 
joints  in  granite  with  quartz,  felspar,  and  mica,  in  the  manner  of  fissures,  including 
mineral  veins,  with  the  granitic  veins  noticed  in  the  text ;  such  modes  of  filling  being 
very  deceptive,  unless  due  care  be  employed.  They  can,  however,  be  usually  well  dis- 
tinguished by  the  manner  in  which  the  minerals  occur  in  them,  showing  a  deposit  from 
solutions  against  the  walls  of  the  granitic  fissures,  the  crystals  pointing  inwards,  and 
arranged  in  the  manner  of  many  common  and  mineral  veins. 


550  SCHORLACEOUS    GRANITES 

Southwestern  England  and  Southeastern  Ireland  seem  little  different. 
The  chief  variations  may  probably  consist  in  the  greater  admixture  of 
schorl  with  the  other  constituent  minerals  in  the  former  than  in  the 
latter ;  indeed,  generally  speaking,  it  is  rare  in  the  granites  of  Southern 
Ireland.  Such  differences  can  readily  be  considered  as  merely  local, 
the  same  molten  matter  beneath  having  supplied  the  portions  upraised 
at  different  geological  times.  Be  this  as  it  may,  the  presence  of  a 
mineral  in  any  abundance  which  contains  boracic  acid  as  an  essential 
ingredient,*  is  one  of  importance,  more  particularly  when  we  refer  to 
the  researches  of  M.  Ebelmen,  he.  having  shown  that  by  employing 
that  acid  as  a  solvent,  at  an  elevated  temperature,  minerals  may  be 
produced  by  the  evaporation  of  this  solvent,  some  of  them  gems,  such 
as  rubies,  which  are  usually  termed  insoluble,  and  infusible  in  our  fur- 
naces,— a  result  having  a  considerable  bearing  upon  the  production  of 
many  igneous  compounds,  f 

Cornwall  and  Devon  present  frequent  and  good  opportunities  for  the 
study  of  schorlaceous  granites  and  rocks  composed  of  schorl  and  quartz 
(usually  termed  schorl  rock)  in  connexion  with  the  granites  of  that 
district.  As  might  be  expected  from  the  comparatively  easy  removal 
of  boracic  acid  by  considerable  heat,  the  chiefly  schorlaceous  compounds 
are  found  at  the  extreme  parts  of  the  granitic  masses.  They  vary  from 
a  simple  binary  compound  of  schorl  and  quartz  to  mixtures  of  schorl, 
felspar,  quartz,  and  mica ;  the  latter  is,  however,  not  an  usual  ingredient 
in  the  granitic  rock  when  schorl  is  present  in  any  abundance.  Complete 
passages  may  frequently  be  traced  between  the  ordinary  compound  of 
quartz,  felspar,  and  mica,  by  the  gradual  loss  of  the  felspar  and  mica, 
into  the  simple  mixture  of  quartz  and  schorl,  the  mica  being  commonly 
the  first  to  disappear.  The  schorl  sometimes  presents  itself  in  radiating 
bunches  of  crystals,  especially  amid  the  quartz. J  Here  and  there  dif- 

*  The  analyses  of  M.  Hermann  give  about  10  per  cent,  of  boracic  acid  in  schorl,  39 
of  silica,  81  of  alumina,  a  variable  quantity  of  protoxide  of  iron  (4  to  12  per  cent.),  2 
to  9  of  magnesia,  with  a  few  other  subordinate,  and,  probably,  accidental  substances, 
such  as  lithia,  soda,  and  potash. 

f  The  researches  of  M.  Ebelmen  on  this  subject  are  marked  by  the  true  spirit  of 
philosophic  investigation.  He  sought  for  a  substance  which  at  a  high  temperature  acts 
like  water,  as  regards  others  dissolved  in  it.  As  by  the  evaporation  of  water  certain 
crystalline  bodies  might  be  formed,  so  he  inferred,  that  by  employing  those  which  could 
be  volatilised  at  high  temperatures,  yet  at  a  given  heat,  while  in  fusion,  be  capable  of 
dissolving  the  greater  part  of  metallic  oxides,  certain  calculated  proportions  of  some 
oxides  would  crystallize,  when  the  dissolving  body  was  evaporated  in  open  vessels  at  a 
great  heat.  Acting  upon  this  view,  and  selecting  boracic  acid  as  the  solvent,  he  was 
completely  successful,  producing  rubies,  sapphires,  spinels,  chrysoberyl,  chrysolite, 
chromate  of  iron,  and  others.  Crystals  of  emerald  were  formed  from  pounded  emeralds, 
when  fused  with  boracic  acid  and  a  little  oxide  of  chromium.  The  crystals  of  chryso- 
beryl were  sufficiently  large  to  have  their  optical  properties  tried,  and  these  were  found 
to  be  identical  with  those  of  the  natural  mineral. 

%  Good  examples  of  nests  of  schorl  in  quartz,  the  crystals  radiating,  may  be  seen  in 


OF    CORNWALL    AND    DEVON. 


551 


ferent  arrangements  of  schorl  and  of  the  other  minerals  present  them- 
selves.    The  following  (fig.  222)  is  a  somewhat  marked  instance  of  the 


Fig.  222. 


-i   2  feet. 


adjustment  of  varied  compounds  round  a  kind  of  central  nucleus.  It 
occurs  in  the  Dartmoor  granite,  towards  Camwood,  a  is  a  cavity 
not  quite  filled  by  long  crystals  of  schorl,  crossing  in  many  oblique 
directions,  but  with  a  general  tendency  towards  the  centre ;  b  is  an 
envelope  of  quartz  and  schorl,  the  former  predominating;  c,  another 
covering  of  the  same  minerals,  the  schorl  being  more  abundant ;  and  d, 
a  light  flesh-coloured  granite,  the  felspar  predominating. 

Large  crystals  of  felspar  are  not  uncommon  in  the  granites  of  Corn- 
wall and  Devon,  rendering  the  rock  a  porphyritic  granite.  That  of 
Dartmoor  is  not  unfrequently  of  this  character,  as  is  also  the  granite  of 
the  Brown  Willy  district,  and  the  same  variety  may  be  seen  in  many 

the  Dartmoor  granite,  or  above  Bowdley,  near  Ashburton.  Schorlaceous  granite  and 
schorl  rock  can  be  well  seen  in  the  same  granitic  district  at  Holne  Lee,  and  on  the 
south  of  the  moor,  as  also  near  Tavistock.  The  granite  of  the  Brown  Willy  mass  is 
not  so  schorlaceous,  though  schorl  is  found,  especially  towards  the  south.  Near  St. 
Cleer,  there  are  compounds  of  schorl,  felspar,  quartz,  and  mica,  similar  to  some  found 
on  Dartmoor.  The  St.  Austell  granite  is  much  more  schorlaceous,  veins  of  that  mineral 
being  common  in  it.  The  decomposed  granite  of  that  district,  furnishing  so  much  clay 
to  the  porcelain  works  of  England,  is  extremely  schorlaceous.  Singular  stripes  of 
schorl  rock  are  found  at  its  outskirts,  as  between  Watch  Hill  and  Long  Lane;  on 
the  north  and  south  of  Burthy  Row,  near  St.  Enoder,  and  at  the  long-celebrated 
Roche  Rock.  Near  Meladore  there  is  an  interesting  mixture  of  schorl  and  quartz, 
containing  large  crystals  of  felspar,  some  of  these  decomposed,  and  crystallized  schorl 
introduced  into  the  cavities  left  by  them.  At  Calliquoiter  Rock  there  are  variable 
mixtures  of  schorl,  quartz,  felspar,  and  mica,  the  outside  portions  formed  of  the  two 
former.  The  granite  of  St.  Dennis  Hill  is  in  like  manner  a  compound  of  these  four 
minerals.  The  Cam  Menelez  granite  is  not  so  schorlaceous,  though  schorl  is  found, 
and  more  especially  at  the  confines  of  the  mass.  The  Land's  End  granite  is  schorla- 
ceous to  a  considerable  extent.  A  variety  of  schorl  rock,  composed  of  a  base  of  schorl 
and  quartz,  with  large  crystals  of  felspar,  is  found  close  to  Trevalga,  near  St.  Ives. 
Here  also,  in  some  parts,  the  crystals  of  felspar  have  been  decomposed  and  removed, 
and  the  cavities  more  or  less  filled  with  crystals  of  schorl. 


552         SLIGHT    COVERING    OF    GRANITE    BY    THE    OLDER 

other  localities.*  The  granites  of  Southeastern  Ireland  are  also  occa- 
sionally porphyritic,  from  the  distribution  of  felspar  crystals  amid  the 
ordinary  triple  compound  of  quartz,  felspar,  and  mica. 

Throughout  these  districts,  though  the  granite  may  enter  the  frac- 
tures of  the  adjacent  and  prior-formed  rocks,  there  is  no  trace  of  an 
overflow  of  the  igneous  matter  in  a  molten  state,  so  that  the  observer  is 
led  to  infer  that,  when  the  intrusion  was  effected,  the  igneous  rock  was 
not  as  now  exposed  to  the  atmosphere,  or  beneath  waters  in  such  a 
manner  that  it  could  pass  beyond  the  broken  portions  of  the  deposits 
now  forming  its  superficial  boundaries,  and  flow  over  them  in  the 
manner  of  lava  discharged  from  a  volcanic  vent.  If  any  portion  of 
these  granites  did  so  pass  over  prior-formed,  consolidated,  and  disrupted 
rocks,  all  traces  of  such  overflows  have  been  removed  by  denudation. 
Molten  matter  in  a  sufficiently  fluid  state  to  enter  the  smaller  ramifica- 
tions of  the  cracks  around  the  masses  of  granite,  would  readily,  if 
elevated  sufficiently  high,  overflow  the  disrupted  and  contorted  deposits 
amid  which  it  was  protruded.  The  covering  of  the  granite  of  South- 
eastern Ireland  is  comparatively  slight :  the  whole  district  adjoining  the 
main  masses  of  that  rock  is  so  pierced  and  cut  by  it,  as  to  show  upon 
the  surfaces  exposed,  that  the  whole  of  the  prior-formed  accumulations 
has  been  upborne,  so  that  upon  the  denudation  of  the  various  inequali- 
ties, the  granite  was  unequally  exposed,  and  this  irregularly,  from  the 
varied  amount  of  denudation  in  different  localities,  and  the  uneven  sur- 
face of  the  granite,  f  The  same  may  be  said  with  reference  to  South- 
western England  between  Dartmoor  and  the  Scilly  Islands.  An  observer 
thus  not  finding  a  mode  of  occurrence  showing  overflows  of  the  molten 
matter,  while  he  sees  an  abundance  of  exposed  surface  of  granite,  often 
rising  above  the  relative  levels  of  the  remains  of  the  prior-formed  rocks 
around,  and  ascertaining  that  these  remaining  parts  are  in  a  great 
measure  somewhat  shallow  coverings  of  a  mass  of  granite  beneath,  far 
more  extensive  than  mere  surface  exposure  shows,  may  be  induced  to 
seek  for  an  explanation  of  the  facts  before  him,  either  in  a  very  consi- 
derable denudation  of  the  matter  which  once  covered  the  whole  of  such 
districts,  or  in  some  combination  of  denudation,  with  a  continued  ele- 
vating force  acting  upon  the  whole  after  the  granite  had  first  broken 

*  As  chiefly  differing  from  the  ordinary  granite,  that  of  St.  Austell  is  probably  the 
most  marked,  a  steatitic  mineral  therein  replacing  mica  to  a  great  extent,  particularly 
in  the  portions  which  are  found  in  a  decomposed  state.  Much  pinite  (a  silicate  of  alu- 
mina and  magnesia,  the  latter  partly  replaced  by  protoxide  of  iron)  is  mingled  with  a 
part  of  the  granite  near  the  Land's  End. 

f  The  granite  of  the  Island  of  Anglesea,  probably  of  about  the  same  date,  is  also 
interesting,  as  showing  how  readily  it  might  be  concealed  from  superficial  exposure,  by 
a  somewhat  more  thick  envelope  of  the  Silurian  rocks  through  which  it  has  risen.  In- 
deed some  of  the  portions  exposed  are  merely  minor  inequalities  cut  into  by  denuda- 
tion. 


WEXFORD,    AND    CORNWALL.       553 

into  the  consolidated  and  prior-formed  accumulations.  As  we  see  that 
huge  masses  of  igneous,  and  for  the  most  part  previously-molten  matter, 
may  be  reheated  in  modern  volcanoes,  we  can  readily  conceive  a  mass 
of  "granite,  after  a  certain  amount  of  cooling,  again  heated,  so  as  to 
yield  to  a  new  movement  of  elevation,  produced  by  a  force  acting  from 
beneath  upwards,  and  which  not  being  opposed  by  matter  easily  frac- 
tured, lifted  the  tenacious  rock  to  a  certain  extent,  either  irregularly  in 
part  or  on  some  larger  scale  in  a  more  general  form,  however  uneven 
the  surface  might  be ;  the  deposits  effected  anterior  to  the  first  intrusion 
of  the  granite  being,  so  to  speak,  firmly  dove-tailed  into  the  surface  of 
the  latter,  and  following  its  movement. 

There  is  yet  another  igneous  product  in  a  part  of  this  limited  area  to 
which  a  relative  geological  date  may  be  assigned.  This  product  is  ser- 
pentine, which  is  chiefly  found  in  considerable  abundance  in  the  Lizard 
district,  in  Cornwall.  It  is  seen  among  the  Devonian  rocks  in  a  manner 
reminding  us  of  the  mode  of  occurrence  of  some  of  the  contemporaneous 
compounds  of  felspar  and  hornblende,  which  have  been  associated,  in  a 
molten  state,  with  the  sedimentary  deposits  of  that  date.  That  it  was 
vomited  forth  anterior  to  the  granite  of  the  district,  would  appear  from 
its  being  traversed  by  veins  of  that  rock,  in  the  same  manner  that  other 
rocks  of  the  district  are  traversed  by  them.  Even  allowing  that  these 
veins  may  be  of  no  greater  antiquity  than  the  elvans  of  the  same  county, 
this  would  limit  the  fissures  for  their  introduction  to  about  the  age  of 
the  lower  new  red  sandstone  deposits  of  that  land.  At  Clicker  Tor, 
south  of  Liskeard,  serpentine  is  found  amid  Devonian  slates,  and  near 
Veryan,  diallage  rock  (diallage  and  felspar)  is  seen  associated  with 
similar  serpentine,  and  in  a  manner  pointing  to  an  ejection  of  these 
rocks  in  the  same  way  as  certain  greenstones  amid  accumulations  of  the 
igneous  products  of  the  district.  The  position  of  the  Lizard  serpentine, 
and  the  diallage  rock  found  with  it,  seems  much  the  same  with  these 
minor  portions  of  serpentine  more  eastward.  It  occupies  a  somewhat 
comparatively  large  area,  reposing  upon  hornblende,  slates,  and  rock, 
which  appear  little  else  than  the  ordinary  volcanic  ash-beds  above-men- 
tioned as  intermingled  contemporaneously  with  the  ordinary  detrital 
deposits  of  the  time  and  locality  (p.  531).*  There  is  often  an  apparent 

*  It  is  not  altogether  clear  whether  this  alteration  may  not  be  due  to  the  influence  of 
some  granitic  mass  beneath,  with  which  the  granite  veins,  traversing  the  serpentine, 
may  be  connected,  such  granitic  mass  closer  to  the  latter  than  might  be  inferred  from 
the  natural  sections,  inasmuch  as  beneath  the  hornblende  rocks  and  slates,  there  are 
talco-micaceous  slates,  to  a  certain  extent  interstratified  with  the  latter,  much  remind- 
ing the  observer  of  the  various  alterations  effected  in  the  proximity  of  the  granites  of 
the  district.  A  glance  at  the  Geological  Survey  Maps  (Sheets  23,  24,  25,  30,  31,  32), 
or  at  the  Index  Map  in  the  Report  on  the  Geology  of  Cornwall,  will  show  that  there 
may  readily  be  a  line  of  granite  concealed  beneath  the  sea,  and  ranging  in  a  somewhat 
general  manner  with  the  granite  from  Dartmoor  to  the  Land's  End,  which  has  caused 


554      SERPENTINE    AND    DIALLAGE    ROCKS    OP    CORNWALL. 

passage  from  the  diallage  rocks  into  the  serpentine,*  while  also  there 
seems  an  intrusion  of  serpentine  amid  the  former,  as  between  Dranna 
Point  and  Porthalla. 

Though  there  may  be  some  intermixtures  of  the  serpentine  and  the 
diallage  rock  rendering  their  relative  antiquity  a  little  doubtful  in  places, 
as  a  whole,  the  latter  would  appear  to  have  been  thrown  up  after  the 
former.  At  the  junction  of  the  diallage  rock  of  Crousa  Downs  and  St. 
Keverne,  with  the  serpentine  at  Coverack  Cove,  veins  of  the  former  cut 
through  the  latter,  f  On  observing,  also,  the  connexion  of  these  two 
rocks,  in  a  range  extending  from  Careglooz  through  Gwinter  towards 
Goonhilly  Downs,  the  diallage  rock  seems  to  have  cut  through  and  dis- 
turbed the  serpentine.  Near  Landewednack,  also,  the  diallage  rock 
appears  to  rise  through  the  hornblende  slates  and  cut  into  the  serpen- 
tine. This  diallage  rock,  as  between  Coverack  Cove  and  St.  Keverne, 
passes  occasionally  into  a  compound,  in  which  hornblende  also  enters  ; 
so  that  while  in  some  places  it  appears  a  mixture  of  diallage  and  felspar, 
in  others  it  more  resembles  one  of  hornblende  and  felspar.  Regarding 
a  mixed  mass  of  matter  in  which  the  proportions  of  the  chief  substances, 
silica,  magnesia,  lime,  alumina,  and  oxide  of  iron,  may  be  unequally 
disseminated,  such  changes  may  be  readily  appreciated,  the  conditions 
for  the  adjustment  of  the  substances  in  crystalline  forms  being  variable.  J 

With  respect  to  the  serpentinous  rocks  in  Anglesea  and  Caernarvon- 
shire, the  relative  and  approximative  dates  are  not  so  certain.  At  Porth- 

the  alteration  of  the  rocks  into  the  mica  slate  and  gneiss  of  the  Start  Point,  and  Bull 
Head,  Devon,  and  produced  the  gneiss  on  which  the  Eddystone  Lighthouse,  in  front  of 
Plymouth  Sound,  is  erected,  and  the  talco-micaceous  slates  of  the  Lizard  Point.  The 
connexion  of  the  hornblende  slates  with  the  latter  may  be  conveniently  seen  near  Pol- 
treath,  on  the  west  of  the  Lizard  Town. 

*  As  we  have  elsewhere  remarked  (Report  on  the  Geology  of  Cornwall,  &c.  p.  30), 
"whatever  the  cause  of  this  apparent  passage  may  have  been,  it  is  very  readily  seen 
at  Mullion  Cove,  at  Pradanack  Cove,  at  the  coast  west  of  the  Lizard  Town,  and  at 
several  places  on  the  east  coast  between  Landewednack  and  Kennick  Cove,  more 
particularly  under  the  Balk,  near  Landewednack,  and  at  the  remarkable  cavern 
and  open  cavity  named  the  Frying  Pan,  near  Cadgwith.  It  will  generally  be  found 
that,  at  this  apparent  passage  of  one  rock  into  the  other,  there  is  calcareous  matter, 
and  a  tendency  to  a  more  red  colour  in  the  serpentine  near  its  base  than  elsewhere." 

•f-  The  veins  of  diallage  rock  in  the  serpentine  between  the  rivulet  in  Coverack  Cove 
and  the  pier  at  the  village,  will  repay  examination.  Some  of  them  are  large-grained, 
the  crystals  of  diallage  of  considerable  size,  reminding  the  geologist  of  the  larger-grained 
gabbro  of  Italy. 

J  Looking  at  the  principal  ingredients  in  hornblende  and  diallage,  as  given  by  a 
mean  of  three  analyses  of  the  former  by  Goschen,  Bonsdorff,  and  Struve,  and  by  a 
mean  also  of  three  analyses  of  the  latter  by  Kohler,  Regnault,  and  Von  Kobell,  the  dif- 
ferences between  these  minerals  would  be  as  beneath: — 

Hornblende.  Diallage. 

Silica 40-86  62-00 

Magnesia  ....     13-64  15-91 

Lime     i     .     .     .     .     12-36  19-59 

Oxide  of  Iron      .     .     14-64  7-47 

Alumina    .  15-96  3-18 


SEKPENTINE    OF    ANGLESEA.  555 

dinlleyn,  a  rock,  which  has  been  commonly  termed  serpentine  from  its 
appearance,  though  not  altogether  agreeing  with  the  usual  varieties  of 
that  rock,  has  apparently  traversed  the  chloritic  and  micaceous  slates  of 
that  part  of  Caernarvonshire ;  but  being  only  covered  by  a  raised  sea- 
bottom  of  comparatively  recent  geological  date  (p.  445),  the  time  when 
this  may  have  been  effected  remains  doubtful,  though  an  impression  of 
its  intrusion  being  even  referable  to  the  date  of  some  of  the  older  rocks 
of  the  district  might  exist.  In  its  greenish  and  red  colours,  it  much 
resembles  the  ordinary  serpentines.  The  component  parts  are  much 
gathered  together  in  some  situations  in  irregular  nodules,  between 
which  much  red  jasper  is  frequently  found,*  as  in  the  subjoined  sketch 
(fig.  223)  taken  towards  the  northwestern  point  of  the  roadstead,  where 

Fig.  223. 


the  dark  portions  represent  the  jasper,  or  other  siliceous  matter  between 
the  nodules,  which  are  sometimes  of  large  size.  Of  the  serpentine  in 
Anglesea,  the  aspect  of  which  presents  much  the  usual  characters  of 
that  rock,  though  some  of  it  may  have  been  in  a  molten  state  when 
included  among  the  beds  where  it  is  now  found,  other  portions  much 
remind  the  geologist  of  some  mingling  of  calcareous  and  serpentinous 
matter,  altered  from  the  state  of  the  original  accumulation  of  their 
component  parts.  This  may  be  the  case  with  part  of  the  serpentine  at 
Cerig-moelion,  as  also  at  Rhoscolyn.  There  are  also  some  appearances 
near  Amlwch,  amid  the  Silurian  rocks  there  found,  as  if  certain  of  the 
contemporaneous  beds  had  taken  a  serpentine  character  from  the  con- 
ditions for  the  adjustment  of  their  constituent  ingredients,  to  which  the 
whole  of  the  associated  beds  had  been  exposed,  having  been  favourable 
to  such  a  modification  of  parts.  As  to  an  accumulation  of  serpentinous 
matter  in  the  manner  of  the  felspathic  and  hornblendic  rocks  so  com- 
mon in  North  Wales,  contemporaneously  with  the  Silurian  deposits, 
there  would  not  appear  any  particular  difficulty,  since,  even  without 

*"  Judging  from  the  frequency  of  jasper  fragments  of  precisely  the  same  kind  in  the 
superficial  drift  of  the  district,  fragments  of  even  several  hundred-weight  being  found 
(Aberdaron),  there  would  appear  to  have  been  much  destruction  of  rocks  similar  to 
that  of  Porthdinlleyn,  perhaps  of  a  softer  kind,  the  jasper,  from  its  hardness,  being 
considerably  preserved  and  included  amid  the  other  hard  detritus  of  the  late  geolo- 
gical period,  when  greater  cold  is  inferred  to  have  prevailed  in  the  area  of  the  British 
Islands. 


556  CHEMICAL    COMPOSITION    OF    SERPENTINE. 

supposing  an  outburst  of  serpentinous  matter  in  the  manner  of  volcanic 
ashes  and  cinders  (though  why  this  may  not  also  have  happened  does 
seem  clear),  the  wearing  away  of  serpentine  rocks,  formed  at  an  earlier 
date,  may  readily  have  supplied  the  detrital  materials  for  deposits, 
which  when  consolidated  presented  the  character  above  mentioned.  At 
all  events  this  appears  a  mode  of  occurrence  which  it  would  be  desirable 
that  the  observer  should  bear  in  mind,  and  the  more  so  that  in  some 
other  localities  for  serpentine  in  the  British  Islands,  as,  for  example,  in 
the  county  of  Galway,  Ireland,  there  are  some  interlaminations  and 
other  modes  of  occurrence  of  serpentinous  and  calcareous  matter,  sug- 
gesting to  the  geologist  that  such  mixtures  may  have  been  arranged  in 
water,  the  accumulations  subsequently  acted  upon  so  that  the  present 
structure  of  the  rocks  was  produced.* 

This  brings  us  to  consider  the  chemical  composition  of  the  serpentines 
mentioned,  viewed  geologically.  They  are  of  very  varied  mixtures  of  a 
kind  of  base  of  silicate  of  magnesia  with  silicate  of  alumina,  and  occa- 
sionally of  soda  and  potash,  as  also  of  oxide  of  iron.  Water  is  like- 
wise a  marked  ingredient.  Amid  all  this  variety,  among  which  those 
serpentines  may  be  included  through  which  diallage  may  be  disseminated 
(a  compound  common  in  parts  of  the  Lizard  district),  more  pure  ser- 
pentine (as  it  is  inferred)  is  to  be  found ;  that  is,  the  serpentine  which 
has  been  often  considered  as  a  distinct  mineral  species  (how  far  cor- 
rectly remains  to  be  determined),  and  which  is  a  silicate  of  magnesia 
combined  with  water  and  a  minor  proportion  of  oxide  of  iron.f  Look- 
ing at  the  chemical  composition  of  the  common  igneous  product  olivine, 
the  observer  finds  that  it  also  is  essentially  a  silicate  of  magnesia  with 
oxide  of  iron,  the  presence  of  water  as  an  essential  ingredient  in  ser- 
pentine being  the  marked  difference  between  it  and  olivine.  J  This  is 
an  interesting  circumstance,  pointing  to  the  very  moderate  modification 

*  An  examination  into  the  chemical  composition  of  some  large  pilasters  of  this 
serpentinous  rock,  in  the  Museum  of  Practical  Geology,  London,  showed  that  it  was  a 
mixture  of  silicate  of  magnesia  and  carbonate  of  lime,  with  minor  quantities  of  oxide 
of  iron  and  alumina.  The  interlamination  of  the  chief  portions  of  the  mixture  is  often 
most  marked  in  parts  of  this  rock. 

f  The  chemical  composition  of  these  selected  portions  of  serpentine  is  inferred  to  be 
Mg3.  Si2.  +  2  H. 

J  Taking  the  composition  of  serpentine  and  of  olivine  from  the  13  analyses  of  each 
by  several  chemists,  such  as  are  given  by  Professor  Nicol,  in  his  Manual  of  Mineralogy, 
the  similarity  or  difference  would  be  as  follows : — 

Serpentine.  Olivino. 

Silica,    .         .         .         .41-99  41-92 

Magnesia,       .         .         .     40-24  46-67 

Oxide  of  Iron,        .         .3-38  10-75 

Water,   ....     12-68 

The  small  quantities  of  alumina,  lime,  soda,  carbonic  acid,  and  oxide  of  magnesia, 
in  a  few  of  the  selected  serpentines,  and  of  oxide  of  alumina,  lime,  and  the  oxides  of 
manganese,  tin,  nickel,  and  chrome  in  some  of  the  olivines,  are  not  here  noticed. 


COMPOSITION   OF   SERPENTINE   AND   OLIVINE   COMPARED.    557 

of  constituent  parts  which  may  produce  mineral  aspects  of  such  a  varied 
kind.  Taken  in  the  mass,  the  serpentine  of  the  Lizard  seems  often  a 
compound  into  which  alumina  enters  as  a  marked  ingredient,  thus  more 
resembling,  in  that  respect,  the  substance  named  soapstone,  occurring 
in  veins  in  it,  and  which  is  a  compound  of  silicate  of  magnesia  and 
alumina.*  As  a  substance  also  worthy  of  notice,  since  so  frequently 
occurring  in  small  veins  in  portions  of  the  rock,  asbestos  should  not  be 
neglected,  its  component  parts  being  apparently  derived  from  the  mass 
of  serpentine  amid  which  it  is  found.  Though  the  minerals  so  named 
appear  of  varied  chemical  composition,  and  have  been  regarded  as 
members  of  the  hornblende  family,  the  asbestos  of  the  Lizard  seems 
chiefly  a  silicate  of  magnesia,  more  like  the  selected  serpentine  inferred 
to  be  a  mineral  species,  without  its  water. 

Quitting  the  minor  area  mentioned,  merely  because  the  igneous  pro- 
ducts noticed  may  be  there  referred  approximately  to  certain  geological 
dates,  and  as  also  the  localities  are  easily  visited,  and  passing  to  more 
extended  and  distant  regions,  the  observer  will  scarcely  fail  to  be  struck 
with  the  similarity  of  various  igneous  products  in  each,  these  being  to  a 
certain  extent  classified.  Those  which  have  been  termed  volcanic  and 
extinct  volcanic,  with  reference  to  the  present  time,  have  already  been 
noticed  as  presenting  certain  marked  resemblances  in  different  parts  of 
the  earth's  surface.  The  same  general  resemblance  will  be  found  in 
those  products  in  which  the  minerals  of  the  felspar  and  the  hornblende 
families  prevail,  with  or  without  an  excess  of  silica  (occurring  as  quartz), 
in  various  regions.  Though  their  real  modes  of  occurrence  may  not 
always  have  been  properly  ascertained  in  the  numerous  and  different 
localities,  whence  specimens  and  notices  of  them  have  been  obtained, 
and  though  certain  accounts  of  their  manner  of  association  with  other 
rocks  may  require  more  attention  to  the  methods  of  investigation  which 
the  progress  of  knowledge  now  requires,  there  is,  nevertheless,  fre- 
quently sufficient  to  show  the  great  mineral  resemblance  of  many  of 
these  igneous  products  in  widely-distributed  parts  of  the  earth's  surface. 
Viewed  chemically,  there  is  yet  much  to  be  accomplished  respecting 
them,  particularly  with  regard  to  any  modifications  as  to  the  prevalence 
of  some  simple  substances  more  at  one  time  than  at  another,  as  also 
more  in  certain  regions  than  in  others.  Of  the  class  of  igneous  pro- 
ducts to  which  the  name  of  greenstone  has  been  given ;  from  that  crys- 
talline state  wherein  the  constituent  minerals,  felspar  and  hornblende, 
are  distinctly  seen  associated  in  variable  proportions,  to  the  rock  wherein 
the  matter  of  these  minerals  has  not  been  exposed  to  the  conditions 

*  According  to  Klaproth,  a  soapstone  from  the  Lizard  district,  contained,  silica,  45 ; 
alumina,  9-25  ;  magnesia,  24-7  ;  peroxide  of  iron,  1 ;  potash,  0-75  ;  and  water,  18. 
Svanberg  found  in  a  soapstone  from  the  same  locality,  silica,  46-8;  alumina,  9  ;  mag- 
nesia, 33-3  ;  peroxide  of  iron,  0-4 ;  lime,  07 ;  and  water,  11. 


558       RESEMBLANCES    AND     DIFFERENCES    BETWEEN    THE 

fitted  for  its  separate  adjustment  in  that  crystalline  form,  there  are  end- 
less varieties.  With  an  excess  of  silica,  beyond  that  required  for  the 
silicates  of  the  component  minerals,  syenite  is  produced,  quartz  being 
then  distinctly  added  to  the  other  two  minerals.  Again,  it  sometimes 
happens  that  while  there  is  a  granular  arrangement  of.  the  felspar  and 
hornblende,  even  occasionally  with  the  addition  of  quartz,  crystals  of 
felspar  are  disseminated  through  the  mass,  forming  a  greenstone  or 
syenitic  porphyry,  as  the  case  may  be.  Some  of  the  compact  varieties, 
termed  compact  felspar,  have  already  been  noticed  (p.  545).  Altogether 
the  shadows  and  shades  of  modification  have  been  found  so  numerous, 
depending  on  variations  of  chemical  composition  on  the  one  hand,  and 
on  different  conditions  for  cooling  on  the  other,  that  there  has  been  a 
disposition  to  seek  some  term  for  the  whole,  which  shall  leave  the  exact 
composition  of  the  rock  open  to  description,  while  a  kind  of  generic 
name  is  preserved.  The  name  of  trappean  rocks*  has  been  somewhat 
adopted  of  late,  particularly  by  British  geologists  for  this  class  of 
igneous  products.  It  is  one,  no  doubt,  open  to  objection,  if  regarded 
as  a  name  to  be  preserved ;  but  in  the  present  state  of  knowledge,  this 
or  some  other  general  term  has  its  convenience  as  massing  together 
certain  products  of  a  family  character. 

This  class  of  igneous  rocks  appears  to  be  found  amid  accumulations 
of  all  geological  ages,  from  the  older  deposits  to  the  accumulations 
which  approximate  to  the  date  of  those  amid  which  the  basalts  and 
associated  products,  previously  mentioned  (p.  395),  are  seen,  having 
been  thrown  out  from  some  points  on  the  earth's  surface,  however  these 
may  have  varied  in  position.  Seeing  that  their  mode  of  occurrence  is 
such,  even  amid  the  old  Silurian  deposits,  as  to  remind  us  of  the  pro- 
ducts of  modern  volcanoes,  it  may  be  inferred  also  as  probable  that  from 
that  geological  date  to  the  present  time,  rocks  of  a  similar  kind  have 
formed  portions  of  the  products  discharged  from  igneous  vents,  similar 
to  those  now  scattered  over  the  surface  of  the  earth. 

Looking  at  the  granitic  rocks  as  a  class,  they  also  are  found  to  pre- 
sent a  great  family  resemblance  in  different  parts  of  the  world,  though 
sharp  distinctions  between  them  and  those  previously  mentioned  cannot 
always  be  found,  the  one  class  passing  into  the  other,  especially  when 
the  hornblendic  minerals  are  absent,  in  a  manner  resembling  the  modifi- 
cations only  of  some  general  amount  of  given  substances.  When  these 
minerals  are  present,  as  is  sometimes  the  case,  the  chief  chemical  dif- 
ferences between  such  mixtures  and  more  ordinary  granites,  appear  to 
consist  in  the  abundance  or  scarcity  of  the  silicates  of  lime  and  mag- 
nesia, these  substances  forming  comparatively  a  small  portion  of  the 

*  This  term  has  been  derived  from  the  Swedish  word  frapp,  a  stair,  it  having  been 
once  supposed  that  an  arrangement  in  stair-like  forms,  on  the  large  scale,  was  charac- 
teristic of  these  rocks. 


ORDINARY    GRANITIC    AND    HORNBLENDIC    ROCKS.        559 

granitic  rocks,  viewed  on  the  large  scale,  while  they  enter  conspicuously 
into  the  composition  of  the  hornblendic  rocks.*  Where  the  two  classes 
are  found  passing  into  each  other,  it  often  becomes  desirable  to  see  how 
far  the  hornblendic  rocks  may  have  been  previously  thrown  out  and 
consolidated,  and  had  been  remelted  by  the  granitic  rocks,  so  as  to  have 
thus  formed  an  addition  to  their  original  molten  mass,  the  whole,  upon 
cooling,  having  its  constituent  parts  so  adjusted  as  to  present  the  ap- 
pearances observed. 

As  a  common  character,  the  granitic  rocks  seem  to  be  chiefly  formed 
of  silica  and  alumina,  after  which  come,  as  principal  ingredients,  potash 
and  soda,  the  latter  sometimes  more  prevalent  probably  than  has  been 
usually  inferred.  The  silica  and  alumina  often  constitute  '8  of  the 
whole  mass,  thus  leaving  only  -2  for  the  other  substances.  In  cases 
where  labradorite  is  the  member  of  the  felspar  family  present  in  gra- 
nitic rocks,  either  altogether  replacing  other  felspars,  or  associated  with 
them,  lime  would  form  an  ingredient  of  importance,  f  though  silica  and 
alumina  would  still  constitute  the  most  marked  substances  in  such  rocks. 
Sufficient  examination  has  not  yet  been  given  to  granitic  rocks  to  show 
us  the  relative  prevalence  of  soda,  potash,  or  lime  (in  cases  of  labrado- 
rite), during  the  progress  of  geological  time.  Taking  the  granite  of 

*  With  reference  to  the  difference  or  resemblance  between  granites  and  greenstones, 
as  we  have  elsewhere  remarked  (Researches  in  Theoretical  Geology,  p.  379,  1834), 
"granites,  no  doubt,  vary  in  their  chemical  composition,  and  so  do  greenstones,  yet 
they  always  so  differ  from  each  other  as  masses  of  matter,  that  the  one  can  never  be- 
come the  other  from  mere  differences  in  cooling."  If  we  suppose  the  felspar  to  be  of 
the  ordinary  potash  kind,  and  a  granite  to  be  formed  of  two-fifths  of  such  felspar,  of 
two  fifths  of  quartz,  and  one  fifth  of  mica  (containing  fluoric  acid),  and  a  greenstone  to 
be  composed  of  the  same  kind  of  felspar,  and  an  equal  proportion  of  hornblende,  the 
calculated  differences  may  be  taken  somewhat  as  follows  (Geological  Manual,  3d  edition, 
pp.  448-50)  :— 

Silica, 

Alumi 

Potash, 

Magn 

Lime, 


f  The  presence  of  lime  amid  igneous  products,  though  it  may  there  occur  as  a  silicate, 
is  interesting  as  affording  the  base  of  a  supply  for  some,  at  least,  of  the  calcareous  mat- 
ter required  by  animal  life,  or  distributed  as  ordinary  limestones.  However  powerful 
silica  may  be,  acting  as  an  acid  where  heat,  and  especially  great  heat,  is  employed,  at 
the  lower  temperatures  it  is  comparatively  weak.  As,  for  example,  at  great  heats  the 
silicates  of  potash  and  soda  are  readily  formed,  whether  carbonic  acid  be  present  or 
not,  but  at  low  temperatures,  solutions  of  the  silicates  of  potash  or  soda  are  easily 
decomposed  by  the  carbonic  acid.  So  also  with  silicate  of  lime,  if  that  substance  were 
in  contact,  in  the  presence  of  water  at  a  moderate  temperature,  with  carbonic  acid,  it 
would  be  decomposed,  forming  carbonate  of  lime,  and  if  the  carbonic  acid  were  in 
sufficient  abundance,  bicarbonate  of  lime  ready  to  be  removed  in  solution. 


Granite. 

Greenstone. 

Difference. 

. 

.     74-84 

54-86 

19-98 

na,      . 

.     12-80 

15-56 

2-76 

i, 

.       7-48 

6-83 

0-65 

ssia,    . 

.       0-99 

9-39 

8-40 

0-37 

7-29 

6-92 

of  Iron, 

.       1-93 

4-03 

2-10 

of  Manganese,  . 

.      0-12 

0-11 

0-01 

c  Acid, 

.      0-21 

0-75 

0-54 

560  GRANITIC,     FELSPATHIC,    HORNBLENDIC,    AND 

Wicklow  and  Wexford,  above  noticed,  it  would  appear  that  soda  oc- 
curred in  some  fair  abundance  in  the  granitic  rocks,  protruded  in  that 
part  of  the  world,  anterior  to  the  accumulation  of  the  old  red  sand- 
stone. 

As  to  the  geological  times  when  granitic  rocks  have  arisen,  through 
prior-formed  and  usually  disturbed  deposits  accumulated  by  the  agency 
of  water,  they  would  appear  to  include  all,  from  the  earliest  even  to 
the  production  of  comparatively  recent  beds  of  the  tertiary  series.  Of 
the  latter  kind,  Mr.  Pratt  has  found  instances  in  Catalonia.*  Thus, 
there  is  no  conclusion  to  be  drawn  as  to  the  relative  antiquity  of  these 
rocks  from  the  mere  fact  of  their  occurrence  in  any  particular  locality. 
This  has  to  be  sought  in  the  manner  in  which  they  may  be  found  asso- 
ciated with  other  accumulations,  the  relative  geological  dates  of  which 
are  determinable. 

The  serpentines,  also,  and  their  not  unfrequent  associate  diallage 
rock,  seem  to  have  appeared  with  somewhat  common  characters  through 
a  long  range  of  geological  time.  They  have  been  above  mentioned  as 
probably  of  early  date  in  Wales.  In  Cornwall,  though  not  of  equal 
antiquity,  they  are  apparently  still  referable  to  the  earlier  geological 
times.  In  Ireland,  also,  they  seem  to  have  been  formed  at  a  remote  geolo- 
gical period.  Various  lands  show  that  they  were  not  confined  to  those 
times,  but  became  associated  with  accumulations  of  less  antiquity  ;  and 
in  Italy,  where  there  are  many  good  opportunities  of  studying  these 
rocks,  they  have  been  found  amid  deposits  up  to  those  of  the  tertiary 
times  included,  it  being  inferred  that  the  rocks  in  that  land  which  con- 
tain the  fossils  named  nummulites  were,  as  pointed  out  by  Sir  Roderick 
Murchison,')"  accumulated  at  a  time  when  the  lower  deposits  of  the  ter- 
tiary series  were  effected  in  several  other  parts  of  Europe.  The  occur- 
rence of  serpentine  and  diallage  rock  amid  the  Alps,  and  among  the 
various  accumulations  of  the  Jurassic  and  cretaceous  series,  usually 
cutting  through  them,  in  Italy,  and  in  the  continuation  of  the  same 
accumulations  eastward  in  different  localities  in  Asia,  is  a  marked  cir- 
cumstance. The  chief  circumstance,  however,  now  under  consideration 
is,  that  these  rocks  were  probably  ejected  from  beneath,  at  various 
geological  times,  over  the  area  of  Europe,  from  the  early  fosiliferous 
deposits  up  to  some  part  of  the  tertiary  series  included.  So  much  of 
various  parts  of  the  world  remaining  to  be  examined  geologically,  it 
would  be  premature  to  conclude  that  these  rocks  have  not  been  ejected 
at  comparatively  recent  geological  times  in  some  localities. 

It  has  been  seen  that  into  the  serpentines,  magnesia  enters  largely, 
the  relative  amount  of  that  substance  being  somewhat  characteristic,  as 
time  and  magnesia  combined,  are  among  the  hornblendic  rocks.  It 

*  Pratt,  MSS.  f  Journal  of  the  Geological  Society  of  London,  vol.  v.  p.  157. 


SERPENTINOUS    ROCKS    EJECTED    AT    VARIOUS    TIMES.      561 

would  not,  however,  be  right  to  infer  that  silicate  of  magnesia  is  alone 
to  be  regarded,  since  the  mixtures  in  which  diallage  is  disseminated 
and  even  prevails,  show  that  other  marked  substances  have  entered  into 
the  composition  of  the  mass  when  in  a  molten  state.  In  such  arrange- 
ments of  parts  of  the  compound,  the  ingredients  needful  for  diallage 
have  merely  separated  out  from  it  under  the  fitting  conditions,  the  lime, 
oxide  of  iron,  and  alumina  having  probably  been  in  a  more  disseminated 
state  previously.*  Sometimes  the  base  of  the  rock,  still  termed  ser- 
pentine, from  its  general  aspect,  and  the  diallage  crystallized  out  from 
the  general  mass,  appear  of  nearly  the  same  composition. f 

With  respect  to  the  fusibility  of  the  igneous  rocks  generally,  they  no 
doubt  present  considerable  diiferences.  At  the  same  time,  it  is  needful 
to  bear  in  mind,  that  experiments  upon  them,  in  the  condition  in  which 
we  find  them,  do  not  exactly  give  us  the  measure  of  their  fusibility  when 
they  were  in  a  molten  state,  prior  to  the  adjustment  of  the  parts  of 
many  into  minerals  of  a  definite  kind,  certain  compounds  being  then 
produced  often  far  more  difficult  to  reduce  by  heat,  than  when  the  whole 
is,  as  it  were,  again  placed  under  its  old  condition  of  a  molten  mass, 
and  the  vitreous  adjustment  of  parts  arranged,  so  that  these  definite 
compounds  have  not  been  again  formed. J  It  hence  becomes  desirable 
to  view  the  fusibility  of  these  rocks,  with  reference  to  a  complete  mix- 

*  M.  Berthier  found  the  diallage  from  La  Spezzia,  a  locality  very  favourable  for  the 
study  of  serpentine  and  diallage  rock,  to  be  composed  of — 

Silica 47-2 

Magnesia 24-4 

Lime 13-1 

Protoxide  of  iron     .....  7-4 

Alumina .  3-7 

Water 3-2 

•f-  According  to  Dr.  Kohler  (Thomson's  Mineralogy,  &c.,  vol.  i.  p.  174),  the  composi- 
tion of  the  diallage,  and  of  the  rock  containing  it  at  Harlzburg,  is  as  follows  : — 

Diallage.  Rock. 

Silica 43-900  42-364 

Magnesia 25-856  28-903 

Protoxide  of  Iron  and  Chromium     .  13-021  13-268 

Protoxide  of  Manganese     ....  0-535  0-853 

Lime 2-642  0-627 

Alumina 1-280  2-176 

Water 12-426  12-074 

J  In  experimenting  upon  the  fusibility  of  igneous  products,  we  have  often  found  very 
considerable  difference  in  that  fusibility,  after  some  crystallized  and  compound  rock 
had  been  formed  into  a  glass,  from  that  which  it  had  exhibited  when  first  acted  upon 
by  the  same  amount  of  heat  employed.  In  the  same  manner,  artificial  glasses  which 
have  been  melted  and  cooled  slowly,  so  as  to  form  a  stony  mass,  or  merely  exposed  to 
a  temperature  at  which  a  certain  crystallized  arrangement  of  their  constituent  parts 
is  produced,  become  more  difficult  of  fusion  than  when  in  their  first  state. 


562  ADDITIONAL    MINERALS    ENTERING    INTO    THE 

ture  of  all  the  constituent  parts,  anterior  to  the  separation  of  any,  or 
the  whole  of  them  into  crystalline  compounds. 

If  we  are  to  regard  certain  of  these  rocks  to  have  been  ejected  from 
volcanic  vents  in  the  manner  of  modern  volcanoes,  it  seems  also  needful 
to  consider  that  they  have  been  accompanied  by  outbursts  of  vapours 
and  gases,  sublimations  of  different  kinds  having  taken  place  at  those 
different  times  as  now.  As  a  substance  very  common  among  the  com- 
pounds of  felspar  and  hornblende,  even  of  those  contemporaneously 
thrown  out  amid  the  older  fossiliferous  rocks,  sulphur  combined  with 
iron  is  very  common,  indeed,  sulphuret  of  iron  is  often  a  marked  ingre- 
dient among  those  which  are  commonly  termed  greenstones.  Not, 
however,  that  it  is  confined  to  them,  for  the  more  felspathic  products 
often  also  contain  it.* 

Amid  the  various  modifications  and  changes  of  structure  to  which 
the  deposits  associated  with  the  latter  class  of  igneous  products  have 
been  often  subjected,  it  would  be  expected  that  these  having  been 
exposed  to  similar  conditions,  would,  in  like  manner,  have  their  parts 
also  often  much  modified.  Indeed,  those  igneous  products  which  have 
been  vesicular,  show,  by  the  various  mineral  substances  found  in  them, 
that  mineral  matter  has  often  been  in  movement  in  proper  solvents,  and 
passing  through  the  pores  of  rock,  had  adjusted  itself  in  the  cavities  of 
the  vesicular  rock  as  definite  mineral  compounds.  Numerous  soluble 
substances  once  disseminated  amid  the  general  mass  of  such  rocks,  may 
readily  have  been  transported  elsewhere,  and  aid  in  forming,  by  new 
combinations,  less  soluble  substances.  Thus  many  are  found  dissemi- 
nated amid  modern  volcanic  products,  which,  assuming  that  they  were 
once  disseminated  amid  those  of  ancient  times,  would  scarcely  be  now 
detected  in  the  latter,  f  As  regards  the  conditions  to  which  igneous 
rocks  of  ancient  geological  date  may  have  been  exposed  during  the 

*  It  sometimes  happens  that  iron  pyrites  is  found  in  prior-formed  deposits  of  ordi- 
nary detrital  matter,  adjacent  to  protrusions  and  dykes  of  these  igneous  rocks,  in  such 
a  manner,  as  if  either  the  sulphur,  or  sulphur  and  iron  had  been  derived  from  them. 
A  good  example  of  this  mode  of  occurrence  may  be  seen  at  Bettws  Disserth,  on  the 
north  of  Builth,  South  Wales,  where  spheroidal  pieces  of  iron  pyrites  occur  in  a  Silu- 
rian slate  adjacent  to  some  hornblendic  rocks  ;  these  spheroids  somewhat  abundant  in 
places,  and  the  slate  having  all  the  appearance  of  having  been  altered  by  the  intrusion 
of  the  igneous  rock.  At  the  falls  of  the  Wye,  near  Builth,  much  iron  pyrites  is  also 
seen  at  the  contact  of  some  igneous  rocks  intruded  among  slates,  in  like  manner  altered, 
certain  fossils  in  them  being  likewise  coated  with  the  same  mineral  near  the  contact  of 
the  two  rocks,  though  this  is  not  observed  at  a  short  distance  from  it.  In  the  latter 
case,  the  slate  is  highly  carbonaceous,  so  that  the  requisite  care  will  have  to  be  taken 
as  to  the  carbonaceous  matter  in  the  rock. 

f  Iron,  either  as  a  protoxide  or  peroxide,  is  so  often  found  in  the  igneous  product  of 
different  geological  times,  as  to  be  a  marked  mineral  among  them.  Thus  magnetic  iron 
is  not  only  found  among  the  dolerites,  and  some  other  rocks  of  modern  volcanoes,  but 
also  in  the  compounds  of  considerable  relative  antiquity,  as,  for  example,  among  cer- 
tain greenstones  in  Cornwall  of  the  age  of  the  Devonian  series. 


COMPOSITION    OF    ORDINARY    IGNEOUS    ROCKS.  563 

lapse  of  time,  it  would  scarcely  be  expected  that  when  they  may  have 
been  subjected  to  the  influence  of  long-continued  heat  from  any  depres- 
sion to  considerable  depths,  especially  beneath  a  thick  covering  of  other 
deposits,  that  any  obsidians  would  preserve  their  vitreous  character, 
such  disappearing  from  the  usual  causes  productive  of  devitrification, 
the  component  substances  taking  a  stony  form. 

As  to  the  minerals  which  appear,  as  it  were,  additions  in  different 
localities  to  the  general  masses  of  granite,  and  even  to  those  rocks 
where  hornblende  .and  felspar  chiefly  constitute  the  component  minerals ; 
they  are  often  very  various,  and,  as  M.  Elie  de  Beaumont  has  remarked 
with  respect  to  granite,  much  distributed  outside  their  masses.*  While 
they  are  often  merely  some  other  arrangements  in  different  proportions 
of  the  simple  substances  contained  in  the  general  mass,f  at  others,  they 
appear  as  if  in  some  manner  the  result  of  an  addition  derived  from  the 
rocks,  against  which  the  molten  mass  has  been  thrown,  and  formed  during 
the  long  continuance  of  those  conditions  (among  which  great  heat  is 
prominent),  that  have  prevailed  after  the  uprise  of  these  igneous  rocks 
in  different  localities.  Among  these  minerals,  garnets  of  different  kinds 
may  be  remarked,  as  occurring  as  well  in  the  igneous  as  in  the  prior- 
formed,  and  subsequently  modified  rock,  against  which  the  former  has 
been  thrust.  When  we  consider  the  various  substances  which  analyses 
seem  to  show,  are,  as  it  were,  entangled  amid  those  constituting  the 
chief  mass  of  the  igneous  matter  ejected, J  it  would  be  anticipated  that 
when  these  were  relatively  abundant,  and  could  make  their  own  adjust- 
ments more  freely,  less  controlled  by  the  influences  of  those  forming 
the  chief  minerals,  compounds  would  be  effected  of  a  definite  kind,  and 
be  separated  from  the  main  mass.  Thus,  occasionally,  mixtures  would 
be  formed  of  more  than  the  usual  substances,  even  constituting  masses 
of  importance  in  parts  of  the  earth's  surface,  where,  though  the  usual 
free  silica  and  silicates  of  ordinary  granite  and  other  compounds  were 
still  the  most  prevalent  substances,  others  are  present,  giving  a  some- 
what modified  character  to  the  general  rock. 

With  respect  to  the  occasional  component  parts  of  granitic  rocks, 

*  Sur  les  Emanations  Volcaniques  et  Me'talliferes.  Bull,  de  la  Soc.  Gdol.  de  France, 
2d  se>ie,  t.  iv.  (1847). 

f  In  talc,  a  mineral  sometimes  associated  with  others  in  granites,  we  seem  to  have 
magnesia  in  a  certain  relative  abundance,  separating  itself  from  a  main  mass  in  which 
it  may  usually  have  been  a  subordinate  substance,  talc  being  essentially  a  silicate  of 
magnesia.  Its  formula  is  considered  to  be  3  M  Si  +  Mg3  Si*. 

J  M.  Elie  de  Beaumont,  in  his  table  of  the  distribution  of  simple  substances  in 
nature  (Bulletin  de  la  Soc.  Ge*ol.  de  France,  2d  serie,  t.  iv.),  considers  the  following  to 
be  found  in  granite,  viz. : — potassium,  sodium,  lithium,  calcium,  magnesium,  yttrium, 
glucinium,  aluminium,  zirconium,  thorium,  cerium,  lanthanium,  didymium,  uranium, 
manganese,  iron,  cobalt,  zinc,  tin,  lead,  bismuth,  copper,  silver,  palladium  ?,  osmium, 
hydrogen,  silicon,  carbon,  boron,  titanium,  tantalum,  nobium,  pelopium,  tungsten, 
molybdenum,  chromium,  arsenic,  phosphorus,  sulphur,  oxygen,  chlorine,  and  fluorine. 


564      GENERAL  CHARACTER  OF  IGNEOUS  ROCKS. 

chlorite  should  be  mentioned  as  one  of  some  importance,  inasmuch  as 
while  it  shows  a  modification  of  the  mixture  and  relative  proportions  of 
some  of  the  ordinary  constituent  ingredients  of  granitic  minerals,  silica, 
alumina,  magnesia,  oxide  of  iron,  and  oxide  of  manganese,  it  also  points 
to  water  as  an  essential  ingredient.  When  disseminated,  therefore, 
among  granitic  rocks,  as  it  is  in  the  Alps,  Scandinavia,  and  some  parts 
of  the  British  Islands,  chlorite  becomes  a  combined  mineral  of  no  slight 
interest,  from  the  addition  of  water  to  the  other  substances  present.* 

With  regard  to  the  various  minerals,  which  are,  as.it  were,  additional 
to  those  usually  constituting  the  mass  of  the  chief  divisions  of  the  igne- 
ous rocks,  not  only  has  the  dispersion,  in  variable  proportions,  of  other 
substances  than  the  usual  ingredients  to  be  regarded,  considering  these 
likewise  in  their  greater  or  less  local  proportions,  but  also  the  additions 
which  may  be  derived  from  the  melting  of  parts  of  prior-consolidated 
accumulations,  even  of  those  thrown  down  from  solutions  in  water,  and 
fused  by  the  intrusion  of  the  igneous  rocks.  Though  a  great  proportion 
of  the  ordinary  detrital  deposits  are  but  abraded  parts  of  previously 
consolidated  igneous  rocks  which  have  been  worn  away,  and  then  dis- 
persed as  above  noticed  (pp.  89—123),  this  has  been  most  frequently  so 
accomplished  that  a  remelting  of  the  deposits  thence  formed,  would  not 
reproduce  the  original  rock,  the  various  parts  having  been  separated 
mechanically  into  different  beds,  and  decomposition  having  deprived 
certain  of  even  the  separated  substances  of  portions  of  their  original 
ingredients.  With  respect  to  the  latter,  for  example,  should  the  sili- 
cates of  soda  or  potash  have  been  removed  in  solution,  as  has  often  hap- 
pened, from  a  felspar  of  which  they  once  constituted  a  part,  the  matter 
again  fused  might  not  contain  any  of  those  silicates,  so  far  as  the  fel- 
spar is  regarded,  silicate  of  alumina  being  then  the  prevailing  sub- 
stance, f  Igneous  matter,  the  usual  granite  compounds  for  instance, 
melting  limestone  rocks,  the  lime  might  be  introduced  into  the  molten 
mass,  and  the  carbonic  acid  being  thrown  off,  the  silicates  of  lime  be 
formed,  ready  for  combination  in  other  minerals  than  those  constituting 
the  mass  of  the  granite,  as  it  rose  from  beneath.  So  also  with  dolomite, 
which  could  thus  furnish  not  only  the  lime,  but  also  the  magnesia  for 
the  production  of  hornblende,  should  the  other  ingredients  of  that 
mineral  be  near  and  not  drawn  elsewhere.  In  this  manner  it  will  be 
obvious  very  material  additions  may  be  made  to  an  original  and  general 
mass  of  rocks  in  a  molten  state. 

There  appearing  so  much  of  a  general  character  in  the  various  igne- 

*  Taking  various  analyses,  from  10  to  11  per  cent,  of  water  enters  into  the  composi. 
tion  of  chlorite.  The  formula  for  chlorite  is  considered  to  be  (Mg3  Si2 -{-3  R  Si)-f-  9 
MgH. 

f  The  substance  constituting  the  base  of  the  clays  employed  in  the  manufacture  of 
porcelain,  and  which  are  formed  from  decomposed  felspars  in  districts  where  that 
mineral  has  been  distributed  in  sufficient  abundance. 


CONSOLIDATION    OF    DETRITAL    ROCKS.  565 

ous  products  of  different  geological  times,  to  call  the  attention  of  an 
observer  towards  some  general  cause,  which,  though  much  modified 
under  certain  circumstances,  has  yet  always  exerted  an  important  geo- 
logical influence,  he  has  carefully  to  consider  the  subject,  so  that,  while 
a  proper  and  close  attention  may  be  given  to  local  sources  of  modifica- 
tion, the  great  cause  of  these  igneous  products,  taken  as  a  whole,  be 
not  neglected.  Whatever  may  have  been  the  conditions  under  which 
substances  were  probably  ejected  in  the  manner  of  modern  volcanoes  in 
past  geological  ages,  from  time  to  time  molten  matter  of  a  very  common 
general  character  seems  as  if  always  ready  to  be  upheaved  in  larger 
masses  whenever  there  were  great  disruptions  of  prior-formed  accumu- 
lations on  the  earth's  surface.  Thus,  while  the  minor  and  perhaps 
modified  manifestations  of  the  conditions  for  throwing  out  igneous  sub- 
stances generally,  were  constant  in  different  points  of  the  earth's  surface 
for  the  time  being,  these  substances  mingled  with  the  ordinary  accu- 
mulations of  the  day,  from  time  to  time  a  greater  amount  of  molten 
matter  was  upheaved,  lifting  such  igneous  products  as  well  as  their 
associated  sedimentary  deposits,  as  if  the  former  action,  however  intense, 
was  but  superficial  as  compared  with  that  from  which  the  more  wide- 
spread and  important  movements  were  derived.  Be  this  as  it  may,  the 
igneous  products  form  objects  of  the  greatest  interest,  whether  regarded 
as  the  source  whence  so  large  a  proportion  of  the  detrital  accumulations 
are  derived,  for  the  modifications  they  have  so  frequently  effected  in 
the  deposits  against  or  amid  which  they  have  risen,  or  been  protruded, 
for  the  differences  and  resemblances  they  exhibit  among  themselves,  or 
for  the  proof  they  afford  that  during  the  long  lapse  of  geological  time 
of  which  we  can  obtain  traces,  and  up  to  the  present  day,  there  have 
been  conditions  for  uplifting  mineral  matter  in  a  molten  state,  that  mat- 
ter chiefly  composed  of  the  oxides  of  a  few  simple  substances — two  of 
them  especially  (sodium  and  potassium) — being  not  only  remarkable  for 
their  comparative  lightness,  but  also  for  an  avidity  for  oxygen  so  great 
that  they  will  decompose  water  in  order  to  obtain  it. 

Consolidation  >and  Adjustment  of  the  Component  Parts  of  Rocks. — 
When  the  gravels,  sands,  silts,  clays,  or  mud  of  various  geological  times 
are  presented  to  the  attention  of  the  geologist  in  the  form  of  conglome- 
rates, sandstones,  arenaceous  and  argillaceous  slates  and  shales,  their 
component  parts,  originally  drifted,  or  otherwise  borne  into  the  relative 
situations  where  they  are  now  found,  have  either  been  joined  together 
by  mineral  matter,  subsequently  introduced  among  them,  or  by  a  change 
in  the  condition  of  some  part  or  parts  of  the  original  deposit  which 
should  permit  such  portions,  in  an  altered  form,  to  cement  the  re- 
mainder. With  carbonate  of  lime,  the  oxides  of  iron  and  manganese, 
and  occasionally  with  silica,  as  substances  cementing  fragments  of  rocks, 
either  angular  or  rounded,  on  hillsides  or  other  subaerial  localities, 


566  ADJUSTMENT    OF    THE    COMPONENT    PARTS 

where  springs  containing  and  depositing  those  substances  occur,  we 
may  consider  the  observer  as  familiar.  That  various  breccias,  conglo- 
merates, and  even  sandstones  so  formed,  occasionally  constitute  parts 
of  a  series  of  geological  products,  may  be  considered  probable.  It  is 
easy  also  to  infer  that  during  geological  changes,  gravels  and  sands 
constituting  the  margins  and  bottoms  of  lakes  and  seas,  may  be  so 
placed  beneath  isolated  portions  of  water,  to  which  the  access  of  rivers 
or  streams  may  be  insufficient  to  meet  the  loss  by  evaporation,  that  cer- 
tain substances  held  in  solution  may  be  slowly  deposited  amid  the  sub- 
jacent gravels,  sands,  clay,  or  mud,  so  as  to  produce  modification, 
change,  or  even  consolidation  of  various  kinds  in  them. 

Independently,  however,  of  these  effects,  the  observer  will  have  to 
direct  his  attention  to  modification,  change,  and  consolidation  of  a  far 
more  general  kind,  and  for  which  some  more  general  cause  appears  to 
be  required.  He  will,  in  the  first  place,  have  to  dismiss  the  view  that 
the  relative  age  of  rocks  is  alone  a  sufficient  cause  for  the  effects  noticed ; 
though,  taken  as  a  whole,  the  relative  geological  age  of  deposits  is  so 
far  important,  that,  other  things  being  the  same,  there  may  be  a  greater 
chance  of  the  older  rocks  being  consolidated  or  modified  in  their  struc- 
ture, inasmuch  as  they  may  have  been  more  exposed,  during  the  lapse 
of  time,  to  the  causes  productive  of  such  consolidation  and  change. 

It  may,  in  the  first  place,  be  desirable  to  consider  the  modification  of 
parts  which  might  arise  in  a  bed  or  mass  of  mud,  or  clay  after  its 
deposit,  the  component  parts  of  such  mud  or  clay  being  variable.  We 
may  take,  by  way  of  illustration,  those  alternations  of  argillaceous 
limestones  and  shales,  often  calcareous,  which  are  observable  in  the  lias 
of  some  parts  of  Western  Europe,  and  which  appear  the  result  of  an 
unequal  supply  of  mud  and  calcareous  matter,  sometimes  the  one  and 
sometimes  the  other  predominating.  Examples  of  irregular  deposits  of 


Fig.  224. 


this  kind  must  not,  however,  be  considered  as  confined  to  any  particular 
age,  since  among  the  older  as  well  as  newer  geological  accumulations, 


OF    CALCAREOUS    AND    ARGILLACEOUS    DEPOSITS.        567 

this  kind  of  deposit  may  often  be  found.  The  preceding  sketch  (fig.  224) 
may  be  taken  as  illustrating  alternations  of  this  kind,  the  surfaces  of 
the  beds  being  irregular. 

In  itself  such  a  section  may  merely  present  us  with  the  evidence  of 
alternating  conditions,  by  which  carbonate  of  lime  was  more  thrown 
down  at  one  time  than  at  another,  though,  with  care,  forms  of  the  sur- 
faces are  often  traced  which  would  seem  to  point  to  an  abstraction  of 
calcareous  matter  from  the  adjacent  original  clays  or  mud ;  a  circum- 
stance which  becomes  more  evident  where  the  calcareous  matter  in  the 
general  deposit  has  decreased,  and  many  irregular  patches  of  the  argil- 
laceous limestone,  and  nodules  of  it,  are  arranged  in  lines  or  are  more 
dispersed  through  the  deposit,  as  shown  in  the  subjoined  section  (fig. 
225).  In  such  cases  the  calcareous  matter  of  given  times  of  deposit, 

Fig.  225. 


irregular  like  those  where  whole  sheets  of  argillaceous  limestone  were 
produced,  seem  gathered  to  different  points  in  or  about  the  same  plane, 
that  upon  which  the  general  deposit  was  accumulated,  the  matter 
arranged  round  these  points,  thus  variously  dispersed  on  the  plane,  so 
that  two  or  more  nodules  may  be  joined  together  while  others  remain 
isolated.  This  gathering  together  of  similar  matter,  distributed  through 
a  soft  muddy  or  clay  mass,  would  be  anticipated,  and  the  more  so,  when 
we  remember  the  manner  in  which  similar  matter  may  be  gathered  to- 
gether from  solutions,  dragged  away,  as  it  were,  forcibly  to  points 
where  some  of  it  may  have  been  first  deposited,  as  noticed  by  Professor 
Bunsen  (p.  371). 

Facts  of  this  kind  are  as  well  seen  among  the  carbonates  of  iron,  of 
so  much  value  in  the  coal  measures  of  the  British  Islands,  as  amid  the 
accumulations  above  noticed ;  and  they,  in  like  manner,  point  to  a 
separation  of  the  carbonates  from  the  muddy  mass,  and,  for  the  most 
part,  in  planes  corresponding  with  the  relative  times  of  their  original 
deposit  in  the  general  accumulation,  one  chiefly  detrital,  and  thrown 
down  from  mechanical  suspension.  It  occasionally  happens  that  this 
gathering  together  of  similar  matter  from  amid  a  mass  through  which 
it  was  originally  dispersed,  usually  in  certain  planes  and  thicknesses, 
can  be  seen  to  have  taken  place  so  that  a  certain  original  lamination  of 
parts  is  not  destroyed.  Instances  of  this  kind  are  to  be  found  in  one 
or  two  of  the  ranges  of  nodules  in  the  lias  of  Lyme  Regis,  Dorset, 
where,  as  beneath  (fig.  226),  these  are  seen  still  preserving  the  lamina- 
tion of  the  general  deposit ;  an  arrangement  of  parts  easily  ascertained 
by  breaking  the  nodules  in  this  plane.  In  these  nodules  some  organic 


568  CENTRAL    FRACTURES    OP    SEPTARIA. 

remain,  such  as  a  fish,  nautilus,  ammonite,  or  a  piece  of  wood,  not  un- 
frequently  seems  to  have  formed  a  point  around  which  the  carbonate  of 


Fig.  226. 


lime  was  aggregated,  though  this  has  by  no  means  been  always  the  case, 
since  some  are  occasionally  found  without  organic  remains,  or  only  con- 
tain them  in  a  dispersed  state. 

Such  aggregations  and  separation  of  parts  are  at  the  same  time  a 
modification  of  the  original  deposit,  and  a  partial  consolidation  of  it. 
As  a  proof  that  the  mass  was  soft  when  the  nodules  were  formed,  the 
observer  will  often  find  that  while  the  same  kinds  of  organic  remains, 
and  especially  thin  shells,  are  flattened,  in  the  same  planes,  in  the 
associated  and  adjoining  clays,  marls,  or  shales,  they  are  comparatively 
well  preserved,  uncompressed,  in  the  nodules,  the  consolidation  of  the 
latter  having  protected  them  from  the  pressure  to  which  those  had 
been  subjected  in  the  remainder  of  the  deposit,  then  in  a  yielding  con- 
dition. 

With  regard  to  the  relative  time  and  mode  of  consolidation  of  the 
nodules,  the  observer  may  be  frequently  enabled  to  study  it  in  those 
commonly  known  as  septaria  and  turtle-stones,  where  after  the  aggre- 
gation of  the  similar  matter,  such,  for  example,  as  the  carbonate  of 
lime  in  many  clay  or  shale  deposits,  and  the  carbonate  of  iron  in  the 
coal  measures  and  some  other  rocks,  a  splitting  of  the  interior  has 
taken  place,  and  subsequently  to  a  certain  amount  of  consolidation, 
since  the  fractures  are  usually  sharp,  pointing  to  a  sufficient  amount  of 
cohesion  of  parts.  The  subjoined  section  (fig.  227)  will  show  the  ordi- 

Fig.  227. 


nary  manner  in  which  such  nodules  are  broken  in  the  interior,  the 
cracks  not  extending  to  their  exterior  surfaces,  as  if  there  had  been  a 
shrinking  of  parts  from  the  centre  outwards,  so  that  the  resulting  largest 
openings  were  central.  In  the  nodules  of  this  kind,  not  uncommon  in 
many  clays,  marls,  and  shales,  the  cracks  are  usually  filled  according  to 
the  character  of  the  general  deposit  of  which  the  nodules  constitute  a 
part ;  thus  carbonate  of  lime  is  frequent  in  those  where  that  substance 
is  much  disseminated,  and  carbonate  of  iron  where  the  latter  is  not 
uncommon.  Occasionally  other  substances  arc  introduced,  such  as,  in 


NODULES  OF  PHOSPHATE  OF  LIME  IN  BOOKS.     569 

the  coal  measures,  ironstone  nodules  of  many  parts  of  the  British  Islands, 
the  sulphurets  of  lead,  zinc,  and  iron,  copper  pyrites,  and  certain  other 
minerals. 

Nodules  and  other  formed  bodies  of  phosphate  of  lime,  also  sometimes 
occur  in  a  manner  pointing  to  the  aggregation  of  their  component  parts 
from  previous  dissemination  amid  surrounding  detrital  deposits.  The 
layers  of  nodules  and  other  forms  of  phosphates  of  lime  in  the  lower 
parts  of  the  cretaceous  series  of  Southeastern  England  and  in  parts  of 
France,  seem  thus  formed.  Mr.  Austen  has  informed  us,*  that  the 
nodules  he  examined  had  a  concentric  arrangement  of  parts,  like  agates, 
and  he  points  to  the  probability  that  the  phosphoric  acid  may  have 
formed  part  of  the  faecal  or  coprolitic  matter  accumulated  with  other 
organic  bodies,  at  the  period  of  the  original  deposit,  and  had  been  dis- 
seminated among  the  sand  and  ooze  of  the  locality  and  time.  Modern 
researches  have  shown  that  phosphate  of  lime  is  far  more  diffused 
among  rocks  than  was  at  one  time  supposed.  When  free  carbonic  acid 
is  present  in  water,  the  phosphate  of  lime  is,  like  the  carbonate,  soluble, 
though  not  to  the  same  extent  as  the  latter ;  so  that  conditions  may 
readily  arise  not  only  for  its  dissemination,  but  also  for  its  aggregation 
into  various  forms  amid  rocks  through  which  its  particles  could  move. 
Not  only  waters  impregnated  with  free  carbonic  acid,  in  the  usual  man- 
ner, would  afford  the  common  means  of  transport  for  such  particles,  but 
also,  in  the  cases  referred  to  by  Mr.  Austen,  for  the  mixture  of  copro- 
litic with  vegetable  matter,  the  decomposition  of  the  latter,  and  often, 
indeed,  of  the  faecal  matter  itself,  producing  carbonic  acid  needful  in 
the  required  solution. 

The  association  of  similar  matter  in  nodules,  is  also  sometimes  well 
seen  amid  deposits  of  siliceous  sands,  these  aggregated  so  that  the 
nodules  protrude  as  marked  objects  on  weathered  banks  or  cliffs.  Some- 
times the  nodules  are  dispersed  among  the  arenaceous  accumulations, 
while  at  others  they  range  in  certain  general  planes,  corresponding 
with  those  of  deposit,  and  thus,  in  their  mode  of  occurrence,  resemble 
the  nodules  of  the  carbonates  of  lime  and  iron,  above  mentioned.  In 
certain  of  the  arenaceous  deposits  the  cementing  substance  of  the 
nodules  is  occasionally  calcareous,  apparently  aggregated  from  that  mat- 
ter once  more  dispersed  amid  the  sands,  and  deposited  amid  the  grains 
from  solution,  as  a  bicarbonate,  in  the  waters  which  either  transported 
the  sands  in  mechanical  suspension,  or  drifted  them  over  the  sea  or  lake 
bottom  of  the  time.  The  oxides  and  hydrates  of  iron  are  also  observed 
gathered  in  nodules,  either  dispersed  or  in  planes,  aggregating  portions 
of  sands. 

Even  amid  the  older  detrital  accumulations  with  which  geologists 

*  Journal  of  the  Geological  Society  of  London,  vol.  iv.  p.  257,  1848. 


570    SPHEROIDAL    CONCRETIONS    IN    THE    SILURIAN    ROCKS. 

have  become  acquainted,  this  structure  is  observable.  The  separation 
of  calcareous  matter  into  nodules  from  among  the  component  parts  of  an 
original  mud  deposit,  can  be  as  well  seen  in  the  old  series  of  rocks, 
known  as  Silurian,  such  as  in  portions  of  the  Wenlock  shales  and  lime- 
stones of  that  series,  as  it  occurs  in  parts  of  Wales  and  the  adjoining 
English  counties,  as  in  far  more  modern  geological  accumulations.  So 
also  with  the  aggregations  of  siliceous  matter  in  the  nodular  or  spheroidal 
forms,  showing  that  similar  conditions  for  these  arrangements  and  adjust- 
ments of  parts  have  continued  to  prevail  through  a  long  range  of  geo- 
logical time.  The  following  section  (fig.  228)  of  part  of  the  upper  portion 

Fig.  228. 


of  the  Silurian  series  (Ludlow  Rocks),  of  Brecknockshire,  to  be  seen  at 
a  considerable  development  of  that  portion,  in  Cwm-ddu,  near  Llangam- 
march,  will  exhibit  the  arrangement  of  parts  of  this  arenaceous  rock,  in 
certain  beds,  in  a  spheroidal  form ;  layer  after  layer,  as  the  decompo- 
sition of  the  rock  shows,  having  been  arranged  round  somewhat  central 
points  of  aggregation  dispersed  in  certain  lines  of  beds.  Aggregations 
of  this  kind  occasionally  measure  many  feet  in  diameter.  Such  aggre- 
gations are  sometimes  only  to  be  detected  on  the  face  of  rocks  by  lines 
arising  from  the  stains  of  peroxide  of  iron,  which,  when  followed  out, 
are  found  to  correspond  with  spheroidal  surfaces. 

When,  geologically,  these  adjustments  of  the  parts  of  deposits  may 
have  been  effected,  it  is  not  easy  to  infer,  since  in  the  instances  of  those 
in  the  older  accumulations,  they  may  have  been  produced,  as  many  of 
those  in  certain  more  modern  accumulations  are  seen  to  have  been, 
before  the  solidification  of  the  sandy  portions  around  the  spheroidal 
aggregations  and  nodules,  the  whole  of  the  bed,  or  beds,  having  been 
submitted  to  further  conditions  for  consolidation,  after  the  separation  of 
certain  portions  of  them  into  such  aggregations  of  similar  matter. 

There  are  certain  other  separations  of  the  original  portions  of  a 
deposit,  where  the  particles  have  possessed  such  free  movement  and 
powers  of  adjustment,  that  they  have  been  enabled  to  gather  themselves 
into  crystals.  Of  this  the  crystals  of  the  sulphuret  of  iron  amid  the 
mud  deposits  of  all  geological  ages  is  an  example,  as  also  the  crystals 
of  sulphate  of  lime  in  numerous  clays.  Cubes  and  other  forms  of  iron 
pyrites  are  as  common  amid  the  oldest  fine  sedimentary  accumulations, 


CRYSTALS    OF    IRON    PYRITES    IN    CLAYS    AND    SHALES.    571 

occurring  in  a  manner  to  leave  little  doubt  of  the  aggregation  of  their 
component  particles  from  the  mud  in  which  they  were  diffused,  as  among 
the  clays  of  tertiary  deposits.  That  iron  pyrites  should  be  gathered 
round  organic  remains  in  rocks  of  different  ages,  particularly  in  those, 
such  as  have  been  mud  and  clays,  where  the  movement  of  its  component 
particles  may  be  inferred  to  have  been,  as  in  the  case  of  the  crystals 
above  noticed,  somewhat  easy,  would  be  anticipated,  inasmuch  as  the 
production  of  iron  pyrites  in  connexion  with  decomposing  animal  matter 
as  well  known.*  Thus  we  frequently  find  the  sulphuret  of  iron  incrust- 
ing  organic  remains,  as  crystals,  and  in  more  irregular  lumps  and 
patches,  particularly  amid  clay  and  shale  accumulations. 

Regarding  sulphate  of  lime  irrespectively  of  its  distribution  in  crys- 
tals, as  selenite,  amid  clays  and  shales,  it  often  constitutes  considerable 
nodules,  and  dispersed  irregular  masses,  as  if,  independently  of  original 
deposit  or  change  from  the  carbonate  by  the  introduction  of  sulphuric 
acid  amid  particles  of  limestone,  it  had  separated  out  from  the  body  of 
the  rock,  and  became  aggregated  amid  a  soft  muddy  deposit,  thrusting 
aside  the  latter.  Certain  nodular  portions  so  occur  in  particular  lines, 
that  we  may  suppose  them  to  have  been  produced  much  in  the  same  way 
by  segregation  as  the  nodules  of  the  carbonates  of  lime  and  iron,  above 
noticed.  At  the  same  time  beds  of  gypsum,  both  on  the  large  and 
small  scale,  also  so  occur  amid  clays,  marls,  and  shales,  especially  well 
seen  amid  portions  of  the  red  and  gray  marls  of  the  upper  new  red 
sandstone  series,  or  trias,  that  there  is  much  difficulty  in  deciding  as  to 
the  probability  of  their  original  production  from  solutions,  amid  the  clays  or 
mud  where  they  were  deposited,  in  a  manner  similar,  as  regards  general 
principles,  with  that  noticed  by  Professor  Bunsen,  or  partly  in  that 
manner,  arid  partly  by  segregation  into  veins  formed  subsequently  to 
the  general  accumulation  and  its  partial  induration.  The  section 
beneath  (fig.  229),  seen  at  Watchet,  Somersetshire,  amid  the  marls  of 
the  trias,  will  illustrate  a  mode  of  occurrence  of  not  an  uncommon  kind, 
wherein  beds  of  gypsum  a,  a,  a,  are  united  by  strings  of  the  same  sub- 
stance traversing  the  intermediate  marls  5,  6,  6,  in  various  directions, 
and  having  somewhat  the  appearance  of  cracks  filled,  inasmuch  as  the 
fibrous  gypsum  in  them  has  the  fibres  usually  at  right  angles  to  the 
walls  of  the  containing  marls,  as  if  crystallization  had  taken  place 

*  Mr.  Pepys,  in  1811  (Transactions  of  the  Geological  Society  of  London,  1st  series, 
vol.  i.)  was  among  the  first  to  publish  a  very  illustrative  case  of  the  production  of  iron 
pyrites  from  the  decomposition  of  the  bodies  of  some  mice  in  a  solution  of  sulphate  of 
iron.  Another  illustrative  instance  of  the  formation  of  iron  pyrites  upon  animal  matter 
in  a  decomposing  state,  occurred  at  the  bottom  of  a  mine-shaft,  near  Mousehole,  Corn- 
wall, where  a  dog  had  fallen  into  a  solution  of  iron,  and  its  body  was  found  surrounded 
by  iron  pyrites.  In  these,  and  other  well-known  cases,  the  hydrogen  evolved  from  the 
decomposition  of  the  animal  matter,  is  considered  to  take  the  oxygen  both  from  the 
sulphuric  acid  and  oxide  of  iron,  so  that  iron  pyrites,  or  bisulphuret  of  iron  is  formed. 


572  MODIFICATION    IN    THE    STRUCTURE    OF    ROCKS 

against  those  walls.     No  doubt  this  appearance  may  be  deceptive,  but 
at  all  events  it  becomes  an  interesting  object  of  inquiry,  to  ascertain 

Fig.  229. 


how  far,  under  such  modes  of  occurrence,  the  evidence  may  be  in  favour 
of  an  original  separation  and  deposit  of  the  sulphate  of  lime,  contempo- 
raneously with  the  matter  of  the  marls,  or  of  a  segregation  of,  at  least, 
part  of  the  same  substance  into  veins,  after  the  general  deposit,  from  a 
more  general  dispersion  of  the  sulphate  of  lime  amid  the  body  of  the 
accumulation. 

When  the  observer  reflects  upon  the  different  conditions,  to  which  the 
various  deposits  in  seas  and  bodies  of  fresh  water  may  have  been  sub- 
jected, posterior  to  their  original  accumulation,  he  will  not  fail  to  appre- 
ciate the  modifications  which  the  whole  mass  of  many  may  have  sustained. 
The  mere  change  from  being  superficial,  on  the  bottoms  of  seas  and 
other  bodies  of  water,  to  being  buried  beneath  many,  and  sometimes 
varied  additional  accumulations,  is  alone  a  condition  under  which  new 
adjustment  of  parts  may  arise,  and  this  without  a  change  in  the  relative 
distance  between  the  surface  of  the  sea  or  other  waters  and  the  deposit 
itself.  Should  the  accumulation  above  it  be  thick,  changes  (p.  427) 
arise  in  its  temperature,  with  their  consequences  as  regards  the  motion 
of  aqueous  solutions  distributed  through  beds  of  different  degrees  of 
porosity. 

The  geologist  should  direct  his  attention  to  the  still  greater  causes  of 
modification  and  change  which  would  follow  the  sinking  of  such  deposits, 
as  regards  the  crust  of  the  earth,  when  they  descended  into  compara- 
tively elevated  temperatures,  so  that  their  component  parts,  and  the 
various  solutions  with  which  they  may  be  moistened,  become  affected  by 
that  temperature.  The  springs  which  issue  from  various  rocks,  and  for 
which  the  supply  is  derived  by  the  simple  percolation  of  atmospheric 
waters  through  porous  beds  of  different  kinds,  until  thrown  out  by  less 
pervious  beds  (p.  47),  suffice  to  show  the  amount  and  kinds  of  substances, 
soluble  under  such  conditions,  and  which  remain  in  the  various  deposits 
effected  beneath  the  sea  or  other  waters,  after  many  of  these  accumu- 
lations have  been  more  or  less  solidified,  and  raised  into  the  atmosphere, 
where  they  now  constitute  portions  of  land  above  the  level  of  the  sea. 
In  the  various  borings  or  sinkings  for  mine  shafts,  the  driving  of  extensive 
tunnels  and  levels,  and  in  wells  of  various  kinds,  especially  of  those  termed 
artesian,  he  has  also  the  opportunity  of  ascertaining  the  soluble  contents 


FROM    EXPOSURE    TO    CHANGES    OF    TEMPERATURE.     573 

of  the  waters  which  may  be  disseminated  among  the  rocks  traversed ; 
and  where  such  waters  may  be  considered  in  a  somewhat  stagnant  state, 
except  so  far  as  movement  through  any  fissures,  joints,  and  the  pores 
of  the  rocks  themselves,  may  be  induced  by  differences  of  temperature 
from  the  surface  of  the  earth  downwards  towards  the  interior.  There 
does  not  exist  so  much  exact  information  as  to  the  substances  in  solution 
among  the  waters  disseminated  amid  rocks  in  this  manner  as  is  desirable ; 
neither  are  the  soluble  contents  of  the  various  waters  rising  through 
faults  on  the  surface  of  the  ground,  or  flowing  up  at  the  bottoms  of 
mines,  with  a  temperature  sufficiently  elevated  to  render  it  probable 
that  they  rose  from  greater  depths,  so  well  known  as  is  required  for 
properly  estimating  the  amount  and  kinds  of  substances,  which  may  be 
thus  circumstanced ;  but  there  still  exists  sufficient  knowledge  on  the 
subject  to  show  the  observer  the  value  of  investigations  in  this  direction. 

The  waters  rising  from  the  chalk  at  the  artesian  well  in  Trafalgar 
Square,  London,  and  which  are  obtained  from  their  dissemination  in 
that  rock,  show,  that  in  68-24  grains  of  solid  matter  in  an  imperial 
gallon,  18  grains  are  composed  of  carbonate  of  soda ;  while  the  car- 
bonate of  lime  contained  among  the  solid  matter  above  mentioned,  only 
amounts  to  3 '255  grains;  and  thus  the  waters  resting,  to  a  certain 
extent,  stagnant  in  the  chalk  beneath  London,  with  its  thick  covering 
of  (London)  clay,  exhibit  a  very  different  character  as  to  the  substances 
in  solution,  than  in  the  springs  which  flow  out  of  the  chalk  on  the  sur- 
face, where  that  rock  arrives  at  or  adjoins  it.* 

Among  the  various  substances  found  in  solution,  either  disseminated 
among  the  pores  of  rocks,  or  which  become,  as  it  were,  washed  out  of 
them  in  solution,  by  waters  percolating  through  them  and  issuing  as 

*  The  following  are  the  substances  contained  in  an  imperial  gallon  of  the  waters  of 
the  Trafalgar  Square  well,  according  to  Messrs.  Abel  and  Rowney : — 

Grains. 

Carbonate  of  lime, 3-255 

Phosphate  of  lime,  .......     0-034 

Carbonate  of  magnesia, 2-254 

Sulphate  of  potash, 13-671 

Sulphate  of  soda, 8-749 

Chloride  of  sodium, 20-058 

Phosphate  of  soda, 0-291 

Carbonate  of  soda, 18-049 

Silica, 0-971 

Organic  matter, 0-908 

In  the  cases  of  soluble  mineral  matter  disseminated  in  rocks,  such  as  the  chalk  be- 
neath London,  it  should  be  borne  in  mind,  that  when  there  is  a  movement  of  the  con- 
tained water  among  their  pores  or  fissures  to  supply  that  raised  to  the  surface  by 
pumping,  or  rising  from  boring  and  overflowing,  the  original  condition  of  somewhat 
stagnant  dissemination  becomes  changed  by  the  amount  of  the  water  thus  required, 
so  that  when  many  wells  reach  into  the  chalk,  as  beneath  London,  a  movement  of 
water  amid  the  body  of  that  rock  is  occasioned  towards  the  various  wells,  which  would 
not  have  taken  place  under  ordinary  natural  circumstances. 


574     CHLORIDE    OF    SODIUM    DISSEMINATED    AMID    ROCKS. 

springs,  the  observer  will  do  well  to  recollect  the  amount  of  chloride  of 
sodium  so  often  found.  That  it  should  be  a  somewhat  abundant  sub- 
stance would  be  expected  in  deposits  of  mud,  silt,  sand,  and  gravel 
effected  beneath  the  sea ;  as  also  that,  when  such  accumulations  were 
elevated  into  the  atmosphere,  and  rain-waters  found  their  way  to  the 
chloride  of  sodium,  it  should  be  removed  by  any  springs  thence  result- 
ing. It  will  be  seen  that  in  the  waters  disseminated  amid  the  chalk 
beneath  London,  this  substance  was  found  to  constitute  somewhat  more 
than  two-sevenths  of  the  whole  solid  contents  obtained  from  it.  Look- 
ing at  chloride  of  sodium  alone,  and  its  dissemination  among  beds  of 
quartz  or  other  siliceous  sands,  and  the  descent  of  the  whole  to  some 
very  elevated  temperature  by  depression  of  the  earth's  surface  in  any 
given  region,  some  effect  might  be  anticipated  from  the  production  of  a 
silicate  of  soda,  aiding  a  consolidation  of  the  sands,  in  the  same  manner 
as  a  salt  glaze  is  produced  by  the  potters. 

While  studying  the  variable  amount  of  consolidation  of  rocks,  the 
observer  cannot  fail  to  have  his  attention  arrested  by  the  different 
states,  in  this  respect,  in  which  he  sometimes  finds  the  beds  amid  a 
series  of  deposits,  grouped  together,  and  which  have  evidently  been 
subjected  to  the  same  general  conditions.  It  would  strike  him,  pro- 
bably, that  the  original  condition  of  the  deposits  could  not  fail  to 
produce  marked  differences  in  this  respect.  He  would  anticipate  that 
a  bed  of  pure  quartz  sand,  unmingled  with  other  and  muddy  matter, 
might,  if  cemented  by  somewhat  pure  silica,  form  a  substance  of  a 
harder  and  more  solid  kind  than  when  ordinary  sand  was  deposited, 
mingled  with  a  certain  portion  of  mud,  or  when  the  grains  were  com- 
posed of  different  substances,  so  that  they  could  be  variably  acted  upon 
by  the  matter  forming  the  cement.  In  the  one  case,  there  may  be  a 
rock,  commonly  known,  from  its  composition,  as  quartz  rock,  wherein 
it  is  sometimes  even  difficult  to  trace  the  original  grains  of  sand,  their 
surfaces  having  been  more  or  less  acted  upon  by  the  mode  in  which  the 
infiltration  of  the  cementing  silica  has  been  effected  ;*  while  in  the 
other,  a  sandstone  of  the  ordinary  amount  of  consolidation  has  been 
alone  produced.  The  occurrence  of  certain  quartz  rocks  among  the 
accumulations  of  all  geological  ages,  and  amid  other  and  contempora- 
neous beds,  can  be  often  well  studied ;  and  sometimes  the  passage  of 

*  The  arrangement  of  parts  in  certain  of  these  quartz  rocks  is  sometimes  such  that 
it  requires  very  careful  examination,  and  even  occasionally  a  thin  slicing  of  a  part,  so 
that  it  can  be  studied  through  transmitted  light,  in  order  to  distinguish  the  original 
grains  of  quartz  sand,  the  cementing  and  external  parts  of  these  grains  having  become 
so  much  blended.  For  the  most  part,  however,  the  detrital  origin  of  the  quartz  grains 
is  sufficiently  evident.  In  examining  these  rocks,  as  they  are  often  traversed  by  veins 
of  quartz,  it  is  needful  carefully  to  distinguish  between  the  latter,  which  are  merely 
the  ordinary  infiltrations  of  silica  into  cracks  and  fissures,  from  the  body  of  the  rock 
itself, — a  circumstance  that  has  not  always  received  attention. 


VAKIABLE    CONSOLIDATION    OF    DETRITAL    DEPOSITS.     575 

an  ordinary  sandstone  bed  into  a  quartz  rock  can  be  well  traced.  Of 
this,  a  quartz  rock,  amid  the  new  red  sandstone  series  near  Bridgend, 
Glamorganshire,  may  serve  for  an  example,  as  the  same  bed  can  be 
readily  followed  from  its  ordinary  sandstone  character  on  the  north  of 
the  town,  to  that  of  quartz  rock  on  the  road  to  Pyle  Inn.  Changes  of 
a  similar  kind  are  sufficiently  common  in  the  course  of  numerous  rocks, 
as  well  in  single  and  marked  beds,  as  in  numbers  of  them  collectively ; 
and  the  observer  will,  no  doubt,  have  to  seek  for  the  causes  of  these 
differences  as  well  in  the  unequal  or  variable  supplies  of  the  cementing 
matter,  according  to  subordinate  local  influences,  as  among  the  different 
original  compositions  of  continuous  deposits  ;  the  latter  often,  neverthe- 
less, appearing  a  sufficient  cause,  in  the  same  way  that,  in  a  series  of 
beds,  wherein  varieties  of  this  kind  are  very  striking,  much  original 
differences  are  apparent.  Certain  hard  quartzose  beds  beneath  others 
of  coal,  between  Swansea  and  the  Mumbles,  may  be  taken  in  illustra- 
tion of  a  probable  change  effected  by  the  introduction  of  silica,  or  some 
silicates,  after  their  original  deposit.  In  these  beds,  the  roots  of  a 
plant,  existing  when  the  coal  measures,  of  which  they  constitute  a 
portion,  were  accumulated  (Stigmarid),  once  as  freely  grew,  spreading 
out  their  finest  parts  in  the  evidently  yielding  ground  of  the  time  (p. 
482),  as  in  any  other  of  the  similarly  circumstanced  beds  of  the  same 
district  supporting  beds  of  coal,  and  known  as  underclays  (p.  491), 
though  now  they  are  bound  up  in  a  hard  siliceous  rock,  upon  which 
atmospheric  influences  have  as  little  action  as  on  ordinary  quartz  rocks, 
the  original  silty  and  looseljfr-aggregated  substance  of  the  beds  being 
converted  into  hard  quartzose  matter. 

Looking  at  the  mass  of  detrital  matter,  more  or  less  consolidated  by 
silica  or  the  silicates,  the  study  of  the  manner  in  which  this  may  have 
been  effected  by  them,  becomes  a  matter  of  no  slight  interest  to  the 
geological  observer.  He  finds  silica  in  a  pure  or  nearly  pure  state  in 
cavities  of  various  rocks,  especially  of  those  of  igneous  origin,  wherein 
hollows  and  vesicles  have  been  left,  it  being  seen  more  or  less  filling 
such  cavities  with  agates,  onyxes,  chalcedony,  and  rock  crystals,  and 
he  can  have  little  doubt  that  this  silica  was  introduced  into  the  hollows 
and  vesicles  by  infiltration  and  in  solution.  Indeed,  the  stalactitic 
forms  of  the  silica  often  sufficiently  show  this,  certain  agates,  as  well 
seen  upon  their  decomposition,  being  merely  forms  of  this  kind  eventu- 
ally filling  hollows.  At  other  times,  the  layers  of  the  siliceous  deposits 
occur  in  planes,  apparently  horizontal  at  the  time  they  were  effected. 
These  modes  of  occurrence  show  him  that  silica  has  been,  and  can  be, 
disseminated  amid  the  pores  of  rock,  often  hard  and  (so-called)  com- 
pact, its  particles  finding  their  way  for  deposit  in  a  pure  or  nearly  pure 
state  in  the  vesicles  and  cavities  of  such  rocks. 

In  investigations  of  this  kind  it  will  be  desirable  that  the  observer 


576  IMPORTANCE    OF    SILICA    AND    THE    SILICATES 

should  bear  in  mind  that  certain  silicates  are  not  difficult  of  decomposi- 
tion, as,  for  example,  those  of  potash  and  soda,  when  free  carbonic  acid 
may  be  present.  Upon  looking  at  this  subject  generally,  such  con- 
ditions may  be  inferred  not  to  be  so  rare  as  might  at  first  be  supposed. 
In  certain  regions  the  decomposition  of  the  felspars  alone  in  granitic 
and  some  other  igneous  rocks,  gives  rise  to  solutions  of  the  silicates  of 
potash  and  soda,  and  the  introduction  of  waters  having  free  carbonic 
acid,  derived  from  the  atmosphere,  in  them,  would  separate  the  potash 
or  the  soda,  as  the  case  might  be,  from  the  silica,  and  the  latter  be 
deposited  under  favourable  conditions  for  dissemination  amid  the  pores 
of  rocks.*  When  we  regard  the  manner  in  which  carbonic  acid  may 
arise  from  the  decomposition  of  organic  bodies,  be  mingled  with  water, 
and  act  upon  certain  silicates,  it  is  also  to  be  inferred  that  favourable 
conditions  may  arise  under  which  silica  could  be  thrown  down,  and 
when  vegetable  matter  afforded  the  carbonic  acid,  amid  the  pores  and 
cavities  of  a  certain  part  of  the  plants  themselves,  preserving  their 
finest  structures.f 

Though  silicic  acid  may  thus,  under  favourable  conditions,  to  which 
it  will  be  here  sufficient  to  direct  the  careful  attention  of  the  observer, 
be  easily  separated  from  certain  silicates  under  the  common  tempera- 
tures which  are  known  on  the  surface  of  the  earth,  or  found  at  moderate 
depths,  circumstances  with  regard  to  this  substance  become  changed 
when  the  heat  to  which  it  is  exposed  in  connexion  with  others  is  consi- 
derable. For  instance,  instead  of  decomposing  the  silicates  of  potash 
or  soda,  in  the  manner  above  mentioned^  the  carbonic  acid  would  be 
driven  off,  and  the  silicic  acid  would  remain  combined  with  the  alkalies. 
Again,  it  is  now  known  that  while  pure  silica,  so  very  important  geolo- 
gically, may  be  very  difficult  to  dissolve  in  water  at  the  temperature 
commonly  termed  ordinary,  when  the  heat  of  water  is  much  increased 
beneath  the  requisite  pressure,  it  may  be  considered  simply,  like  many 
other  substances,  as  more  soluble  in  highly-heated  waters  than  in  those 
of  more  moderate  temperatures.  Hence,  when  the  observer  regards  the 
facility  with  which  pressure,  and  elevated  temperature  may  be  obtained, 
by  descent  beneath  the  surface  of  the  earth,  he  will  see  that  no  slight 
modification  and  change  may  be  effected  by  the  mere  lowering  of  beds, 
moistened  with  water,  to  situations  where  such  water  could  act  upon  the 
silicates  of  the  rocks  among  which  it  may  be  disseminated,  and  even 
upon  silicic  acid  itself,  existing  as  grains  of  pure  quartz,  this  solution 
ready  to  be  affected  by,  and  to  produce  various  modifications  and 

*  Mr.  Henry  informs  me  that  when  experimenting  upon  silica,  he  found  that  a  sili- 
cate of  soda  was  decomposed  even  by  the  carbonic  acid  of  the  atmosphere,  and  the 
silica  deposited,  its  state  and  appearance  being  much  affected  by  the  degree  of  concen- 
tration of  the  solution. 

f  Fossil  siliceous  wood  is  thus  often  beautifully  preserved. 


IN    THE    CONSOLIDATION    OF    DETRITAL    DEPOSITS.       577 

changes  among  the  substances  forming  the  original  deposit,  or  an  admix- 
ture of  other  matter  subsequently  introduced  amid  its  parts.* 

The  action  of  considerable  heat  upon  rocks,  producing  change  and 
modification  of  their  component  parts,  can  often  be  so  studied  among  a 
minor  mixture  or  juxtaposition  of  igneous  rocks  and  those  evidently  pro- 
duced by  chemical  or  mechanical  deposit  in  water,  as  much  to  assist 
inquiries  into  the  manner  in  which  more  general  changes  and  modifica- 
tions may  be  aided,  and  even  sometimes  effected  on  a  great  scale.  In 
volcanic  regions,  substances,  such  as  clays,  become  hard,  in  fact  baked, 
as  any  tile  or  brick  may  be,  by  the  overflow  of  a  lava  current  among 
them,  the  result  being  the  same  as  might  be  expected  from  our  know- 
ledge of  the  action  of  heat  upon  '  different  varieties  of  clays  in  our 
potteries  and  porcelain  manufactures,  some  clays  burning  or  baking 
well,  others  ill.  In  such  cases  the  usual  result  is  the  production  of  cer- 
tain changes  by  the  action  of  the  heat  communicated  from  the  liquid 
lava.  A  still  further  modification  of  parts  is  effected  when,  without  loss 
of  the  original  form  of  the  deposit  acted  upon,  some  of  the  constituent 
particles  have  separated  from  the  main  mass  in  which  they  were  disse- 
minated, and,  joining  together,  have  produced  crystals,  there  having 
existed  a  power  of  movement  in  these  particles,  similar,  so  far  as  regards 
conditions  for  separation  from  the  main  mass,  and  the  movement  ob- 
tained, to  that  above-mentioned,  as  having  taken  place  in  yielding 
deposits,  such  as  clays. 

This  modification  in  the  arrangement  of  the  component  parts  of  rocks 
is  common  to  certain  igneous  products  of  all  geological  times.  It  can 
be  as  well  seen  amid  the  accumulations  of  igneous  matter  deposited  with 
the  old  Silurian  series  of  the  British  Islands,  as  in  various  regions 
among  the  volcanic  products  of  the  present  time,  and  is  one  requiring 
some  attention,  since  it  might  otherwise  much  interfere  with  the  conclu- 
sions of  an  observer  as  to  the  condition  under  which  the  component 
parts  of  a  rock  may  have  been  originally  gathered  together.  A  por- 
phyritic  character,  from  the  dissemination  of  certain  crystals,  as  for 
example,  those  of  some  of  the  felspars,  may  be  too  hastily  assumed  as 
indicating  the  rock  thus  characterized  to  have  been  in  a  complete  molten 
state. f 

*  It  is  to  be  hoped  that  investigations  in  this  direction  may  more  occupy  the  attention 
of  chemists  than  has  hitherto  occurred.  The  subject  is  full  of  interest,  and  appears 
one  likely  to  reward  the  labours  of  those,  who  taking  a  certain  class  of  geological  facts 
for  their  guide,  unite  with  them  the  conditions  of  high  temperature  beneath  great  pres- 
sure, as  also  exclusion  from  the  atmosphere,  such  as  may  be  inferred  to  exist  beneath 
given  depths  in  the  earth,  upon  the  hypothesis  that  heat  increases  downwards  towards 
the  central  portions  of  the  earth,  for  at  least  the  distance  at  which  water,  should  it 
continue  to  exist  as  such,  can  be  heated  up  to  a  very  elevated  temperature. 

f  Modifications  of  this  kind,  by  which  crystals  of  felspar  have  been  developed  in  rocks 
which  still  preserve  their  original  planes  of  deposit,  are  not  uncommon. 

37 


578  FORMATION    OF    CRYSTALS    IN    ALTERED    ROCKS. 

In  those  instances  where  the  rocks  have  evidently  been  fissured  prior 
to  the  introduction  of  the  igneous  matter,  which  thus  forms  a  simple 
dyke,  as  it  is  usually  termed,  or  some  tortuous  form  of  vein,  the  observer 
would  necessarily  infer  consolidation  sufficient  for  the  production  of  the 
fracture,  so  that  any  change  or  modification  found  in  the  rock  fractured 
would  have  taken  place  after  such  consolidation.  Cases  of  this  kind  of 
alteration  are  far  from  uncommon.  In  studying  them  it  becomes  need- 
ful to  recollect  that  not  only  the  mere  action  of  heat  may  be  brought  to 
bear  under  such  circumstances,  as  it  might  be  with  regard  to  the  clay  of 
a  brick  or  a  porcelain  vase,  but  also  that  moisture  and  solutions  would 
probably  be  disseminated  in  the  usual  manner  amid  the  pores  and  cracks 
of  the  rock  so  acted  upon,  and  this  often  beneath  much  pressure ;  any 
exposure  of  the  changes  thus  found  by  an  observer  being  due  to  some 
of,  or  all,  the  causes  of  denudation,  removing  former,  and  often  consi- 
derable, pre-existing  and  covering  portions  of  rocks. 

Changes  and  modifications  in  such  cases  must  necessarily  depend 
much  upon  the  substances  acted  upon,  and  the  manner  in  which  their 
component  parts  may  have  been  arranged.  The  most  simple  forms  of 
modification  are  those  where  some  substance,  such  as  common  lime- 
stone, may  have  its  parts  so  modified  that  a  crystalline  adjustment  of 
them  is  effected ;  the  portions  of  rock  in  contact  with  the  igneous  matter 
being  thus  altered,  the  greatest  modification  effected  nearest  the  igneous 
rock,  and  becoming  less  as  the  distance  from  it  is  increased.  Of  this 
kind  of  modification  the  often-quoted  instance  of  the  chalk  in  the  Isle 
of  Raghlin  may  be  taken  as  an  example.  In  this  case,  as  shown  beneath 
(fig.  230),  dykes,  a,  a,  a,  of  basaltic  rock  traverse  the  chalk  of  that  part 

Fig.  230. 


a    c  ac  a 


of  Ireland  (so  much  broken  up  by  eruptions  of  igneous  matter  at  a  period 
subsequent  to  the  chalk),  converting  that  rock,  between  and  adjoining 
them,  into  a  more  crystalline  substance,  <?,  c,  this  character  gradually 
disappearing  on  each  side,  b,  b.  The  alteration  at  the  contact  of  dykes 
of  igneous  rocks  is  not  confined  to  the  more  crystalline  arrangement  of 
the  traversed  and  adjacent  beds,  certain  minerals  being  very  often 
formed  by  the  movement  of  their  component  particles,  under  conditions 
when  they  could  adjust  themselves  into  crystals,  the  surrounding  matter 
giving  way  to  their  forms.  These  minerals  vary  much  according  to  the 
chemical  composition  and  physical  structure  of  the  deposits  acted  upon, 
and  also  according  to  the  volume  as  well  as  kind  of  the  igneous  rocks 
introduced. 

A  far  larger  amount  of  modification  and  change  is  necessarily  effected 
when  the  mass  of  igneous  rock,  introduced  amid  prior  accumulations,  is 


ALTERATIONS    OF    ROCKS    NEAR    GRANITIC    MASSES.     579 

considerable,  and  when  it  may  be  inferred,  as  is  often  the  case,  that 
this  intrusion  has  been  effected  at  depths  beneath  the  surface,  where 
there  was  no  contact  with  the  atmosphere ;  but  where,  on  the  contrary, 
any  water  distributed  amid  the  pores  or  crevices  of  the  previously- 
formed  rock,  consolidated  or  otherwise,  as  may  have  happened,  could 
not  escape,  with  any  solutions  it  contained,  having  been  confined  to  a 
certain  range,  beyond  which  a  continuation  of  the  same,  or  other  rocks, 
with  their  disseminated  moisture,  remained  much  in  its  condition  prior 
to  the  intrusion.  As  has  been  previously  remarked,  certain  of  the 
granitic  intrusions  appear  to  have  effected  much  change  in  adjacent 
accumulations.  In  various  parts  of  the  world,  such  modifications  of 
previously-formed  rocks  of  all  kinds,  in  contact  with  the  intrusions  and 
upheavals  of  granitic  matter,  is  most  marked,  the  altered  rocks  being 
traceable  to  their  more  usual  forms  of  ordinary  limestones,  argillaceous 
and  arenaceous  slates,  sandstones,  or  the  like  ;  some  even  of  these  rocks 
being  fossiliferous,  and  so  occurring,  that  their  relative  geological  age 
can  be  readily  assigned  them. 

Changes  and  modifications  of  this  kind  can  be  well  seen  to  have  been 
produced  upon  the  Cambrian  and  Silurian  rocks,  prior  to  the  accumula- 
tion of  the  old  red  sandstone,  in  parts  of  Ireland  (in  the  counties  of 
Wicklow,  Wexford,  &c.) ;  and  in  Southwestern  England,  upon  deposits 
of  a  later  date  before  the  deposit  of  the  new  red  sandstone ;  the  rocks 
acted  upon  being  of  varied  composition,  including  different  igneous 
accumulations,  as  well  thrown  out  in  a  molten  state,  as  deposited  as 
ashes  and  lapilli  beneath  water  (p.  529).  In  such  situations,  the  ob- 
server will  find,  as  he  might  anticipate,  the  consolidation  by  silica  and 
the  silicates  often  very  considerable,  beds  of  ordinary  sandstone  some- 
times exhibiting  their  component  grains  as  if  passing  into  the  matter 
cementing  them.  Judging  from  the  solvent  effects  of  water  and  steam, 
at  high  temperature,  upon  the  usual  silicates  employed  in  glass,  when 
moisture  is  disseminated  in  rocks,  and  raised  to  a  very  high  temperature, 
under  the  conditions  above  noticed,  the  silicates,  so  common  among 
various  argillaceous  and  arenaceous  slates  and  sandstones,  would  be 
acted  upon,  so  that  considerable  consolidation  by  them  became  frequent 
among  these  accumulations. 

Such  conditions  could  be  scarcely  otherwise  than  favourable  to  the 
aggregation  of  certain  substances  into  a  crystalline  state  upon  a  more 
extended  scale  than  in  the  case  of  the  smaller  bodies  of  molten  rock 
intruded  among,  or  rising  through  fractures  in,  prior  and  consolidated 
accumulations.  Certain  igneous  rocks  seem  sometimes  to  have  had  the 
volume  of  their  component  minerals  increased,  as,  for  example,  the 
crystals  of  hornblende  and  felspar  to  have  become  enlarged  near  the 
contact  with  the  granite,  as  if  the  volumes  of  two  or  more  of  the 
originally-sized  crystals  had  been  combined  into  one.  Sometimes  either 


580    PRODUCTION  OF  MINERALS  IN  ALTERED  ROCKS. 

with  or  without  increase  of  volume,  the  particles  of  the  hornblende  and 
felspar  of  an  ordinary  greenstone  become  so  adjusted  as  to  present  far 
greater  brilliancy  of  aspect,  so  that  the  rock  takes  the  appearance  of 
that  commonly  known  as  hornblende  rock.  Good  instances  of  this  kind 
are  to  be  seen  in  the  county  of  Wicklow.  In  like  manner,  the  old 
Silurian  volcanic  ash-beds  of  the  same  district  will  be  seen,  under 
similar  conditions,  with  the  brilliant  aspect  of  hornblende  slates.  The 
hornblende  rock  and  slate  of  the  Lizard  district,  Cornwall,  seem,  in 
like  manner,  little  else  than  ordinary  greenstone,  and  the  volcanic  ash 
of  the  Devonian  series,  modified  either  by  the  action  of  a  great  mass 
of  serpentine  which  has  flowed  over,  and  remained  upon  them,  or  by 
that  of  granitic  matter  beneath.  Seeing  the  slight  chemical  differences 
usually  noticed  between  hornblende,  augite,  and  hypersthene,  it  would 
be  expected  that  changes  would  be  effected  in  the  aspect  of  the  rocks 
containing  them,  under  the  circumstances  mentioned.  The  hypersthene 
rock  of  some  localities,  as,  for  example,  that  of  Cocks  Tor,  near  Tavis- 
tock,  Devon,  appears  to  come  under  this  head.  "While  on  this  subject, 
it  may  be  remarked  that  other  modifications  are  sometimes  observable, 
as  if  the  substances  composing  the  rocks  being  originally  more  varied, 
or  certain  others  having  entered  among  them  from  without,  after  expo- 
sure to  change  from  the  consequences  of  juxtaposition  to  great  masses 
of  molten  matter,  minerals  appeared  not  found  beyond  the  limits  which 
may  be  assigned  to  these  alterations  and  that  of  other  associated  accu- 
mulations. 

In  some  regions,  as,  for  example,  in  the  counties  of  Wicklow  and 
Wexford,  in  Ireland,  the  manner  in  which  andalusite  has  been  deve- 
loped, forging  off  other  portions  of  the  rock,  such  as  Arnica,  the  old 
stratification  of  the  deposit  being  still  retained,  is  highly  instructive. 
Near  the  intruded  granite,  the  crystals  of  this  mineral  are  occasionally 
found  of  large  size ;  and  while  they  have,  as  it  were,  shouldered  off  the 
other  substances  in  the  way  of  their  formation,  they  sometimes  exhibit 
portions  of  entangled  matter,  such  as  mica,  as  might  be  expected  in 
such  a  mode  of  production.  This  mineral,  not  uncommon  under  similar 
conditions,  is  precisely  one  of  those  which  would  be  expected  to  be  thus 
formed,  being  essentially  a  silicate  of  alumina  (the  base  of  the  clays),  a 
compound  forming  a  prominent  part  of  the  original  deposits  in  which 
these  andalusites  become  developed.  Ohiastolite  is  also  a  form  in  which 
the  silicate  of  alumina  appears  amid  altered  rocks,  and  is  one  not  un- 
common among  the  old  sedimentary  deposits  modified  in  contact  with 
granite  in  Devon  and  Cornwall.  Staurolite,  another  common  mineral 
developed  amid  mechanically-formed  deposits,  when  acted  upon  by 
masses  of  granitic  and  of  other  igneous  rocks  in  a  molten  state,  is  again 
one  which  might  be  expected,  being  essentially  composed  of  silica, 
alumina,  and  peroxide  of  iron,  with  the  addition  of  a  small  portion  of 


MINERAL  MATTER  TRANSMITTED  INTO  ALTERED  ROCKS.  581 


magnesia.  Cyanite  is  also  another  form  in  which  silicate  of  alumina 
occurs  developed  amid  altered  rocks.  Garnets  are  often  very  common 
in  those  which  have  suffered  modification  in  the  adjustment  of  their 
component  parts.  When  the  observer  refers  to  the  chemical  composi- 
tion of  these  minerals,  as  shown  by  various  analyses,  he  will  see,  by 
duly  considering  the  isomorphism  of  certain  substances,  that  their  com- 
ponent parts  may  be  readily  gathered  together  under  conditions  for 
their  movement,  from  amid  rocks  apparently  of  different  kinds.  While 
peroxide  of  iron  constitutes  a  prominent  portion  of  some  garnets,  it  is 
replaced  by  alumina  in  others ;  and  while  lime  forms  an  important  sub- 
stance in  most  garnets,  it  may  be  considered  as  replaced  by  protoxide 
of  iron  in  others.  Amid  the  various  altered  rocks  in  which  garnets 
have  been  developed,  the  pushing  aside,  as  it  were,  of  other  parts  of 
associated  mineral  matter,  when  their  crystallization  was  effected,  may 
be  well  studied.  Among  their  modes  of  occurrence,  those  where  they 
have  been  developed  amid  sandstones,  as  for  example,  near  Killan,  in 
the  county  of  Wexford,  are  highly  interesting,  the  grains  of  sand 
being  forced  asunder  to  permit  the  development  of  the  crystals  of 
garnets.* 

The  transmission  of  mineral  matter  from  the  igneous  and  heating 
body  into  the  prior-formed  rocks,  whether  these  were  or  were  not  con- 
solidated, seems  well  shown  when  boracic  acid  is  present  among  the 
former.  This  appears  to  have  been  the  case  around  much  of  the  gra- 
nite in  Devon  and  Cornwall,  where  schorl,  as  above  mentioned  (p.  550), 
is  not  only  found  disseminated  around  the  general  mass  of  granite  in 
numerous  localities,  but  also  constitutes  the  outer  portion  of  that  rock 
in  many  situations.  The  matter  of  the  schorl  (chiefly  silicic  acid, 
boracic  acid,  and  alumina)f  has  passed  into  the  pre-existing  and  me- 
chanically-formed rocks  in  many  places,  among  which  Fatwork  Hill 
and  Gastle  an  Dinas,  near  St.  Colomb,  Cornwall,  may  be  noticed  as 
localities  where  this  circumstance  can  be  well  seen.  The  boracic  acid 
might,  indeed,  have  solely  escaped  out  of  the  granitic  mass,  and 
meeting  with  the  other  essential  parts  of  schorl,  have  produced  the 

*  The  following,  among  the  numerous  analyses  of  garnet,  may  show  their  varied 
composition,  chiefly  due  to  isomorphism : — 


No. 
1 

2 
3 
4 

Silica. 

Alumina. 

Iron. 

Manganese 
Protoxide. 

Magnesia. 

Lime. 

Potash. 

Protoxide. 

Peroxide. 

39-85 
35-64 
42-45 
36-45 

20-60 

22-47 
2-06 

24-85 
9-29 

30-00 
24-48 

0-46 
3-02 

6-27 
0-28 

9-93 

13-43 
0-06 

3-51 
29-31 
6-53 
30-76 

2-35 

1.  Greenland  (Karsten) ;  2.  Altenau,  Hartz  (Trolle-Wachtmeister) ;  3.  Arendal  (Trolle- 
Wachtmeister) ,  4.  Beaujeux  (Ebelmen). 

f  The  analyses  of  schorl,  by  M.  Hermann,  gave  for  the  composition  of  black  schorl 


582 


MICA    SLATE    AND    GNEISS. 


latter  mineral  amid  the  grains  of  the  mechanically-formed  rocks  thus 
acted  upon. 

With  respect  to  mica,  also,  its  component  parts  often  appear  as  if 
introduced  from  the  igneous  rocks  into  many  of  the  sedimentary  de- 
posits against,  or  amid  which  they  have  been  intruded,  at  the  same  time 
that  certain  mechanically -formed  rocks,  such  as  arenaceous  deposits  con- 
taining detrital  mica,  seem  merely  to  have  had  the  micaceous  matter  so 
acted  upon,  as  to  form  better-developed  films  of  that  mineral,  its  com- 
ponent parts  having  adjusted  themselves  in  a  manner  more  resembling 
an  original  formation  of  mica.  In  like  manner,  also,  ordinary  felspar 
seems  to  have  been  thus  produced,  so  that  an  original  deposit  in  which 
grains  of  quartz,  felspar,  and  mica  have  been  accumulated  (the  detritus 
of  some  pre-existing  granite  rock),  would  become  the  laminated  com- 
pound of  that  character  known  as  gneiss,  while  one  formed  only  of  grains 
of  quartz  and  mica  would  become  mica  slate.*  Paying  due  regard  to 
the  original  composition  of  the  rocks  acted  upon,  with  proper  reference 
to  the  conditions  under  which  mineral  matter  may  be  passed  out,  and 
move  among  the  parts  of  the  igneous  rocks,  gradually  cooling  down 
during  a  long  lapse  of  time,  and  also  amid  the  pores  and  fissures  of  the 

from  Gornoschit,  near  Katherenenburg  (1),  of  brown,  from  Mursinsk  (2),  and  of  green, 
from  Totschilnaja,  Ural  (3),  and  of  black,  from  Monte  Rosa,  by  Le  Play  (4) :— 


1 

2 

3 

4 

Silica, 

39-00 

37-80 

40-54 

44-10 

Boracic  Acid,     . 

10-73 

9-90 

11-79 

5-72 

Alumina,    . 

30-65 

30-66 

31-77 

26-36 

Protoxide  of  Iron, 

1-58 

0-50 

— 

11-96 

Peroxide  of  Iron, 

6-10 

12-07 

3-65 

— 

Manganese  Protoxide 

— 

2-50 

0-90 

— 

Magnesia, 

9-44 

1-42 

6-44 

6-96 

Lime, 

— 

— 

— 

0-50 

Lithia, 

— 

0-50 

2-09 

— 

Potash, 

— 

— 

— 

2-32 

Soda, 

— 

2-09 

— 

— 

Carbonic  Acid,  . 

2-50 

1-66 

1-66 

— 

Chrome, 





1-17 

— 

Water, 

— 

— 

— 

0-60 

*  When  considering  the  various  kinds  of  modification  of  parts  which  deposits  may 
sustain  from  the  contact  of  great  masses  of  igneous  rocks  in  a  fused  state,  or  from  de- 
scent towards  the  interior  of  the  earth,  so  that  somewhat  similar  conditions  may  be 
produced,  it  is  not  a  little  interesting  for  the  geologist  to  direct  his  attention  to  those 
which  certain  of  them  would,  in  consequence,  present.  If,  for  example,  the  thick  beds 
of  the  millstone  grit,  forming  the  lower  part  of  the  coal-measure  series  (as  this  grit  occurs 
in  the  midland  and  northern  counties  of  England,  composed  of  quartz,  mica,  and  felspar, 
the  latter  usually  decomposed),  were  exposed  to  the  conditions  for  alteration  above 
noticed,  the  compound  would  have  a  granitic  appearance,  the  more  especially  if  the 
silicates  of  potash  or  soda,  or  both,  were  introduced,  and  again  united  with  the  remains 
of  the  previous  felspar.  This  rock,  even  as  it  is,  has  often  the  appearance  of  a  some- 
what decomposed  granite,  as  is  the  case  with  many  sandstones  of  the  coal  measures  of 
the  British  Islands  generally. 


CLEAVAGE    AND    JOINTS    OF    ROCKS.  583 

prior-formed  rocks,  the  observer  would  anticipate  very  numerous  com- 
binations, producing  great  modifications  and  changes  in  the  original 
composition  of  deposits.  He  will  find  the  study  one  of  great  interest, 
well  repaying  the  time  he  may  devote  to  it. 

Whether  such  modifications  and  changes  have  been  produced  by  the 
depression  of  deposits  to  depths  beneath  the  earth's  surface,  where  high 
temperature  may  cause  the  effects  noticed,  be  brought  about  by  similar 
action  from  the  juxtaposition  of  great  masses  of  rocks  elevated  or  intruded 
in  a  state  of  igneous  fusion,  or  consolidation  be  produced  chemically  in 
any  other  way,  affecting  great .  masses,  an  observer  may  not  be  unpre- 
pared to  consider  that  the  matter  thus  acted  upon  might  sometimes  ex- 
hibit an  arrangement  of  parts  corresponding  with  some  adjustment  on 
the  greater  scale.  Whether  those  arrangements  of  the  parts  of  rocks 
to  which  the  terms  cleavage  and  joints  have  been  given,  may  have  taken 
place  during  their  first  consolidation,  may  be  due  to  some  action  on 
the  large  scale  after  their  consolidation,  as  a  whole  or  in  part,  or  some- 
times have  been  produced  under  both  conditions  by  an  influence  acting 
independently  of  consolidation,  the  subject  is  one  which  would  appear 
to  require  more  extended  observation,  and  a  better  digested  body  of 
facts  than  has  as  yet  been  obtained. 

When  an  observer  has  before  him,  as  in  the  slate  quarries  of  North 
Wales,  a  mass  of  mineral  matter  which  he  has  reason  to  conclude  has 
once  been  a  bed  of  clay  or  mud,  now  not  only  consolidated,  but  also 
rendered  highly  fissile  in  planes  which  do  not  correspond  with  that  of 
the  original  deposit ;  such  planes  constituting  a  part  of  certain  others 
traversing  the  rocks  of  a  district  generally,  that  he  should  be  led  to 
infer,  with  Professor  Sedgwick  and  some  other  geologists,  that  the  finely 
divided,  yet  mechanically  deposited  matter  had  been  gathered  together  by 
some  force,  resembling  that  which  unites  the  particles  of  crystals  of  some 
given  combination  of  substances,  might  appear  probable.  The  cleavage 
of  crystalline  mineral  substances  in  planes  affording  solids  of  definite 
forms,  not  necessarily  resembling  those  which  are  external,  such  minerals 
composed  of  substances,  some  of  which  are  essential  to  the  mineral,  while 
others  seem  accidentally  caught  up  during  the  adjustment  of  the  former, 
may  still  further  induce  the  geologist  to  consider  the  subject  under  this 
point  of  view.  The  well-known  crystallized  sandstone,  as  it  has  been 
termed,  of  Fontainebleau,  wherein  mechanically-formed  siliceous  grains 
are  entangled  by  carbonate  of  lime,  the  whole  taking  the  external  ap- 
pearance of  crystallized  carbonate  of  lime,  show  him  how,  under  fitting 
conditions,  matter,  foreign  to  the  substance  crystallized,  may  be  en- 
tangled mechanically  in  it. 

Upon  studying  the  districts  where  the  cleavage  of  rocks  occurs,  the 
geologist  usually  finds  a  considerable  degree  of  uniformity  of  direction 
in  the  course  of  the  cleavage  planes,  where  they  cut  the  horizon,  through 


584 


CLEAVAGE    IN     SANDSTONES    AND    SHALES. 


a  variety  of  rocks,  and  over  considerable  areas.  In  certain  of  the  masses 
or  beds  in  which  this  has  taken  place,  the  effect  appears  to  have  been 
more  easily  produced  than  in  others,  and  it  may  be  sometimes  seen  that 
while,  in  associated  coarse  and  fine  grained  beds,  the  latter  are  beauti- 
fully cleaved,  the  former  appear  unaffected,  as  if  the  fine  particles  of 
the  one  could  be  easily  acted  upon,  while  the  coarser  grains  better  re- 
sisted a  new  adjustment.  This  conclusion  requires,  however,  much 
caution,  since  though  the  coarser  beds  may  not,  at  first  sight,  appear 
affected  by  the  arrangement  of  parts  producing  cleavage,  they  may  be 
found  when  broken  to  exhibit  divisional  .planes,  though  these  may  not 
be  so  numerous,  in  the  direction  of  those  in  the  finer-grained  beds  asso- 
ciated with  them.  Thus,  in  the  following  section  (fig.  232),  representing 
sandstone  beds,  a,  a,  a,  associated  with  argillaceous  beds,  6,  b,  5,  while 

Fig.  232. 


the  cleavage  may  be  well  developed  and  easily  seen  in  the  latter,  in  the 
former  it  may  also  be  found  by  fracture  of  the  beds,  or  by  their  decom- 
position from  atmospheric  influences.  This,  however,  by  no  means  con- 
stantly occurs,  the  conditions  under  which  the  fine-grained  beds  were 
cleaved,  not  having  apparently  adjusted  the  parts  of  the  other  beds,  so 
that  they  became  thus  divisible. 

In  certain  of  the  carboniferous  limestone  districts  in  Ireland,  where 
shales  are  associated  with  the  limestone  beds,  the  cleavage  of  the  former 
is  apparent,  while  the  latter  are  either  unaffected  by  it,  or  so  obscurely 
as  not  to  have  their  component  parts  adjusted  to  the  same  amount  by 


Fig.  233. 


a 


this  action.    The  preceding  section  (fig.  233),  at  Clonea  Castle,  County 
Waterford,  will  serve  to  illustrate  the  circumstance,  a,  a,  a,  being  beds 


MINOR    INTERRUPTIONS    IN    CLEAVAGE    ACTION.         585 

of  limestone  which  do  not  exhibit  cleavage,  while  the  shales,  6,  5,  usually 
more  or  less  calcareous,  and  associated  with  them,  are  cleaved.  The 
same  locality  also  shows  that  where  the  limestone  beds  becomes  some- 
what argillaceous,  partaking  partly  of  the  character  of  the  shales,  and 
partly  of  the  more  pure  limestones,  they  exhibit  marks  of  cleavage  ac- 
tion, as  if  the  particles,  being  then  less  coherent,  had  more  readily  given 
way  before  that  influence. 

The  following  sketch  (fig.  234)  may  be  found  useful  in  illustration  of 
the  modified  passage  of  cleavage  through  dissimilar  substances,  or  of 

Fig.  234. 


those  the  coherence  of  the  parts  of  which,  at  the  time  of  the  cleavage 
action,  may  have  been  different.  It  represents  a  portion  of  the  Devo- 
nian series,  on  the  east  of  Hillsborough,  near  Ilfracombe,  North  Devon, 
5,  5,  6,  being  thin  seams  of  limestone,  about  two  or  three  inches  thick, 
a,  a,  #,  argillaceous  slates  ;  the  argillaceous  slates  being  made  so  by 
cleavage.  The  true  planes  of  deposit  are  shown  by  those  of  the  in- 
terstratified  seams  of  limestone.  The  planes  of  cleavage  lamination 
traverse  the  whole  with  a  general  southern  dip,  slightly  interrupted  at 
the  seams  of  limestone,  where  their  course  is  modified ;  and  though  the 
limestone  is  divided  in  the  same  general  direction,  it  is  so  in  a  some- 
what contorted  manner,  as  shown  by  the  carbonate  of  lime  which  has 
been  subsequently  infiltrated  and  deposited  in  the  fissures  so  formed. 
The  somewhat  contorted  modification  of  the  cleavage  in  the  limestone  is 
shown  at  c.  In  such  cases  as  these  the  observer  may  consider  the  lime- 
stone to  have  been  consolidated  so  as  to  have  been  capable  of  a  certain 
amount  of  fracture,  while  the  mud  or  clay,  now  consolidated  as  well  as 
cleaved,  so  as  to  form  hard  slates  in  the  direction  of  the  cleavage,  had 
the  whole  of  its  component  parts  more  or  less  rearranged  in  certain  di- 
rections by  the  cleavage  action. 

At  times  an  interruption  may  be  traced  even  between  argillaceous 
beds  themselves,  when  these  are  piled  upon  each  other  in  a  manner 
marking  a  pause  in  the  deposit,  so  that  a  clear  surface  has  been  formed 
between  the  production  of  one  bed  and  the  accumulation  of  another. 


586 


CLEAVAGE  ON  THE  LARGE  SCALE. 


The  following  section  (fig.  235),  seen  near  Wiveliscombe,  West  Somerset, 
shows  that  while  the  planes  of  cleavage  take  a  general  direction,  a,  a, 


Fig.  235. 


they  are  slightly  bent,  and  undulate  where  the  partings  of  the  beds,  £>,  5, 
occur.  Whether,  at  the  time  of  the  cleavage  the  mere  break  in  the 
continuity  of  the  argillaceous  matter  was  sufficient  to  produce  this  effect, 
or  whether  any  kinds  of  substances  may  have  been  in  solution  in  water, 
occupying  the  interstices  between  the  beds,  causing  the  effects  observed, 
becomes  matter  for  investigation. 

These  interruptions  and  modifications  of  cleavage,  though  important 
for  the  study  of  its  cause  and  mode  of  action,  and  which  are  far  from 
being  always  observable,  become  lost  when  cleavage  is  traced  through 
considerable  masses  of  rocks,  and  viewed  on  the  large  scale.  We  find 
it,  as  Professor  Sedgwick  long  since  (1835)  pointed  out,  in  a  large  por- 
tion of  North  Wales,*  traversing  all  kinds  of  rocks,  in  given  directions, 
over  wide  areas,  notwithstanding  the  varied  position  of  their  beds.  In- 
deed, it  may  sometimes  be  readily  traced  through  them  when  contorted 
in  all  directions,  as  well  horizontally  as  vertically.  As  the  cleavage 
thus  cuts  through  even  contorted  rocks,  it  must  clearly  often  happen 
that  it  passes  through  their  planes  of  direction  at  various  angles.  This 
will  be  found  to  occur  more  frequently  than  might,  without  very  careful 
examination,  at  first  sight  appear ;  however  it  may  arise  that,  in  certain 
districts,  the  general  direction  of  the  true  bedding,  or  planes  of  deposit, 
may  be  found  to  coincide  with  that  of  the  cleavage,  as  regards  horizontal 
range,  whatever  variation  the  dip  of  the  cleavage  may  exhibit  as  regards 
itself,  or  the  true  bedding  of  the  rocks.  With  respect  to  a  mass  of 

*  "  The  whole  region,"  the  Professor  observes,  with  reference  to  the  country  near 
Rhaiadr  to  the  gorges  of  the  Eolan  and  Towy,  "  is  made  up  of  contorted  strata  ;  and  of 
the  true  bedding  there  is  not  the  shadow  of  a  doubt.  Many  parts  are  of  a  coarse 
mechanical  structure,  but  subordinate  to  them  are  fine  crystalline  chloride  slates.  But 
the  coarser  beds  and  the  finer,  the  twisted  and  the  straight,  have  all  been  subjected  to 
one  change.  Crystalline  forces  have  rearranged  whole  mountain  masses  of  them,  pro- 
ducing a  beautiful  crystalline  cleavage,  passing  alike  through  all  the  strata.  And 
again,  through  all  this  region,  whatever  be  the  contortions  of  the  rocks,  the  planes  of 
the  cleavage  pass  on,  generally  without  deviation,  running  in  parallel  lines  from  one 
end  to  the  other,  and  inclining  at  a  great  angle,  to  a  point  only  a  few  degrees  west  of 
magnetic  north." — "  On  the  Structure  of  Large  Mineral  Masses,  Trans,  of  the  Geological 
Society  of  London,"  2d  series,  vol.  iii.  p.  477. 


RANGE  OF  CLEAVAGE  THROUGH  CONTORTED  ROCKS.  587 

rocks  of  varied  kinds,  detrital  and  igneous,  with  some  admixture  of 
limestone,  traversed  by  cleavage  ranging  diagonally  to  the  general 
bedding,  the  chain  of  hills  known  as  the  Chair  of  Kildare,  Ireland,  may 
be  taken  as  a  good  example,  easily  visited.  The  range  of  the  cleavage 
coincides  generally  with  that  of  the  neighbouring  districts  in  the  counties 
of  Wicklow  and  Wexford ;  while  the  beds  have  a  direction  diagonally 
across  the  cleavage.  Among  these  hills  highly-crystalline  porphyries 
will  be  found  cut  by  cleavage,  as  well  as  the  argillaceous  and  arenaceous 
beds  of  the  Silurian  series  of  which  they  are  principally  composed.  As 
illustrative  of  variation  in  the  dip  of  the  cleavage,  and  of  the  true  beds 
seen  vertically,  and  especially  when  the  latter  are  contorted,  the  follow- 
ing section  (fig.  236)  of  part  of  the  Devonian  series,  on  the  coast  between 

Fig.  236. 


&  a  6 

Morte  and  Bull  Point,  near  Ilfracombe,  may  be  useful,  inasmuch  as  the 
true  beds,  chiefly  of  argillaceous  matter,  have  been  so  cleaved  in  a  con- 
stant direction,  that  while  the  cleavage  planes,  a,  a,  sometimes  cut  the 
bedding  at  right  angles,  at  others  they  coincide  with  it,  as  at  5,  b. 

Among  the  contorted  and  cleaved  rocks,  some  will  be  found  which 
may  lead  an  observer  to  consider  how  far  the  cleavage  took  place  after 
their  consolidation  into  the  hard  sandstone,  and  even  quartz  rock,  which 
he  may  find,  or  had  occurred  while  that  consolidation  was  in  progress. 
The  following  sketch  (fig.  237)  of  the  cleavage  of  hard  sandstone  beds, 

Fig.  237. 


with  some  slate,  part  of  the  Cambrian  series,  at  Bwlchhela,  nearly  oppo- 
site the  Penrhyn  slate  quarries,  North  Wales,  may  serve  to  illustrate 
this  subject,  a,  a,  being  the  lines  of  cleavage  traversing  the  disturbed 
beds.  Cleavage  of  this  kind  is  exhibited  on  a  much  larger  scale  at  the 
Holyhead  Mountain,  Anglesea,  amid  its  quartz  rock,  thus  rendered 
fissile  in  a  great  measure  across  the  bedding,  as  is  shown  in  the  follow- 
ing section  (fig.  238),  seen  on  the  cliff  opposite  the  South  Stack  Light- 
house ;  the  nearly  vertical  lines,  a,  a,  a,  representing  the  direction  of 


588 


ELONGATION    AND    DISTORTION    OF    ORGANIC 


those  of  cleavage,  varying  somewhat  in  their  amount  of  dips,  the  con- 
torted beds  being  composed  of  sandstone  and  slate  ;  the  former,  for  the 
most  part,  converted  into  quartz  rock. 


Fig.  238. 


Occasionally  the  observer  will  find  a  double  cleavage,  one  set  of  planes 
cutting  another,  as  in  the  annexed  section  (fig.  239),  where  two  sets,  a  a 


b  b 

and  b  5,  cross  the  beds  <?,  <?,  and  each  other,  dividing  up  the  mineral 
matter  of  the  deposit  into  elongated  forms  of  a  prismatic  character.* 
To  the  same  kind  of  action  we  may,  perhaps,  assign  those  somewhat 
regularly  formed  solids  into  which  arenaceous  beds  are  occasionally 
divided  in  countries  where  cleavage  has  been  effected.  In  such  cases 
the  cleavage  planes  cut  those  of  deposed  or  true  bedding,  either  at  right 
or  considerable  angles,  so  as  to  produce  forms  of  the  following  kind  (fig. 
240).  The  resulting  portions  of  rock  vary  considerably  in  size.  We 

Fig.  240. 


have  seen  some  not  much  larger  than  four  times  that  above  represented, 
though  they  are  usually  much  larger. 

As  to  the  relative  date  of  the  cleavage,  the  observer  may  sometimes 
obtain  evidence  of  importance.  Thus  in  Ireland,  in  the  old  red  sand- 
stone series  of  the  counties  Waterford,  Kerry,  and  Cork,  which  affords 
such  excellent  examples  of  cleavage,  it  will  probably  have  been  effected 
after  that  of  the  Silurian  rocks  of  Wicklow,  Wexford,  and  Waterford ; 

*  When  the  joints,  to  be  hereafter  noticed,  are  numerous  and  somewhat  close  to  each 
other,  the  rock  becomes  broken  up  into  a  multitude  of  short  irregular  prismatic  por- 
tions, of  a  marked  character. 


KEMAINS    BY    CLEAVAGE    ACTION. 


589 


inasmuch  as  portions  of  Silurian  slates  are  to  be  found  in  the  conglome- 
rates of  the  old  red  sandstone  of  Waterford,  clearly  worn  off  in  a  cleaved 
condition  from  the  subjacent  upturned  and  contorted  rocks,  on  which 
this  conglomerate  has  been  deposited.  Hence,  also,  it  may  be  inferred 
that  the  cleavage  of  the  mountain  or  carboniferous  limestone  shales 
found  in  some  parts  of  Ireland,  occurred  after  that  of  the  Silurian  rocks 
above  mentioned.  In  the  section  beneath  (fig.  241),  representing  veins 

Fig.  241.  a 


of  a  porphyritic  rock,  a,  a,  traversing  some  Devonian  slates,  6,  6, 
between  Cawsand  and  Redding  Point,  Plymouth  Sound,  the  slates  and 
the  igneous  rock  presenting  one  common  lamination  from  cleavage,  the 
latter  would  be  effected  after  the  intrusion  of  the  porphyry.  Upon 
studying  the  mode  of  occurrence  of  the  rocks  in  the  district,  it  will  be 
found,  as  above  noticed  (p.  542),  that  porphyries  of  this  kind  might 
belong  to  the  period  of  those  known  as  elvans  in  Cornwall  and  Devon. 

By  examining  the  conglomerates  usually  forming  the  lower  part  of 
the  new  red  sandstone  series  of  Devonshire,  the  observer  detects  portions 
of  the  prior-formed  rocks  laminated  in  a  manner  so  agreeing  with  cleav- 
age, that  he  may  infer  that  the  cleavage  of  the  older  Devonian  rocks 
was  effected  before  the  deposit  of  the  new  red  sandstone  in  that  district, 
and  subsequently  to  the  intrusion  of  the  granite. 

Upon  following  out  the  modification  and  adjustment  of  parts  in  rocks 
traversed  by  cleavage,  it  will  in  many  districts  be  seen  that  there  has 

Fig.  242. 


been  a  movement  and  rearrangement  of  them  in  directions  corresponding 
with  the  planes  of  cleavage.  There  have  often  been  elongations  in  those 


590 


DIFFERENT    DIRECTIONS    OF    CLEAVAGE    IN 


directions,  so  that  any  organic  remains  contained  in  the  beds  become 
distorted,  and  seem  as  if  pulled  out,  as  in  the  preceding  sketch  (fig.  242), 
where  several  shells  of  Strophomena  expansa  have  suffered  this  elonga- 
tion, in  the  direction  of  the  plane  of  cleavage,  a,  b,  at  Cwm  Idwal,  Caer- 
narvonshire, the  real  form  of  this  shell  being  that  represented  beneath 

Fig.  243. 


(fig.  243).     Sometimes  a  fossil,  such  as  a  trilobite,  may  be  doubled  down 
on  both  sides  as  over  a  ridge,  in  the  following  manner  (fig.  244),  the 


Fig.  244. 


sides  of  a  Oalymene  Blumeribachii,  a,  having  been,  as  it  were,  pulled 
down  by  the  cleavage,  the  real  form  of  this  trilobite  being  that  shown 
at  &.*  This  adjustment  of  a  fossil  to  the  planes  of  cleavage  has  been 
regarded  by  some  geologists  as  effected  by  a  purely  mechanical  move- 
ment, cleavage  being  referred  to  a  pressure  of  the  component  parts  of 
rocks  productive  of  the  effects  seen.  The  observer  will  do  well  to  con- 
sider the  evidence  adduced  in  support  of  this  view.f  At  the  same  time 
he  will  have  to  direct  his  attention  to  the  lamination  of  clays  effected 
by  electrical  action,  as  shown  by  Mr.  Robert  Were  Fox,J  and  Mr. 

*  The  specimen  whence  the  sketch  is  taken  is  from  the  lower  Silurian  rocks  of  Hen- 
dre  Wen,  near  Cerrig  y  Druidion,  North  Wales. 

f  See  writings  of  Mr.  Sharpe,  GeologicalJournal,  vol.  ii.  p.  74;  vol.  v.  p.  111. 

j  Mr.  Robert  Were  Fox  having  produced  lamination  of  clays  by  means  of  long-conti- 
nued voltaic  electricity,  pointed  out  (in  1837)  the  bearing  of  his  experiments  in  the 
Report  of  the  Polytechnic  Society  of  Cornwall  for  that  year  (pp.  20,  21,  and  68,  69). 
He  found  that  the  planes  of  the  lamina*  were  formed  at  right  angles  to  the  direction  of 
the  electric  forces.  With  reference  to  the  cleavage  of  rocks,  Mr.  Fox  considered  "the 


THE    SAME,    OR    JUXTAPOSED    DISTRICTS.  591 

Robert  Hunt,*  and  bear  in  mind  that  great  masses  of  rocks  are  often 
extended  layers  of  dissimilar  or  variously  aggregated  matter,  moistened 
by  saline  solutions,  in  which  common  salt  frequently  occupies  a  promi- 
nent place.  He  has  also  to  recollect  that  these  layers,  as  has  been 
pointed  out  by  Professor  Rogers,  f  may,  under  certain  conditions,  be 
differently  heated,  one  portion  descending  to  depths  beneath  the  surface 
of  the  earth,  where  a  high  temperature  could  act  on  such  parts  of  the 
rocks,  and  the  solutions  in  them,  so  that  thermal  electricity  may  be 
brought  to  influence  the  arrangement  of  their  component  parts. 
Viewing  the  subject  in  this  light,  the  particles,  all  other  things  being 
equal,  which  were  the  most  readily  movable,  such  as  those  of  clays  or 
unconsolidated  accumulations  of  silt,  would  appear  to  be  the  deposits 
most  readily  acted  upon,  and  there  appears  little  difficulty  in  inferring 
that  the  particles  of  matter,  such  as  those  which  have  composed  slight 
organic  bodies,  or  represent  such  particles  at  the  time  when  the  cleav- 
age action  was  in  force,  would  yield,  like  those  amid  which  they  were 
placed,  to  the  same  influence,  so  that  at  the  final  adjustment  of  all  the 
component  parts  of  a  cleaved  rock,  they  would  be  found  so  arranged,  as 
regards  their  original  position,  as  to  present  an  elongated  form. 

An  observer  will  sometimes  find  cleavage  occupying  a  somewhat  iso- 
lated position  in  a  given  area,  as  also  a  portion  of  a  generally-cleaved 
district  apparently  unaffected  by  any  action  of  the  kind.  Facts  illus- 
trating the  causes  of  these  differences  are  very  desirable,  as  are,  indeed, 
all  careful  observations  on  the  subject  of  cleavage,  considered  as  a  whole. 
Whatever  view  may  be  taken  of  its  cause,  extended  research  is  required 
as  to  the  direction  of  cleavage  through  many  and  variously  situated  re- 
gions, the  composition  and  mode  of  occurrence  of  the  rocks  traversed, 
and  the  changes  in  the  dips  of  the  planes  of  cleavage,  as  well  as  in  their 
directions.  In  certain  districts,  where  different  directions  of  cleavage 
seem  much  to  correspond  with  that  of  the  ranges  of  the  rocks  them- 
selves, and  these  are  of  different  geological  ages,  as,  for  example,  the 
northeast  portion  of  North  Wales,  where  certain  Upper  Silurian  depo- 
sits have  been  accumulated  upon  rocks  of  the  Lower  Silurian  series, 
upturned,  with  others  of  the  Cambrian  series  supporting  them,  it 
becomes  desirable  to  ascertain  how  far  one  direction  of  cleavage  is 
limited  to  the  rocks  of  one  general  range  and  not  found  in  the  other. 
In  other  words,  endeavouring  to  ascertain  how  far  the  cause  of  cleavage, 
or  its  mode  of  action,  may  have  depended  upon  the  general  position  of  the 
beds  in  the  rocks  themselves.  Now,  in  the  case  mentioned,  the  cleavage 

prevailing  directions  of  the  electrical  forces,  depending  often  on  local  causes,  to  have 
determined  that  of  cleavage,  and  the  more  or  less  heterogeneous  nature  of  the  rock  to 
have  modified  the  extent  of  their  influence." 

*  Experiments  carried  on  by  Mr.  Robert  Hunt  at  the  Museum  of  Practical  Geology, 
showed  similar  results  ;  Memoirs  of  the  Geol.  Survey,  vol.  i.  p.  433. 

f  Athenaeum,  Proceedings  of  British  Association,  Birmingham,  1849. 


592  JOINTS. 

of  the  older  rocks  (Lower  Silurian  and  Cambrian)  differs  considerably 
from  that  found  in  those  more  recently  deposited  (Upper  Silurian). 
When  the  observer  connects  this  with  the  circumstance  that  in  the  same 
country  (North  Wales)  one  set  of  rocks  (the  former)  had  been  disturbed 
and  contorted,  even  in  parts  probably  constituting  dry  land  (certain  of 
its  rocks,  at  least,  so  consolidated  that  they  could  be  broken  off  and  form 
the  materials  for  beaches,  with  vein  quartz,  pointing  to  the  filling  of 
cracks  and  fissures),  he  may  be  led  to  inquire  not  only  into  the  evidence 
of  the  cleavage  having  been  effected  in  the  older  deposits  anterior  to 
that  in  the  more  recent,  but  also  into  the  probability  of  this  action 
having  coincided  with  the  different  geological  times  during  which  the 
consolidation  of  both  may  have  taken  place. 

In  some  districts,  it  requires  no  slight  care  on  the  part  of  a  geologist 
to  ascertain  whether  the  lamination  of  a  rock  before  him  may  be  due 
to  that  of  original  deposit  or  to  cleavage,  far  more  without  some  expe- 
rience, than  might  at  first  be  thought  probable.  This  difficulty  is  occa- 
sionally also  increased  by  such  arrangements  of  parts,  apparently  pro- 
duced during  the  action  effecting  cleavage,  that  the  matter  of  the  rock 
is  gathered  under  somewhat  different  forms  in  the  planes  of  cleavage, 
causing  a  diversified  kind  of  lamination  of  a  very  deceptive  kind. 
Instances  of  this  fact  may  be  well  seen  in  Wales  and  in  Southern  Ire- 
land. Where  such  difficulties  present  themselves,  the  observer  should 
very  carefully  search  for  lines  of  organic  remains,  which  usually  afford 
clear  evidence  of  the  true  planes  of  bedding ;  a  slight  seam  of  such 
remains  may  often  suffice  to  place  him  right  with  respect  to  the  true 
bedding  of  a  mass  of  cleaved  rocks.  Sandstone,  limestone,  or  other 
rocks  marking  the  bedding,  should  also  be  carefully  sought,  so  that 
errors,  easily  committed  in  some  regions,  leading  to  the  confusion  of 
the  range  and  direction  of  the  true  bedding,  may  be  avoided.  In  a 
section  such  as  the  following  (fig.  245),  a  stratum  of  this  kind,  as  at  a, 

Fig.  246. 


may  show  the  true  bedding,  perhaps  otherwise  very  indistinct,  the 
cleavage,  6,  prominent,  so  as  to  give  a  false  appearance  of  deposit 
lamination  in  another  direction. 

Independently  of  the  arrangement  of  the  component  parts  of  rocks 
into  cleavage,  under  certain  conditions,  there  is  another  adjustment  of 
them,  to  which  the  term  joint  has  been  applied.  It  is  one  to  which 
the  observer,  among  consolidated  deposits  and  igneous  matter,  will 
often  have  to  direct  his  attention.  Joints  are  of  far  more  extended  oc- 
currence than  cleavage,  though  they  are  to  be  found  as  commonly  in 


DIRECTIONS    AND    RANGE    OF    JOINTS. 


593 


districts  -affected  by  the  latter,  as  in  others.  They  are  seen  as  fre- 
quently among  rocks  which  have  been  ejected  or  protruded  in  igneous 
fusion,  as  among  those  which  are  detrital,  or  which  may  have  been 
deposited  from  solution.  They  traverse  the  coarsest  conglomerates  as 
well  as  accumulations  of  the  finest  sediment,  such  as  once  may  have 
been  common  argillaceous  clay  or  mud.  The  distinction  between  coarse 
cleavage  and  closely-approximated  joints  may  be  sometimes  difficult  to 
determine,  as,  for  example,  in  the  section  beneath  (fig.  246),  represent- 
ing. 246. 


ing  a  porphyry  traversed  by  planes,  dividing  it  into  slabs  of  moderate 
thickness  in  a  given  direction,  on  the  summit  of  the  mountain  on  the 
south  of  Clynog  Vawr,  Caernarvonshire.  As  a  whole,  however,  the 
joints  so  traverse  all  kinds  of  rocks,  cutting  through  such  varied  bodies, 
those,  for  example,  often  gathered  together  in  a  coarse  conglomerate, 
and  in  such  definite  and  perfect  planes,  that  powerful  as  cleavage  has 
often  been,  the  action  productive  of  joints  sometimes  appears  to  have 
been  more  capable  of  dividing  the  mineral  matter  brought  within  its 
influence. 

It  is  often  by  means  of  the  minor  solids  into  which  many  rocks  are 
divided  from  the  intersection  of  joints,  or  by  that  of  the  latter  and  the 
planes  of  true  bedding,  that  they  can  be  employed  for  useful  purposes. 
Though  from  the  last  circumstance  long  known,  joints  have  only  at- 
tracted attention  as  among  objects  of  geological  interest  within  the 
present  century.  The  joints  of  granitic  rocks  appear  to  have  been 
among  the  earliest  of  those  observed  as  having  definite,  or  nearly  defi- 
nite directions  for  considerable  distances  in  given  areas.*  The  planes 

*  With  respect  to  the  directions  of  joints  in  Southwestern  England,  Professor  Sedg- 
wick  remarked  in  1821  (Cambridge  Philosophical  Transactions,  vol.  i.),  that  "  whenever 
any  natural  section  of  the  country  (Devon  and  Cornwall)  exposes  an  extended  surface 
of  the  granite,  we  find  portions  of  it  divided  by  fissures,  which  often,  for  a  considerable 
extent,  preserve  an  exact  parallelism  among  themselves."  He  further  adds,  that  "  these 
masses  are  not  unfrequently  subdivided  by  a  second  system  of  fissures,  nearly  perpendi- 
cular to  the  former,  in  consequence  of  which  structure  the  whole  aggregate  becomes 
separated  into  blocks  of  rhomboidal  form."  In  1833  Mr.  Enys  pointed  out  that  the 
vertical  joints  of  the  Penryn  granite  ranged  from  N.N.W.  to  S.S.E.,  varying  but  a  few 
degrees  from  those  points. — ("On  the  Granite  District  near  Penryn,  Cornwall,"  London 
*and  Edinburgh  Phil.  Mag.,  May,  1833.) 

From  very  careful  research  in  the  granitic  districts  of  Cornwall  and  Devon,   we 


594  JOINTS    IN    GRANITE. 

of  joints  in  these  rocks  not  only  present  much  interest  in  themselves, 
as  dividing  the  matter  of  the  rock,  so  that  in  some  which  contain  large 
crystals  of  felspar,  as  in  the  southwest  of  England,  and  other  districts, 
the  parts  of  the  divided  crystals  exactly  face  one  another  on  each  side 
of  the  joints,  but  also  as  coinciding  with  a  kind  of  cleavage,  usually 
found  ranging  parallel  to  the  fissures  of  jointing,  so  that  the  quarry- 
men  will  work  off  minor  portions  of  the  granite  by,  as  they  term  it, 
taking  the  grain  of  the  stone,  .this  grain  being  parallel  with  the  planes 
of  the  joints.  Though  the  joints  are  sufficiently  obvious,  this  grain 
may  not  be  perceptible  to  the  eye  of  an  observer,  at  the  same  time 
that  the  quarry-men,  working  from  experience  in  certain  directions  and 
planes,  produce  the  effect  desired  by  forming  holes  and  driving  nume- 
rous wedges  in  such  planes. 

The  columnar  appearance  of  granite,  produced  by  the  occurrence  of 
block  upon  block,  as  if  artificially  piled  on  each  other,  is  often  to  be 
seen  on  exposed  mountain  peaks,  bosses  protruding  from  more  rounded 
and  less  elevated  masses  of  that  rock,  and  on  sea  cliffs.  The  following 
sketch  (fig.  247)  may  serve  to  illustrate  the  appearance  of  jointed  granite 

Fig.  247. 


on  sea-coasts,  such  as  those  of  the  Land's  End  district,  Cornwall.  The 
horizontal  planes  shown  are  due  to  the  structural  arrangement  of  the 
granite  of  that  county,  and  to  be  seen  in  many  other  parts  of  the 
world,  in  accordance  with  the  external  form  of  the  general  mass.  It 
may  be,  that  in  the  joints  of  granitic  rocks  we  only  have  the  structural 
arrangement  of  parts  effected  at  their  consolidation,  so  that  the  diffe- 
rent origin  of  the  horizontal  from  the  vertical  planes  may  be  somewhat 

found,  as  elsewhere  stated  (Report  on  the  Geology  of  Cornwall  and  Devon,  1839),  that 
many  hundreds  of  observations  gave  about  80  per  cent,  of  cases  in  which  the  great 
joints  differed  only  14°  from  N.  25°  W.,  and  about  15  per  cent,  of  instances  in  which 
they  varied  between  14°  to  20°  from  that  point,  leaving  5  per  cent,  of  cases  in  which 
the  northerly  and  southerly  joints  more  approximate  to  the  cross  joints.  The  prevail- 
ing direction  of  the  joints  in  the  serpentine  district  of  Cornwall  ranges  within  a  few 
degrees  of  N.  25°  W.  In  this  body  of  rock,  as  in  the  various  granitic  portions  of  the 
same  district,  there  are  numerous  variations  in  direction,  but  viewed  as  a  whole  the- 
general  range  of  joints  is  as  above  stated. 


JOINTS  AMID  SEDIMENTARY  ROCKS.         595 

imaginary.  The  more  or  less  vertical  joints  of  some  granitic  areas  are 
certainly  often  continued,  as,  for  example,  in  Cornwall,  into  the  sedi- 
mentary rocks  amid  which  they  may  occur,  but  how  far  it  can  thence 
be  inferred  that  these  were  produced  subsequently  to  the  horizontal 
planes  in  the  granite  may  be  questionable,  inasmuch  as  the  jointing  of 
the  whole  area  may  have  been  effected  at  one  geological  period.  In- 
deed, as  above  noticed  (p.  552),  the  granite  may  often  be  inferred  to 
be  at  comparatively  slight  depths  beneath  such  districts,  supporting  the 
sedimentary  rocks  that  have  been  upraised. 

Though  it  may  be  sometimes  doubted,  regarding  the  more  or  less 
vertical  jointing  of  granitic  rocks,  how  far  it  may  be  considered  as 
originally  structural,  like  the  divisions  in  certain  felspathic  and  horn- 
blendic  rocks,  giving  a  columnar  character  to  them,  in  the  manner  of 
basalts  (p.  398),  there  can  be  no  doubt  as  to  the  joints  in  the  sedimen- 
tary rocks.  Here  the  observer  certainly  sees  the  matter  of  consoli- 
dated gravels,  sand,  silt,  and  clay,  or  mud,  distinctly  divided  by  planes 
cutting  through  them  in  marked  directions  for  considerable  distances. 
Such  appearances  as  the  following  (fig.  248),  are  often  presented  to  the 

Fig.  248. 


attention  of  an  observer  amid  sedimentary  accumulations,  particularly 
when  these  are  well  consolidated,  two  sets  of  joints,  shown  by  the 
planes  a  and  5,  intersecting  at  <?,  and  a  joint  parallel  to  a  appearing  at  d. 
The  most  striking  illustrations  of  the  action  of  the  power  productive 
of  joints  is  to  be  seen  in  conglomerates,  where  a  great  variety  of  peb- 
bles, and  of  different  sizes,  is  sometimes  found  divided  as  smoothly,  in 
given  planes,  as  if  these  pebbles  had  been  formed  of  soft  yielding  sub- 
stances, and  had  been  cut  by  some  thin  sharp  instrument,  dividing  them 
asunder  in  one  plane.  Good  illustrations  of  this  circumstance  may  be 
seen  in  the  conglomerates  amid  the  older  rocks,  and  perhaps  are  no- 
where better  exhibited  than  among  the  old  red  sandstone  conglomerates 
in  the  county  of  Waterford.  Huge  masses  of  the  conglomerate,  com- 
posed of  quartz  pebbles,  and  of  portions  of  older  arenaceous  and  other 
deposits,  as  also  of  igneous  rocks,  in  certain  localities,  may  be  found 


596 


JOINTS    AMONG    CONGLOMERATES. 


smoothly  cut  through,  and  separated  by  joint  planes.  In  the  Com- 
merachs,  as  for  example,  in  the  cliffs  rising  several  hundred  feet  above 
the  lakes,  they  seem  to  divide  the  mass  of  conglomerate  into  huge 
columns.  Upon  careful  examination,  the  division  presents  no  trace  of 
dislocation  or  movement,  the  faces  of  the  divided  parts  of  the  pebbles 
fitting  each  other  exactly.  Joints  of  this  kind  are  very  accessible,  and 
readily  seen  in  the  old  red  sandstone  conglomerate  resting  upon  up- 
turned Silurian  rocks,  opposite  the  town  of  Waterford.  Of  the  manner 
in  which  these  divisional  planes  pass  through  conglomerates,  without 
the  slightest  trace  of  movement  of  the  beds,  or  of  the  pebbles  in  them, 
the  best  opportunities  are  sometimes  afforded  on  sea-coasts,  especially 
where  the  beds  may  be  nearly  horizontal,  and  well  defined,  and  where 
the  tide  may  recede  considerably  from  the  shore.  Of  this  kind,  the 
following  sketch  (fig.  249)  of  a  joint  traversing  a  remarkable  conglo- 

Fig.  249. 


£_^ 


a 


merate  amid  the  mountain  limestone  series  on  the  coast,  near  Skerries, 
County  Dublin,  the  pebbles  being  of  considerable  size,  may  be  found 
illustrative.  The  surfaces  of  the  divided  pebbles,  composed  of  portions 
of  Cambrian  rocks,  probably  derived  from  masses  of  them  still  in  part 
remaining  in  the  vicinity,  are  as  smooth  as  if  no  divisional  plane  of 
the  kind  passed  through  them,  yet  it  is  one  not  only  cutting  through 
this  conglomerate,  but  the  mountain  limestones  with  which  it  is  asso- 
ciated. 

Joints  in  limestones  are  often  of  the  most  marked  kind.  In  many 
cases  there  is  no  difficulty  in  distinguishing  the  bedding  from  the  joints. 
In  others,  however,  the  observer  will  not  find  it  so  easy  to  determine 
between  the  two  surfaces,  without  much  care.  It  sometimes  happens, 
that  the  joints  have  a  much  more  marked  appearance  than  the  divisions 
of  true  bedding.  As,  for  example,  in  the  following  sketch  (fig.  250). 
wherein  the  joints  are  prominently  shown,  one  in  particular  being  some- 
what opened  at  a,  while  the  true  bedding,  b  b,  is  more  obscure.  In 
such  cases,  the  observer  has  carefully  to  search  for  lines  of  organic 
remains,  dissimilar  beds,  or  partings  of  shale  or  other  substances,  in 
order  to  be  sure  of  the  true  bedding. 


MOVEMENTS     OF    ROCKSAFTER    JOINTING.  597 

The  courses  of  joints,  though  often  of  a  marked  kind,  through  various 
rocks  in  the  same  district,  and  in  the  same  general  directions  for  long 

'  Fig.  250. 


distances,  as  if  the  power  producing  them  had  been  brought  into  action 
under  some  great  leading  influence,  affecting  a  great  mass  of  mineral 
matter  in  that  district,  however  modified  in  character  its  parts  may  be, 
appear  not  a  little  adjusted,  as  in  cleavage,  to  the  main  position  of  the 
component  beds,  there  being  frequently  a  tendency  in  joint  divisions  to 
take  courses  at  right  angles,  as  a  whole,  to  them.  As  in  cleavage,  also, 
divisions  resembling  jointing,  so  far  as  their  distance  from  each  other  is 
concerned,  appear  to  run  through  certain  beds  of  a  general  accumula- 
tion more  abundantly  than  in  others.  Of  this  kind,  the  divisions 
through  parts  of  the  shales  of  the  lias  near  Lyme  Regis  may  be  taken 
as  an  example.  Though  joints  are  not  there  observed  in  the  mass  of 
the  argillaceous  limestones  composing  that  deposit,  in  certain  beds  of 
shales,  on  the  west  of  the  town,  divisions,  perpendicular  to  the  beds, 
may  be  seen  to  run  like  so  many  planks  on  a  floor,  stretching  as  far  as 
the  beds  are  exposed  at  low  water. 

As  there  appears  little  reason  to  doubt  that  joints,  like  cleavage, 
have  been  formed,  under  suitable  conditions,  at  different  geological 
times,  and  as  these  cleaved  or  jointed  rocks  may  readily  have  been 
moved  after  they  were  divided  in  this  manner,  it  would  be  expected 
that,  sometimes,  the  position  of  the  one  and  the  other,  as  regards  their 
direction  with  the  horizon,  is  not  that  in  which  either  the  cleavage  or 
jointing  was  effected.  Cleaved  and  jointed  rocks  are  sometimes  found 
in  positions  to  render  such  subsequent  movements  probable.  For  ex- 
ample, the  old  red  sandstone  series  of  Southern  Ireland  reposes  upon 
Silurian  rocks  cleaved,  if  they  were  not  also  jointed,  prior  to  the  accu- 
mulation of  the  former,  and  the  same  series  is  also  traversed  by  similar 
divisions.  Upon  studying  that  portion  of  Ireland,  the  observer  finds 
that  the  old  red  sandstone,  with  also  the  carboniferous  or  mountain 
limestone  series,  resting  upon  it,  has  been  also  disturbed  since  its  de- 
posit ;  hence,  the  lower  rocks  having  been  again  moved  to  permit  the 
rolling  and  bending  of  the  great  mass  of  matter  resting  upon  them, 


598   COMPLICATION   OF   BEDDING,    JOINTING,    AND   CLEAVAGE. 

their  original  planes  of  cleavage,  if  not  of  joints  also,  can  scarcely  be 
in  their  original  position.  The  probability  of  such  movements  may, 
therefore,  somewhat  interfere  with  first  views  as  to  the  original  position 
of  cleavage  and  joints,  and  the  geologist  should  bear  in  mind,  that  the 
movement  of  a  body  of  rock,  divided  in  this  manner,  into  flexures, 
might  be  accompanied  by  the  friction  of  some  of  the  surfaces  of  the 
divisional  planes  upon  each  other,  thus  embarrassing  his  researches 
into  the  original  condition  of  such  surfaces.  Movements  of  this  kind 
may  give  an  uncertainty  to  the  slightly-inclined  planes  of  joints  which 
are  sometimes  found,  though  there  is,  as  yet,  no  evidence  to  show  that 
joints  have  originated  in  a  manner  to  render  divisions  in  the  mineral 
matter  improbable  at  these  angles  with  the  horizon.  Such  planes  of 
joints  require  to  be  well  distinguished  from  those  of  true  beds,  which 
they  often  much  resemble,  as,  for  example,  in  the  following  section 
(fig.  251),  where  a  mass  of  argillaceous  matter,  originally  a  thick  accu- 

Fig.  251. 


mulation  of  clay  or  mud,  though  now  consolidated  into  hard  rock,  shows 
joint  lines,  a  a  a,  and  sections  of  the  planes  of  cleavage,  b  b. 

Occasionally,  the  division  of  an  original  deposit  of  clay  or  silt,  by 
cleavage  and  joints,  becomes  most'  complicated,  requiring  no  slight  care 


Fig.  252. 


on  the  part  of  an  observer  to  arrive  at  the  surfaces  of  the  true  beds, 
more  especially  when  organic  remains  are  absent,  and  the  mineral  matter 


BENDING  AND  FRACTURE  OF  ROCKS.         599 

is  of  a  common  character  throughout.  Of  this  kind  of  complication, 
the  preceding  sketch  (fig.  252)  of  a  quarry  at  Brewer's  Hill,  County 
Wicklow,  may  be  useful  as  an  illustration.  The  true  bedding  is  a  plane, 
facing  the  reader,  while  there  are  divisional  planes  ranging  in  the  di- 
rection a,  a,  in  that  of  I,  b,  and  in  that  of  c,  c. 

Bending,  Contortion,  and  Fracture  of  Rooks.—  Though  it  has  been 
necessary  to  allude  to  the  disturbance  of  various  accumulations,  as  well 
igneous  as  those  formed  by  means  of  water,  while  noticing  rocks  of  dif- 
ferent kinds  which  have  been  more  or  less  moved  after  their  deposit  or 
intrusion,  it  may  be  desirable  to  call  attention  to  this  subject  as  one 
which  may  also  be  conveniently  considered  by  itself.  It  will  have  been 
seen,  when  pointing  out  the  intrusion  of  igneous  rocks,  that  the  disturb- 
ance of  mineral  matter  accumulated  at  one  geological  period,  while  the 
deposits  of  another  were  comparatively  unmoved,  assisted  in  affording 
evidence  of  the  relative  time  when  the  igneous  rock  may  have  been 
elevated  in  a  molten  state  from  beneath  (p.  538) ;  and  also  that  the 
arrangement  of  conglomerates  and  sandstones  against  or  around  beds  of 
prior-formed  disturbed  rocks  was  useful  in  showing  the  probability  of 
ancient  dry  lands  having  occurred  in  particular  situations,  edged  by 
beaches  and  coast  cliffs  (p.  459). 

Though  mountains  by  no  means  present  us  with  the  only  means  of 
studying  the  bending,  contortion,  and  fracture  of  rocks  on  the  large 
scale,  they  become  important  from  the  masses  of  matter  raised  in  them 
comparatively  high  into  the  atmosphere  and  sometimes  continuous  for 
considerable  distances,  the .  frequent  adjustments  of  lower  grounds  to 
them,  and  the  opportunities  afforded  for  obtaining  illustrative  sections 
in  various  planes.  A  glance  at  any  artificial  globe  of  fair  dimensions 
will  be  sufficient  to  show  the  ranges  or  chains,  as  they  have  been  termed, 
of  those  mountains  which  constitute  marked  ridges  upon  the  surface  of 
the  earth.  With  such  a  globe  before  him,  and  bearing  in  mind  the 
heights  of  the  various  ranges  or  chains  of  mountains  as  compared  with 
the  diameter  of  our  planet,  an  observer  may,  probably,  be  led  to  infer 
that,  however  elevated  and  important  these  may  be  considered  by  those 
wandering  amid  their  depressions,  or  striving  to  ascend  their  heights, 
viewed  as  ridges  on  the  surface  of  the  earth,  they  constitute  very  minor 
protrusions,  interfering  little  with  the  general  form  of  the  world.  It  is 
somewhat  important,  in  searching  for  facts  illustrative  of  the  production 
of  mountains,  that  their  relative  proportion  to  the  volume  and  diameter 
of  the  earth  should  not  be  neglected.  If,  in  the  following  diagram  (fig. 
253),  a,  I,  e,  represent  a  section  of  a  portion  of  our  planet,  from  its 
surface  a,  I,  to  its  centre  e;  the  thick  line,  a,  b,  would  be  the  elevation 
of  even  the  highest  mountains  as  compared  with  the  radius  of  the  earth. 
Hence  it  is  not  difficult  to  conceive  that  the  rending  of  any  portion  of 
consolidated  or  partly-consolidated  mineral'matter,  distributed  in  various 
ways  over  the  surface  a  b,  and  the  squeezing  of  the  sides  of  these  rents 


600       THE  VOLUME  OF  THE  EARTH  COMPARED 

or  fissures  against  each  other  (with  or  without  the  propulsion  upwards 

of  any  molten  substances  amid  interstices  in  the  squeezed  masses  of 

Fi   253  consolidated  or  partly-consolidated  mineral  matter), 


a 

el 


,£  would  present  ridges  of  varied  forms  more  or  less 
\fj  corresponding  with  the  lines  of  the  fissures. 

I  It  has  been  seen  that  igneous  rocks  have  been 

ejected  in  various  ways,  that  mineral  matter  worn 
|     from  them  by  the  action  of  the  sea  and  atmospheric 
J     influences,  or  obtained  in  solutions,  has  been  spread 
i  j      over  differently-sized  areas,  that  these  have  sometimes 

\  I      moved  up  and  down  as  regards  the  surface  of  the 

I      ocean,  and  that,  considering  rocks  to  have  met  with 
I  |       more  elevated  temperatures  when  depressed  (particu- 

I       larly  when  covered  by  superadded  mineral  matter 
I  i       above),  than  when  raised  into  the  atmosphere,  modifi- 


i 


cations  have  been  effected  in  the  arrangement  of  their 
component  parts.    Bearing  all  this  well  in  mind,  and 
giving  considerable  latitude  to  views  of  the  thickness  of 
I  the  earth's  surface  which  may  thus  have  been  moved,  if 

j  we  assume  this  thickness  to  extend  in  depth  even  to 

|         100  miles  (a  c,  b  d,  fig.  253),  we  merely  arrive  at  the 


(         relative  proportion  of  volume  and  thickness  of  the 
j          exterior  of  our  planet  shown  in  the  accompanying 
\  \          diagram  (fig.  254),  wherein  the  depth  of  the  100  miles 

is  represented  by  the  thick  line  forming  the  circle. 

Fig.  254. 


I 


[I 

',,  Having  prepared  himself  by  this  general  view  of 

J  the  relative  importance  of  the  volume  and  diameter 

of  the  earth  and  of  the  mountain  ridges  on  its  sur- 
face, the  observer  will  probably  feel  also  disposed  to  regard  the  con- 
tortions and  fractures  of  various  rocks  which  he  may  discover  in  such 


WITH  THAT  OF  MOUNTAIN  RANGES.         601 

ridges  with  reference  to  some  cause  acting  generally  over  the  surface 
of  our  planet,  since  he  finds  marked  mountain  ranges  in  all  extensive 
areas  of  dry  land.  If,  upon  further  investigation,  he  obtains  evidence, 
as  he  will  not  fail  to  do,  that  all  mountain  ranges  have  not  been  elevated 
to  their  present  positions  contemporaneously,  the  deposits  of  particular 
geological  periods  resting  upon  prior-formed  and  disturbed  beds  in  some, 
while  in  others  equivalents,  in  geological  time,  to  these  unmoved  de- 
posits are  themselves  disturbed  and  broken,  even,  perhaps,  covered  tran- 
quilly by  subsequently-formed  beds,  he  may  be  induced  to  conclude 
that  whatever  the  cause  of  mountain  ranges,  it  may  have  continued  in 
action  during  a  long  lapse  of  geological  time,  and  may  still  exist.* 

*  The  following  section  (fig.  255)  may  probably  be  useful  in  showing  the  relative  age 
of  disturbed  beds  of  rock  in  mountain  ranges.  If  the  rocks,  a  «,  are  found  resting 
quietly  on  the  upturned  strata,  b  b,  it  is  inferred  that  b  b  have  been  disturbed  prior  to 

Fig.  255. 


be  b 

the  accumulation  of  a  a;  and,  consequently,  if  a  a  be  a  known  rock  in  the  geological 
series,  a  relative  date  is  obtained  for  the  movement  of  the  beds  b  b,  so  far  as  relates  to 
a  a.  If  it  should  so  happen  that  there  are  no  commonly  known  deposits  absent  between 
them,  the  approximate  relative  date  of  the  uplifting  of  b  b  is  obtained.  Should  it  also 
occur,  in  any  range  of  mountains  or  disturbed  country,  that  other  accumulations,  c, 
are,  in  like  manner,  so  placed  relatively  to  the  deposits  b  b,  that  another  and  anterior 
movement  of  rocks  can  be  inferred,  then,  in  such  range  of  mountains  or  disturbed  dis- 
trict, there  would  have  been  two  distinct  movements,  one  prior  to  the  production  of  b  b, 
the  other  anterior  to  the  accumulation  of  a  a.  In  the  case  of  beds  covering  contortions, 
it  becomes  very  needful  carefully  to  observe  them  sufficiently  on  the  large  scale.  For 
example,  let  beds  a  a,  in  the  annexed  section  (fig.  256),  repose  quietly  on  the  contorted 

Fig.  256. 


b  c  b 

strata  b  b,  and  let  the  only  portion  exposed  to  view  be  where  they  are  cut  by  the  line  c; 
then  all  the  beds  would  appear  undisturbed,  and  it  would  be  only  by  moving  to  the 
right  or  left,  and  where  the  disturbed  strata  beneath  might  chance  to  be  fairly  exposed, 


that  the  real  mode  of  occurrence  may  be  found.     This  is  by  no  means  so  needless  a 
caution  as  might,  at  first  sight,  be  supposed,  particularly  when  the  bends  and  contor- 


602     EFFECTS  ON  A  GRADUALLY  COOLING  GLOBE. 

Upon  connecting  the  form,  volume,  and  diameter  of  the  earth  with 
the  relative  proportion  of  the  volume  and  height  of  mountain  ranges, 
such  as  those  of  the  Alps,  Andes,  and  Himalaya,  it  may  suggest  itself 
to  the  observer  to  consider  how  far  some  general  cause  for  these  compa- 
ratively trifling  ridges  and  rugosities,  little  interfering  with  the  even 
character  of  the  surface  of  the  world,  may  not  have  followed  some 
change  in  the  volume  of  the  earth  itself.  Should  he  try  the  hypothesis 
of  a  spheroid,  such  as  that  of  the  earth,  losing  heat  by  radiation  into 
surrounding  space,  by  which  a  given  volume  of  matter  parted  gradually 
with  its  temperature,  one  sufficient  at  first  to  keep  the  whole  in  a  liquid 
state,  perhaps  he  might  be  led  to  infer  that  an  oxidised  and  compara- 
tively cooled  superficial  covering  of  solidified  mineral  matter,  having  a 
prevailing  crystalline  arrangement  of  parts,  especially  in  its  lower  porr 
tion,  might  be  brought  under  conditions  by  which  it  would  have  to  crack 
and  ridge  up,  with  various  adjustments  as  to  foldings  and  fractures,  in 
order  to  adjust  itself  to  a  mass  below,  gradually  ceasing  to  occupy  some 
originally-supporting  space  beneath  it.  Upon  this  hypothesis,  the 
oxidation  of  the  various  elementary  substances  constituting  the  mass  of 
the  mineral  matter  known  to  us  on  the  surface  of  the  globe,  has  to  be 
regarded,  inasmuch  as  such  oxidations  would  add  to  the  volume  of  the 
elementary  substances  on  that  surface,  and  thus  alone  aid  in  altering 
the  exact  fitting  of  a  crust  of  mineral  matter  upon  the  remaining  por- 
tion of  the  earth  beneath,  the  elementary  substances  in  which  had 
remained  unchanged. 

Be  this  as  it  may,  and  whatever  the  hypothesis  employed  to  arrive 
at  the  cause  of  mountain  chains,  it  appears  desirable  so  to  examine  into 
the  facts  connected  with  the  arrangement  of  the  masses  of  mineral 
matter  of  which  mountain  ranges  may  be  composed,  that,  while  all  due 
regard  be  paid  to  individual  chains,  observation  should  also  be  directed 

lions  are  upon  the  large  scale.  While  on  this  subject  it  may  be  useful  to  notice  the 
imperfect  knowledge  of  the  dip,  or  inclination  of  beds,  from  one  view  of  them  only,  since 
they  may  even  appear  horizontal,  as  in  the  preceding  sketch  (fig.  257),  while  in  reality 
they  have  been  much  disturbed,  forming  a  portion  of  some  bent  or  contorted  rocks,  as 
is  shown  in  the  following  view  (fig.  258),  supposed  that  of  the  same  cape  on  a  coast  (pt 
in  both  figures)  projecting  from  the  main  land,  a  a. 

Fig.  268. 


DIRECTIONS    OF    MOUNTAIN    CHAINS.  603 

to  the  subject  on  the  larger  scale.  The  earth  so  little  differs  from  a 
sphere  in  form,  that,  in  investigations  of  this  kind,  it  may  be  regarded 
as  one  composed  of  matter  upon  which  some  general  action  tending  to 
ridge  its  surface  might  also  produce  results  on  that  surface  of  a  definite 
general  kind,  supposing  forces  and  resistances,  and  all  other  circum- 
stances, equal.  It  is  in  this  supposition  of  exactly  equal  conditions 
that  there  may  be  much  difficulty  with  such  relatively  minor  volumes  of 
matter  as  mountain  chains,  so  that  even  inferring  some  constant  action, 
it  may  be  so  modified  by  circumstances  as  to  be  materially  concealed 
from  observation.  To  the  direction  of  lines  of  disturbances  on  the 
earth's  surface,  productive  of  mountain  chains,  or  otherwise,  as  may 
have  occurred,  much  attention  has  been  given  of  late  years,  in  conse- 
quence of  the  labours  of  M.  Elie  de  Beaumont  on  this  subject.*  He 
has  inferred  that  there  is  evidence  to  show  that,  during  the  lapse  of 
geological  time,  the  disturbances  of  the  earth's  crust  have  been  effected 
in  given  directions,  at  certain  times,  and  that  these  disturbances  have 
taken  place  along  considerable  fractions  of  the  great  circles  of  our 
planet,  f  He  has  further  considered  that  there  have  been  several  dis- 
tinct systems  of  disturbance,  each  marked  by  a  given  direction.  When 

*  The  first  account  of  the  views  of  M.  Elie  de  Beaumont  on  this  subject  was  commu- 
nicated to  the  Academy  of  Sciences  of  Paris,  in  June,  1829. 

f  M.  Elie  de  Beaumont  remarks,  in  a  communication  to  the  author,  in  1831  (Geolo- 
logical  Manual,  1831),  "Pursuing  the  subject,  as  far  as  my  means  of  observation  and 
induction  will  permit,  it  has  appeared  to  me  that  the  different  systems  (of  mountains 
and  disturbed  rocks),  at  least  those  which  are  at  the  same  time  the  most  striking  and 
recent,  are  composed  of  a  certain  number  of  small  chains,  ranged  parallel  to  the  semi- 
circumference  of  the  earth's  surface,  and  occupying  a  zone  of  much  greater  length  than 
breadth  ;  and  of  which  the  length  embraces  a  considerable  fraction  of  one  of  the  great 
circles  of  the  terrestrial  sphere.  .  .  .  The  secular  refrigeration,  that  is  to  say,  the 
slow  diffusion  of  the  primitive  heat  to  which  the  planets  owe  their  spheroidal  forms, 
and  the  generally-regular  disposition  of  their  beds  from  the  centre  to  the  circumference, 
in  the  order  of  specific  gravity,— the  secular  refrigeration,  on  the  march  of  which  M. 
Fourier  has  thrown  so  much  light,  does  offer  an  element  to  which  these  extraordinary 
effects  (the  elevation  of  mountain  chains)  may  be  referred.  This  element  is  the  rela- 
tion which  a  refrigeration  so  advanced  as  that  of  the  planetary  bodies  establishes 
between  the  capacity  of  their  solid  crusts  and  the  volume  of  their  internal  masses. 
For  a  given  time,  the  temperature  of  the  interior  of  the  planets  is  lowered  by  a  much 
greater  quantity  than  that  on  their  surfaces,  of  which  the  refrigeration  is  now  nearly 
insensible.  We  are,  undoubtedly,  ignorant  of  the  physical  properties  of  the  matter 
composing  the  interior  of  these  bodies;  but  analogy  leads  us  to  consider,  that  the 
inequality  of  cooling  above  mentioned  would  place  their  crusts  under  the  necessity  of 
continually  diminishing  their  capacities,  notwithstanding  the  nearly  rigorous  constancy 
of  their  temperature,  in  order  that  they  should  not  cease  exactly  to  embrace  their 
internal  masses,  the  temperature  of  which  diminishes  sensibly.  They  must  therefore 
depart,  in  a  slight  and  progressive  manner,  from  the  spheroidal  figure  proper  to  them, 
and  corresponding  to  a  minimum  of  capacity ;  and  the  gradually-increasing  tendency 
to  revert  to  that  figure,  whether  it  acts  alone,  or  whether  it  combines  with  other  internal 
.causes  of  change  which  the  planets  may  contain,  may,  with  great  probability,  completely 
account  for  the  ridges  and  protuberances  which  have  been  formed  at  intervals  on  the 
external  crust  of  the  earth,  and  probably  also  of  all  the  other  planets." 


604  CONDITIONS    EFFECTING    THE    OBLITERATION 

more  recently  describing  some  lines  of  this  kind  which  he  considers 
referable  to  certain  systems,  succeeding  each  other  in  the  order  of  geo- 
logical time,  and  all  of  relatively  ancient  geological  date,  M.  Elie  de 
Beaumont  takes  occasion  to  remark,  after  alluding  to  the  systems  of 
small  arcs  of  great  circles,  that  "  the  fundamental  problem  presented 
by  a  like  system  of  small  arcs  observed  on  the  surface  of  the  globe, 
where  they  are  marked  by  the  crests  of  mountains  or  by  the  outcrop  of 
beds,  consists  in  determining  the  great  circle  of  comparison,  to  one  of 
the  elements  of  which  each  of  the  small  arcs  observed  is  parallel."* 
Thus  while  estimating  the  directions  of  disturbance  at  different  geolo- 
gical times,  with  reference  to  the  views  of  M.  Elie  de  Beaumont,  the 
observer  would  have  to  bear  in  mind  the  great  circles  of  comparison  to 
which  the  directions  of  any  ranges  of  mountains  or  masses  of  disturbed 
beds  are  to  be  referred. 

In  investigations  of  this  kind,  the  geologist  has  to  consider  not  only 
any  exertion  of  force  tending  to  disrupt  portions  of  the  earth's  surface, 
acting  generally  or  partially,  but  also  the  kind  of  resistance  offered, 
one  which  may  be  materially  modified  by  any  variable  thickness  of  the 
solid  matter  acted  upon,  and  by  variations  in  the  coherence  of  portions 
of  that  matter.  As  in  all  movements  of  this  order,  differences  in  the 
lines  of  least  resistance  to  some  given  force,  independently  of  those  in  that 

*  "  The  small  arcs  determined  by  observation,"  continues  M.  Elie  de  Beaumont 
(Bulletin  de  la  Soc.  Ge"ologique  de  France,  t.  1846-7),  "maybe  generally  considered 
as  being  themselves  infinitely  small  secants  or  tangents  to  so  many  small  circles 
resulting  from  the  intersection  of  the  surface  of  the  sphere  with  planes  parallel  to  the 
great  circle  of  comparison,  forming  the  equator  of  the  whole  system.  Each  of  these 
small  circles  is  a  parallel  with  respect  to  the  equator  of  the  system  ;  it  has  the  same 
poles  as  it,  and  these  poles  are  the  two  points  where  all  the  great  circles  perpendicular 
to  the  small  arcs,  constituting  the  system  of  parallel  traces  determined  by  observation, 
intersect. 

"The  problem  arising  from  such  a  system  of  parallel  traces  observed  on  the  surface 
of  the  globe  consists  in  determining  these  two  poles,  "or,  which  amounts  to  the  same 
thing,  its  equator,  i.e.,  the  great  circle  of  comparison  to  which  each  of  the  small  arcs 
observed  may  be  considered  as  parallel.  This  determination,"  observes  M.  Elie  de 
Beaumont,  "would  be  easy,  and  might  be  made  after  two,  or  at  least  a  few  observa- 
tions, if  the  condition  of  parallelism  were  rigorously  satisfied ;  since,  however,  this  in 
general  is  but  approximately  accomplished,  the  determination  of  the  great  circle  of 
comparison  can  only  follow  from  the  means  of  numerous  observations,  well  combined 
with  each  other ;  and  thus,  while  the  observations  are  not  very  multiplied  or  spread 
over  a  wide  space,  we  can  only  advance  towards  this  determination  by  successive 
approximations." 

As  it  would  be  quite  impossible  to  present  a  correct  view  of  the  different  systems  of 
disturbance,  without  the  needful  tables  and  calculations  on  which  he  has  founded  them, 
and  which  would  be  here  out  of  place ;  and  as  it  would  moreover  be  extremely  difficult 
satisfactorily  to  abridge  the  very  condensed  statements  of  M.  Elie  de  Beaumont,  wo 
would  refer  the  geological  observer  to  his  memoir  in  the  "  Dictionnaire  Universelle 
d'Histoire  Naturelle,"  t.  xii.  p.  167,  for  his  most  extended  and  recent  general  memoir 
on  this  subject;  one  which,  it  is  understood,  will  be  treated  still  more  at  large,  nnd  uj> 
to  the  present  time,  in  a  work  now  preparing  by  M.  Elie  de  Beaumont,  and  devoted  to 
his  views  respecting  the  great  disturbances  on  the  earth's  surface,  produced  at  distinct 
geological  times. 


OR  PRESERVATION  OF  MOUNTAIN  RANGES.      605 

force  itself,  would  produce  very  marked  differences  in  the  ranges  of 
disturbed  rocks,  especially  on  the  minor  scale ;  and  in  researches  of 
this  kind  it  may  not  be  easy  always  to  estimate  very  correctly  the 
value  of  a  so-called  minor  scale.  If  an  observer,  aware  of  the  general 
geological  structure  of  the  British  Islands,  and  of  a  few  thousand 
square  miles  of  the  adjoining  portion  of  the  continent  of  Europe,  and 
duly  weighing  the  probability  of  the  mode  of  occurrence  of  the  different 
rocks  to  a  depth  not  extending  to  even  more  than  three  or  four  miles, 
supposes  this  mass  of  variably-accumulated  matter  to  be  ridged, 
squeezed,  and  contorted  by  a  force  acting  in  some  given  direction,  so 
as  to  produce  a  lofty  chain  of  mountains  like  the  Alps  or  the  Himalaya, 
he  would  expect  that  very  material  minor  modifications  are  not  unlikely 
to  be  produced  in  the  direction  of  the  various  parts,  and  even  that  these 
might  extend  and  interfere  with  the  direction  of  the  range  itself.  If 
the  great  masses  of  igneous  rocks,  such  as  the  granites  of  various  parts 
of  the  area  mentioned,  are  to  be  inferred  as,  so  to  speak,  anchored 
somewhat  firmly  beneath,  a  crush  acting  upon  them  and  the  detrital 
accumulations  by  which  they  may  be  surrounded  superficially,  or  be 
covered  by,  to  various  depths,  would  be  expected  to  be  marked  by  an 
arrangement  of  the  mineral  matter  in  accordance  with  its  different 
coherence,  form,  and  thickness. 

As  during  the  progress  of  geological  time  so  much  of  the  earth's  sur- 
face, formed  of  either  igneous  products  or  strewed  over  with  detrital  or 
chemically-deposited  matter  of  various  kinds,  as  also  with  the  remains 
of  animal  and  vegetable  life,  has  been  covered  by  more  modern  accu- 
mulations of  the  like  kind,  even  now,  over  wide-spread  areas,  conceal- 
ing them,  it  becomes  no  easy  task  for  the  geologist  to  picture  to  him- 
self the  surface  conditions  of  our  planet  at  given  periods,  so  that  the 
disturbed  and  undisturbed  portions  may  be  duly  estimated.  This 
becomes  the  more  difficult  as  his  investigations  extend  to  the  earlier 
periods,  since  not  only  may  so  much  of  the  then  surfaces  of  the  earth 
be  now  buried  beneath  more  modern  accumulations,  but  even  the  ridg- 
ing of  such  surfaces,  constituting  mountains,  may  have  been  obliterated 
by  that  action  of  the  sea  and  atmospheric  influences  to  which  the  term 
denudation  has  been  applied.  Looking  at  these  sources  of  the  removal 
of  mineral  matter,  and  for  the  moment  inferring  all  other  conditions 
to  be  equal,  the  older  a  range  of  mountains  the  less  should  we  expect 
the  remains  of  it ;  and  conversely,  the  more  modern  the  range  the  more 
should  we  expect  to  find  it  unaltered  in  its  form  and  general  character. 
Here  at  once  the  differences  in  the  other  conditions  present  themselves. 
Contemporaneously-produced  ranges  of  mountains,  and  even  portions 
of  them,  may  have  been  acted  upon  very  variously.  One  range,  or 
part  of  it,  in  some  given  area,  might  remain  as  when  thrust  into  the 
atmosphere,  modified  only  by  the  influences  to  which  it  has  been  therein 


606        LATERAL    PRESSURE    OF    BEDS    AMID    MOUNTAINS. 

exposed,  while  in  another  area,  or  part  of  one,  the  land  may  have  been 
depressed  beneath  and  raised  above  the  sea  level,  even  several  times, 
with  the  attendant  consequences  of  either  new  coverings  or  the  removal 
of  mineral  matter  thence  arising. 

Fortunately  in  Europe  and  America  large  tracts  are  found,  where 
the  beds  of  the  older  fossiliferous  rocks  still  occupy  positions  not  very 
different  from  those  of  their  accumulation,  and  wide-spread  areas  have 
changed  their  relative  levels,  as  regards  that  of  the  sea,  so  in  mass, 
that  these  old  sea-bottoms  became  large  portions  of  dry  land,  without 
the  folding  and  crushing  of  their  component  beds.  Other  considerable 
areas  of  like  kinds  may  probably  be  detected  when  extended,  and  as 
yet  little  explored  regions  become  better  known.  Be  that  as  it  may, 
these  old  undisturbed  portions  of  the  world's  surface  become  important, 
from  pointing  out  those  portions  of  it  which  have  escaped  the  ridging, 
squeezing,  and  contortions  to  be  found  in  many  other  localities.  If  we 
could  obtain  such  somewhat  widely  dispersed,  they  would  aid  conside- 
rably in  separating  the  undisturbed  from  the  disturbed  portions  of  the 
earth's  crust,  so  far  as  regards  the  squeezing  or  contortion  of  them, 
though  not,  as  is  obvious,  those  which  may  have  been  lifted  and  let 
down  bodily  in  a  horizontal  or  nearly  horizontal  manner.  When  we 
find,  as  in  the  great  north  and  south  range  of  the  Ural  Mountains, 
these  same  accumulations  squeezed  and  disturbed  as  a  whole,  and  in  a 
marked  line,  and  the  relative  date  of  this  disturbance  can  be*  approxi- 
mately inferred,  as  has  been  done  by  Sir  Roderick  Murchison  and  his 
colleagues,  Count  Keyserling  and  M.  de  Yerneuil,*  the  geologist 
obtains  a  knowledge,  not  only  of  the  time  up  to  which  these  portions  of 
the  earth's  surface  may  have  remained  without  such  disturbance,  but 
also  of  the  direction  of  the  line  or  lines  along  which  it  was  effected. 

The  mountain  ranges  of  the  world  occurring  in  so  many  parts  of  its 
surface,  seem  all  marked  by  evidence  of  the  squeezing  and  contortion 
of  the  different  accumulations  disturbed,  as  far  as  researches  have  yet 
extended.  While  some  show  igneous  matter  to  have  risen  up  in  some- 
what considerable  abundance,  and  apparently  when  these  disturbances 
were  effected,  it  is  not  discovered  so  commonly  in  others.  This  may 
merely  depend,  all  other  things  being  equal,  upon  the  amount  of  mine- 
ral matter  of  another  character  which  has  been  removed,  or  upon  that 
matter  having  been  so  adjusted  as  to  conceal  them.  Much  caution  is 
therefore  needed  when  an  observer  may  be  engaged  in  this  kind  of 
inquiry.  Thus,  in  some  granitic  ranges,  such,  for  example,  as  those 
above  noticed  (p.  546)  in  Southwestern  England  and  Southeastern 
Ireland,  we  may  only  have  the  remains  of  former  chains  of  mountains. 

To  obtain  very  close  approximations  in  ranges  of  mountains,  to  the 
amount  of  folding,  contortion,  or  fracture  of  the  various  rocks  acted 
*  "  Geology  of  European  Russia  and  the  Ural  Mountains." 


EVIDENCE  OF  LATERAL  PRESSURE  IN  MOUNTAINS.   607 

upon  in  the  manner  mentioned,  sections  should  be  formed  proportionally 
representing  these  circumstances.  Usually,  however,  no  great  exacti- 
tude is  attempted,  so  that  sections  of  mountain  districts  merely  afford 
very  general  views  on  the  subject.  Even  these,  nevertheless,  are  suffi- 
cient to  show  the  great  lateral  pressure  to  which  the  whole,  abstracting 
any  igneous  rocks  (apparently  introduced  during  the  time  or  times  of 
such  disturbing  action),  has  been  commonly  subjected.  The  observer 
often  finds  that  when  following  some  given  series  of  beds,  presenting 
characters  sufficiently  marked  for  the  purpose,  and  duly  weighing  the 
evidence  as  to  gaps,  due  to  the  openings  from  fractures,  that  if  such 
contorted  beds  could  be  again  laid  out  flat,  as  when  deposited,  they 
would  have  to  be  spread  over  a  greater  superficial  area  than  they  now 
occupy.  Thus,  if  in  the  annexed  section  (fig.  259),  the  curved  and 
contorted  line  represents  the  foldings  and  contortions  of  a  given  series 
of  beds,  <?,  6,  on  the  flank  of  some  mountain  chain,  such  as  the  Alps, 
and,  allowing  for  fractures  and  portions  removed,  if  that  line  be  reduced 
to  a  straight  one,  a,  #,  it  will  be  evident,  that  a  lateral  extension  to  the 
amount  of  the  distance  a,  c£,  will  be  required  for  the  return  of  these 

Fig.  259. 


a  d 

beds  to  their  original  position,  supposing,  for  illustration,  the  point  b 
to  have  remained  firm.  In  like  manner,  if  instead  of  one  flank  only  of 
a  range  of  mountains,  thus  exhibiting  a  folding  and  contortion  of  its 
beds,  both  flanks  do  so,  and  a  section  across  the  whole  range  shows 
these  to  be  of  the  kind  represented  beneath  (fig.  260),  then  the  line 


c  a  f  b  d 

c,  d,  would  represent  the  distance  required  for  the  flattening  of  the 
folded  and  contorted  beds,  instead  of  that  of  a  0,  giving  the  distance 
now  occupied  by  them.  If  the  points  a  and  b  be  inferred  to  have 
remained  relatively  firm,  as  respects  distances  outside  them,  then  there 
has  been  a  diminution  in  the  distance  between  them,  equal  to  c  a  -f  b  d, 
the  beds  previously  occupying  the  distance  c  d,  being  so  folded  and 
bent  as  not  to  extend  beyond  a  b.  Hence,  also,  a  motion  from  c  to  a, 
and  from  d  to  b  is  inferred,  and  supposing  the  substances  of  these  beds 
sufficiently  yielding,  this  might  be  accomplished  without  a  break  at  /. 
Considering  breaks  to  have  been  formed  at  the  chief  bends,  as  at  0,  0, 


608       EVIDENCE    OF    LATERAL    PRESSURE    IN    MOUNTAINS. 

o,  o,  the  distances  for  the  relative  movement  c  a,  and  b  d,  may  be 
somewhat  altered,  fractures  of  the  kind  represented  in  fig.  261  being  to 
be  taken  into  account,  c  being  a  line  of  fracture  along  which  the  beds  a 
are  considered  to  have  slid  to  b. 


Fig. 


A  diminution  of  the  area  previously  occupied  by  these  folded  and 
contorted  beds  having  been  thus  effected,  the  observer  has  to  see 
whether  on  the  one  side  of  a  mountain  chain  or  the  other,  or  on  both, 
there  may  be  any  evidence  in  favour  of  lateral  pressure  acting  from 
without  inwards,  or  if  there  may  appear  any  in  favour  of  a  great  fissure 
or  fissures,  in  the  ranges  of  the  mountains  themselves,  against  the  sides 
of  which  the  rocks  moved,  and  had  adjusted  themselves  according  to 
the  action  of  gravity,  and  the  lateral  thrust  upon  yielding  materials 
outwards.  The  usual  impression  left,  by  even  the  general  sections 
given  of  ranges  of  mountains,  such,  for  example,  as  those  of  the  Alps, 
is,  that  there  has  been  an  elevation  of  their  component  rocks  in  the 
direction  of  these  main  ranges,  and  that  they  have  adjusted  themselves 
laterally  to  meet  the  force  of  gravity  acting  vertically  upon  the  upraised 
mass.*  Inferring  the  needful  pressure,  it  would  be  expected,  that 

*  Respecting  the  folding  of  beds  by  vertical  and  lateral  pressure,  Sir  James  Hall,  as 
long  since  as  1813  (Transactions  of  the  Royal  Society  of  Edinburgh,  vol.  vii.  p.  86), 
showed  that  this  could  easily  be  imitated  artificially  by  taking  various  pieces  of  cloth, 


placing  them  horizontally  on  some  table,  c  (fig.  262),  pressing  them  downwards  by  :i 
weight,  a,  acting  parallel  to  the  plane  of  the  table  beneath,  and  by  applying  force  late- 
rally, b,  b.  In  experiments  of  this  kind,  it  is  not,  however,  necessary  to  have  the  top 
weight,  a,  since  if  the  cloth  be  in  proper  quantity,  its  gravity  alone  will  be  sufficient  to 
produce  the  contortions,  and  a  more  exact  resemblance  to  nature  be  obtained.  By 
moving  only  one  side  or  both,  as  thought  desirable,  a  very  interesting  illustration  of 
the  contortions  of  beds  may  thus  be  easily  seen. 


BENDING     AND    FOLDING    OF    KOCKS    IN   APPALACHIANS.    609 

molten  matter  beneath  the  masses  moved,  would  he  ready  to  enter  amid 
any  openings  effected,  as  far  as  that  pressure  permitted,  this  intruded 
matter  tending  to  brace  much  of  the  fractured  beds  together,  upon 
cooling.  An  intrusion  of  such  molten  rocks  might,  therefore,  be  among 
the  consequences  of  the  action  producing  the  elevation  of  the  mountain 
range,  and  be  more  or  less  important,  according  to  circumstances. 

Geologists  are  indebted  to  the  Professors  Rogers  for  observations  on 
an  extensive  district  in  North  America,  one  of  about  195,000  square 
miles,  which  have  led  them  to  point  out  an  arrangement  of  the  bends 
and  foldings  of  disturbed  rocks  in  accordance  with  the  distance  from 
the  application  of  force.  A  careful  examination  of  the  Appalachian 
zone,  as  they  term  that  region,  showed  that  it  is  marked  by  five  great 
belts,  which,  when  crossed  from  southeast  to  northwest,  exhibit  the 
greater  flexures  in  the  first  belt,  or  that  on  the  southeast  of  the  Blue 
Ridge  or  Green  Mountain  Chain.  The  component  beds  of  the  belt  are 
doubled  into  enormous,  closely  compressed,  alternate  folds,  dipping 
almost  exclusively  to  the  southeast  at  angles  varying  from  45°  to  70°. 
In  the  third  belt,  the  beds  are  less  compressed,  the  northern  side  of 
each  anticlinal  curve*  approaching  nearly  to  verticality.  In  the  fourth 
belt,  that  of  the  central  Appalachians  of  Pennsylvania,  Virginia,  and 
Tennessee,  the  convex  and  concave  flexures  progressively  expand,  the 
steepness  of  the  northwest  side  of  each  anticlinal  gradually  diminishing. 
In  the  fifth  belt,  that  of  the  coal  region  of  the  Alleghany  and  Cumber- 
land Mountains,  the  curves  dilate,  and  subside  into  broad  symmetrical 
undulations  with  gentle  dips.  The  folds  and  undulations  of  the  beds 
occur  in  groups,  and  the  several  axes  being  very  nearly  parallel  and 
similar  in  the  character  of  flexures,  many  of  the  larger  anticlinals 
having  a  length  of  80  or  100  miles.f  With  respect  to  dislocations  of 
these  beds,  two  systems  are  noticed,  one  of  short  fractures  ranging  with 
them,  and  often  of  considerable  amount.  The  longitudinal  dislocations 
(and  some  in  Virginia  have  a  length  exceeding  100  miles)  are  inferred 
to  be  broken  flexures,  the  fracture  almost  invariably  occurring  on  the 
northwestern  or  inverted  sides  of  the  anticlinals,  and  having  a  mode- 
rately steep  southeastern  dip.  Some  of  these  great  fractures  have 

*  In  a  vertical  section  of  rocks,  of  which  the  following  line  b,  c  (fig.  263),  represents 
the  bends  from  pressure,  a,  a,  <z,  would  be  the  anticlinal,  and  s,  s,  s,  the  synclinal 
curves. 

Fig.  263. 


f  As  regards  the  distances  of  the  contiguous  great  folds,  they  are  stated  to  be  less 
than  one  mile  in  the  southeastern  belt,  in  the  central  belt  between  one  and  two  miles, 
and  in  the  northwestern  belt  the  flexures  have  an  amplitude  of  from  five  to  ten  miles. 

39 


610       FLEXURE    AND    PLICATION    OF    BEDS    IN    THE    ALPS. 

thrown  the  portions  of  once  continuous  beds  not  less  than  8000  feet 
asunder,  measured  perpendicularly  to  the  surfaces  of  the  strata.  After 
an  examination  of  the  disturbed  rocks  of  the  Alps,  Jura,  and  of  the 
district  of  the  more  ancient  fossiliferous  rocks  of  the  Rhine,  Professor 
H.  Rogers  considers  that  in  these  localities  also  the  like  flexures  and 
plications  are  observable.* 

To  produce  a  system  of  flexures  and  plications,  such  as  that  de- 
scribed by  the  Professors  Rogers  as  occurring  in  North  America,  would 
not  only  seem  to  require  great  lateral  pressure,  but  also  a  somewhat 
uniform  and  general  yielding  of  the  various  beds  moved,  during  the 
whole  time  that  the  needful  action  was  prolonged.  Had  there  been 
large  volumes  of  intermingled  or  deep-seated  masses  of  igneous  rocks, 
offering  different  resistances  to  the  force  employed,  much  modification 
in  the  resulting  flexures  and  plications  would  be  expected,  the  softer 
and  less  consolidated  beds  being  even  occasionally  squeezed  over  the 
large  masses  of  the  hard  igneous  rocks.  Thus  it  might  happen,  that 
when  such  igneous  rocks  were  in  abundance,  many  masses  being  deep- 
seated,  the  results  of  an  application  of  force  along  an  extended  line  of 
action  would  be  so  modified  as  to  offer  considerable  difficulty  in  tracing 
the  various' flexures  and  plications  to  such  lines.  In  all  cases,  as  well 
that  of  the  great  Appalachian  zone,  as  in  the  masses  piled  up  to  more 
marked  heights,  such  as  in  the  Alps  and  Himalaya,  a  shortening  of  the 
space  previously  occupied  by  the  component  beds  appears  required  (fig. 
260,  p.  607). 

Whether  the  observer  be  engaged  upon  the  examination  of  the  flex- 
ures or  plications  amid  ranges  of  mountains  or  less  highly  elevated 
portions  of  country,  it  is  very  desirable  not  only  that  he  should  duly 
appreciate  the  amount  of  the  folding  and  bending  of  the  accumulations 
disturbed,  but  also  the  real  outline  of  the  districts.  Without  a  proper 
reference  to  this  outline,  the  most  exaggerated  views  may  be  enter- 

*  Upon  examining  the  Devonian  rocks  of  the  Rhine,  Prof.  H.  Rogers  inferred,  that 
the  entire  region  composed  of  these  and  the  carboniferous  series  exhibits  the  effects  of 
the  laws  of  flexure  and  plication  found  in  the  Appalachians,  and  he  points  to  a  section 
from  southeast  to  northwest,  either  through  the  Taunus  to  Westphalia,  or  by  the  Rhine 
from  Bingen  to  Remagen,  or  from  the  Hunsdruck  to  the  coal  regions  of  Lie'ge,  as 
showing  an  almost  universal  southeastern  dip,  resulting  from  the  close  oblique  folds 
with  steep  or  inverted  dips  to  the  northwest  of  each  large  anticlinal.  He  further  re- 
marks, that  on  approaching  the  northern  side  of  the  district  the  flexures  become  pro- 
gressively more  open,  and  that  the  inequality  in  the  dip  of  the  sides  of  the  anticlinals 
diminishes,  so  that  in  this  case  also  the  force  would  appear  to  have  been  applied  on 
the  southeast.  In  the  Jura,  the  Professor  considers  the  anticlinals  to  have  one  side  of 
the  arch  more  incurved  than  the  other,  but  not  inverted,  and  that  while  the  ridges  are 
higher  next  the  great  plain  of  Switzerland,  all  the  individual  flexures  are  steepest 
towards  the  Alps.  In  the  Alps,  he  infers  the  axis-planes  to  dip  inwards  from  both 
flanks  towards  the  central  portion,  so  that  the  masses  are  folded  in  opposite  directions  ; 
the  plications  of  the  Bernese  Oberland  dipping  south,  those  of  the  chain  of  the  St. 
Gothard  and  the  Simplon  towards  the  north. 


PROPORTIONAL    SECTION    OF    THE    ALPS.  611 

tained  of  the  importance  of  heights  and  depressions,  especially  of 
mountainous  regions,  relatively  to  their  distances ;  an  exaggeration 
very  detrimental  to  that  just  appreciation  of  the  relative  mass  of 
such  mountains  as  compared  with  the  less  elevated  and  more 
moderately  marked  features  of  countries  amid  which  they  may 
occur.  The  accompanying  Section  (fig.  264)  may  serve  to  show 
the  relative  importance  of  the  elevation  and  mass  of  the  Alps, 
from  the  Jura  to  the  central  ridge,  in  a  line  traversing  the  lake  of 
Geneva  and  the  summit  of  Mount  Blanc,  the  scale  being  the  same 
for  heights  and  distances.*  In  this  section,  j  represents  the  Jura ; 
g,  the  lake  of  Geneva ;  v,  the  Voirons ;  m,  the  Mole  ;  a,  the  Aiguille 
de  Varens ;  5,  the  Breven ;  M  B,  the  Mount  Blanc,  and  <?,  the  Cra- 
mont. 

In  certain  regions  where  the  diminution  of  an  area,  once  occu- 
pied by  a  given  series  of  beds,  spread  out  horizontally,  is  effected 
by  flexures  and  plications,  these  deposits  even  crumpled  in  various 
planes,  and  where  also  larger  flexures  may  still  be  traced  amid  the 
complicated  adjustment  of  particular  portions,  considerable  masses 
of  igneous  rocks,  often  granitic,  may  be  detected.  The  chance  of 
some  of  these  masses  having  risen  in  a  molten  state  when  they 
could  move  upwards  from  the  required  pressure  upon  them,  has 
been  already  noticed.  While  the  exposure  of  certain  of  them  may 
have  resulted  from  the  removal  of  mineral  matter  by  denudation 
(p.  546),  others  again  appear  more  to  have  occupied  some  space 
against  or  between  folded  and  contorted  beds,  into  which  they 
could  freely  enter  in  a  viscous  or  pasty  state.  The  Professors 
Rogers  have  pointed  out  that  the  mere  injection  of  liquid  and 
molten  matter  could  scarcely  produce  the  effects  observed  in  the 
disturbed  beds  adjoining  them,  when  such  matter  is  considered  to 
form  a  portion  of  a  general  mass  of  the  same  kind  beneath.  What- 
ever the  cause  of  such  juxtapositions  of  masses  of  igneous  matter, 
they  have  to  be  properly  considered,  and  it  is  always  desirable  to 
compare  the  space  occupied  by  them  with  that  lost  by  the  folding 
and  plication  of  the  beds  disturbed,  so  that  the  resemblance  or  dif- 
ference may  be  apparent,  f  Under  any  hypothesis,  the  sliding  of 
no  inconsiderable  portion  of  mineral  matter  on  the  earth's  surface 
seems  required,  and  duly  to  appreciate  its  amount,  it  becomes 

*  Reduced  from  the  section  by  the  Author,  inserted  in  "  Sections  and  Views 
illustrative  of  Geological  Phenomena,"  1830. 

f  With  regard  to  large  and  wide-spread  masses  of  granite  amid  disturbed  de- 
trital  beds,  it  may  be  desirable  to  bear  in  mind,  that,  like  volcanic  matter  of  the 
present  time,  these  may  themselves  be  re-heated  in  part  after  consolidation  in 
their  higher  portions,  and  after  the  first  uplifting,  when  fissures  formed  in  the  prior 
deposits  were  even  filled  with  the  then  molten  rock,  so  that  pressure  continuing  these 
re-softened  portions  could  be  squeezed  up  like  the  beds  of  the  prior-formed  deposits, 
still  further  thrusting  the  latter  on  one  side. 


612        CONTORTED    COAL    MEASURES    OF    SOUTH    WALES. 

needful  to  bear  in  mind  the  probable  proportion  of  the  original  depth 
of  the  strata  moved  to  the  breadth  of  the  surface  acted  upon.  If,  for 
example  (some  of  the  faults  observed  where  plications  in  the  Appala- 
chian zone  have  snapped,  being,  according  to  the  Professors  Rogers, 
8000  feet),  we  take  two  miles  of  thickness  for  the  beds  moved,  150 
miles  for  their  present  breadth,  measured  across  their  range,  and  allow 
one-fifth  more  for  their  breadth  in  their  prior  extended  form,  the  pro- 
portion of  the  thickness  to  the  breadth  of  the  mass  disturbed  and  more 
or  less  slid  over  some  fitting  surface  beneath,  would  be  about  1 :  90. 

Of  flexures  and  plications  of  beds,  the  fossiliferous  rocks  of  Europe  in 
many  localities  afford  excellent  examples,  and  of  various  geological 
dates.  In  the  British  Islands,  there  are  abundant  opportunities  for 
their  study,  as  well  on  the  minor  as  the  larger  scale.  Some  of  those 
in  Wales  and  parts  of  Ireland  are  well  worthy  of  attention,  not  only 
for  the  folding  of  igneous  products  of  various  kinds  amid  the  ordinary 
detrital  deposits  with  which  they  are  associated^  but  also  for  tne  appa- 
rent adjustment  of  more  yielding  to  more  resisting  rocks  to  each  other 
when  exposed  to  lateral  pressure.  Some  of  the  contortions  of  the  coal 
measures  of  South  Wales  are  of  a  very  illustrative  kind.  As  an  exam- 
ple, the  following  section  near  Tenby  (fig.  265)  may  be  noticed,  as  the 

Fig.  265. 


lowest  part  of  the  rocks  shown  near  that  town  are  tilted  over,  so  as  to 
have  the  false  appearance  of  having  been  deposited  after  those  which 
they  really  support;  the  mountain  limestone  series,  a,  appearing  to 
repose  at  Tenby,  r,  from  the  part  of  the  curve  there  visible,  upon  the 
coal  measures.  Certain  lower  beds  of  this  limestone  series  are  brought 
up,  by  a  bend  of  the  strata,  at  b.  c,  c,  c,  represent  various  shales  and 
sandstones  of  the  coal  measures.  There  are  dislocations,  or  faults,  at 
//,  and  w  v  is  Waterwinch,  on  the  northward  of  Tenby.  A  still  more 
considerable  apparent  inversion,  from  the  same  reason,  is  to  be  seen  on 
the  shores  of  part  of  Milford  Haven  (Langum  Ferry),  at  a  few  miles 
westward  from  Tenby,  where  old  red  sandstone  rests  inclined  on 
mountain  or  carboniferous  limestone,  and  this  again  upon  the  coal  mea- 
sures.* 

In  movements  of  this  kind,  even  disturbances  in  the  arrangement  of 
the  component  parts  of  the  beds  themselves  would  be  expected  accord- 
ing to  their  relative  positions,  and  that  of  such  component  parts.  Thus, 

*  With  respect  to  such  inversions,  as  they  are  sufficiently  common  amid  series  of 
beds  bearing  the  same  geological  names,  their  occurrence  in  a  sequence  of  accumula- 
tions is  merely  the  same  thing  made  to  appear  somewhat  more  important  from  different 
names  being  assigned  to  different  parts  of  the  accumulations  moved. 


FAULTS, 


613 


with  an  interstratification  of  sand  and  mud,  slightly,  if  at  all,  consoli- 
dated, if  a  squeezing  lateral  motion  be  applied  to  these  beds  collectively, 
they  would  yield  relatively  to  their  respective  resistances.  Of  this 
class  the  minor  contortion  of  the  component  parts  of  some  sandstones 
interstratified  with  shale  beds,  of  the  older  fossiliferous  rocks  at  Bewly 
Bay,  Waterford  Harbour,  as  shown  in  the  accompanying  section  (fig. 
266),  may  be  taken  as  an  example.  The  minor  portions  of  the  sand- 
rig.  266. 


stone  beds,  a,  a,  a,  a,  are  there  seen  contorted,  as  in  disturbed  masses 
of  rock  on  the  large  scale,  while  the  shale  6,  5,  b  (formerly  mud),  has 
slid  and  adjusted  itself  in  a  less  marked  manner,  though  its  particles 
may  have  been  also  moved.  The  sliding  of  more  consolidated  over  less 
hard  beds  the  observer  will  often  find  well  shown,  as  also  the  marks  of 
friction  produced  upon  the  adjustment  of  such  consolidated  beds  as 
could  move  upon  or  against  each  other,  the  striation  being  often  beau- 
tifully exhibited.  Pressure  movements  of  this  kind  may  be  well  seen 
in  Pembrokeshire  among  the  coal  measures,  some  coal  beds  having  so 
given  way  before  the  general  force,  that  their  component  parts  have 
been  squeezed,  in  the  manner  represented  beneath  (fig.  267),  into  the 
outer  portions  of  the  flexures,  #,  #,  while  the  roofs  and  bases  of  the 
coal  beds  are  brought  into  contact  between  them. 

Fig.  267. 


Not  only  has  the  observer  to  direct  his  attention  to  the  fracture 
effected  by  the  snapping  of  plications,  when  the  rocks  acted  upon  have 
been  incapable  of  further  flexure,  as  a  mass  or  in  part ;  but  also  to 
numerous  lines  of  fracture,  sometimes  of  considerable  length,  which 
traverse  beds  and  masses  of  rocks,  where  violent  squeezing  into  great 
plications  and  flexures  has  not  occurred.  For  such  lines  of  fracture, 


614  PRODUCTION    AND    DIRECTION    OF    FISSURES. 

the  mining  term,  fault,  has  now  been  adopted.*  Sometimes,  when 
even  of  considerable  length,  they  are  accompanied  by  very  minor  dislo- 
cation, the  sides  of  the  fracture  nearly  corresponding ;  at  others,  the 
fracture  has  resulted  in  a  separation  of  the  beds,  perpendicular  to  their 
surfaces,  of  several  thousand  feet,  and  yet  the  fracture  not  be  on  the 
bend  of  a  plication.  Being  of  importance  in  mining  districts,  and 
mineral  veins  being  commonly  the  filling  up  of  spaces  consequent  on 
them,  the  range  of  these  fractures  become  better  known  in  such  dis- 
tricts than  they  would  otherwise  be ;  at  the  same  time,  however,  in 
numerous  other  districts,  where  beds  of  marked  and  dissimilar  mineral 
structure  occur,  they  may  be  readily  traced,  f 

The  range  of  these  fractures  and  the  relative  time  of  their  production 
have  of  late  occupied  much  attention.  Their  mode  of  occurrence  has 
especially  engaged  the  attention  of  Mr.  Hopkins,  who  has  investigated 
the  conditions  under  which  directions  would  be  taken  by  fissures,  either 
formed  at  the  same  time,  or  at  periods  subsequently  to  each  other,  see- 
ing if  the  anticlinal  lines  and  other  disturbances  and  dislocations  of 
rocks  may  not  be  referable  to  some  "  widely  diffused  action  of  some 
simple  cause,  general  in  its  nature  with  respect  to  every  part  of  the 
globe,  and  general  in  its  action,  at  least  with  respect  to  the  whole  of 
each  district,  throughout  which  the  phenomena  are  observed  to  approxi- 
mate, without  interruption,  to  the  same  geometric  laws."{  Mr.  Hop- 
kins commences,  as  to  the  action  of  an  elevating  force,  with  as  simple 
an  hypothesis  as  he  conceives  the  subject  will  admit.  "  I  assume  this 
force,"  he  observes,  "to  act  under  portions  of  the  earth's  crust  of  con- 
siderable extent  at  any  assignable  depth,  either  with  uniform  intensity 
at  every  point,  or  in  some  cases  with  a  somewhat  greater  intensity  at 
particular  points ;  as,  for  instance,  at  points  along  the  line  of  maximum 
elevation  of  an  elevated  range,  or  at  other  points  where  the  actual  phe- 
nomena seem  to  indicate  a  more  than  ordinary  energy  of  this  subterra- 
nean action.  I  suppose  this  elevatory  force,  whatever  may  be  its 
origin,  to  act  upon  the  lower  surface  of  the  uplifted  mass,  through  the 
medium  of  some  fluid  which  may  be  conceived  to  be  an  elastic  vapour, 
or  in  other  cases  a  mass  of  matter  in  a  state  of  fusion  from  heat."§ 

*  A  term  derived  from  the  miners,  chiefly  those  working  coal,  who,  when  these  dislo- 
cations are  met  with,  often  find  themselves  at  fault,  the  amount  of  the  dislocation  pro- 
duced not  being  always  clear.  They  are  also  known  as  troubles  by  the  miners. 

f  The  geologist  will  find  faults  traced  with  great  care  in  many  of  the  maps  of  the 
Geological  Survey  of  the  United  Kingdom,  as,  for  example,  in  Sheets  36,  37,  41,  42,  56, 
56,  61,  74,  and  79  of  the  Great  Britain  series. 

J  Hopkins,  Researches  in  Physical  Geology,  Transactions  of  the  Cambridge  Philoso- 
phical Society,  vol.  vi.,  part  i. 

\  "  The  first  effect  of  our  elevatory  force,"  continues  Mr.  Hopkins,  "will,  of  course, 
be  to  raise  the  mass  under  which  it  acts,  and  to  place  it  in  a  state  of  extension,  and, 
consequently,  of  tension.  The  increase  of  intensity  in  the  elevatory  force  might  be  so 
rapid  as  to  give  it  the  character  of  an  impulsive  force,  in  which  case  it  would  be  im- 


PRODUCTION    AND    DIRECTION    OF    FISSURES.  615 

After  investigating  the  action  of  the  elevatory  force  supposed  upon  a 
thin  lamina,  and  the  direction  of  the  fissures  according  to  various  con- 
ditions, parallel  upon  the  single  application  of  that  force,  Mr.  Hopkins 
in  applying  his  researches*  to  a  mass  of  three  dimensions,  deduces, 
among  other  important  conclusions,  that,  "  if  the  mass  be  subjected  to 
two  systems  of  parallel  tensions  of  which  the  directions  are  perpendicular 
to  each  other,  two  systems  of  parallel  fissures  may  be  produced,  of  which 
the  directions  will  be  perpendicular  to  each  other."  "  No  two  systems  of 
parallel  fissures,"  he  infers,  "  could  be  thus  formed,  of  which  the  direc- 
tions should  not  be  perpendicular  to  each  other."  "  If  the  fissures  in  either 
of  the  systems  be  near  to  each  other,  they  could  not  have  been  formed 
by  such  tensions  as  we  have  been  considering,  in  succession.  They 
must  have  been  formed  simultaneously  in  each  system.  One  system, 
however,  might  be  formed  at  any  time  subsequently  to  the  other." 
The  modifications  produced  by  different  conditions  are  pointed  out, 
and  Mr.  Hopkins  remarks  upon  the  sense  in  which  the  term  parallelism 
in  these  investigations,  should  be  regarded.  He  observes  that,  "if  the 
size  of  the  mass  be  comparatively  small,  and  its  boundary  irregular, 
this  property  would  altogether  cease  to  characterize  the  phenomena,  "f 

possible  to  calculate  the  dislocating  effects  of  it."  He,  therefore,  always  assumes 
"this  intensity,  and  that  of  the  consequent  tension,  to  increase  continuously,  till  the 
tension  becomes  sufficient  to  rupture  the  mass,  thus  producing  fissures  and  disloca- 
tions," the  nature  and  position  of  which  are  his  first  objects  of  investigation.  "  These 
will,"  he  proceeds,  "  depend  partly  on  the  elevatory  force,  and  partly  on  the  resistance 
opposed  to  its  action  by  the  cohesive  power  of  the  mass.  Our  hypotheses  respecting 
the  constitution  of  the  elevated  mass  are  by  no  means  restricted  to  that  of  perfect 
homogeneity ;  on  the  contrary,  it  will  be  seen  that  its  cohesive  power  may  vary  in 
general,  according  to  any  continuous  law,  and,  moreover,  that  this  power,  in  descend- 
ing along  any  vertical  line,  may  vary  according  to  any  discontinuous  law,  so  that  the 
truth  of  our  general  results  will  be  independent,  for  example,  of  any  want  of  cohesion 
between  contiguous  horizontal  beds  of  a  stratified  portion  of  the  mass.  Vertical,  or 
nearly  vertical,  planes,  however,  along  which  the  cohesion  is  much  less  than  in  the 
mass  immediately  on  either  side  of  them,  may  produce  considerable  modifications  in 
the  phenomena  resulting  from  the  action  of  an  elevatory  force.  The  existence  of  joints, 
for  instance,  or  planes  of  cleavage  in  the  elevated  mass,  supposing  the  regularly  jointed 
or  slaty  structure  to  prevail  in  it  previously  to  its  elevation,  might  affect  in  a  most  im- 
portant degree  the  character  of  these  phenomena." 

*  As  it  is  out  of  place  in  a  work  of  this  kind  to  enter  sufficiently  into  the  investiga- 
tions of  Mr.  Hopkins,  further  than  to  show  their  general  bearing,  we  would  refer  for 
the  mode  of  investigation,  and  the  manner  in  which  the  varied  results  are  progressively 
developed,  to  the  Memoirs  themselves,  as  given  in  the  Cambridge  Philosophical  Trans- 
actions, where  the  observer  will  find  the  subject  fully  treated. 

•}•  Mr.  Hopkins  remarks,  "that  if  we  suppose  the  superficies  of  our  elevated  mass  to 
be  of  finite  length,  and  to  be  bounded,  for  instance,  by  a  line  approximating  to  the  form 
of  an  elongated  ellipse,  the  direction  of  the  fissures,  in  the  transverse  system,  as  we 
approach  towards  either  extremity  of  the  elevated  range,  will  gradually  change  from 
perpendicularity  with  the  major  axis  (the  axis  of  elevation)  till  they  become  parallel 
to  it  at  the  extremities  of  the  ellipse,  always  preserving  their  approximate  coincidence 
with  the  lines  of  greatest  inclination  of  the  general  surface  of  the  mass.  The  fissures 
of  the  other  system  will  be  approximately  perpendicular  to  these  lines.  In  this  case, 


616  PRODUCTION    AND    DIRECTION    OF    FISSURES. 

Reflecting  upon  the  modes  of  accumulation,  as  well  of  igneous  as  of 
aqueous  deposits,  and  upon  their  variable  admixture  in  different  locali- 
ties and  at  different  times,  the  observer  will  be  led  to  infer  that  homo- 
geneity of  structure  in  considerable  masses  of  the  mineral  matter  dis- 
tributed over  the  earth's  surface  would  not  very  frequently  be  found. 
Bearing  this  in  mind,  as  also  that  in  the  active  volcanic  districts  of  the 
world  there  is  evidence  of  the  varied  intensity  of  igneous  action  some- 
what irregularly  distributed  beneath  a  certain  amount  of  the  earth's 
crust,  interferences  with  fractures  of  the  regular  kind  above  mentioned 
will  probably  suggest  themselves.  Nevertheless,  it  is  highly  desirable 
that  he  should  endeavour  to  classify  the  fractures  found  so  commonly 
in  various  parts  of  the  world  with  reference  to  views  on  the  large  scale, 
so  that  he  may  look  beyond  the  details  of  some  given  locality,  and 
endeavour  to  arrive  at  general  conclusions  as  to  the  cause  of  any  faults 
and  disturbances  of  deposits  in  it,  by  following  out  their  directions, 
differences  of  date,  and  such  other  circumstances  as  the  conditions 
under  which  they  are  presented  to  his  attention  may  permit. 

The  directions  of  fractures,  whether  merely  such  without  that  move- 
ment of  either  of  their  sides  which  should  cause  them  to  be  faults, 
having  been  carefully  noted,  the  relative  geological  dates  of  their  pro- 
duction may  not  always  be  so  easy  to  ascertain.  It  is  found  that  in 
certain  districts,  we  may  have  several  of  different  geological  dates,  and 
yet  the  whole  be  uncovered  by  any  deposits  of  which  the  relative  time 
of  accumulation  may  be  ascertained,  so  that  the  probable  date  of  the 
whole  or  some  of  these  faults  and  fissures  may  remain  uncertain.  Un- 
fortunately this  uncertainty  too  often  prevails.  At  the  same  time, 
careful  observation  will  sometimes  enable  the  geologist  to  obtain  some- 
what fair  evidence  of  the  relative  dates  of  these  fractures,  and  from 
such  evidence  probable  inferences  as  to  those  of  others  may  be  occa- 
sionally drawn.  For  example,  there  is  evidence  of  north  and  south 
fractures  having  traversed  the  old  red  sandstone,  mountain  limestone, 
and  coal  measures  of  Somersetshire,  anterior  to  the  accumulation  of 
the  new  red  sandstone  series  of  that  district,  and  posterior  to  the 
bending  and  contortion  of  the  former  rocks,  the  faults  traversing  these 
contortions  even  at  right  angles,  and  the  older  rocks  having  been  worn 
down  after  the  fractures,  the  lowest  beds  of  the  new  red  sandstone 
series  of  that  county  reposing  tranquilly  upon  the  faulted  and  abraded 
older  rocks.  We  may  refer,  in  further  illustration  of  this  circumstance, 
to  the  geological  map  of  the  Mendip  Hills,  previously  given  (fig.  167, 
p.  462),  where  faults,  r,  r,  r,  r,  somewhat  parallel  to  each  other,  ami 
having  a  north  and  south  direction,  cut  through  old  red  sandstone  (1), 

then,  the  two  systems  will  be  no  longer  characterized  by  any  constant  relations  which 
their  directions  bear  to  that  of  the  axis  of  elevation,  and,  therefore,  the  terms  longitu- 
dinal and  transverse  will  cease  to  designate  them  so  correctly  ns  in  other  cases." 


RELATIVE  DATES  OF  DIFFERENT  FISSURES.     617 

carboniferous  limestone  (2),  and  coal  measures  (3),  so  that,  from  an 
irregular  curve  of  these  beds  having  been  traversed,  scarcely  any  hori- 
zontal movement  in  the  present  denuded  exposure  of  this  part  of  the 
Mendip  Hills  is  seen  on  the  north,  while  there  appears  a  considerable 
shift  on  the  south.  These  faults  are  observed,  as  far  as  the  surface  is 
concerned,  to  stop  at  the  lias  (6),  and  new  red  sandstone  (5)  on  the 
north,  and  the  only  one  traced  completely  across  to  terminate  at  the 
inferior  oolite  (7)  on  the  south.  This  apparent  and  superficial  termina- 
tion of  the  faults,  arises  from  their  having  been  formed  anterior  to  the 
deposits  of  the  inferior  oolite,  lias,  and  new  red  sandstone.  The  chief 
fault  is  well  known  to  traverse  the  coal  mines  beneath  a  continuation  of 
these  rocks,  on  its  range  northward,  and  is  ascertained  to  be  covered 
over  horizontally  by  them  all  northwest  from  Radstock.  Thus,  in  this 
case,  the  date  of  these  faults  would  be  after  the  disturbance,  and  the 
flexure  of  the  coal  measures  in  that  district,  and  anterior  to  the  accu- 
mulation of  the  new  red  sandstone  series  (including  its  dolornitic  con- 
glomerate) in  the  same  district.  Hence,  other  faults  in  the  vicinity 
having  the  same  range  might  be  inferred  to  have  been  contemporane- 
ously produced  with  them,  the  more  especially  as  at  Wick  Rocks,  five 
miles  from  Bath,  there  is  also  evidence  of  faults  traversing  the  coal 
measures,  these  having  been  subsequently  and  quietly  covered  by  beds 
of  the  new  red  sandstone  series.  That  all  the  faults  traversing  any 
denuded  or  uncovered  portion  of  the  older  rocks  of  the  same  district, 
were  of  the  same  relative  date,  is  shown  not  to  be  probable  by  finding 
some  traversing  the  higher  deposits  themselves,  both  on  the  north  and 
south  of  the  Mendip  Hills,  the  chief  of  these  taking  an  east  and  west 
direction,  so  that,  fortunately,  in  this  limited  district,  an  observer  may 
learn  the  value  of  caution,  as  to  the  relative  dates  of  faults.* 

As  to  the  exposure  of  faults,  and  inferences  as  to  the  dislocation  of 
one  series  by  others,  much  caution  is  also  often  needed.  For  example, 
it  does  not  follow,  as  in  the  subjoined  plan  (fig.  268),  that  the  fissure 

Fig.  268. 


*  As  regards  these  subsequent  faults,  which  have  commonly  an  east  and  west  direc- 
tion, they  are  seen  to  have  traversed  deposits  up  to  the  chalk  inclusive.  A  very  con- 
siderable fault  of  the  latter  kind  (see  Sheets  18  and  19  of  the  Geological  Survey  of  Great 
Britain)  brings  chalk  into  contact  with  the  bed  known  as  the  Kimmeridge  Clay,  one  of 
the  oolitic  series,  at  Mere,  Wilts.  Thus,  in  this  district,  there  is  evidence  of  an  east 
and  west  disturbance  between  the  deposit  of  the  coal  measures  and  that  of  the  new  red 
sandstone  series,  and  of  another  posterior  to  the  deposit  and  consolidation  of  the  chalk. 


618  FALLACIOUS    APPEARANCE    FROM    A    SINGLE 

a  5,  is  posterior  to  another,  c  d,  and  has  shifted  it  at  e,  because  the  one 
line  is  continuous  and  the  other  not,  since  such  fractures,  under  fitting 
conditions,  may  have  been  contemporaneous  portions  of  some  far  larger 
dislocation,  of  which  these  are  only  minor  parts,  with  adjustments  due 
to  minor  conditions.  Such  apparent  shifting  of  one  fissure  by  another 
is  of  the  same  kind  as  those  small  complicated  fractures  close  to,  or 
forming  parts  of,  the  fissures  or  faults  themselves,  and  of  which  the 
following  (fig.  269)  is  an  example,  from  St.  Agnes,  Cornwall ;  small 
contemporaneous  fractures  in  slate  having  been  filled  by  peroxide  of 
tin,  and  so  that  an  apparent  heave  or  shift  took  place  at  h,  h.  When 
such  appearances  present  themselves,  it  is  needful  to  ascertain  that  any 
mineral  matter,  filling  a  fissure  c  d  (fig.  268),  has  been  dislocated  and 
traversed  by  the  fissure  a  b. 

Fig.  269. 


Evidence  of  this  kind  of  dislocation  mentioned  is  often  to  be  found, 
so  that  no  doubt  remains  of  one  fissure  or  sets  of  fissures  having  been 
first  formed,  and  also  altogether  or  partially  filled,  prior  to  the  pro- 
duction of  another  or  others.  Mining  districts  often  present  abundant 
opportunities  for  investigations  of  this  kind.  As  an  example  we  may 
notice  a  well-known  district  near  Redruth,  Cornwall,  where,  as  repre- 
sented beneath  (fig.  270),  granite,  #,  slates,  s,  elvan  dykes,  e,  e,  e,  and 


lodes  or  mineral  veins,  J,  ?,  Z,  are  all  cut  through  and  dislocated  by  a  fault 
a  b,  one  of  the  great  cross  courses,  as  they  are  termed,  of  that  country, 
having  northerly  and  southerly  ranges.  This  plan  is  also  useful  in 
showing  the  range  of  the  fissures,  e,  e,  filled  with  the  granitic  matter 


MOVEMENT    SHIFTING    VARIOUS    FISSURES. 


619 


(elvan)  introduced  after  the  production  of  the  granitic  masses,  g  (p. 
539),  and  the  coincidence  in  range  of*  parts  of  the  fissures,  ?,  Z,  of  the 
country,  containing  copper  and  tin  ores,  and  subsequently  formed, 
since  they  traverse  these  elvans  in  the  vertical  section  downwards. 

With  respect  to  sections  in  any  planes,  the  horizontal,  for  example, 
in  countries  complicated  by  the  occurrence  of  different  rocks  variably 
situated  as  respects  each  other,  or  by  fissures  ranging  differently  and 
filled  more  or  less  with  mineral  substances  of  various  kinds,  even  by 
mineral  matter  which  has  been  raised  in  them  in  a  molten  state,  some 
care  is  needed,  so  that  an  observer  may  properly  appreciate  the  rela- 
tive position  of  the  parts  of  the  general  solid  rock  broken,  shifted,  and, 
as  it  were,  rubbed  down  to  some  given  plane.  Let,  for  illustration,  the 
following  section  (fig.  271)  represent  one  of  such  a  district  as  that  of 


Fig.  271. 


W 


Cornwall,  a  b,  being  the  surface  of  the  country,  e  e,  elvan  dykes,  and 
Z,  ?,  I,  lodes  or  mineral  veins.  Let  this  country  be  now  dislocated  in  a 
plane  perpendicular  to  the  section,  a'  I'  on  the  one  side  be  lifted  verti- 
cally above  a  b  on  the  other.  It  will  be  seen  that,  on  the  level  a  b, 
though  the  amount  of  vertical  elevation  has  been  common  to  all  the 
lodes  and  elvans,  these  now  occupy,  on  the  surface  a  b,  very  different 
distances  from  each  other,  according  to  the  portions  of  their  various 
lips  or  underlies  intersected  on  that  surface  after  the  movement  men- 
tioned. This  will  be  still  further  illustrated  by  the  subjoined  plan  (fig. 
272),  supposed  to  be  taken  on  the  level  a  5,  all  above  it,  after  the  fault 
was  effected,  being  considered  as  removed  by  denudation,  as  is  corn- 


n 


11  1'2 

e'l 

Tig.  272. 
B              Z'3  T4  Z'O                         e  2  Z'5 

j  ! 

J-L 

St 

%&i       • 

II  i          fit 

2JJJ2 

m 

1 

1112      el 


13 


e2 


monly  the  case.     As  the  letters  and  figures  correspond  on  both  the 
section  and  plan,  it  will  be  found  that  while  the  lodes  1 1,  I  2,  and  the 


620  EVIDENCE    OF    A    SUCCESSION    OF    FISSURES. 

elvan  e  1,  are  shifted  to  the  right  on  the  side  of  the  dislocation  marked 
B,  the  lodes  I  3  and  I  4  are  shifted  to  the  left ;  and  that,  in  the  latter 
part  of  the  section  and  plan,  a  lode  or  branch  from  a  lode  V  0,  appears 
on  the  side  B,  which  was  not  at  the  surface  on  the  side  A,  so  that  three 
lodes  appear  on  the  side  B  as  continuations  of  the  two  lodes  visible  at 
the  surface,  on  the  side  A.  The  elvan  e  2,  which  was  close  to  the  lode 
I  4,  on  the  side  A,  is  apparently  removed  far  from  it  on  the  side  B,  and 
moreover  contains  the  lode  I  5  in  the  latter  case,  one  which  was  far 
removed  from  it,  on  the  surface,  on  the  side  A.* 

The  evidence  of  a  succession  of  fissures  is  often  extremely  interesting. 
While  some  clearly  dislocate  and  shift  the  whole  of  a  mass  of  rocks, 
with  any  prior-formed  fissures  included  in  them,  others  appear  as  mere 
fissures,  with  their  walls  slightly,  if  at  all,  moved  from  their  former 
relative  positions  as  continuous  portions  of  the  same  mass  of  rocks.  In 
the  annexed  plan  (fig.  273),  one  of  the  mineral  veins  of  the  Charles- 
town,  Pembroke,  and  Crinnis  mines,  St.  Austell  district,  Cornwall,  it 

Fig.  273. 


will  be  seen  that  the  granite  boundary,  g  g,  as  well  as  the  lodes  I  I,  are 
shifted  by  the  fault  or  cross  course  a  b  (the  same  circumstance  attend- 

*  Figures  of  this  kind  serve  to  illustrate  the  apparently  contradictory  facts  some- 
times observable  on  the  sides  of  dislocations,  denuded  down  to  a  common  level,  where 
elvans,  or  other  dykes,  and  faults,  or  mineral  veins,  dip  at  various  angles  in  opposite 
directions.  In  the  illustration  given  in  the  text,  the  motion  has  been  supposed  vertical. 
As  such  movements  are  frequently  otherwise,  when  it  is  desired  to  see  how,  by  the  use 
of  such  sections,  explanations  of  apparently  complicated  phenomena  may  be  afforded, 
it  becomes  necessary  not  only  to  have  the  sections  strictly  accurate  and  proportional 
in  all  their  details,  but  also  to  make  the  movement  correspond  with  that  found  among 
the  rocks  themselves.  If  an  observer  will  paint  on  two  pieces  of  flat  glass,  a  variety 
of  sections  of  this  kind,  the  same  on  both  pieces,  so  that  when  held  together  they 
appear  as  one,  and  slide  the  glasses  on  their  flat  surface,  a  variety  of  interesting  cir- 
cumstances will  be  made  apparent  as  to  the  consequences  of  fault  movements  in  diffe- 
rent directions ;  the  surfaces  of  ground  being  supposed,  as  in  nature,  to  be  denuded 
down  to  some  common  levels. 


FISSURES    SPLIT    AT    THEIR    ENDS.  621 

ing  the  fault,  c  d,  though  not  shown  on  plan  ;)  while  another,  and  sub- 
sequent fissure,  ef,  traverses  the  whole  without  shifting  it. 

Fissures  are  often  found  to  split  at  their  ends  after  no  very  conside- 
rable course,  when  regarded  in  their  horizontal  range.  Of  mineral 
veins  so  divided  at  their  extremities,  when  viewed  horizontally,  the  fol- 
lowing plan  (fig.  274)  of  the  Wheal  Fortune  range  of  mines,  Breague 


district,  Cornwall,  may  be  taken  as  a  good  example.  The  main  lode  is 
there  seen  to  be  split  on  both  the  east  and  west  after  a  range,  as  a 
marked  fissure,  for  about  a  mile  and  a  quarter  (the  plan  is  on  a  scale 
of  one  inch  to  the  mile).  The  lodes,  m,  are  those  of  Wheal  Friend- 
ship mine,  and,  if  prolonged,  would  also  fall  into  the  main  vein  of  the 
Wheal  Fortune  mines.  These  various  lodes  traverse  elvan  dykes,  e,  e, 
or  courses,  as  they  are  termed  in  Cornwall,  and  are  cut  by  faults  or 
cross  courses,  d,  d,  subsequently  produced.  It  should  be  remarked, 
with  reference  to  beds  or  other  arrangements  of  rocks  of  variable 
toughness,  traversed  by  fissures,  that  occasionally  some  care  is  needed 
not  to  be  misled  by  minor  appearances,  for  the  fissures  taking  lines  of 
least  resistance  may  so  run  against  or  along  harder  beds,  or  dykes  of 
mineral  matter,  as  to  lead  to  false  impressions.  Thus,  in  the  annexed 
section  or  plan  (it  is  immaterial  which  it  may  be  considered),  a  fissure 
being  opened  from  d  towards  e,  and  encountering  an  elvan  dyke  a,  5, 

Pig.  275. 


might  have  resistances  to  the  forces  employed  so  adjusted  that  it  only 
traversed  the  latter  at  e,  passing  up  the  wall  of  the  elvan  dyke  for 
some  distance,  thence  taking  its  course  onwards  to  the  right  in  a 
parallel  line  c  e.  It  might  be  inferred,  and  in  somewhat  similar  cases 
has  been  inferred,  that  the  elvan  filled  a  fissure,  #,  b,  produced  sub- 


622  RANGES    OF    MINERAL    VEINS    AND    COMMON 

sequently  to  that  noticed,  d  c  the  opening  against  the  elvan  on  the  side 
c  being  very  slight,  even  forming  a  mere  slide  along  the  old  plane  of 
the  fissure  a  b.  The  reverse  would,  in  such  a  case,  be  the  fact.  Cir- 
cumstances of  a  similar  kind  have  sometimes  occurred  as  respects  the 
intermixture  of  an  igneous  rock  locally  known  as  toadstone  (p.  533), 
and  the  limestone  associated  with  it  in  Derbyshire,  as  will  be  hereafter 
noticed.  Caution,  therefore,  on  this  head,  is  occasionally  more  needed 
than  at  first  sight  might  appear  probable. 

With  respect  to  arrangements  of  the  parts  of  a  faulted  country,  and 
it  is  important  to  bear  in  mind  how  very  extensively  faults  often  prevail 
in  otherwise  undisturbed  districts,  their  occurrence  on  the  surface  of 
land  is  sometimes  such  as  to  remind  the  geologist  of  inlaid  marble  work, 
curiously  fitted  together,  and,  as  it  were,  polished  down  to  some  given 
plane.  As  a  piece  of  natural  inlaid  work  of  this  kind  the  observer  will 
find  a  good  example  in  Pembrokeshire,  where  the  coal  measures  of  Nolton 
and  Wood  appear  as  if  inlaid  among  faults  on  the  north,  east,  and 
south.*  As  to  the  smoothing  off  of  countries  traversed  by  faults,  these 
often  considerable,  so  many  regions  present  evidence  of  it  that  probably 
there  are  few  portions  of  the  earth's  surface,  even  when  offering  scarcely 
any  bending  or  contortion,  which  are  not  more  or  less  cracked  and 
broken  in  some  form.  It  has  been  seen  (p.  416)  that  in  the  earth- 
quakes of  the  present  day  fissures  are  frequent,  and  there  is  every 
reason  to  suppose  that  such  have  occurred  at  all  geological  times. 
Whether  faults  arise  from  minor  adjustments  of  the  earth's  crust,  the 
bending,  contortion,  and  squeezing  of  various  accumulations  being  re- 
garded as  more  considerable  consequences  of  those  adjustments,  or  from 
other  causes,  together  with  the  greater  plications  and  flexures,  they 
show  a  broken  and  dislocated  condition  of  that  crust  which  it  requires 
the  geologist  most  carefully  to  bear  in  mind,  when  endeavouring  to 

*  See  Maps  of  the  Geological  Survey  of  Great  Britain,  Sheet  40.  On  the  south  a 
considerable  fault  throws  the  coal  measures  against  lower  Silurian  rocks,  on  the  north 
another  brings  them  in  contact  with  Cambrian  rocks ;  both  one  and  the  other  class  of 
deposits  being  at  the  same  time  overlapped  by  them,  so  that  it  becomes  needful  to  have 
a  clear  view  of  the  amount  of  the  overlaps  as  well  as  of  the  mode  of  occurrence  due 
alone  to  the  faults ;  no  difficult  task  in  the  district  mentioned.  The  following  section 
(fig.  276),  north  of  Newgale  Sands,  N,  will  show  the  manner  in  which  the  coal  mea- 

Fig.276. 


sures,  b,  b,  are  brought  into  contact  with  purple  and  gray  sandstones,  of  the  Cambrian 
series,  a,  a,  by  the  fault,  /  /* ;  c  is  a  dyke  of  igneous  rock  filling  a  fissure  traversing  the 
latter  beds. 


FAULTS    IN    SOUTHWESTERN    ENGLAND. 


623 


trace  the  facts  lie  may  observe  in  connexion  with  deposits  and  their 
subsequent  movements  to  their  sources. 

As  illustrative  of  the  modes  of  occurrence  of  fissures  and  faults  in 
mining  districts,  which  usually  afford,  as  above  remarked,  such  good 
opportunities  for  their  study,  the  following  plans  may  be  found  useful. 
The  first  plan  (fig.  277)  represents  a  general  view  of  the  fissures,  whe- 
ther coming  under  the  heads  of  mineral  veins  or  ordinary  fissures  and 
faults,  in  Cornwall,  Devon,  and  West  Somerset.  On  the  east,  there  is 

Fig.  277. 


a  tendency  of  nearly  north  and  south  faults  to  traverse  others  running 
east  and  west,  while  on  the  west,  fissures  usually  ranging  about  N.N.W. 
and  S.S.E.,  cross  others  which  take  a  course  from  W.S.W.  to  E.N.E., 
or  from  E.S.E.  to  W.N.W.  It  will  be  observed  that  towards  the  great 
metalliferous  district  of  Cornwall  the  lines  c  c  c  take  a  direction  some- 
what parallel  to  the  general  range  of  land,  which  is  that  also  of  the 
granitic  masses  of  the  district.  Other  lines,  d  d  d,  are  observed  as  of 
importance  in  three  situations  (St.  Austell,  Marazion,  and  St.  Just 
districts).  The  fissures  and  faults,  c  c  c  and  d  d  d,  contain  the  chief  of 
the  tin  and  copper  ores  of  the  district,  while  in  the  cross  courses,  b  b  6, 
those  of  lead*  and  iron  and  some  others  are  commonly  found.  The  tin 
and  copper  veins  or  lodes,  a  a,  near  Tavistock,  have  a  more  east  and 
west  direction,  the  cross  courses  traversing  them,  b  b,  having  a  some- 
what marked  north  and  south  range.  The  lines,  both  east  and  west, 
a  a  a,  and  north  and  south,  b  b  b,  on  the  east  side  of  the  plan,  come 
under  the  heads  of  common  faults ;  one,  however,  of  the  east  and  west 
lines,  «,  near  Exeter,  being  connected  with  parallel  fractures  holding 
manganese,  f 

*  The  lead  of  Cornwall  and  Devon  is  not  confined  to  the  north  and  south  fissures, 
though  in  certain  districts  they  occur  in  a  somewhat  marked  manner  in  them. 

f  The  following  section  illustrates  these  faults,  one  of  which,  /,  can  be  traced  for  10 
miles  from  Poltimore,  on  the  east,  to  Venny  Tedborn,  near  Posbury  Hill,  on  the  west ; 


624  FAULTS    IN    SOUTHWESTERN    ENGLAND. 

With  respect  to  the  relative  geological  age  of  these  fissures,  there  is 
evidence  Jhat  those  having  an  easterly  and  westerly  direction  on  the 
west,  c  c  c  and  d  d  d,  were  formed  anterior  to  those  traversing  them  in 
a  northerly  and  southerly  direction,  since  the  former  are  not  only 
shifted  by  the  latter,  but  their  contents  are  also  broken  through  by 
them.  The  east  and  west  fissures,  a  a,  near  Exeter,  on  the  west  of 
Dartmoor,  were  produced  after  the  deposit  and  consolidation  of  the  new 
red  sandstone  of  that  district,  since  that  series  has  been  dislocated  by 
them.  Fissures  with  the  same  direction,  near  Watchet,  Somerset,  a  a, 
on  the  northeast  corner  of  the  plan,  were  produced  after  the  deposit  and 
consolidation  of  the  lias.  How  far  these  latter  may  be  contemporaneous 
with  those  containing  tin  and  copper  ores  on  either  side  of  Dartmoor, 
and  having  the  same  direction,  may  not  be  clear,  though  they  might  be 
supposed  to  be  so.  Be  this  as  it  may,  north  and  south  faults  have  dis- 
located the  chalk  with  other  prior-formed  deposits  (of  the  oolitic  series) 
near  Lyme  Regis,  Chard,  and  Membury  (b  b  on  the  southeast  of  the 
plan).  Taking  these  last  in  connexion  with  the  north  and  south  faults 
of  the  Men  dip  Hills  district,  near  at  hand  eastward  (fig.  167,  p.  462), 
there  have  been  fissures  formed  in  the  same  general  directions,  north 
and  south,  at  two  distinct  periods,  in  this  part  of  Southwestern  England, 
one  anterior  to  the  deposit  of  the  new  red  sandstone,  and  posterior  to 
the  flexures  and  plications  of  the  coal  measures,  and  the  other  after  the 
deposit  and  consolidation  of  the  chalk.  The  movements  of  different 
dates  in  east  and  west  directions  have  already  been  noticed  (p.  618).* 

a  minor  fault  or  vertical  branch  of  the  same  fault,  m,  running  parallel  to  it,  and  having 
afforded  a  large  quantity  of  valuable  oxide  of  manganese  (at  Huxham,  Upton  Pyne,  and 

Fig.  278. 
Shutehays. 

Newton  St.  Gyres. 


Newton  St.  Gyres),  a,  a,  are  beds  of  the  new  red  sandstone  series  of  the  district,  brought 
into  contact  with  the  coal  measure  sandstones  and  shales,  b  b,  of  the  same  country,  in 
which  there  is  another,  and  apparently  parallel  fissure,  Z,  containing  sulphuret  of  lead. 

*  We  would  refer  for  more  ample  detail  on  the  mode. of  occurrence  of  the  faults  and 
lodes,  or  mineral  veins,  of  Cornwall,  Devon,  West  Somerset,  and  a  part  of  Dorsetshire, 
to  the  Author's  Report  on  the  Geology  of  that  district,  1839. 

As  regards  the  range  of  east  and  west  faults  in  neighbouring  parts  of  England,  it  may 
be  desirable  to  call  the  attention  of  the  observer  to  the  considerable  fractures  having 
that  direction  near  Bridport  and  Weymouth  (see  Maps  of  the  Geological  Survey,  Sheets 
17,  18,  where  they  have  been  most  carefully  laid  down  by  Mr.  H.  W.  Bristow),  traversing 
a  variety  of  beds  up  to  the  chalk  inclusive ;  in  the  latter  case,  therefore,  formed  during 
some  portion  of  the  supracretaceous  or  tertiary  period.  In  the  Isle  of  Wight,  a  great 
disturbance,  having  an  east  and  west  direction,  is  seen  to  have  occurred  after  a  con- 
siderable portion  of  the  supracretaceous  or  tertiary  rocks  of  that  district  had  been  ac- 
cumulated. 


FAULTS    NEAR    SWANSEA. 


625 


The  following  plan  (fig.  279)  of  part  of  Glamorganshire  exhibits 
numerous  parallel  fractures  traversing  both  mountain  or  carboniferous 


Fig.  279. 


B.C. 


limestone  and  coal  measures  near  Swansea;  the  working  of  the  coal 
measures  affording  the  needful  evidence  of  many  faults  which  are  not 
so  easily  traced  in  an  accumulation  of  such  a  general  mineral  aspect  as 
the  carboniferous  limestone  of  that  locality.  In  this  plan,  a  a  a  repre- 
sent the  lines  of  faults,  A  the  coal  measures,  and  L  the  carboniferous 
limestone,  rising  from  beneath  them ;  s,  is  Swansea,  and  B  c,  Bristol 
Channel.  In  this  case  there  is  no  evidence  to  mark  the  relative  date 
of  the  fissures ;  and,  supposing  them  contemporaneous  with  those  having 
the  same  directions  on  the  opposite  side  of  the  Bristol  Channel,  they 
may  have  been  of  either  of  the  dates  previously  noticed.  It  may  not 
be  improbable,  however,  that  they  were  formed  after  the  deposit  of  the 
lias,  since  somewhat  more  eastward,  towards  Cardiff,  in  the  same  gene- 
ral district,  parallel  faults  dislocate  the  various  accumulations  up  to 
that  deposit  inclusive.* 

With  respect  to  the  manner  in  which  portions  of  fractured  masses 
are  brought  into  contact  in  vertical  sections  by  faults,  the  following 
sketch  will  serve  to  illustrate  that  of  a  simple  kind,  when  the  amount 

*  The  observer  is  referred  to  various  maps  of  the  Geological  Survey  of  the  United 
Kingdom,  for  numerous  examples  of  faults  traversing  different  rocks.  Great  care  has 
been  taken  to  have  them  properly  examined  and  laid  down,  so  that  they  may  eventually 
constitute  a  body  of  evidence,  of  an  accurate  kind,  for  a  due  consideration  of  the  various 
dislocations  which  the  rocks  in  the  area  of  the  British  Islands  may  have  suffered  during 
the  lapse  of  the  geological  time  of  which  such  rocks  may  be  the  records. 

40 


626    PARTS  OF  DEPOSITS  PRESERVED  BY  FAULTS. 

* 

of  difference  in  the  relative  levels  of  the  dislocated  and  once-continuous 
beds  has  been  small,  and  the  fissure  nearly  vertical,  part  of  the  bed  a 

Fig.  280. 


on  the  one  side  of  the  fault/,  being  separated  from  the  portion  a',  on 
the  other.  Faults  are,  as  may  be  readily  inferred,  of  all  inclinations 
as  regards  the  horizon,  being  sometimes  sloping,  as  beneath  (fig.  281), 


Fig.  281. 


so  that  to  measure  the  amount  of  geological  dislocation  produced  by 
one  at  /,  the  distance  5,  extending  vertically  from  the  plane  of  the 
same  bed  a  (supposed  horizontal)  on  the  one  side,  and  c  on  the  other, 
has  to  be  ascertained.  In  some  coal  districts  faults  of  a  highly-inclined 
kind  are  said  to  double,  the  coal  for  a  short  distance,  when  dislocated 
parts  of  the  same  bed  of  coal  have  been  worked  on  one  side  of  a  fault 
above  a  portion  on  the  other,  as  is  seen  by  supposing,  in  the  section 
above  (fig.  281),  a  bed,  a  c,  to  be  one  of  coal. 

In  some  districts  faults  are  observed  so  to  have  occurred  that  several 
portions  of  country  have  been  dropped  down  in  one  direction,  prolong- 
ing the  surface  appearance  of  some  rocks  beyond  that  which  would 
otherwise  have  happened  after  the  various  denudations  to  which  they 
might  have  been  exposed ;  portions  being  thus  preserved  which  would 
otherwise  have  been  swept  away.  The  following  section  (fig.  282)  may 


Knighton. 


Fig.  282. 

a 


Bcnhole  Farm.        Bristol  Channel. 


a      f          b      f          b          f          b      f  f 

be  taken  in  illustration  of  this  subject,  as  also  of  the  vertical  mode  of 
occurrence  of  the  faults  near  Watchet  (a  a,  northeast  corner  of  the 
plan,  fig.  277),  previously  noticed.  The  deposits  dislocated  are  lias,  a, 
and  new  red  marl  and  sandstone,  b ;  and  it  will  be  seen  that  parts  of 
the  lias  have  been  preserved  from  denudation  by  being,  as  it  were, 


COMPLICATED    FAULTS.  627 

dropped  down  by  five  faults,  /,  /,  /,  /,  /  (parallel  to  each  other),  into 
five  sheltered  depressions,  succeeding  each  other  in  a  southward  direc- 
tion. In  this  manner  valuable  coal,  in  some  coal  districts,  has  been 
preserved  from  that  removal  by  geological  causes  which  it  would  other- 
wise have  suffered.  The  amount  of  accumulations  thus  preserved,  or 
the  reverse,  by  systems  of  faults,  is  a  subject  which  should  "engage  the 
attention  of  the  observer  as  one  of  importance  in  investigations  of  this 
kind.  The  amount  of  various  rocks  so  circumstanced  is  often  very  con- 
siderable. 

As  might  be  expected,  lines  of  faults  frequently  exhibit  minor  compli- 
cation and  even  disturbance,  showing  a  certain  amount  of  lateral  pres- 
sure during  the  adjustment  of  their  sides  after  the  action  of  the  force 
producing  the  original  fracture.  The  following  section,  easily  seen,* 

Fig.  283. 


g  h  i 

of  a  fault  on  the  coast  of  Glamorganshire,  west  of  Lavernock  Point,  will 
illustrate  minor  complications  of  fracture,  and  a  bending  of  certain  of 
the  beds  acted  upon,  m,  m,  ra,  being  minor  parts  of  the  same  dislocation 
which  has  traversed  earthy  dolomitic  limestone  and  marl  a,  varieties 
of  dolomitic  limestone,  5,  c,  d,  e,  and  /;  dolomitic  conglomerate,  g  (all 
these  of  the  new  red  sandstone  series) ;  and  lias,  I.  The  beds  at  h  cor- 
respond with  those  on  the  left.  While  the  fractures  have  merely  broken 
the  former  deposits,  the  edges  of  the  lias  have  been  turned  up,  as  if  by 
a  certain  amount  of  lateral  pressure.  In  some  faults  this  turning  up  of 
a  portion  of  the  beds  acted  upon,  occasions  the  observer  to  suspect  that 
after  the  fracture  there  has  been  some  settlement  from  an  upraised  posi- 
tion (for  the  time),  producing  the  needful  friction  even  for  upturning 
the  edges  of  beds  on  the  under  part  of  a  fault,  as  shown  at  m  on  the 
right  of  the  section  (fig.  283).  Usually  the  side  relatively  lowered  is 
found  raised  at  the  edge  in  an  inclined  fault,  the  consequent  friction 
turning  up  the  end  of  the  superior  rock  conformably  with  the  movement. 
As  a  vertical  section  may  only  give  the  apparent  movement  of  the 
parts  of  rocks  fractured  and  faulted,  it  is  desirable  that  the  observer 
should  search  for  the  direction  of  any  friction-marks  attending  pressure 
of  the  rocks  on  one  side  against  those  on  the  other,  in  order  to  discover 

*  Respecting  illustrations  of  the  various  geological  phenomena  noticed,  the  author 
has  endeavoured  in  this  work  as  much  as  possible  to  select  such  localities  as  may  be 
easily  visited. 


628        FILLING    OF    FISSURES    WITH    MINERAL     MATTER. 

that  in  which  the  movement  has  really  been  effected.  This  investigation 
will  sometimes  lead  him  to  find  that,  though  the  general  plane  of  a  fault 
may  dip  in  a  given  direction,  the  movement  has  not  always  corresponded 
with  it.  Some  of  these  friction-marks  bear  evidence  of  the  action  of 
enormous  pressure,  more  especially  in  those  cases  where  the  dislocation 
may,  in  its  plane,  amount  to  several  thousand  feet,  and  yet  the  rocks 
thus  moved  against  each  other,  and  once  so  far  asunder,  be  now  closely 
jammed  together.  The  contents  of  dislocations,  whether  known  as  com- 
mon faults  or  mineral  veins,  often  present  beautiful  impressions  of  these 
friction-marks,  parts  of  the  walls  of  the  fractures,  after  grating  against 
each  other  in  their  movement,  having  finally  left  cavities  in  which  various 
mineral  substances  were  accumulated,  taking  the  form  of  the  surfaces 
against  which  their  first  deposit  was  effected. 

The  filling  of  fissures  and  other  cavities  with  mineral  matter. — This 
subject  may,  to  a  certain  extent,  be  considered  as  part  of  that  relating 
to  the  changes  and  modifications  of  rocks  above  mentioned,  since  from 
the  filling  of  minor  cavities  and  fissures,  such  as  occur  in  or  traverse 
small  portions  of  an  accumulation,  whether  of  igneous  or  aqueous  origin, 
much  change  or  modification  may  arise  in  the  containing  rocks.  The 
filling  of  cavities,  such  as  those  previously  noticed  in  vesicular  lava  and 
molten  matter  of  all  geological  times,  converting  a  highly  porous  and 
often  originally  light  substance  into  a  very  solid  rock,  effects  a  marked 
change  of  structure.  The  infiltrations  of  the  mineral  substances  into 
the  cavities,  in  these  cases,  become  important  in  the  consideration  of 
those  which  have  filled  various  fissures  and  dislocations  as  well  as  cavities, 
of  far  greater  size,  since  they  seem  to  point  to  the  solution  of  some  sub- 
stances, or  of  the  elementary  matter  composing  them,  and  to  the  power 
of  such  solutions  to  traverse  the  pores  of  rocks,  even  of  those  which  are 
considered  very  solid  and  compact,  in  a  manner  which,  at  first  sight,  might 
not  be  expected.  Let  the  observer,  for  example,  study  certain  of  the 
nodules  of  the  impure  carbonate  of  iron,  known  as  clay  ironstones,  in  many 
of  the  localities  where  they  are  obtained  from  the  coal  measures  of  the 
British  Islands,  opportunities  for  which  are  abundant  in  South  Wales, 
Monmouthshire,  Staffordshire,  Derbyshire,  and  elsewhere.  While  in 
many  of  these  nodules,  the  cracks,  when  they  present  themselves,  as 
they  often  do,  in  the  manner  mentioned  previously  (fig.  227,  p.  568), 
only  contain  more  pure  carbonate  of  iron,  or  are  entirely  empty,  at 
others  they  are  incrusted  or  filled  with  such  substances  as  copper  pyrites, 
and  the  sulphurets  of  lead,  zinc,  nickel,  and  iron,  with  the  occasional 
occurrence  of  other  minerals  of  a  different  class.  In  such  cases  the 
observer  can  have  little  doubt  that  the  component  parts  of  these  sub- 
stances have  come  by  infiltration  from  without  into  the  cracks  of  the 
nodules  of  impure  carbonate  of  iron,  through  their  exterior  pores,  and 


SULPHUEET    OF    LEAD,    ETC.,    REPLACING    SHELLS.        629 

through  those  and  the  laminae  of  the  surrounding  argillaceous  shales. 
He  is  therefore  prepared  to  infer  that  these  bodies,  or  their  component 
parts,  were  in  a  soluble  state  when  they  entered  the  cavities  formed  by 
the  cracks  in  the  nodules. 

When  he  examines  the  minerals  which  have,  under  certain  conditions, 
replaced  organic  remains  in  various  rocks,  the  geologist  may  still  further 
be  prepared  to  regard  the  matter  of  these  and  other  compound  sub- 
stances as  being  introduced  in  solution  into  cavities  left  by  the  decom- 
position and  disappearance  of  mollusc  shells,  or  other  organic  bodies. 
Copper  pyrites  has  been  found  to  replace  the  shells  of  Spirifera,  at  Dod- 
dington,  Somersetshire* — sulphuret  of  lead  various  cavities  left  by  the 
shells  of  molluscs  in  the  lias  near  Merthyr  Mawr,  Glamorganshiref — 
and  sulphate  of  baryta  portions  of  corals  in  the  mountain  limestone  of 
Cromford,  Derbyshire. J  Sulphuret  of  iron  very  frequently  occupies 
places  of  mollusc  shells  in  many  rocks,  especially  those  which  are  argil- 
laceous, even  insinuating  itself  amid  the  matter  of  fossil  bones,  such  as 
those  of  saurians  in  the  lias,  and  other  deposits.  Silica,  as  might  be 
expected  also,  occupies  the  cavities  left  by  shells,  of  which  the  chalce- 
donic  replacements  of  the  various  shells  of  the  greensand  series  at 
Blackdown,  Devon,  and  Somerset,  are  beautiful  examples.  Even  the 
carbonate  of  lime  of  many  fossil  mollusc  shells  does  not  always  appear 
to  be  that  of  the  original,  but  to  have  been  infiltrated  into  cavities  left 
upon  the  disappearance  of  the  matter  of  the  actual  shell,  the  particles 
of  the  carbonate  of  lime  not  being  adjusted  in  the  manner  they  usually 
are  in  shells  of  the  same  class  by  living  animals,  but  as  they  would  be 
upon  simple  infiltration  and  crystallization  in  any  cavity.  Again,  in 
the  crystals  of  felspar,  decomposed  in  the  body  of  a  rock,  the  original 
substance  of  the  crystals  removed,  and  replaced  by  peroxide  of  tin,  even 
part  of  the  original  felspar  crystal  sometimes  remaining,  while  the  rest 
of  its  form  is  replaced  by  the  peroxide  of  tin,  as  in  an  elvan  at  St. 
Agnes,  Cornwall,  the  observer  has  another  example  of  the  inflow  of 
mineral  matter  in  solution  into  cavities  and  through  the  pores  of  the 
rock  in  which  such  cavities  may  be  situated.  In  fact,  looking  at  the 
subject  generally,  the  various  cavities  in  the  rocks  composing  the  crust 
of  the  earth,  have  a  tendency  to  be  filled  by  mineral  matter,  the  com- 
ponent parts  of  which  find  their  way  to  them  in  solution. 

*  In  this  locality  there  was  a  vein  of  copper.  The  ores  raised  were  principally  green 
and  blue  carbonates,  and  were  first  obtained  in  the  new  red  sandstone  conglomerate  of 
the  locality  above  a  vein  in  the  Devonian  rocks  beneath.  Horner,  Trans.  Geol.  Soc. 
London,  vol.  iii.  pp.  352  and  363. 

f  The  sulphuret  of  lead  is  much  disseminated  in  this  part  of  South  Wales,  and  often 
in  cavities.  It  occurs  in  the  cracks  of  fossil  wood  in  the  lias  near  Dunraven  Castle,  in 
the  same  manner  that  the  sulphuret  of  iron  is  often  seen  in  coal  beds,  and  in  fossil 
wood  in  numerous  clays  of  different  geological  dates. 

J  This  fact  is  interesting  in  connexion  with  the  considerable  quantity  of  sulphate  of 
baryta  found  in  the  lead  veins  and  other  cavities  of  that  part  of  Derbyshire. 


630  SOLUBILITY    AND    DEPOSIT    OF 

Passing  from  these  cavities  to  those  produced  by  cracks,  these  of 
minor  size,  and  confined  either  to  one,  two,  or  some  small  number,  of 
beds  of  sedimentary  deposits,  or  some  very  limited  volume  of  an  igneous 
accumulation,  it  would  be  expected  that,  as  a  whole,  the  matter  infil- 
trated into  such  cracks  would  chiefly  partake  of  the  mineral  character 
of  the  rocks  so  broken,  so  that  the  substances  principally  filling  the 
cracks  in  limestones  would  be  calcareous,  while  those  amid  siliceous 
rocks  would  be  quartzose,  as  is  usually  the  fact.  From  the  prevalence, 
however,  of  particular  conditions,  quartz  veins  are  occasionally  found  in 
limestones,  and  calcareous  matter  among  the  siliceous  rocks.  This 
usually  occurs  when  the  limestone  beds  form  a  very  subordinate  portion 
of  a  sandstone  or  argillaceous  accumulation,  chiefly  composed  of  silicates, 
or  when  calcareous  deposits  predominate  among  those  of  other  kinds,  as, 
for  example,  is  the  case  with  the  igneous  rocks  of  Derbyshire,  where 
the  vesicles  and  minor  veins  of  the  latter  are  often  filled  with  calcareous 
spar.* 

Proceeding  to  examine  the  filling  of  cavities  and  fissures  of  larger 
dimensions,  and  such  as,  not  confined  to  minor  volumes  of  rocks,  can  be 
traced  for  considerable  distances,  and  the  depths  of  which  are  unknown, 
an  observer  will  have  not  only  to  bear  in  mind  the  incrustations  of  the 
sides  of  such  fissures  by  the  substances,  which,  passing  amid  the  pores 
or  small  fissures  of  rocks  on  the  minor  scale,  are  ready  to  fill  up  or 
incrust  any  cavities  presenting  themselves,  no  matter  of  what  kind  or 
how  formed,  but  also  to  consider  the  kind  of  substances,  and  their  mode 
of  action  upon  each  other,  which  may  be  derived  from  various  distances 
and  sources.  Viewing  a  considerable  fissure,  in  its  simple  form,  some- 
what vertically  traversing  various  beds  of  dissimilar  rocks,  as  in  the 
following  section  (fig.  284),  a  to  /,  each  affording  some  different  or 
variously  combined  matter  in  solution,  and  confining  his  attention,  at 
first,  to  solutions,  the  geologist  has  a  more  complicated  problem  pre- 
sented to  his  attention  than  the  mere  infiltration  of  mineral  matter 
through  the  pores  of  rocks  into  small  cavities  and  fissures  in  them.  He 
has  to  regard  not  only  the  probable  combinations  and  decompositions 
effected  by  a  mixture  of  substances  introduced  into  the  fissure,  but  also 
the  motion  of  the  whole  of  the  liquid  in  it,  according  to  temperature. 

*  The  filling  of  cavities  and  small  fissures  in  igneous  rocks  by  carbonate  of  lime  is 
not  unfrequent,  even  when  calcareous  rocks  do  not  constitute  any  very  large  proportion 
of  a  general  mass  of  mixed  accumulations.  Thus  at  Trecarrell  Bridge,  between  Laun- 
ceston  and  Tavistock,  the  highly  vesicular  rock  of  that  locality,  contemporaneously 
formed  with  the  Devonian  rocks  amid  which  it  occurs,  is  rendered  solid  by  the  infiltra- 
tion of  carbonate  of  lime  from  adjacent  calcareous  beds  of  no  great  purity  or  importance. 
The  ready  solubility  of  the  carbonate  of  lime,  when  sufficient  free  carbonic  acid  is  pre- 
sent, has  occasioned  the  passage  of  the  former  substance  from  the  calcareous  beds  into 
the  vesicles  of  the  igneous  and  juxtaposed  rock,  and  its  deposit  there,  when  unless  de- 
composed and  again  removed,  it  would  prevent  the  deposit  of  other  substances  passing 
in  solution  through  the  pores  of  the  rock. 


% 

MINERAL    MATTER    IN    FISSURES.  631 

The  fissure  may  either  be  one  through  which  waters  rise  to  the  surface 
of  land,  and  overflow  it,  thus  discharging  large  volumes  of  water  con- 
rig.  284. 


taining  mineral  matter  in  solution  of  various  amount  and  kind,  or  the 
liquid  may  merely  rise  to  such  a  height  in  the  fissure  as  to  remain  con- 
fined to  it,  and  the  portions  of  rocks  adjacent,  amid  the  pores  and  inter- 
stices of  which  it  may  also  enter.  According  to  temperature  also  will 
he  have  to  bear  in  mind  the  solubility  or  deposit  of  the  matter  generally 
in  the  liquid,  permitting  some  of  it  to  remain  in  solution  while  other 
parts  were  deposited,  coating  the  walls  of  the  fissures. 

The  geologist  will  thus  have  to  consider  the  probability  of  certain  of 
the  fissures  extending  to  depths  where  the  temperature  may  become 
very  elevated,  even  to  those  depths,  where  water,  notwithstanding  the 
great  pressure,  might  be  converted  into  steam,  and  numerous  substances 
be  vaporized.  No  doubt  there  is  much  to  be  accomplished  with  respect 
to  our  knowledge  of  the  effects  which  would  be  produced  under  the 
conditions  supposed.  We  may  expect  water  to  exist  under  pressure  as 
such  up  to  very  high  temperatures,  and  its  power  of  dissolving  various 
substances  in  that  state  to  be  so  increased,  that  many  viewed  as  insolu- 
ble at  those  temperatures  at  which  experiments  have  been  undertaken, 
would  become  readily  soluble. 

The  experiments  of  M.  Gustav  Bischoff  on  this  subject  are  highly 
valuable.  Impressed  with  the  importance  of  the  agency  of  steam,  in 
volcanic  productions,  and  viewing  the  connexion  of  such  agency  and 
many  substances  found  in  mineral  veins,  he  found  that  when  galena 
(sulphuret  of  lead)  was  gently  heated  in  a  porcelain  or  glass  tube,  and 
steam  driven  over  it,  that  sulphuretted  hydrogen  and  sulphurous  acid 
were  evolved,  and  the  ore  reduced,  and  that  if  the  lead  thus  obtained 
were  wetted  with  distilled  water,  it  was  covered  by  the  carbonate  of 
lead.  He  remarks  that  some  substances  not  known  to  us  as  evaporating 
at  any  temperature,  are  carried  off  by  steam,  as,  for  example,  silica. 
Artificial  sulphuret  of  silver  was  found  to  be  very  readily  decomposed 
by  steam,  and  more  easily  so  at  a  moderate  heat.  At  a  temperature 
under  the  melting  point  of  zinc,  this  was  soon  effected,  and  the  silver 
effloresced  in  such  forms  as  to  induce  M.  Gustav  Bischoff  to  regard  the 
moss-like  and  filamentous  occurrence  of  native  silver  in  veins  as  very 


632  SOLUBILITY    OF    SULPHATE    OF    BARYTA. 

probably  the  result  of  the  decomposition  of  the  sulphurets.  With  respect 
to  sulphate  of  baryta,  usually  termed  insoluble,  and  yet  so  frequent  in 
the  veins  of  some  districts,  and  in  a  manner  to  leave  little  doubt  that  it 
has  been  deposited  from  a  solution,  he  found,  by  experiment,  that  when 
heated  water,  containing  carbonate  of  soda  or  potash,  came  into  contact 
with  it  (even  when  the  temperature  was  not  much  elevated,  and  the 
water  was  only  slightly  charged  with  those  substances),  a  partial  decom- 
position took  place,  and  that  when  the  temperature  was  again  lowered, 
a  readjustment  was  effected,  sulphate  of  baryta  being  again  produced, 
and  the  carbonic  acid  with  which  it  was  previously  united,  returning  to 
the  soda  or  potash.  In  this  manner,  M.  Bischoff  remarks,  baryta  may 
be  separated  from  sulphuric  acid  in  the  lower  part  of  a  vein,  where  it 
could  be  exposed  to  the  needful  heat  in  waters  containing  the  carbonates 
of  soda  or  potash,  and  be  removed  to  a  cooler  part  of  the  vein,  and  be 
there  deposited,  again  united  with  sulphuric  acid.*  Such  decomposi- 
tions and  recompositions  are  evidently  most  important  in  explanation 
of  the  often  complex  contents  of  veins. 

When  we  know  that  certain  fissures  in  the  earth's  surface  result  from 
dislocations  so  great  that  beds  of  rock,  once  continuous,  are  thrown 
even  several  thousand  feet  distant  from  each  other  in  the  planes  of  the 
fissures,  and  vertically  to  the  stratification,  the  depth  to  which  some  of  these 
fissures  must  extend  can  scarcely  have  been  otherwise  than  sufficiently 
considerable  to  afford  conditions  of  an  important  kind,  as  respects  the 
heating  of  water  in  them,  and  the  consequent  solubility  of  various  sub- 
stances not  readily  acted  upon  by  water  at  more  moderate  temperatures, 
even  to  the  solution  of  some  forming  parts  of  the  rocks  fissured. 

The  experiments  of  Professor  Forchhammer  have  shown,  though 
potash  felspar,  one  so  frequent  among  granites  and  felspar  porphyries, 
may  be  exposed  to  the  action  of  boiling  water,  under  the  ordinary  pres- 
sure of  the  atmosphere,  without  obtaining  the  potash  from  it,  that  when 
that  pressure  is  considerably  increased,  and  the  temperature  augmented, 
this  substance  is  obtained  in  solution. 

As  regards  fissures,  and  heat  at  their  greater  depths  sufficiently  con- 
siderable to  convert  water  into  steam,  even  under  great  pressure,  it  may 
occur  to  the  observer  that,  after  these  fissures  were  produced,  many 
solutions  percolating  through  the  pores,  or  amid  the  beds  and  joints  of 
the  rocks  broken  through,  would  endeavour  to  deliver  themselves  into 
them.  Where  they  entered  any  water  in  the  cleft  and  various  solutions 
in  it,  they  would  mix  with  them,  obeying  the  same  movements  from 
differences  of  temperature,  and  acting  upon  them,  or  being  acted  upon, 
according  to  circumstances.  Where  the  fissure  was  only  filled  by  heated 
vapours,  percolations  into  it  at  those  depths  might  have  a  tendency  to 

v   *  Poggendorf  s  Annalen,  vol.  Ix. 


DEPOSITS    FROM    SOLUTIONS    IN    FISSURES. 


633 


be  vaporized  also,  and  if  any  of  them  contained  matters  then  rendered 
insoluble,  it  might  be  inferred  that  they  were  left  incrusting  the  sides 
of  the  fissures,  in  the  same  manner  that  stalactitic  incrustations  of  car- 
bonate of  lime  cover  the  sides  of  caves  and  fissures  when  the  water  is 
evaporated,  and  the  carbonic  acid,  rendering  the  carbonate  of  lime 
soluble,  is  removed. 

Having  considered  the  fissures  with  reference  to  waters  dispersed 
amid  rocks,  and  finding  their  way  into  them,  as  would  happen  when 
they  rose  to  the  surface  of  dry  land,  or  were  opened  out  only  to  situations 
where  they  did  not  reach  any  considerable  superincumbent  volumes  of 
water,  the  geologist  should  direct  his  attention  to  the  conditions  which 
would  obtain  when  these  fissures  rose  to  the  bottom  of  the  sea,  either 
wholly,  or  so  that  the  sea  waters  could  readily  rush  into  the  clefts 
formed  partly  through  dry  land  and  partly  under  the  sea.  While, 
looking  at  the  present  distribution  of  land  and  sea  on  the  surface  of  the 
earth,  many  long  and  important  fissures  could  be  placed  under  the  con- 
ditions first  noticed,  a  large  proportion  would  be  expected  to  occur 
beneath  the  sea,  under  those  last  mentioned.  If 

a  5,   in  the  annexed  section  (fig.  285),  be  the  & 

level  of  the  sea  ;  a  c  and  b  d,  depths  of  water ;  a^ 
e  e,  rocks,  such  as  argillaceous  slates,  resting 
upon  or  raised  up  by  granite,  //;  and  li,  a  fissure 
traversing  the  whole,  and  opening  to  the  sea- 
water  above,  the  latter  would  rush  into  the  cleft 
or  clefts  at  the  prolongation  of  the  fissure  to  the 
sea-bottom,  descending  as  far  as  any  temperature 
in  the  cleft  would  permit.  It  may  be  assumed, 
for  illustration,  that,  whatever  may  have  been 
the  effects  of  the  first  communication  between 
considerable  depths  and  the  surface  of  the  bot- 
tom of  the  sea,  a  time  would  come  when  the  sea- 
water  could  enter  the  fissure,  unless  any  outflow 
of  waters  reaching  it  from  the  rocks  traversed 
could  prevent  it.  In  certain  situations,  obstruct- 
ing conditions  of  this  kind  might  exist,  the 
fissures  answering  the  purpose  of  artesian  wells 
to  large  tracts  of  country.  Taking,  however, 
the  conditions  to  be  such  as  to  permit  the  en- 
trance of  the  sea-water,  and  that  at  some  depth,  a  -''••  •*  g 
such  as  8  s,  the  water  was  converted  into  steam, 

notwithstanding  any  pressure  there  might  there  be,  the  saline  solutions, 
chloride  of  sodium  constituting  the  important  portion  of  them  (p.  45), 
would  be  left  to  be  dealt  with  according  to  the  temperature  existing  at 
s  «,  acted  upon  by  any  vapours  rising  from  beneath,  A,  where  a  still 


634  HEATED    DEEP    FISSURES    BENEATH    SEAS. 

higher  temperature  might  prevail.  The  production  of  chlorides  of  a 
volatile  kind,  such  as  those  of  copper,  and  others,  might  thence  take 
place  to  a  considerable  extent,  such  chlorides  again  changed  into  other 
combinations  in  the  higher  parts  of  the  fissures.* 

When  fissures  are  regarded  as  of  depths  so  considerable  as  to  extend 
to  such  elevated  temperatures,  the  geologist  can  scarcely  fail  to  turn  to 
the  evidence  respecting  fissures,  and  the  heated  gaseous  substances  dis- 
charged from  them,  during  earthquakes,  whether  these  may  traverse 
volcanic  regions  now  exhibiting  activity,  or  show  no  immediate  con- 
nexion with  them,  and  to  observe  the  emanations  which  take  place  from 
volcanic  vents  themselves,  since  from  such  sources  of  communication 
between  the  interior  and  exterior  parts  of  the  earth,  evidence  would  be 
expected  as  to  the  substances  vaporized  by  heat  beneath,  and  dis- 
charged upwards.  Neither  would  he  neglect  the  contents  of  thermal, 
or  as  most  of  them  are  termed,  mineral  springs,  since  so  many  appear 
only  to  be  the  condensation  of  vapours  and  gases  effected  in  portions 
of  fissures,  when  the  temperature  becomes  sufficiently  lowered.  With 
respect  to  the  vapours  and  gaseous  substances  thus  discharged  from 
volcanoes  and  found  in  mineral  waters,  M.  Elie  de  Beaumont  has 
pointed  out,f  that  the  substances  contained  alike  in  them  and  in 

*  M.  Elie  de  Beaumont  remarks  (Note  surles  Emanations  Volcaniques  et  M6talliferes) 
that  "iron  as  a  chloride,  often  changing  into  peroxide  (specular  iron,  fer  oligiste),  is 
among  the  most  abundant  of  the  substances  derived  from  volcanic  emanations.  Oxidu- 
lated  iron  is  commonly  disseminated  in  the  lavas  ejected  from  volcanoes,  and  it  cannot 
be  doubted  that  it  exists  in  the  lavas  consolidating  in  subterranean  cavities.  Iron  in 
the  form  of  an  oxide  or  chloride  is  necessarily,  therefore,  deposited  in  the  fissures  which 
volcanic  emanations  traverse  before  they  reach  the  surface."  M.  Elie  de  Beaumont 
also  points  out  copper  as  among  volcanic  emanations,  and  it  may  be  observed,  that 
chloride  of  copper  is  readily  vaporized. 

j-  Note  sur  les  Emanations  Volcaniques  et  Me'talliferes  (Bulletin  de  la  Soc.  Geol.  de 
France,  2de  se"rie,  t.  iv.  p.  1249,  1847),  wherein,  under  this  simple  title,  a  mass  of 
important  information  will  be  found  bearing  on  this  subject. 

Adverting  to  the  various  hypotheses  which  have  been  formed  to  account  for  the 
filling  up  of  mineral  veins,  M.  Elie  de  Beaumont  remarks,  that  the  one  "which  attri- 
butes ordinary  mineral  veins  to  emanations  in  the  form  of  vapours  and  to  mineral 
waters,  enables  us  to  comprehend  the  varied  facts  observable  in  mineral  veins,  espe- 
cially the  development  of  those  chemical  affinities  which  have  long  been  observed  as 
influencing  the  manner  in  which  the  metals  are  associated.  Substances  which  are 
usually  associated  have  much  in  common  between  them,  and  often  exhibit  properties 
altogether  analogous.  Nickel  and  cobalt,  so  often  found  together,  much  resemble  each 
other  in  their  properties,  and  the  same  with  iron  and  manganese.  Antimony  and 
arsenic,  the  properties  of  which  are  so  analogous,  occur  in  a  similar  manner,  and  are 
frequently  associated.  Silver  and  lead  have  much  in  common,  and  are  very  frequently 
united  in  veins.  It  is  rare  to  find  silver  unaccompanied  by  lead,  and  this  scarcely 
happens  except  when  the  silver  occurs  native  or  as  a  chloride,  two  states  of  silver 
which  most  differ  from  the  corresponding  conditions  of  lead.  It  is  still  more  rare  to 
find  lead  which  is  not  argentiferous,  the  most  widespread  ore  of  lead  being  the  sul- 
phuret,  the  properties  of  which  are  very  analogous  with  the  sulphuret  of  silver.  Lead 
and  zinc,  the  sulphurets  of  which  possess  analogous  properties,  are  found  associated 
together  in  the  form  of  galena  and  blende. ;  and  the  same  facts  are  observable  in  the 


OCCURRENCE    OF    SULPHUR,    ETC.,    IN    MINERAL    VEINS.     635 

mineral  veins,  may  be  taken  as  19,  viz.,  potassium,  sodium,  cal- 
cium, aluminium,  manganese,  iron,  cobalt,  lead,  copper,  hydrogen, 
silicon,  carbon,  boron,  arsenic,  nitrogen,  selenium,  sulphur,  oxygen, 
and  chlorine.  The  substances  found  in  mineral  waters  and  veins,  and 
not  hitherto  noticed  in  volcanic  emanations,  he  notices  as  lithium, 
barium,  strontian,  magnesium,  phosphorus,  iodine,  bromine,  and  fluo- 
rine.* 

When  the  observer  thus  directs  his  attention  to  the  consequences 
which  may  arise  from  the  production  of  fissures,  extending  to  portions 
of  the  earth  where,  either  from  any  inferred  high  temperature  at  con- 
siderable depths  in  our  planet  itself,  or  certain  conditions  for  great 
heat  in  portions  of  it,  such,  for  example,  as  the  source  of  that  in  vol- 
canic regions,  when  supposed  independent  of  the  former,  he  should  bear 
in  mind  that,  of  the  substances  occupying  the  interior  of  the  earth, 
beyond  such  slight  depths  as  the  reasoning  respecting  the  thicknesses 
of  various  rock  deposits  renders  probable,  nothing  is  known,  except 
that  their  density,  as  a  whole,  must  be  much  greater  than  that  of  the 
rocks  at  the  surface,  since,  according  to  Laplace,  the  mean  density  of 
the  earth  is  1'55,  while  that  of  its  solid  surface  is  only  1.  The  mass 
of  substances  forming  the  solid  surface  of  the  earth  are  oxides,  those 
which  are  not  of  that  character  are  very  limited,  and  it  is  not  a  little 
interesting  to  find  the  latter,  to  a  great  extent,  in  the  fissures  under 
consideration,  or  so  disposed  as  readily  to  have  entered  the  cavities  of 
deposits  after  their  accumulation,  there  forming  combinations  other 
than  oxides,  from  conditions  prevailing  in  these  deposits,  or  to  have 
been  included  amid  the  igneous  rocks  thrown  up  from  beneath.  As 
respects  the  frequent  occurrence  of  certain  of  the  metals  with  sulphur, 
arsenic,  and  other  substances,  which  have  been  termed,  with  reference 
to  their  occurrence  in  veins,  mineralizers,  their  frequent  combinations 
with  these,  under  conditions  that  may  often  be  inferred  as  those  which 
governed  their  original  deposit  in  mineral  veins,  secondary  actions 
having  effected  subsequent  modifications  and  changes,  is  highly  in- 
teresting. M.  Elie  de  Beaumont  has  remarked,  when  treating  of  an 
initial  volatilization  of  the  metallic  substances  found  in  veins,  that  this 
hypothesis  agrees  with  the  fact  that  the  metals,  properly  so  called,  are 
found  in  them  much  less  frequently  combined  with  oxygen  than  with 
sulphur,  selenium,  arsenic,  phosphorus,  antimony,  tellurium,  chlorine, 
iodine,  and  bromine.  "These  substances,"  he  observes,  "  are  not  only 
in  general  volatile,  as  well  as  bismuth,  which  often  accompanies  them, 

great  family  of  metals  occurring  in  the  stanniferous  veins,  such  as  tin,  tungsten,  tan- 
talium,  &c." 

*  With  respect  to  the  substances  contained  in  mineral  waters,  M.  Elie  de  Beaumont 
mentions  that  he  has  taken  them  from  the  works  of  many  chemists,  and  especially  from 
those  of  MM.  Berzelius,  Bischoff,  and  Kopp. 


636  REACTION    OF    SUBSTANCES    UPON    EACH 

but  they  have  likewise  the  property  of  rendering  many  of  those  with 
which  they  combine  also  volatile.  It  is  difficult  to  believe,  that  this 
property  has  not  acted  a  part  in  the  filling  of  the  veins."*  We  should 
expect  to  find  in  the  contents  of  fissures,  or  in  cavities  communicating 
with  them,  or  disseminated  amid  such  portions  of  rocks  as  may  be 
inferred  to  have  presented  the  ready  means  for  the  introduction  of 
mineral  matter  from  them,  some  substances  not  common  elsewhere,  and 
under  forms  and  combinations  often  of  a  peculiar  kind,  as  well  as  those 
with  which  we  may  be  familiar,  as  more  or  less  forming  the  com- 
ponent parts  of  rocks  generally,  though  these  also  may  be  sometimes 
discovered  under  new  combinations.  The  geologist  would  expect  also 
to  find  numerous  compound  substances  which  he  might  refer  to  the 
reactions  of  certain  prior  combinations,  and  to  the  readjustment  of 
their  component  parts,  according  to  the  governing  conditions  of  the 
time. 

With  reference  to  slow  secondary  electrical  action,  caused  by  feeble 
currents,  M.  Becquerel  pointed  out,  many  years  since  (1835),  that 
various  compounds  are  produced  which  are  not  formed  by  the  usual 
kind  of  experimental  investigations,  disunited  elements  being  presented 
to  each  other  in  a  nascent  state,  one  highly  favourable  to  such  produc- 
tions.f  He  observed  that  substances,  commonly  termed  insoluble, 
became  crystallized,  because  the  electrical  action  being  slow,  the  chemi- 
cal action  was  slow  also,  so  that  the  component  molecules  had  time  to 
arrange  themselves  according  to  the  laws  governing  crystallization,  an 
advantage  not  obtained  when  the  chemical  forces  have  more  intensity. 
M.  Becquerel  produced  various  minerals  by  means  of  these  secondary 
actions,  such  as  the  oxides  of  copper  and  zinc,  the  sulphurets  of  silver, 
copper,  tin,  lead,  iron,  &c.J  The  action  of  bodies  upon  each  other,  as 

*  "These  bodies,"  continues  M.  Elie  de  Beaumont,  "are,  at  the  same  time,  those 
found  among  volcanic  emanations,  and  also  in  thermal  springs,  and  their  presence  in 
the  veins  contributes  to  corroborate  the  relations  previously  noticed  as  existing  between 
these  veins,  volcanic  emanations,  and  mineral  waters." 

f  Trait6  Experimental  de  I'Electricit^  et  du  Magnetisme,  Paris,  1885.  M.  Becquerel 
there  remarked  (t.  iii.  p.  295),  that  "it  could  not,  for  a  long  time,  be  conceived  how, 
with  apparently  feeble  electrical  forces,  strong  affinities  could  be  overcome  in  order  to 
decompose  bodies  and  produce  new  combinations ;  it  being  considered  that  the  action 
of  more  or  less  energetic  currents  should  always  be  employed.  As  soon,  however,  as 
the  electrical  effects  which  take  place  in  chemical  action  had  been  analyzed,  it  became 
clear  that  the  same  end  might  be  obtained  by  skilfully  employing  these  effects.  It  can 
be  readily  understood  that  when  any  voltaic  couple  is  plunged  into  a  solution  which 
reacts  on  one  of  the  elements  of  this  couple,  the  particles  of  the  solution,  the  moment 
they  are  brought  into  play  by  the  operation  of  chemical  action,  are  then,  being  in  a 
nascent  state,  in  the  most  favourable  condition  for  obeying  the  action  of  the  electric 
current  produced  by  the  couple." 

J  The  observer  will  find  much  to  interest  him,  bearing  on  the  subject  of  mineral 
veins,  in  those  experiments  in  which  M.  Becquerel  employed  a  bent  tube  in  the  form  of 
a  U,  with  clay  moistened  at  the  bottom,  thus  separating  it  into  two  portions,  in  which 


•k 

OTHER    IN    FISSURES    AND    CAVITIES.  637 

shown  in  the  experiments  of  M.  Becquerel,  so  that  after  the  production, 
and  even  crystallization  of  some  substances,  they  were  again  decom- 
posed by  the  new  action  then  set  up  among  them,  appears  to  have  an 
important  bearing  upon  the  filling,  and  modifications  of  the  contents  of 
fissures  and  cavities.*  He  concluded,  from  his  experiments,  "  that  to 
obtain  an  insoluble  crystallized  substance  by  electro-chemical  reactions, 
it  is  sufficient  to  make  it  combine  with  another  which  is  soluble,  and 
afterwards  operate  by  means  of  very  slow  decomposition,  "f 

In  1830,  Mr.  Robert  Were  Pox  commenced  a  series  of  experiments 
in  the  mines  of  Cornwall,  to  ascertain  the  electro-magnetic  properties  of 
the  mineral  veins  of  that  metalliferous  district.^  In  1837  he  treated 
the  connexion  of  electricity  and  mineral  veins  more  at  length,  chiefly 
referring  to  the  veins  in  Cornwall,  §  observing,  with  respect  to  the  pre- 
sent condition  of  mineral  veins,  that  he  found,  "  by  an  examination  of 
water  taken  from  different  mines,  and  from  various  parts  of  the  same 
mine,  that  different  varieties  of  saline  solutions  now  exist  in  neighbour- 
ing strata."  In  many  instances  the  proportion  of  foreign  matter  in  the 
water  was  very  small,  whilst  in  others  it  was  very  considerable ;  "  but 
I  have  not,"  he  adds,  "yet  tried  any  mine- water  that  would  not  produce 
very  decided  electrical  action,  when  the  native  sulphuret  of  copper,  or 
of  copper  and  iron  (copper  pyrites)  were  plunged  into  it,  and  the  voltaic 
circuit  was  completed.  The  very  superior  conducting  power  of  the  saline 
water  in  the  fissures,  in  relation  to  the  merely  moistened  rocks,  would 
always  tend  to  supersede  the  transfer  of  electricity  more  or  less  through 
the  latter.  The  contact  of  large  surfaces  of  rock,  clay,  &c.,  with  water, 
differing  in  its  saline  contents  from  them,  must  also  have  been  an  efficient 
cause  of  electrical  excitement,  and  it  should  not  be  forgotten  that  the 
circulation  of  water  would  be  liable  to  very  frequent  changes  of  velocity, 

solutions  were  placed  to  be  acted  upon,  -wires  being  introduced  to  form  the  voltaic  cir- 
cuit ;  as  also  in  those  in  which  he  placed  substances  in  a  tube,  afterwards  hermetically 
sealed,  so  that  they  formed  voltaic  circuits  in  the  tube  itself,  the  substances  acting 
upon  each  other. 

*  M.  Becquerel  remarks,  after  describing  some  substances  obtained  by  his  experi- 
ments, "that  all  the  chemical  actions  which  led  to  these  compounds,  could  only  have 
arisen  from  certain  electrical  influences  possessing  little  energy  ;  for  if  we  operate  with 
apparatus  the  action  of  which  is  too  strong,  all  the  elements  are  isolated,  and  no  com- 
bination is  possible." 

f  Traite"  de  1'Electricite,  t.  iii.  p.  298.  It  is  remarked,  respecting  truncations  of  the 
crystals  of  certain  double  chlorides  obtained  in  some  of  the  experiments,  that,  in  the 
beginning,  the  crystals  are  perfectly  formed  ;  "but  that  when  the  apparatus  has  been 
in  action  for  a  long  time,  truncations  of  the  angles  are  gradually  produced  ;  whence  it 
seems  to  follow,  that  when  the  particles  of  the  crystallizing  substance  are  less  abun- 
dant, the  force  which  determines  the  regular  grouping  of  them  has  no  longer  sufficient 
energy  to  complete  the  crystal." 

J  Philosophical  Transactions,  1830. 

g  "  Observations  on  Mineral  Veins ;"  Report  of  the  Royal  Polytechnic  Society  of  Corn- 
wall for  1836;  Falmouth,  1837. 


638  CHARACTER    OF    METALLIFEROUS    VEINS 

in  consequence  of  obstruction  in  the  fissures  or  their  occasional  enlarge- 
ment, so  that  the  contents,  as  well  as  the  temperature  of  the  water, 
would  be  subject  to  many  modifications."* 

The  contents  of  fissures  and  cavities  through,  and  in  rocks,  will  not 
long  have  engaged  the  attention  of  an  observer  before  he  will  find  that 
in  those  districts  where  the  ores  of  the  useful  metals  are  worked,  there 
is  noLunfrequently  a  marked  association  of  dissimilar  rocks,  one  or  more 
of  them  being  often  of  igneous  origin.  This  condition  is  far  from  being 
constant ;  at  the  same  time  it  is  one  which  has  long  engaged  the  atten- 
tion of  miners,t  and  in  some  mining  countries,  much  importance  has 

*  Robert  Were  Fox ;  Report  of  the  Cornwall  Polytechnic  Society  for  1836 ;  Falmouth, 
1837,  p.  110. 

Adopting  the  view  of  M.  Ampere,  that  the  direction  of  terrestrial  magnetism  is  due 
to  the  circulation  of  currents  of  electricity  from  east  to  west  round  the  globe,  Mr.  Fox 
considers,  that  "if  fissures  happened  to  have  opposite  horizontal  bearings,  and  were 
equally  filled  with  water  charged  with  saline  matter,  the  electric  currents  would  be  de- 
termined, in  preference,  through  such  of  them  as  nearly  approximated  to  the  magnetic 
east  and  west  points  at  the  time."  The  consequence,  he  conceives,  would  be  the  de- 
composition of  the  saline  substances,  and  the  determination  of  the  metals  or  base  to  the 
electro-negative,  and  the  acids  to  the  electro-positive  rock.  "However  slow,"  he  re- 
marks, "  this  process  at  first  may  have  been,  the  deposition  of  the  metals  would  cause  it 
to  become  more  and  more  energetic.  The  metals  and  metalliferous  deposits  would,  like- 
wise, react  on  each  other,  and  give  rise  to  new  combinations  and  arrangements  till  they 
arrived  at  a  state  of  comparative  equilibrium.  This  may  be  said  to  be  very  much  the 
case  with  the  lodes  (mineral  veins)  at  present,  as  most  of  the  ores  which  are  capable  of 
conducting  electricity  very  nearly  approximate  to  each  other  in  the  electrical  scale, 
being  more  electro-negative  than  silica,  and  many  of  them  as  much  so  as  platina ; 
indeed,  the  gray  oxide  of  manganese  and  the  loadstone  are  electro-negative  in  a  still 
higher  degree.  Arsenical  pyrites,  iron  pyrites,  and  copper  pyrites  hold  rather  a  high 
place  in  the  scale,  and  are  electro-negative  with  respect  to  purple  copper  and  galena, 
but  especially  to  the  sulphuret  or  vitreous  copper  ore,  which  will  produce  a  very  decided 
action  on  the  galvanometer  when  connected  in  the  voltaic  circuit  with  copper  or  iron 
pyrites."— p.  113. 

M.  Becquerel  considers  (Traite"  de  I'Electricit^,  t.  v.  pp.  163,  164),  that  at  a  certain 
depth  in  the  earth  a  multitude  of  electric  currents  exist,  with  very  different  directions, 
the  general  result  of  which  would  produce  an  action  on  the  magnetic  needle.  He  infers, 
that  these  are  produced  by  the  permanent  communication  kept  up  by  numerous  fissures 
through  which  sea-waters  percolate  either  to  the  metals  of  the  earths  and  alkalies,  or  to 
metallic  chlorides,  causing  the  metals  to  take  negative  electricity,  and  the  steam  or 
other  vapours  positive  electricity.  A  part  of  the  latter  electricity,  he  considers,  would 
be  carried  into  the  atmosphere  by  volcanic  eruptions,  and  the  other  would  tend  to  com- 
bine with  the  negative  electricity  of  the  bases,  by  passing  through  all  the  conducting 
bodies  which  established  the  communication  between  the  metals  or  their  chlorides  in 
the  solid,  liquid,  or  gaseous  substances  that  filled  the  fissures.  Hence,  he  observes,  a 
number  of  partial  electrical  currents  would  circulate  in  the  interior  of  the  globe,  pro- 
ducing electro-chemical  reactions,  of  which  we  cannot  appreciate  the  whole  extent,  but 
which  certainly  would  give  rise  to  numerous  compounds. 

f  This  somewhat  common  association  of  igneous  rocks  has  also  long  since  engaged 
the  attention  of  geologists.  Professor  Necker  adduced  abundant  evidence  on  this  head 
in  1832  and  1833  (Proceedings  of  the  Geological  Society  of  London,  March,  1832,  vol. 
i.  p.  392,  and  Jameson's  Edinburgh  Philosophical  Journal,  1838).  He  thence  inferred 
the  filling  of  metalliferous  veins  by  means  of  sublimation. 


AMID    ASSOCIATED    DISSIMILAR    BOCKS.  639 

been  attached  to  its  practical  bearings.  In  the  same  countries  also  long 
experience  has  shown  the  miner  that  the  ores  he  seeks  are  more  likely 
to  be  found  amid  or  against  certain  rocks  than  others,  though  the  fissures 
in  which  they  are  found  traverse  several  different  kinds  or  modifications 
of  rocks.  It  is  very  desirable  that  an  observer  should  collect  all  facts 
of  this  kind,  however  ill-arranged  they  may  sometimes  be  by  those  from 
whom  he  may  derive  them,  and  however  needful  their  proper  classifica- 
tion, from  personal  research,  subsequently.  At  the  contact  of  certain 
granites  with  other,  and  for  the  most  part,  sedimentary  rocks,  and  espe- 
cially where  there  may  have  been  some  modification  or  alteration  of  the 
latter  from  the  intrusion  of  the  former,  fissures  traversing  them  are 
often  found  productive  of  the  ores  of  the  useful  metals,  sufficiently 
abundant  to  be  worked,  provided  the  districts  generally  are  metallife- 
rous. In  other  words  such  conditions,  in  a  metalliferous  district,  are 
not  uncommonly  those  under  which  the  ores  are  the  most  abundant.  In 
the  mining  districts  of  Cornwall  and  Devon  the  fissures  through  the 
junctions,  or  the  vicinity  of  the  junctions  of  the  granite  and  schistose 
rocks,  in  those  localities  which  may  be  termed  metalliferous,*  have  been 
found  to  produce  much  ore,  often  not  in  the  least  quantity  when  they 
also  traverse  dykes,  or  channels  as  they  are  locally  termed,  of  the  por- 
phyries and  granitic  rocks  known  as  elvans  (p.  539).  Those  irregular 
accumulations  of  ore  usually  termed  bunches  are  often  found  at  the 
junction  of  granite  and  schistose  rocks.  In  illustration  also  of  the  oc- 
currence of  similar  accumulations  of  either  tin  or  copper  ores,  in  the 
same  mining  country,  when  a  fissure  traversing  schistose  and  porphy- 
ritic  dykes  (elvans),  passes  through  the  latter,  the  following  section  (fig. 
286),  across  the  lode  at  Wheal  Alfred,  Gwiriear,  may  be  useful.  The 
elvan  dyke,  a  6,  is  about  300  feet  thick,  having  a  direction  about  N.E. 
and  S.W.,  and  dipping  at  about  an  angle  of  45°  northerly.  The  lode 
c  d,  dipping  at  an  angle  of  72°  to  the  north,  traverses  the  elvan,  a  b, 
obliquely  in  its  descent,  at  e  f.  While  the  fissure  traversed  the  upper 
and  adjoining  slate,  on  the  north,  no  great  amount  of  ore  was  obtained, 
but  upon  entering  the  elvan  it  became  more  rich,  and  while  passing 

The  observer  will  find  the  connexion  of  igneous  rocks  and  mineral  veins  treated  by 
M.  Elie  de  Beaumont  with  precision,  and,  at  the  same  time,  with  ample  detail,  in  his 
"  Note  sur  les  Emanations  Volcaniques  et  Metalliferes." — Bulletin  de  la  SocietS  de 
France,  1847,  2de  serie,  t.  iv. 

*  In  illustration  of  the  different  distribution  of  chiefly  metalliferous  districts  into 
which  some  areas,  not  unproductive  of  the  useful  metals,  are  sometimes  naturally  di- 
vided, it  may  be  useful  to  mention,  that  Cornwall  and  Western  Devon  may  be  separated 
into  six  chief  metalliferous  districts.  1.  That  of  Tavistock  (including  Dartmoor,  and 
the  mining  country  of  Callington  and  Linkinghorne) ;  2,  that  of  St.  Austell  (including 
the  granitic  mass  of  Hensbarrow,  and  its  schistose  skirts) ;  3,  the  St.  Agnes  district;  4, 
that  of  Gwennap,  Redruth,  and  Camborne  ;  5,  that  of  Breague,  Marazion,  and  Gwinear ; 
and  6,  the  district  of  St.  Just  and  St.  Ives,  comprising  the  granitic  country  between 
these  two  places. 


640         MINERAL     VEINS    TRAVERSING    ELVAN    DYKES. 

through  that  rock,  the  ore  was  found  to  be  so  abundant  as  to  afford  a 
considerable  profit.*     After  quitting  the  elvan  at  /,  in  its  descent,  and 


entering  the  slate  benea.th,  on  the  south,  the  lode  became  poor,  and 
eventually  the  mine  was  abandoned  from  the  scarcity  of  ore,  the  amount 
of  it  in  the  depths  not  repaying  the  cost  of  raising,  f 

The  connexion  of  bunches  of  tin  and  copper  ores  in  fissures  where 
these  traverse  elvan  dykes,  viewing  the  subject  generally,  is  well  known 
practically  to  the  Cornish  miners,  and  its  importance  as  regards  the 
abundant  and  profitable  contents  of  the  mineral  veins  in  that  metallife- 
rous land,  can  be  conveniently  studied  in  many  places. {  An  observer 
may  sometimes  find  it  remarked  that  a  lode  is  split  up  into  strings  upon 
its  entrance  into*  an  elvan,  and  it  may  also  be  stated  that  it  is  thence 
impoverished.  Usually,  however,  when  the  facts  are  well  investigated, 
it  appears  in  such  cases,  that  the  ore  itself  continues  sufficiently  abun- 
dant, occasionally  even  more  abundant,  though  so  divided  into  strings, 
branching  amid  fractured  and  highly  separated  portions  of  the  elvan,  as 
not  to  be  so  profitably  worked  as  previously.  If  elvans  have  been  divided 
into  joints,  as  often  seems  to  have  been  the  case  before  the  formation  of 
the  fissure  traversing  it  and  the  adjoining  rocks,  it  would  probably  hap- 
pen that  upon  passing  through  them  from  these  adjoining  and  less  divided 
rocks,  such  joints  would  be  the  courses  through  which  the  force  pro- 
ducing the  general  fissure  would  act,  multiplying  the  parts  of  the  general 
fracture  in  the  elvan,  so  that  when  filled  subsequently  by  mineral  matter, 
the  vein  should  appear  split  up  into  strings  where  the  elvan  occurred. 
If,  as  in  the  following  section  (fig.  287),  a  country  composed  of  slate  a  6, 
be  traversed  by  an  elvan  dyke,  c  d,  having  a  jointed  structure,  and  a 
fracture,  e  /,  be  made  across  the  whole,  it  would  be  expected  that  where 
the  fissure  was  effected  across  the  jointed  elvan  dyke,  the  solids  formed 

*  Those  engaged  in  this  mine  reaped  a  profit,  it  is  stated,  of  140, GOO/,  at  that  time. 

f  The  width  of  the  lode  was  from  six  to  nine  feet  in  the  slate  above  the  elvan,  in- 
creased in  the  latter  to  25  feet,  and  decreased  in  the  slate  beneath  to  10  feet. 

J  If  the  observer  will  direct  his  attention  to  the  Geological  Survey  Map  of  Cornwall, 
he  will  find  numerous  examples  of  the  intersection  of  elvan  dykes  and  mineral  veins. 
The  percentage  of  cases  is  considerable  in  which  these  intersections  are  accompanied 
by  bunches  of  ore  in  fair  quantities. 


ELVAN  DYKES  IN  CORNWALL.  641 

in  the  latter  by  the  joints  would  be  much  dislocated,  so  that  when  the 
complicated  fracture  was  subsequently  filled  by  mineral  manner,  viewing 

Fig.  287, 


such  contents  and  their  course  alone,  as  is  commonly  the  custom  in 
mining  countries,  the  vein  would  be  considered  as  split  into  strings 
at  i  g. 

The  mineralogical  modification  of  the  various  rocks  in  metalliferous 
districts,  very  commonly  bearing  the  same  names,  is  also  a  subject  of 
no  slight  anxiety  on  the  part  of  the  miner,  since,  from  experience  in 
such  districts,  he  finds  that  when  it  presents  certain  characters  his 
chances  of  success  as  to  the  occurrence  of  the  ores  he  seeks,  are  con- 
siderably increased.  Thus,  in  Cornwall  or  Devon,  he  usually  prefers  a 
granite  or  elvan  which  is  to  a  certain  extent  decomposed.  The  parti- 
cular character  of  the  various  kinds  of  the  schistose  rocks  and  the  harder 
beds  associated  with  them,  are  also  carefully  noted,  and  from  experience, 
some  kinds,  when  forming  the  walls  of  the  fissures,  are  known  to  carry 
more  ore  than  the  others,  while  some  again  are  regarded  as  unfavour- 
able.* In  districts  where  the  rocks  are  more  generally  bedded,  excellent 

*  As  we  have  elsewhere  stated  (Report  on  the  Geology  of  Cornwall,  &c.,  1839),  in 
Gwennap  (Cornwall)  the  more  experienced  miners  seem  to  prefer  those  argillaceous 
beds  which  accompany  the  red'  or  variegated  slates  of  the  district,  and  which  have  a 
fine  grain  and  a  blue-gray  colour.  Respecting  the  value  of  the  red  beds  themselves, 
opinions  somewhat  differ.  Mr.  Carne  states,  that  when  the  copper  lodes  in  Gwennap 
intersect  the  red  beds  they  become  unproductive,  an  immediate  change  taking  place 
when  they  pass  beyond  them  into  another  slate.  In  most  lodes  the  miners  have  their 
favourite  kind  of  rock  or  country,  so  that  the  whole  tendency  of  their  experience  goes  to 
show  that  particular  mineral  structures,  other  circumstances  being  the  same,  are  more 
favourable  to  the  occurrence  of  the  ores  sought  than  others.  The  principal  lode  at 
Fowey  Consols  mine  would  seem  to  afford  a  good  example  of  ore  accompanying  a  parti- 
cular set  of  beds.  The  slate  in  this  productive  mine  dips  away  from  the  granite  of  St. 
Blazey,  on  which  it  rests,  towards  the  east,  so  that,  as  the  lode  has  a  general  east  and 
west  direction,  the  beds  traversed  by  it  on  the  lower  part  of  the  mine  on  the  east  rise 
towards  the  western  end,  and  it  is  found  that  the  bunches  of  ore  accompany  this  dip, 
coinciding  with  certain  beds,  viewing  the  subject  on  the  large  scale.  The  mode  in 
which  the  gossan  and  other  marks  of  the  usually  higher  parts  of  a  copper  lode  in  Corn- 
wall dip  to  the  eastward  in  this  mine  is  very  interesting :  gossan,  with  its  very  common 
accompaniment  of  native  copper,  green  carbonate  of  copper  and  gray  sulphuret,  de- 
scending above  the  bunches  of  copper  pyrites  to  the  depth  of  about  600  feet  from  the 
surface,  with  the  dip  of  the  beds,  on  the  eastern  part  of  the  mine.  It  is  often  very 

41 


642      INFLUENCE    OF    THE    DIFFERENT    ROCKS    TRAVERSED 

opportunities  may  often  be  obtained  for  studying  the  modification  of  the 
contents  of  the  metalliferous  fissure,  according  to  the  variation  of  the 
rocks  forming  its  walls.  In  Derbyshire,  for  example,  where  the  same  fis- 
sure not  only  passes  through  the  mountain  limestone,  often  with  its  asso- 
ciated igneous  rocks  (p.  533),  but  also  across  the  surrounding,  and  higher 
accumulations  of  shales  and  sandstones,  the  lead  ore,  sulphuret  of  lead, 
that  chiefly  found  in  the  Derbyshire  veins,  keeps  generally,  though  not 
altogether,  to  the  limestone  series,  and  appears  most  prevalent  in  the 
upper  part  of  it.  The  igneous  rocks,  commonly  compounds  of  felspar 
and  hornblende,  sometimes  dense  and  hard,  at  others  originally  vesicular, 
though  the  vesicles  may  be  now  filled  by  infiltrated  matter,  are  considered 
unfavourable  for  these  ores  of  lead.  Indeed,  at  one  time,  the  opinion 
of  the  Derbyshire  miners  was  that  the  vein  did  not  traverse  the  toad- 
stones  (p.  533),  or  MacJcstones,  as  these  igneous  rocks  are  locally  termed, 

difficult  to  convey  by  words  the  differences  in  a  rock  which  the  practised  eye  readily 
seizes  as  distinctive  in  these  cases. 

Regarding  the  changes  in  the  metallic  contents  of  the  Cornish  mineral  veins  according 
to  the  character  of  the  adjoining  rock,  Mr.  Carne  observes,  that,  "in  Godolphin  the  lodes 
were  rich  where  the  killas, (argillaceous  slate)  was  of  a  bluish-white  colour,  but  poor 
where  it  was  black.  In  Poldice  and  Huel  Fortune,  the  lodes  in  the  killas  continued 
productive  until  they  entered  a  stratum  of  blue  hard  killas,  which  cut  out  the  riches. 
In  Huel  Squire,  the  copper  lodes  were  very  productive  when  in  the  soft  light-blue  killas ; 
but  a  stratum  of  hard  black  killas  underlying  (dipping)  rapidly  met  one  lode  at  the  depth 
of  44  fathoms,  and  the  other  at  120  fathoms,  under  the  adit,  and  at  these  levels  both 
the  lodes  became  poor.  At  Penstruthal  copper  mine  the  lode  had  been  tried  unsuccess- 
fully at  various  times  in  parts  where  the  granite  was  hard,  but  trial  being  made  where 
that  rock  was  soft,  it  became  one  of  the  most  profitable  mines  in  Cornwall." — Trans. 
Geol.  Soc.  Cornwall,  vol.  iii.  p.  81 ;  1827.  . 

M.  Fournet  has  remarked  on  this  subject  that,  commonly  in  Upper  Hungary,  the 
largest  copper  lodes  are  found  in  fine  clay  slates ;  that  in  Saxony  the  silver  ores  occur 
in  gneiss  ;  and  that  in  the  Hartz  certain  ores  are  intimately  connected  with  grauwacke. 
The  veins  of  Konigsberg,  Norway,  are  sterile  in  mica  slate,  and  become  very  produc- 
tive in  beds  known  by  the  name  of  Faalbcendre.  At  Andreasberg,  Hartz,  the  veins  which 
pass  from  argillaceous  slate  into  flinty  slate  lose  their  riches  in  the  latter  rock. 

M.  Fournet  gives,  from  the  information  of  M.  Voltz,  the  following  remarkable  example 
of  the  contents  of  a  mineral  vein  varying  according  to  the  character  of  the  rocks  on  its 
gides: — The  Wenzal  vein  at  Furstenburg  runs  nearly  vertically  from  N.  to  S.,  across 
many  beds  of  gneiss,  about  60  feet  thick,  dipping  east.  Each  of  these  beds  forms  a  dis- 
tinct variety  of  rock.  The  first  is  very  micaceous ;  the  second  passes  into  argillaceous 
slate ;  the  third  is  hornblendic,  and  scarcely  any  mica  can  be  detected  in  the  fourth. 
This  vein  is  shifted  in  the  depth  to  the  westward  by  several  cross  courses ;  and  it  was 
between  two  of  these  cross  courses,  distant  from  each  other  about  240  feet,  that  it  con- 
tained those  riches  for  which  it  has  become  so  celebrated.  In  the  first  bed  of  gneiss  the 
vein  merely  formed  a  nearly  imperceptible  string  of  clay ;  in  the  second  it  suddenly 
acquired  a  thickness  of  from  12  to  18  inches,  and  was  composed  of  sulphate  of  baryta, 
antimonial  silver,  red  silver,  and  argentiferous  gray  copper.  The  antimonial  silver  was 
always  found  in  large  masses.  In  the  third  bed  the  thickness  of  the  vein  is  preserved, 
and  the  sulphate  of  baryta  is  continued  in  it;  but  the  silver  ores  disappear,  nnd  a  little 
sulphuret  of  lead  is  the  only  ore  found.  In  the  fourth  bed  the  silver  ores  become  a.s 
abundant  as  in  the  second,  but  they  gradually  disappear  in  depth  and  are  replaced  by 
selenite  (sulphate  of  lime),  a  little  sulphuret  of  lead,  and  some  traces  of  pure  sulphur. 


ON    THE    MINERAL    CONTENTS    OF    FISSURES.  643 

so  unproductive  are  they.*  It  is  now,  however,  well  known  that  the 
veins,  the  true  fissures,  those  locally  termed  rakes,  pass  through  these 
rocks  as  well  as  the  limestones,  the  ores  being  commonly  absent  where 
these  igneous  rocks  constitute  the  walls  of  the  vein,  its  contents  in  those 
situations  being  composed  of  other  mineral  substances. f  Among  the 
limestone  beds  themselves,  some  are  considered  as  more  favourable,  as 
walls  to  the  vein,  than  others,  and  certain  of  them  in  which  much  carbo- 
nate of  magnesia  occurs,  are  disliked,  and  looked  upon  as  somewhat 
unfavourable.  Though  the  veins  are  known  to  be  often  continued  into 
certain  shales,  not  unfrequently  black  and  containing  much  carbonaceous 
matter,  above  the  limestones,  and  though  these  shales  have  occasionally 
borne,  as  the  term  is,  a  fair  amount  of  ores ;  looking  at  the  district 
generally  this  is  the  exception,  and  it  is  a  still  greater  exception  when 
the  sandstones  surmounting  these  shales  contain  any  appreciable  amount 
of  them,  though  a  fissure  may  have  traversed  all  these  various  rocks, 
arranged  as  beds,  and  have  been  open  to  solutions  of  a  similar  kind  at 
the  same  time.  Taken  as  a  whole,  the  upper  part  of  the  mountain  lime- 
stone series  is  the  most  metalliferous,  and  in  it  certain  beds  appear  more 
favourable  for  the  occurrence  of  the  ores  of  lead  than  others.  This 
seems  to  hold  equally  well  whether  the  sulphuret  of  lead  be  found  in 
fissures  traversing  all  the  rocks,  or  in  the  joints  and  cavernous  places  in 
the  limestone  series.  The  metalliferous  deposits  are  not  confined  to  the 
irregular  cavities  so  frequent  in  many  limestone  countries  in  different 
parts  of  the  world,  but  extend  to  those  which  are  situated  between  the 
beds  themselves,  and  arise  either  from  the  partial  removal  of  clays 
which  were  once  interposed  between  some  of  the  beds,  or  from  the  ori- 
ginal small  spaces  between  them  having  been  enlarged  by  the  same 
causes  as  those  which  have  formed  the  other  irregular  and  greater 
cavities. 

Many  of  the  small  metalliferous  veins  in  the  Derbyshire  limestone 

*  With  reference  to  this  rock,  which  appears  to  be  chiefly  a  compound  of  felspar  and 
hornblende,  with  oxide  of  iron,  and  thus  unfavourable  generally  as  the  wall  of  fissures 
for  the  lead  ore  in  Derbyshire,  it  may  not  be  out  of  place  to  remark  that  the  greenstone 
of  Devon  and  Cornwall,  commonly  of  much  the  same  composition,  may  be  considered, 
as  a  whole,  unfavourable  to  the  ores  of  tin,  copper,  and  lead.  The  mode  of  occurrence 
of  these  greenstones,  as  to  proximity  to  granite,  intermixture  with  elvan  dykes,  and  the 
intersection  of  cross  courses,  is  the  same  as  that  of  the  slates  with  which  they  are 
accompanied ;  the  fissures,  moreover,  traversing  them  have  the  directions  and  are  of 
the  same  kinds  as  those  bearing  ores  elsewhere.  Though  certain  mines  at  St.  Just 
might  be  considered  as  exceptions,  this  is  more  apparent  than  real,  abundant  ores  rarely 
being  detected  in  the  greenstone  itself,  which,  from  the  dip  of  the  beds  near  St.  Just, 
often  appears  to  occupy  more  of  the  mass  of  rocks  there  found  than  is  really  the  fact. 

j-  In  the  cases  where  a  fair  proportion  of  galena  has  been  found  in  fissures  through 
the  loadstones,  it  has  usually  happened  that  the  vein  traversing  the  limestones  above  or 
beneath,  and  sometimes  both,  contained  much  ore,  it  thus  appearing  as  if  a  superabun- 
dance of  the  ore  found  its  way  amid  the  toadstone,  the  effects  due  to  the  limestone  being, 
sufficiently  powerful  for  the  purpose. 


644  METALLIFEROUS    DEPOSITS    OF    DERBYSHIRE. 

are  but  joints  (p.  592)  in  that  rock  that  have  been  so  open  as  to  receive 
a  deposit,  which,  when  sufficiently  composed  of  the  sulphuret  of  lead, 
the  miner  will  follow  in  his  workings.*  From  finding  these  above  a 
bed  of  toadstone  or  blackstone,  and  also  beneath  that  igneous  rock,  with 
no  connecting  joints  through  it,  the  impression  seems  in  a  great  measure 
to  have  arisen  that  the  veins  did  not  traverse  the  toadstone.  The  cavi- 
ties in  that  district  wherein  sulphuret  of  lead  has  been  discovered  are 
very  numerous.  When  they  rise  through  the  beds  they  are  usually 
termed  pipes,  and  when  interposed  between  them,  flat  works.  Upon 
studying  the  cavities  in  limestone  districts  of  this  character,  it  will  be 
evident  that  these  distinctions  are  not  always  very  applicable,  and  that 
irregular  cavities  rising  upwards  may  have  numerous  branches  from 
them  running  amid  the  beds  themselves,  that  joints  may  cross  the  cavi- 
ties, and  real  dislocations  traverse  the  whole.  When  carefully  exa- 
mined, leaders,  as  they  are  termed,  seem  always  found  in  such  situa- 
tions, so  that  dislocations  having  been  effected,  a  communication  was 
formed  between  them  and  the  other  kinds  of  cavities,  and  thus  any 
solutions  or  gaseous  matters  rising  through  the  dislocations  would  enter 
into  them.  One  of  the  largest  cavities  worked  for  lead  ore  seems  to 
have  been  that  at  Crich,  whence  a  few  years  since  large  quantities  were 
raised,  the  sulphuret  of  lead  encrusted,  as  well  overhead  as  on  the  sides, 
by  layers  of  fluor  spar  and  sulphate  of  baryta,  two  very  common  vein- 
stone minerals  in  certain  parts  of  Derbyshire. 

If,  in  the  annexed  section  (fig.  288)  a  a  represent  a  part  of  the  lime- 


stone series  of  Derbyshire,  and  b  an  interposed  bed  of  toadstone,  formed 
after  the  beds  of  limestone  a',  and  prior  to  the  deposit  of  those  at  a, 
and  that  i,  &,  m,  are  fissures  traversing  all  the  rocks ;  h,  A,  A,  A,  ordi- 
nary joints  in  the  limestone  which  do  not  traverse  the  toadstone ;  p,  p9 
irregular  cavities  in  the  limestone,  and  //,  the  common  interstices 
between  the  beds,  enlarged  by  the  removal  of  parts  of  the  adjacent 
limestone  in  the  usual  manner,  in  solution,  a  variety  of  spaces,  diffe- 
rently communicating  with  each  other,  may  be  all  filled  with  mineral 
matter  contemporaneously  derived  from  the  same  supply,  and  be  all 
known  by  different  terms  among  the  miners.  The  fissures  g,  i,  d,  &, 

*  Many,  though  not  nil  of  the  strings  of  ore  which  the  Derbyshire  miners  term  skrinf. 
are  in  joints. 


FLAT    OF    LEAD    ORE,    FAWNOG,    FLINTSHIRE.  645 

and  c  m,  would  be  the  channels  through  which  the  various  mineral  sub- 
stances introduced  from  beneath  could  pass  into  the  irregular  cavities 
p  p  (pipes),  the  enlarged  spaces  between  the  beds  /,  /  (flat  work\  and 
into  the  joints  A,  A,  A,  h  (skrins)',  all  these  varieties  of  open  spaces 
occasionally  intermingled,  according  as  they  locally  occurred.  The 
main  fissures  would  be  considered  as  passing  through  all  the  rocks, 
while  the  joints,  or  at  least  a  large  proportion  of  them,  might  terminate 
at  the  toadstone.* 

Of  the  occurrence  of  the  ores  of  lead  in  spaces  between  beds  which 
were  open  when  they  and  the  other  contents  of  such  cavities  were  accu- 
mulated, that  at  Fawnog,  two  miles  west  from  Mold,  Flintshire,  may  be 
selected  as  an  instructive  example.  From  the  information  of  Mr. 
Warington  Smyth,  it  appears  that  after  some  unprofitable  search  for 
lead  in  shallow  workings  between  the  carboniferous  limestone  and  its 
covering  of  the  arenaceous  rocks  known  as  millstone  grit,  it  was  disco- 
vered that  ore  was  abundantly  distributed  in  a  flat,  or  streak  of  ore, 
between  these  rocks,  the  streak  being  elongated  on  an  E.N.E.  direction, 
that  of  many  of  the  prevailing  fissures,  containing  lead,  in  the  adjoining 
country.  By  following  this  "flat"  downwards,  on  the  dip  of  the  beds, 
many  thousand  tons  of  very  excellent  sulphuret  of  lead  were  obtained 
in  a  few  years.  Subsequently,  another  mining  company  sunk  a  shaft 
still  further  upon  the  dip  of  the  beds,  and  cut  the  same  kind  of  deposit 
in  a  continuation  of  the  same  plane  between  the  millstone  grit  and  car- 
boniferous limestone.  From  this  other  streak,  or  flat  of  ore,  several 
thousand  tons  were  also  raised  in  a  few  years.  The  ground  being  thus 
proved  for  half  a  mile  in  length,  and  pierced  by  several  shafts,  a  very 
good  illustration  is  aiforded  of  the  extensive  occurrence  of  a  metalli- 
ferous deposit  between  two  different  kinds  of  rock,  and  probably  also 
after  their  deposit,  the  accumulation  of  the  lead  ore  being  simply  in  a 
cavity  partially  existing  between  dissimilar  beds,  instead  of  in  a  vertical 
fissure,  f 

*  The  joint  fissures  through  the  toadstone  appear  to  be  very  few  when  compared 
with  those  in  the  limestone.  Although  to  render  the  complicated  mode  of  occurrence 
somewhat  more  clear,  the  joints  alone  are  noticed  in  the  section  (fig.  288),  it  should  be 
stated  that  in  some  parts  of  Derbyshire,  and  independently  of  the  joints,  the  fractures, 
when  a  main  dislocation  was  effected,  seem  to  have  been  more  extensive  in  the  lime- 
stone than  in  the  toadstone,  as  might  be  expected  from  the  application  of  the  same 
force  to  bodies  so  different  in  tenacity,  so  that  the  same  crack  is  more  ramified  in  the 
one  than  in  the  other,  and  the  minor  fractures  appear  to  terminate  at  the  toadstone. 

•j-  Warington  Smyth,  MSS.,  who  further  adds,  that  the  underlying  limestone  is  semi- 
crystalline  and  gray,  abounding  in  stems  of  encrinites,  and  occasionally  pierced  by 
"  swallow-holes,"  or  water  channels  running  in  various  directions,  the  surfaces  of  which 
are  smooth  except  where  projecting  fossils  are  found  showing  their  better  resistance  to 
the  power  which  removed  their  once-containing  limestone.  The  roof  (millstone  grit) 
is  generally  a  sand,  partially  calcareous  (also  containing  stems  of  encrinites),  about 
18  feet  thick,  surmounted  by  a  bed  of  hard  sandstone  30  to  36  feet  deep ;  this  succeeded 
by  various  sandstone  and  conglomerate  beds,  amid  which  there  are  occasional  lenticular 


046        METALLIFEROUS  DEPOSITS  IN  JOINTS. 

As  regards  the  deposits  of  mineral  matter,  including  those  of  the 
useful  metals,  in  joints  of  rocks  (and  the  crossing  of  small  veins  is 
sometimes  little  else  than  the  latter),  the  partial  filling  of  joints,  tra- 
versing alike  granite,  the  veins  from  it,  and  the  schistose  rocks  through 
which  it  has  been  protruded,  may  be  easily  studied  at  St.  Michael's 
Mount,  Cornwall.  The  joints,  well  exposed  from  the  insular  position 
of  St.  Michael's  Mount,  and  from  the  united  action  of  the  sea  and  at- 
mosphere, give  the  granite  the  false  appearance  of  being  regularly 
divided  into  vertical  beds,  ranging  about  E.  10°  N.,  and  W.  10°  S.  A 
change  in  the  structure  of  the  granite  is  clearly  perceptible  towards  the 
joints,  and  in  them  are  found  quartz,  mica,  topaz,  apatite  (phosphate  of 
lime),  peroxide  of  tin,  wolfram  (tungstate  of  iron),  tin  pyrites  (sulphuret 
of  tin  and  copper),*  schorl,  and  occasionally  other  minerals.  These 
are  but  mineral  veins  of  a  particular  kind,  and  on  the  small  scale.  As 
to  the  peroxide  of  tin,  it  is  one  of  the  common  ores  in  the  fissure  veins 
of  the  vicinity ;  and  as  to  wolfram,  more  of  it  accompanies  the  tin  ores 
in  certain  parts  of  Cornwall  than  is  convenient  for  the  miner.  Quartz 
is  the  most  abundant  mineral  in  the  open  spaces,  sometimes  crystallized, 
at  others  filling  the  joint  wholly  to  its  sides.  Where  these  joints  tra- 
verse the  granite  veins,  and  the  adjoining  (altered)  schistose  rocks,  they 
sometimes  also  present  interesting  examples  of  differences  in  their  con- 
tents, according  to  the  kind  of  rock  forming  their  walls.  The  following 
plan  (fig.  289)  is  one  part  of  St.  Michael's  Mount  (N.E.  side),  wherein 
the  granite  veins,  #,  a,  a,  are  seen  to  traverse  the  altered  slate  rocks 
(which  are  shaded),  a  small  included  portion  of  the  latter  being  seen  in 
the  largest  granite  vein  at  c.  A  joint,  b,  5,  traverses  both  the  granite 
veins  and  the  schistose  rock,  and  d  d  is  a  parallel  joint  less  wide.  The 
latter  is  filled  with  mica  where  it  crosses  the  slate,  but  contains  also 

masses  of  limestone.  The  flat  itself  was  composed  of  light-coloured  argillaceous  matter, 
from  15  inches  to  8  feet  in  thickness;  the  metalliferous  portion  averaging  14  inches 
thick,  but  in  some  places  attaining  the  full  height  of  8  feet,  and  consisting  entirely  of 
sulphuret  of  lead.  Several  streaks  of  ore  were  found  with  the  same  general  direction. 
The  third  "flat"  found  (working  in  1849)  was  often  surmounted  by  6  or  8  inches  of 
compact  carbonate  of  lead.  "The  fact,"  observes  Mr.  Warington  Smyth,  "of  strings 
of  ore  from  the  main  '  flat'  having  been  traced  for  30  feet  downwards  amid  the  lime- 
stone, and  18  feet  into  the  arenaceous  beds  above,  is  sufficient  to  show  that  the  intro- 
duction of  the  sulphuret  of  lead  has  been  effected  subsequently  to  the  deposit  of  the 
millstone  grit."  As  to  the  loose  sandy  character  of  the  surmounting  bed  of  rock,  this 
would  readily  arise  either  from  the  decomposition  of  the  millstone  grit  above,  while  the 
lead  ore  was  being  deposited,  or  from  subsequent  decomposition  by  the  passage  of 
water  amid  its  cementing  calcareous  particles. 

*  The  variety  of  tin  pyrites  which  we  thence  obtained  also  contained  zinc.  The  fol- 
lowing is  an  analysis  of  specimens  of  this  mineral  from  St.  Michael's  Mount : — 

Tin, 31-618 

Copper,       ....     23-649 

Zinc, 10-113 

Iron, 4-790 

Sulphur 29-929 


CARGLAZE    TIN    MINE,     CORNWALL. 


647 


quartz,  and  is  even  occasionally  altogether  cemented  together  by  that 
mineral  where  it  traverses  the  granite  veins. 


Fig.  289. 


The  long-celebrated  Carglaze  tin  mine,  near  St.  Austell,  Cornwall, 
also  shows  joints  filled  with  mineral  matter,  including  peroxide  of 
tin.  Many  of  these  have  been  worked  profitably,  the  granite  in  which 
they  occur  being  soft  from  decomposition.  The  granite  being  also 
white,  these  joint  veins,  composed  of  black  schorl  and  peroxide  of  tin, 
mingled  with  quartz,  have  a  marked  appearance,  as  represented  in  the 
annexed  sketch  (fig.  290).  A  large  portion  of  these  lines  will  be  found 
dipping  beneath  the  adjoining  slates,  as  is  usual  with  joint  lines  bound- 
ing the  masses  of  Devonian  and  Cornish  granite,  and  they  are  crossed 
by  other  joint  lines,  also  in  the  usual  manner.  A  large  proportion 
of  the  granite  country  on  the  north  of  St.  Austell,  particularly  in 

Fig.  290. 


the  vicinity  of  Hensborough,  exhibits  similar  strings,  in  which  schorl 
and  peroxide  of  tin  are  intermixed,  and  so  agree  with  lines  repre- 
senting joints,  that  they  appear  little  else  also  than  the  filling  of  spaces 
among  such  divisional  planes  by  mineral  substances  finally  much  harder 
than  the  granite  amid  which  they  were  deposited,  the  latter  having 


648  DIFFERENT    DATES    OF    MINERAL    VEINS. 

become  to  a  considerable  extent  decomposed.*  With  respect  to  the 
schorl  in  these  joint  veins,  the  observer  will  find,  upon  studying  many 
of  the  highly  schorlaceous  portions  of  the  Devonian  and  Cornish  granites, 
at  their  boundaries  towards  the  slates,  or  surrounding  bosses  of  them, 
that  it  may  often  be  found  occupying  a  position  near  the  joints,  and, 
with  quartz,  sometimes  entirely  filling  up  the  space  between  their  walls, 
both  minerals  appearing  to  have  been  derived  from  the  adjacent  granite. 

Not  only  are  certain  minerals,  including  the  ores  of  the  useful  metals, 
found  in  a  fissure  more  frequently  adhering  to,  or  accumulated  near, 
particular  rocks  or  modifications  of  the  same  rock,  in  the  manner  above 
noticed,  but  also  in  some  districts,  where  more  ores  than  one  occur  in 
sufficient  abundance  to  be  profitably  worked,  so  that  the  ground  is 
well  explored,  fissures  in  given  directions  are  observed  to  contain  certain 
of  these  minerals  more  than  others.  Even  as  regards  these  also,  there 
would  appear  to  have  frequently  been  conditions  under  which  minerals, 
chiefly  found  in  fissures  taking  given  directions,  were  accumulated  more 
in  some  parts  of  the  same  fissure  than  in  others.  The  mining  districts 
of  Devon  and  Cornwall  may  be  studied  with  advantage  in  this  respect, 
though  similar  facts  are  well  known  in  other  mining  countries  in  dif- 
ferent parts  of  the  world. 

Referring  back  to  one  of  those  districts  (fig.  216,  p.  540),  it  is  chiefly 
in  the  fissures,  v,  v,  v,  having  an  easterly  and  westerly  direction,  that 
the  tin  and  copper  ores  are  obtained  in  profitable  abundance,  while 
those  ranging  northerly  and  southerly,  d,  <#,  d,  often  contain  the  ores 
of  lead,  iron,  and  some  others.  There  are  exceptions,  but,  as  a  whole, 
this  distribution  of  ores  is  somewhat  marked.  Upon  careful  investiga- 
tion it  has  been  found  that  the  north  and  south  dislocations  have  been 
formed  subsequently  to  those  having  an  easterly  and  westerly  direction, 
the  proof  being  (p.  618),  that  the  contents  of  the  latter  have  been 
broken  through,  as  well  as  the  rocks  forming  their  walls,  and  that  new 
matter  has  been  accumulated  in  the  new  fissures.  The  observer  has, 
therefore,  in  such  cases,  not  only  to  bear  in  mind  the  direction  of  the 
fissures,  but  also  the  difference  in  time  when  each  of  the  two  sets  may 
have  been  produced,  so  that  if  at  one  time  the  conditions  for  the  forma- 
tion of  the  ores  of  tin  and  copper  prevailed,  and  those  of  other  ores  at 
another,  the  opportunity  for  the  production  of  various  ores  in  all  the 
fissures  were  not  contemporaneous,  but  different.  This  circumstance 
has  to  be  fully  regarded,  as  well  as  any  influences,  causing  the  deposit 

*  The  works  upon  these  small  joint  veins  and  upon  the  fissure  veins  also  traversing 
the  country,  the  channels  it  may  have  been  through  which  part,  at  least,  of  the  con- 
tents of  the  former  have  been  derived,  are  very  extensive  in  that  part  of  Cornwall,  tin- 
tin  ore  having  been  of  excellent  quality,  and  the  granite  of  the  district  being  easily 
worked,  from  its  state  of  decomposition. 


DIFFERENT    DATES'   OF    MINERAL    VEINS.  649 

of  certain  substances,  which  the  direction  of  a  fissure  itself  might  occa- 
sion.* 

Taking  certain  minerals  for  study,  and  especially  the  ores  of  the 
useful  metals,  the  observer  will  often  find  much  of  interest  in  the  manner 
in  which  they  may  be  distributed,  as  it  were,  contemporaneously  in  the 
same  fissure.  Certain  combinations  of  rocks  will  sometimes  suggest 
themselves,  if  not  as  the  chief  cause,  at  least  as  among  the  conditions 
which  may  have  assisted  in  rendering  the  ores  of  one  metal  more  abun- 
dant than  those  of  another  in  the  range  of  parts  of  the  same  mineral 
vein.  At  other  times  this  view  does  not  so  well  accord  with  the  facts 
observed.  The  continuation  of  the  great  Crinnis  lode,  running  from 
the  coast  near  Crinnis  Island  into  the  granite,  may  be  noticed  as  an 
example  of  the  same  fissure  being  cupriferous  amid  the  slate  country, 
and  chiefly  stanniferous  towards  the  granite.  With  respect  to  the  dis- 
tribution of  tin  and  copper  ores  in  Cornwall,  certain  of  the  copper 
mines  in  that  county  are  well  known  to  have  been  worked  for  tin  upon 
their  backs,  as  the  upper  parts  of  mineral  veins  are  often  termed  in 
some  mining  districts,  and  to  have  been  abandoned  when  the  copper  ore 
was  attained  beneath,  such  ores  not  being  considered  as  worth  raising 
at  that  time.f  Some  of  these  cases  would  not  appear,  as  will  be  here- 
after seen,  to  justify  the  view  that  the  tin  ores  occurred  to  the  exclu- 
sion of  those  of  copper,  but  they  nevertheless  seem  to  show  that  tin 
ores  were  present  in  the  higher  parts  of  these  lodes,  and  were  scarce, 
if  not  absolutely  absent,  beneath.  J 

Points  of  this  kind  in  connexion  with  other  ores  are  also  well  known, 

*  The  study  of  the  different  fissures  in  Cornwall,  some  containing  ores,  others  not, 
induced  Mr.  Carne,  in  1822  (Trans.  Geol.  Society  of  Cornwall,  vol.  ii.)  to  class  them 
under  eight  divisions,  on  the  principle  that  the  fissures  of  one  epoch  had  a  given  direc- 
tion, and  were  only  cut  through  by  those  of  subsequent  times.  By  east  and  west  lodes 
Mr.  Carne  says  that  he  means  "metalliferous  veins  whose  direction  is  not  more  than 
30°  from  those  points ;  by  contra-lodes,  metalliferous  veins  whose  direction  is  from  30° 
to  60°  from  east  and  west ;  and  by  cross  courses,  veins  whose  direction  is  not  more  than 
30°  or  40°  from  north  and  south." 

•j-  Mr.  Carne  (Copper  Mining  of  Cornwall ;  Trans.  Geol.  Soc.  of  Cornwall,  vol.  iii.  p. 
37)  notices  Wheal  Damsel  and  Wheal  Spinster  copper  mines  as  instances  where  the 
upper  parts  of  the  veins  were  taken  away  for  the  tin  they  contained.  "The  granite 
walls  of  the  lode  are  still  visible,"  he  remarks,  "  at  the  surface  and  to  the  depth  of 
three  or  four  fathoms,  having  a  space  of  about  4  feet  between  them.  It  is  probable, 
that  if  the  rubbish  were  taken  away  the  space  would  be  found  to  extend  lo  the  depth, 
perhaps,  of  10  fathoms  (60  feet),  or  as  deep  as  the  ancient  miners  could  go  without 
being  obstructed  by  water.  From  this  space  the  fine  gossan  of  the  copper  lode  was 
wholly  taken  away,  and  the  tin  ore  extracted  from  it." 

J  At  Dolcoath  mine,  Camborne,  one  which  has  been  long  in  work,  it  has  lately  been 
found  that  tin  occurred  in  profitable  quantities  in  the  depth  after  the  vein  had  been 
worked  chiefly  for  copper,  the  higher  portions  having  formerly  furnished  tin  as  the 
principal  ore.  The  ores  of  copper  and  tin  are  sometimes  more  mixed  in  Cornish  mines 
than  the  distinctive  names  of  "copper  lode"  or  "tin  lode"  would  lead  those  not  fami- 
liar with  those  mines  -to  suppose. 


650  MODIFICATIONS    IN    THE     CONTENTS    OF 

and  require  similar  attention,  as,  for  instance,  the  frequent  presence  of 
copper  pyrites  on  the  backs  of  many  of  the  lead  veins  in  Cardiganshire 
(Goginan,  Cwm  Sebon,  and  others).  In  veins  of  mixed  ores  of  different 
metals,  where  some  of  each  are  found  disseminated  through  them,  the 
relative  abundance  of  the  ores  is  sometimes  found  most  materially 
modified  at  different  depths,  and  this  occasionally  even  to  a  certain 
extent  irrespective  of  the  kinds  of  rock  forming  the  walls  of  the  veins, 
though  this  influence  requires  always  to  be  steadily  borne  in  mind. 
Thus  with  some  ores  of  zinc,  lead,  and  copper,  as,  for  example,  in  the 
well-known  Ecton  mine,  Staffordshire,  the  sulphuret  of  zinc  was  found 
most  abundant  in  the  depth,  the  sulphuret  of  copper  occupied  a  central 
position,  and  sulphuret  of  lead  was  found  in  the  higher  parts.*  In  the 
Spital  vein  at  Schemnitz,  according  to  Mr.  Warington  Smyth,  where 
the  sulphurets  of  silver  and  lead  are  raised,  though  the  latter  is  argen- 
tiferous beneath,  the  ores  towards  the  higher  portions  of  the  vein  are 
chiefly  sulphurets  and  other  ores  of  silver,  in  which  either  lead  is  scarce 
or  absent. 

In  this  kind  of  investigation  it  is  very  requisite  that  the  observer 
should  regard  not  only  the  kinds  of  rock  which  may  be  traversed  by 
the  veins  as  above  noticed,  but  also  the  decomposition  and  changes 
which  may  have  taken  place  in  a  fissure,  or  other  cavity,  after  some 
original  condition  of  its  contents,  a  subject  itself  of  no  slight  impor- 
tance. There  are  certain  facts  known  which  appear  clearly  to  show 
material  changes  and  modifications  from  a  previous  state  of  mineral 
veins,  among  which  those  from  surface  influences  are  often  most  marked. 
In  veins  where  copper  pyrites  is  abundant,  for  instance,  the  changes 
from  decomposition  often  extend  to  depths  more  considerable  than  at 
first  might  be  expected.  This  ore,  essentially  a  combined  sulphuret  of 
copper  and  iron,  when  exposed  to  surface  waters  finding  their  way  to  it, 
becomes  decomposed,  sulphuric  acid  being  apparently  produced  by  the 
action  of  oxygen  upon  the  sulphur,  this  acid  then  attacking  the  metallic 
parts  of  the  ore  under  the  conditions  in  which  it  is  placed,  in  such  a 
manner  that  sulphate  of  copper  is  removed,  and  the  iron,  in  the  ores, 
is  left,  forming  eventually,  from  a  continuance  of  the  same  influences, 
a  hydrated  oxide  of  iron,  in  which  other  substances,  originally  entangled 
in  the  ore,  may  still  remain.  To  these  hydrated  oxides  of  iron  the 
term  gossan  has  been  applied  by  the  Cornish  miners, f  and  in  them  are 

*  In  this  mine  particular  beds  of  limestone  were  found  so  much  more  favourable  than 
others,  that  they  were  always  followed  by  the  miners ;  and  as  the  beds  of  that  part  of 
Staffordshire  (adjoining  Derbyshire)  are  much  contorted,  the  workings  have  a  remark- 
able appearance  in  consequence. 

f  The  German  miners  term  this  decomposed  ore  eiscrne  Hut,  and  the  French  clmi>«tu 
defer,  expressive  names  showing  their  higher  position  in  the  mineral  veins.  The  former 
say— 

44  Es  ist  nie  ein  Gang  so  gut, 
Der  trtigt  nicht  einen  eisernen  Hut." 


MINERAL    VEINS    IN    DEPTH    AND    RANGE.  651 

sometimes  found  disseminated  tin,  silver,*  and  some  other  ores,  those 
which  were  mingled  with  the  original  ore  of  copper  pyrites.  Modi- 
fications of  this  kind  would  require  not  only  a  certain  amount  of  geolo- 
gical time  during  which  they  could  be  effected,  but  also  sufficient 
proximity  to  atmospheric  influences.  It  will  be  evident,  if  geological 
changes  should  be  such  as  to  remove  a  large  portion  of  the  present 
surface  in  mineral  districts,  so  that  numerous  bunches  of  ore  in  the 
veins  should  be,  for  the  first  time,  exposed  to  atmospheric  influences, 
that,  to  whatever  other  sources  of  change  and  modification  the  contents 
of  the  veins  containing  them  may  have  been  exposed,  such  newly 
exposed  portions  would  have  to  undergo  the  alteration  noticed  in  the 
cases  of  copper  pyrites,  and  that  the  copper  in  solution,  as  a  sulphate, 
would  percolate  to  some  situation  where  it  would  remain  as  such,  or 
suffer  subsequent  change.  The  attention  of  the  observer  will  not  long 
have  been  directed  to  the  conditions  of  a  vein  containing  gossan,  above 
bunches  of  copper  pyrites,  before  he  will  find  that  not  only  metallic 
copper,  but  also  the  oxides  and  carbonates  of  copper  are  somewhat 
frequent  between  them,  as  well  as  in  situations  where  it  may  readily 
have  happened  that  a  solution  of  sulphate  of  copper,  derived  from  de- 
composed copper  pyrites  above,  could  find  its  way.  He  may  often, 
moreover,  see  the  metallic  copper  in  chinks  and  other  situations, 
reminding  him  of  the  deposit  of  copper  by  the  electrotype  process  from 
solutions  of  the  same  kind.  He  thus  has  to  consider  the  vein  and  its 
walls  with  reference  to  their  electrical  conditions.  If  metallic  copper 
were  thrown  down  in  fitting  situations,  he  would  probably  have  no 
difficulty  in  inferring  that  the  oxides  resulted  from  the  action  of  the 
oxygen  contained  in  the  surface  waters,  as  part  of  the  common  air 
disseminated  in  them,  and  that  the  carbonates  were  formed  by  the  sub- 
sequent action  of  carbonic  acid  also  contained  in  the  same  waters,  f 
Bearing  in  mind  the  mode  of  occurrence  of  the  mixed  ores  of  tin  and 
copper  of  Cornwall,  and  that  some  of  the  mines  were  formerly  worked 
for  tin,  with  a  prevalence  of  copper  ore  beneath,  it  may  readily  have 
happened  that  the  stanniferous  parts  of  such  veins  may  once  have  been 

*  Several  of  the  gossans  in  Cornwall  have  been  found  to  contain  silver,  though  this 
metal  has  not  always  been  obtained  in  quantities  sufficient  to  be  profitably  worked. 

f  The  condition  of  many  small  Roman  copper  coins  found  a  few  years  since  near 
Aberystwyth,  Cardiganshire,  illustrated  these  changes  with  more  than  the  usual  evidence, 
though  the  common  patina  or  erugo  upon  ancient  copper  coins  also  shows  the  same  thing. 
The  pot  in  which  the  coins  were  buried  was  found  not  far  from  the  surface,  and  the 
coins  themselves  had  been  exposed  to  the  action  of  atmospheric  influences ;  the  waters, 
containing  common  air  and  carbonic  acid,  finding  their  way  to  them,  had  produced  the 
red  oxide  of  copper  on  the  surface  of  some  of  the  coins,  beautifully  crystallized,  while 
on  others  the  further  change  into  the  carbonate  had  been  so  effected  as  to  present  the 
usual  mammillated  character  of  malachite,  sections  of  it  showing  the  common  variations 
in  colour  of  that  mineral.  Illustrative  specimens  of  these  coins  are  now  in  the  collec- 
tions of  the  Museum  of  Practical  Geology. 


652    MODIFICATIONS    OF    THE    UPPER    PARTS    OF    MINERAL 

more  rich  in  copper  pyrites,  and  that  the  latter  had  been  removed,  in 
the  manner  above-mentioned,  and  the  tin  chiefly  left  in  the  gossan,  so  as 
to  render  it  principally  stanniferous. 

Changes  and  alterations  of  a  similar  kind  are,  as  might  be  expected, 
found  at  the  higher  parts  of  veins  containing  other  metals,  especially  of 
those  the  ores  of  which  seem  more  or  less  easily  acted  upon  by  atmo- 
spheric influences.  Thus,  on  the  backs  of  veins  containing  sulphuret 
of  lead,  the  carbonates  of  that  metal  may  be  often  found.  M.  Haus- 
man  has  suggested  that  the  change  has  been  effected  by  the  conversion 
of  the  sulphur  of  the  sulphuret  of  lead  into  sulphuric  acid,  which  com- 
bining with  calcareous  matter,  set  free  carbonic  acid,  that,  in  its  turn, 
combined  with  the  lead,  forming  the  carbonate.  In  those  cases  where 
the  veins  of  sulphuret  of  lead  are  found  amid  limestone,  and  the  car- 
bonates in  their  higher  parts  are  sufficiently  common,  this  change  may 
readily  have  been  thus  effected. 

In  illustration  of  the  conversion  of  the  native  sulphuret  of  lead  into  a 
carbonate,  it  may  be  useful  to  remark  that  in  the  underground  refuse 
of  the  old  workings*  of  the  Derbyshire  mines,  some  of  which  may  reach 
back  to  about  1700  years,  f  and  which  is  still  turned  over  for  the  ores 
it  may  contain,  the  small  pieces  of  sulphuret  of  lead  are  found  wholly 
changed  into  the  carbonate,  and  the  larger  pieces  are  thickly  coated 
with  the  same  substance.  The  miners  observe  that  in  the  places  where 
there  has  been  most  water,  the  alteration  is  most  marked  and  consi- 
derable. J  A  further  illustration  of  this  kind  of  alteration  is  to  be 
found  in  those  cases  where  pieces  of  sulphuret  of  lead  are  distributed 
in  marl  or  loam,  with  fragments  of  limestone,  in  a  few  localities  in  the 
same  district ;  as,  for  example,  at  a  mine  named  the  Green  Linnets, 
near  Brassington,  where  pieces  of  lead  ore  appearing  to  have  been 
detached  from  some  neighbouring  vein  and  distributed  in  the  marl  or 
loam,  probably  at  the  tertiary  period,  are  found.  The  fragments  of  sul- 
phuret of  lead  are  sometimes  wholly,  at  others  partially  converted  into 
a  crystalline  carbonate  of  lead.  Similar  illustrations  of  changes  into 
the  phosphate  are  also  to  be  well  observed,  whole  fragments  of  sul- 
phuret of  lead  having  been  in  a  like  manner  converted  into  the  phosphate 
of  lead,§  a  substance  also  found  not  only  in  the  higher  pasts  of  lead 
veins  in  other  situations,  but  also  at  the  depth  of  150  feet  and  more,  as, 

*  Among  the  ancient  pigs  of  lead  found  in  Derbyshire,  one  was  discovered  in  1777,  at 
Cromford  Moor,  with  the  inscription,  in  raised  letters,  of  IMP.  CAES.  HADRIANI. 
AUG.  MEL  LVI.  According  to  Mr.  Pegge  (Archseologia,  vol.  iv.),  this  pig  may  have 
been  cast  about  the  year  130. 

f  This  refuse,  left  in  the  workings,  is  locally  known  as  Old  Man. 

%  It  should  be  noticed,  with  reference  to  this  water,  that  it  usually  contains  much  bi- 
carbonate of  lime  in  solution. 

8  Illustrative  specimens,  exhibiting  these  modifications  and  changes,  will  be  found  in 
the  collections  of  the  Museum  of  Practical  Geology. 


I 

VEINS    FKOM    ATMOSPHERIC    INFLUENCES.  653 

for  example,  at  the  Golden  Valley  mine,  and  at  other  places  in  the 
vicinity  of  Winster,  Derbyshire. 

Calamine  seems  frequently  little  else  than  blende,  changed  in  a  simi- 
lar manner,  the  sulphuret  being  converted  into  the  carbonate  of  zinc, 
the  sulphur  having  disappeared,  and  being  replaced  by  oxygen  and 
carbon.  The  conditions  under  which  a  large  proportion  of  calamine  is 
so  often  found,  especially  in  limestone  districts,  would  appear  to  render 
this  view  extremely  probable.  In  Talar-goch,  Flintshire,  it  is  seen  now 
forming,  and  apparently  from  a  decomposition  of  the  sulphuret  of  zinc 
in  the  same  vein,  being  brought  in  solution,  like  carbonate  of  lime  into 
limestone  caves,  and  deposited  in  the  workings  of  the  mine.* 

Independently  of  these  modifications  and  changes  in  the  higher  por- 
tions of  mineral  veins,  there  are  others  to  be  found  occasionally  in  all 
parts  of  them,  showing  that  the  substances  thrown  down  in  them  or  against 
the  walls  of  the  fissures  have  been  again  removed,  their  places  either 
vacant  or  replaced  by  other  substances,  filling  the  cavities  which  were 
thus  left.  A  large  proportion  of  the  pseudomorphous  crystals  of  diffe- 
rent substances  have  been  thus  produced — at  least  those  of  them  which 
have,  as  it  were,  filled  moulds  prepared  for  them  in  a  vein,  by  the 
removal  of  some  first-formed  substances,  coated  by  others  prior  to  such 
removal.  Of  this  kind  of  change  the  observer  may  often  study  examples 
in  the  fissures  and  cavities  of  mining  districts,  as  also  in  the  half- decom- 
position and  partial  removal  of  various  mineral  bodies.  Vein  quartz  is 
sometimes  found  as  if  it  had  been  partially  attacked  by  solvents  and 
left  in  a  highly  porous  state,  evidently  from  a  loss  of  a  portion  of  its 
substance,  and  not  from  the  removal  of  more  soluble  substances  which 
may  have  been  once  included  in  it,  a  circumstance  to  be  carefully  inves- 
tigated, since  the  latter  has  sometimes  been  clearly  the  case. 

In  some  veins  the  changes  of  conditions  for  the  deposit  and  removal 
of  mineral  matter  are  highly  interesting.  Some  circumstances  observed 
in  the  Virtuous  Lady  Mine,  near  Tavistock,  Devon,  a  few  years  since, 
may  serve  to  illustrate  these  changes.  The  fissure  in  which  this  vein 
occurred  was  very  irregular,  and  sometimes  the  cavity  between  the 
walls  extended  to  many  feet.  Upon  the  walls  there  had  been  first  de- 
posited, (1)  a  mixture  of  quartz  and  copper  pyrites,  the  latter  often 
crystallized,  the  original  tetrahedrons  so  elongated  as  to  form  rough 
prisms  with  pyramidal  summits ;  (2)  upon  these  cubic  crystals,  often  of 
considerable  size,  were  accumulated,  and  were  probably  of  fluor  spar 
(fluoride  of  calcium) ;  (3)  an  incrustation  of  carbonate  of  iron  then  com- 

*  The  composition  of  calamine  is  very  variable.  According  to  the  analyses  of  M. 
Berthier,  the  carbonate  of  zinc  varies  in  its  ores  from  30  to  90  per  cent. ;  the  other 
substances  in  the  ore  being  carbonates  of  iron,  manganese,  lead,  and  lime.  It  often 
appears  as  if  the  carbonate  of  zinc  has  been  deposited  from  solution,  and  was  mixed 
with  other  substances  thrown  down  at  the  same  time,  these  commonly  carbonates,  the 
whole  not  unfrequently  deposited  in  veins  amid  limestones. 


654       REPLACEMENT  OF  MINERAL  MATTER  OF 

pletely  covered  the  whole ;  and,  (4)  the  substance  forming  the  cubes 
being  dissolved  and  removed,  and  so  as  not  to  injure  the  carbonate  of 
iron,  (5)  cavities  were  left  in  which  silica  and  the  sulphuret  of  copper 
and  iron  (copper  pyrites)  entered  and  became  crystallized,  these  latter 
minerals  not,  however,  entirely  filling  the  cavities.  Thus,  after  the 
formation  of  the  fissure,  there  appear  to  have  been  at  least  five  changes 
of  condition  in  that  part  of  the  vein  where  these  facts  were  observed, 
during  one  of  which  the  fluoride  of  calcium  previously  deposited  in  a 
crystallized  form  was  removed,  while  its  coating  of  carbonate  of  iron 
remained  uninjured.  It  is  very  desirable  that  modifications  and  changes 
of  this  kind  should  be  carefully  investigated,  especially  with  reference 
to  the  structure  of  the  rocks  in  which  the  fissures  and  other  cavities  may 
be  found,  and  to  the  probabilities  of  any  new  fractures  being  the  means 
of  introducing  new  solutions  or  gaseous  matters  which  should  act  on  any 
substances  previously  accumulated  in  them.  Not  only  will  the  observer 
have  to  study  the  pseudomorphous  crystallizations  above  noticed,  where 
one  substance  is  deposited,  becomes  coated  by  another,  and  is  removed 
and  replaced  by  a  third  substance,  in  the  manner  above  noticed,  but 
also  the  removal  and  replacement  of  certain  minerals,  as  if  molecule  by 
molecule,  the  form  of  the  original  crystal  remaining  unchanged.  With 
regard  to  the  substitution  of  the  carbonate  for  the  sulphuret  of  lead,  as 
previously  mentioned,  though  fragments  would  serve  to  show  this  change, 
the  original  form  of  the  sulphuret  of  lead  being  still  retained,  crystals 
of  the  latter  have  been  found  completely  replaced  by  the  carbonate  of 
lead,  as  for  example,  in  Derbyshire,  at  a  mine  in  the  Long  Tor,  Mat- 
lock.  Copper  pyrites  has  been  found  in  Cornwall  and  elsewhere,  re- 
placing carbonate  of  iron,  the  forms  of  the  crystals  of  the  latter  com- 
pletely preserved,  and  numerous  other  changes  are  well  known,  where 
there  seems  no  reason  to  suppose  that  they  have  been  the  result  of 
deposit  in  moulds,  the  latter  removed,  so  that  no  trace  of  them  has  been 
left,*  though  no  doubt  this  is  a  circumstance  to  be  regarded  and  care- 
fully considered  at  all  times  in  investigations  of  this  kind.f 

*  M.  Becquerel,  while  noticing  these  changes,  mentions  the  following  fact  as  illus- 
trating their  production  from  those  analogous  to  cementation,  to  which  he  attributes 
an  electrical  origin.  M.  Darcet  left  a  plate  of  steel  during  eight  years  in  a  case  at  the 
Mint  at  Paris,  in  contact,  by  means  of  one  of  its  ends,  with  a  solution  of  nitrate  of 
silver,  which  reached  it  very  slowly  from  a  fissure  in  the  vessel  containing  it.  One  half 
of  this  steel  plate  was  entirely  changed  into  very  pure  silver,  offering  a  resisting  mass 
without  the  least  trace  of  iron.  The  volume  of  the  plate  of  silver  was  visibly  the  same 
with  that  of  the  plate  of  steel. 

I  With  reference  to  these  changes,  it  may  often  have  happened,  as  now,  with  certain 
solutions  flowing  over  the  surface  of  land  from  fissures  as  springs,  that  the  metallifei-ous 
matter  in  some  of  these  solutions  was  borne  away  in  a  manner  to  be  combined  with 
some  ordinary  sedimentary  deposits  within  moderate  distances.  In  some  localities  de- 
posits of  this  kind  forming  bands  in  detrital  strata  may  aid  in  assisting  the  geologist  in 
the  relative  dates  for  the  filling  of  fissures  with  ores  in  a  district.  For  example,  at  the 


ONE    KIND    BY    ANOTHER    IN    VEINS.  655 

Examining  the  manner  in  which  the  substances  have  been  arranged 
in  the  fissures,  or  other  cavities,  after  the  action  regulating  the  deposit 
of  certain  bodies  against  their  walls,  more  upon  some  rocks  than  others, 
and  the  direction  of  the  fissures  themselves  are  considered ;  the  most 
simple  mode  of  occurrence  presented  to  the  observer  is  that  where  a 
single  substance  may  be  found  in  them.  This  substance  may  either 
have  been  derived  from  the  adjoining  rocks,  by  solutions  formed  in  and 
percolating  through  them,  such  as  is  shown  by  quartz  veins  amid  sili- 
ceous rocks,  and  calcareous  veins  among  limestones,  or  be  derived,  such 
as  the  peroxide  of  tin,  the  sulphurets  of  lead,  copper,  and  antimony, 
and  other  ores,  from  other  sources,  strings  even  of  metallic  silver  and 
larger  breadths  of  metallic  copper  presenting  themselves.  In  the  first 
case  it  may  be  apparent  from  successive  coatings  of  crystals, -each  point- 
ing inwards,  and  from  both  sides  of  the  fissure,  that  the  filling  has  been 
a  work  of  time,  during  which  the  conditions  only  for  the  deposit  of  the 
single  substance  prevailed  in  the  part  of  the  fissure  seen.  The  follow- 
ing section  (fig.  291)  will  illustrate  these  successive  deposits,  a  5,  being 


a  line  of  fissure,  cutting  through  any  class  of  rocks,  d  d ;  successive 
coatings  of  a  single  substance,  c  c  e  c,  filling  it  up  towards  the  centre, 
where,  for  still  further  illustration,  occasional  cavities  may  be  supposexl 
to  remain.  The  probability  of  the  single  substance  so  found  being 
more  or  less  directly  or  indirectly  derived  from  the  rocks  traversed, 
will  have  to  be  weighed  with  reference  to  the  conditions  of  the  locality. 
If  in  a  limestone  country,  such  as  the  mining  districts  of  Derbyshire, 

Hook  Point,  County  Wexford,  and  also  nearer  the  town  of  Wexford,  the  upper  part  of 
the  old  red  sandstone  series  contains  carbonate  of  copper  mingled  with  vegetable  re- 
mains, the  bands  with  this  interspersed  carbonate  of  copper  several  times  repeated. 
It  might  thence  be  inferred  that  this  carbonate  had  been  derived  from  veins  of  copper 
ores  traversing  the  adjacent  Silurian  rocks,  so  that  these  veins  were  formed  anterior^ 
to  the  deposit  of  the  old  red  sandstone  of  that  part  of  Ireland.  In  certain  mining 
districts  solutions  of  sulphate  of  copper  are  sufficiently  strong  to  produce  marked  effects 
among  any  ordinary  deposits  to  which  they  could  flow  uninterruptedly  for  a  long  lapse 
of  time.  The  cupriferous  slates  of  Mansfield  are  well-known  examples  of  detrital  accu- 
mulations containing  disseminated  copper,  usually  copper  pyrites,  profitably  worked. 
And  here  again  organic  matter  is  often  mingled  with  the  ore,  reminding  us  of  the  mode 
of  occurrence  of  certain  iron  pyrites. 


656       FISSURES    COATED    BY    DISSIMILAR    SUBSTANCES. 

an  observer  found  the  successive  coatings  composed  of  calcareous  spar, 
he  might  be  led  to  infer  that  this  substance  was  derived  from  the  lime- 
stone beds,  so  abundant  around,  and  in  which  the  fissures  may  be  formed, 
while,  if  composed  of  sulphate  of  baryta,  a  common  mineral  in  parts  of 
that  district,  he  might  be  induced  to  seek  other  sources  of  supply. 
Should  the  single  substance  in  a  vein  amid  limestones  be  fluoride  of 
calcium  (fluor  spar),  while  he  would  see  that  an  abundant  supply  of 
calcium  was  at  hand  to  combine  with  fluorine,  he  might  question  the 
limestone  having  been  the  source  of  the  latter  substance  in  the  quan- 
tities found  in  the  veins. 

Single  substances  are  not  only  found  thus  joining  the  walls  of  fissures 
together,  but  also  cementing  fragments  which  have  fallen,  or  have  been 
introduced  into  them,  and  sometimes  in  a  manner  to  show  that  such 
fragments  may  have  fallen  in  upon  the  cementing  matter  while  it  was 
being  deposited,  since  they  are,  as  it  were?  isolated,  and  suspended  amid 
the  cementing  substance  that  may  thus  not  only  bind  those  together 
which  have  clearly  touched  one  another  previous  to  its  introduction, 
but  also  envelope  some  which  are  occasionally  well  separated  from  any 
others,  and  therefore  could  not  have  received  support  from  them.  The 
fragmentary  condition  of  mineral  veins  is  to  be  seen  in  some  parts  of 
most  mining  districts,  and  may  often  be  as  well  studied  in  fissures,* 
wherein  the  ores  of  the  useful  metals  do  not  occur,  and  as  they  are  ex- 
hibited in  natural  sections,  such  as  in  cliffs  on  the  sea-coasts  or  inland. 
The  cementing  substance  may  be  any  of  those  contained  in  fissures, — 
as  well  the  ores  of  lead,  copper,  tin,  and  the  useful  metals  generally,  as 
others.  Where  the  fragments  are  those  of  rocks,  which  may  be  easily 
removed  by  decomposition  from  the  action  of  solutions  or  gaseous  matter 
in  the  veins,  as  for  example,  those  of  limestone  by  carbonic  acid  in 

*  In  Cornwall,  where  fragmentary  lodes  are  not  uncommon  (Report  on  the  Geology 
of  Cornwall,  &c.,  p.  323),  that  of  the  Relistian  mine  was  remarkable  as  showing  rounded 
pebbles  of  slate  and  quartz  (the  latter  from  their  character  evidently  having  formed 
parts  of  some  vein)  cemented  by  peroxide  of  tin  and  copper  pyrites.  The  chief  mass  of 
this  conglomerate  was  about  12  feet  long  and  as  many  in  width  and  thickness,  and  was 
found  in  the  lode  (stanniferous)  about  GOO  feet  from  the  surface.  Scattered  pebbles  of 
the  same  kind  were  discovered  beyond  the  chief  mass.  In  Wheal  Badger  lode,  one 
near  Relistian,  pebbles  of  granite  were  seen  mixed  with  others  of  slate  and  quartz,  and 
Mr.  Came  mentions  pebbles  having  been  found  in  the  tin  lode  of  Ding  Dong  Mine,  near 
Penzance,  and  in  the  lode  of  Wheal  Alfred,  near  Guinear.  The  rounded  state  of  these 
fragments  renders  them  interesting,  from  showing  that  they  had  been  introduced  in 
that  condition  into  the  fissure  prior  to  the  time  when,  in  that  part  of  the  fissure,  at 
least,  the  deposit  of  the  tin  and  copper  ores  was  effected.  In  other  respects  the  mode 
of  occurrence  is  the  same  with  the  ordinary  fragments  cemented  by  similar  substances. 
M.  Fournet  (Etudes  sur  les  D6pots  Me"talliferes)  notices  pebbles  of  gneiss  as  found  in 
the  vein  at  Joachimsthal,  at  the  depth  of  192  fathoms  (1,152  feet).  With  respect  to 
the  fragments  of  the  adjoining  rocks  in  veins,  as  might  be  anticipated,  they  are  usually 
more  common  when  the  fissure  is  somewhat  inclined  than  when  it  becomes  vertical, 
though  they  are  also  often  discovered  in  the  latter. 


SEVERAL    MOVEMENTS    IN    THE    SAME    FISSURES.         657 

water,  cavities  are  then  left,  into  which  other  substances,  those  found 
in  other  parts  of  the  vein,  may  be  introduced,  in  the  same  manner  as 
the  cavities  left  by  the  crystals  above  noticed  have  been  filled  by  any 
other  substances  introduced  into  them.* 

The  coatings  of  different  kinds  of  mineral  matter  on  the  sides  of  fis- 
sures, as  if  from  successive  deposits  of  dissimilar  substances  from  solu- 
tions in  them,  seems  to  have  been  first  clearly  pointed  out  by  Werner, 
in  1791. f  Among  the  examples  adduced,  he  particularly  noticed  the 
vein  at  Segen-Gottes,  Gersdorf,  "which,  reckoning  from  the  middle 
(composed  of  two  layers  of  calcareous  spar,  in  which  small  druses  here 
and  there  occur),  thirteen  beds  of  different  minerals  are  arranged  in  the 
same  order  on  each  side  of  the  vein,  these  are  fluor  spar,  heavy  spar, 
galena,  &c.  In  the  southern  vein,  Gregorius,  the  two  layers  which  ad- 
here to  the  sides  of  the  vein  are  composed  of  crystallized  quartz ;  next 
to  these,  on  each  side,  is  a  layer  of  sulphuret  of  zinc,  mixed  with  sul- 
phuret  of  iron  ;  this  is  followed  by  sulphuret  of  lead,  carbonate  of  iron, 
sulphuret  of  lead,  carbonate  of  silver,  red  silver  ore,  and  sulphuret  of 
silver.  The  central  part,  which,  of  course,  is  most  recently  formed,  is 
of  calcareous  spar."{ 

That  this  regularity  should  always  be  found,  even  in  a  fissure  which 
has  probably  remained  in  its  first  state,  as  regards  any  subsequent  move- 
ment of  sides,  could  scarcely  be  expected,  more  especially  in  cases  where 
the  walls  opposite  to  each  other  may  be  formed  of  different  rocks  (when 
the  fissure  is  a  fault),  or  where,  from  any  other  cause,  one  side  may 
have  received  deposits  which  the  other  did  not.  One  main  cause  of  dif- 
ference often  appears  to  arise  from  that  of  the  rocks  on  each  side,  a  de- 
posit first  being  formed  on  one,  continuing  to  receive  additions  to  it  in 
preference,  according  to  the  circumstance  previously  noticed  as  to  de- 
posits from  solutions  (p.  371). 

The  geologist,  when  studying  the  contents  of  fissures  in  mining  dis- 
tricts, where  so  many  small  strings  of  different  substances  are  found  in 
chinks  and  cavities,  more  or  less  in  connexion  with  the  main  veins,  or 
even  in  them,  will  have  his  attention  arrested  by  the  evidences  of  many 
main  fissures  having  been  moved  more  than  once,  while  the  new  cracks 

*  In  the  cases  of  fragmentary  veins  in  limestone  districts,  interesting  removals  of  the 
ordinary  calcareous  matter,  with  the  preservation  of  organic  remains  in  a  fragment, 
may  occasionally  be  seen.  A  good  example  of  this  fact  occurred  in  a  large  vein  of  per- 
oxide of  iron  (hematite)  in  the  carboniferous  limestone  near  Wrington,  Somersetshire, 
where,  from  a  somewhat  considerable  fragment  containing  a  fossil  coral,  one  common 
in  beds  of  the  fissures  above,  the  ordinary  calcareous  matter  had  been  removed,  proba- 
bly by  the  action  of  water  containing  carbonic  acid  derived  from  the  atmosphere,  and 
the  parts  so  removed  were  replaced  by  the  peroxide  of  iron  of  the  vein,  so  that  the  piece 
of  fossil  coral,  preserving  all  the  angular  character  of  the  original  fragment,  appeared 
in  the  midst  of  the  vein  of  iron  ore. 

f  "Theory  of  Mineral  Veins,"  published  at  Freiburg  in  1791. 

j  Ibid.,  chap,  iv.,  sec.  52. 

42 


658  SEVERAL    SUCCESSIVE    MOVEMENTS    THROUGH 

thus  produced  have  sometimes  not  only  traversed  any  mineral  deposits 
which  may  have  been  previously  formed  in  the  fissure,  in  its  first  state, 
but  also  the  adjacent  country.  Werner  seems  to  have  been  aware  of 
this  circumstance  when  he  remarked  that  "  we  meet  with  distinct  ex- 
amples of  new  veins  formed  in  the  direction  of  those  of  older  date  (either 
within  their  substance  or  by  the  side  of  them),  forming  with  them  the 
same  individual  substance."*  Very  material  changes  and  modifications 
of  veins  may  thence  arise,  both  as  to  the  decomposition  and  removal  of 
substances  previously  in  the  fissure,  and  the  introduction  of  other  mineral 
matter.f  Good  evidence  of  such  movements,  independently  of  the  first 
contents  of  a  vein  being  traversed,  such  contents  forming  as  much  a 
part  of  the  walls  of  the  subsequent  fissure,  as  any  other  portion  of  the 
mineral  mass  broken  through,  will  be  often  found  in  the  mode  of  occur- 
rence of  contents  themselves,  even  where  these  still  retain  a  certain 
parallelism  to  each  other.  Thus,  in  the  following  section  (fig.  292), 
part  of  the  lode  at  Wheal  Julia,  Binner  Downs,  Cornwall,  the  central 


cd 


deposit  of  quartz  crystals,  pointing  inward  to  e,  is  only  one  of  four  other 
similar  arrangements  of  parts,  6,  d,  g,  and  h.  To  effect  this  crystalliza- 
tion, the  increase  of  the  crystals  having  taken  place  inwards,  five  diffe- 
rent openings,  at  different  times,  have  been  effected,  so  that  the  needful 
walls  for  the  commencement  of  crystallization  in  each  case  could  be 
afforded.  Without  additional  evidence,  such  as  the  openings  in  other 
parts  of  the  vein,  or  amid  the  adjoining  rocks,  might  present,  it  would 
be  difficult  to  determine  which  of  these  openings  might  have  preceded 
the  others.  Commencing  on  the  left,  a,  the  section  gives  a  layer  of 
copper  pyrites  and  sulphuret  of  zinc  (blende)  upon  the  wall  of  the  lode 
in  that  direction,  to  this  succeeds  quartz  crystals  pointing  inwards,  b ; 

*  "Theory  of  Mineral  Veins,"  chap,  v.,  sec.  65. 

•j-  When  describing  the  successive  openings  of  the  veins  near  Pontgibaud,  M.  Fournet 
(Etudes  sur  les  Depots  Me'talliferes)  points  out  that  deposits  of  different  mineral  sub- 
stances, or  modifications  of  such  substances,  are  seen  to  characterize  five  of  the  six  suc- 
cessive dislocations  which  he  was  enabled  to  trace,  the  sixth  being  marked  by  the  intro- 
duction of  pebbles  and  sand,  a  continuation  of  the  accumulation  which  still  covers  the 
country  in  many  places,  and  which  is  itself  covered  by  the  lavas  of  the  extinct  volcanoes1 
of  Louchadiere  and  Pranal. 


THE    SAME    LINE    OF    FISSURES. 


659 


indurated  argillaceous  matter,  0,  and  another  collection  of  quartz  crys- 
tals pointing  inwards  at  d,  then  a  set  of  crystals,  e,  commencing  on 
either  side  upon  a  layer  of  crystallized  copper  pyrites  and  zinc  blende, 
/,  /,  first  lining  the  opening  in  which  this  arrangement  is  seen.  Still 
proceeding  from  left  to  right,  quartz  crystals  have  been  deposited  upon 
another  cavity,  leaving  an  open  space  at  g  (vug,  of  Cornish  miners), 
these  succeeded  by  layers  of  quartz  crystals,  pointing  inwards  at  A,  rest- 
ing against  the  wall  of  the  vein  in  that  direction.  Examples  of  this 
kind,  with  considerable  modifications,  could  be  readily  multiplied  to  a 
great  extent. 

With  reference  to  the  occurrence  of  lines  of  different  substances,  when 
they  do  not  resemble  each  other  on  both  sides  of  a  vein,  though  it  may 
be  suspected  that  there  has  been  more  than  one  movement  in  the  fissure 
containing  them,  after  its  first  production,  the  evidence  is  often  by  no 
means  so  clear.  As  for  example,  in  the  subjoined  section  (fig.  293)  of 
part  of  a  lode  at  Godolphin  Bridge,  Cornwall,  where  a  represents  a 


Fig.  293. 
2 


be  d 

layer  of  quartz  resting  against  the  wall  of  the  vein  in  that  direction,  b 
quartz  crystals  pointing  inwards,  and  based  on  agatiform  bands  of  silica 
on  either  side  c  c,  and  d  a  thick  layer  of  copper  pyrites,  mingled  with 
some  quartz.  At  b  there  appears  decisive  evidence  that  when  the  silica 
there  found  was  deposited,  the  walls  of  the  opening  extended  from  1  to 
2 ;  but  in  the  absence  of  any  arrangement  of  parts  showing  that  the 
copper  pyrites,  with  its  quartz,  had  2  for  one  of  its  walls,  it  could  not 
be  proved  that  there  was  a  distinct  opening  between  2  and  3,  in  which 
it  was  accumulated.  It  may  have  happened  that  the  copper  pyrites, 
with  some  intermingled  quartz,  was  deposited  against  the  wall  of  the 
vein  on  the  right,  while  quartz  only  was  accumulated  on  the  wall  to  the 
left. 

With  respect  to  the  movements  producing  these  parallel  arrangements 
of  parts,  without  much,  if  any,  evidence  of  the  previous  mineral  accu- 
mulations in  the  veins  having  been  broken  or  disturbed,  it  will  soon  be 
found,  while  studying  those  fissures  which  are  not  simple  cracks,  but 
faults  (p.  614),  that  this  may  be  produced  by  the  mere  slipping  of  the 
uneven  sides  of  the  fractures,  with  certain  intervals  of  repose  between 
each  movement,  so  that  mineral  matter  may  be  deposited  in  the  cavi- 
ties during  each  period  of  repose.  If  a  b  in  the  following  diagram  (fig. 


660  SLIDING    OF    SIDES    OF    FISSURES    ON    MINERAL 

294)  represent  a  line  of  fissure,  and  a  movement  be  effected  so  that  one 
side,  a'  b',  be  slid  in  a  manner  by  which  the  parts  o  o  o  o  touch,  support- 


rig.  294. 
. —ft 


ing  the  pressure  on  either  side  of  the  fissure,  cavities  will  be  formed  at 
c  c  c,  and  at  d,  the  latter  somewhat  more  extended  than  the  first.  If 
the  movement  has  taken  place  in  a  contrary  direction,  to  the  left  (as  in 
the  third  line),  to  the  same  amount  as  previously  to  the  right,  the  open- 
ings, c  c>  would  be  more  considerable,  so  far  as  respects  the  illustration 
given,  and  the  points  of  contact  less  numerous.* 

In  a  fracture  across  rocks,  the  irregularities  of  the  fissures  being  usually 
in  a  variety  of  directions,  and  the  points  of  contact  in  consequence 
variously  situated,  the  general  inequality  of  the  walls  of  veins  has  to 
be  regarded. 

When  movements  have  been  considerable,  a  polish  and  striation  of 
the  sides  have  often  been  effected,  the  striation  corresponding  with  the 
direction  of  the  movement ;  evidence  of  importance  when  that  direction 
may  not  be  clearly  seen  by  the  bedding  or  other  mode  of  occurrence 
of  the  rocks  fractured.  In  fissures  where  there  has  been  more  than 
one  movement  they  are  also  valuable,  especially  when  the  evidence  of 
crystallization  having  taken  place  at  separate  times  in  different  cavities 
being  absent,  the  contents  of  the  veins  themselves  exhibit  this  striation 
and  polish  in  given  directions.!  In  illustration  of  movements  not 
marked  by  considerable  dislocations,  yet  where  successive  new  apertures 
or  cavities  have  been  formed,  filled  either  in  the  manner  above  noticed, 
crystallization  towards  the  interior  spaces  affording  evidence  on  this 
head,  or  where  simple  polish  and  striation  may  appear,  perhaps  the 
following  diagram  (fig.  295)  may  be  useful.  If  a  b  be  a  fissure, 
and  the  portions  of  separated  rock,  m  n,  slide  against  each  other,  so 
that  the  beds  at  n  are  lowered  to  c  along  the  line  of  the  fissure,  touch- 

*  If  a  piece  of  paper  or  card  be  cut  in  this,  or  any  other  manner  representing  the 
section  of  an  irregular  fissure,  as  such  fractures  more  or  less  are,  and  the  pieces  be 
slid  on  a  table,  so  that  parts  of  the  cut  paper  touch  each  other,  this  illustration  will 
readily  be  seen. 

f  When  either  the  striation  or  polish  has  been  effected  in  accumulations  of  ores  them- 
selves, or  coatings  of  ores  have  covered  them  over,  taking  as  it  were  a  cast  of  them  in 
their  uninjured  state,  these  polished  and  striated  surfaces  are  commonly  termed 
sides. 


MATTER    ACCUMULATED    AT    INTERVALS. 


661 


ing  in  sufficient  points  for  support,  until  a  fresh  set  of  cavities  be 
formed,  represented  by  the  dark  portion,  5,  and  these  cavities  be  filled 
by  mineral  matter,  a  further  movement  in  the  same  direction  would 
cause  friction  on  these  contents,  which  would  thus  constitute  an  uneven 


Fig.  295. 


surface  towards  the  side  n.  Assuming  these  contents  somewhat  solid 
(they  may  be  even  more  so  than  the  sides  of  the  old  fracture),  this 
second  movement  might  extend,  for  illustration,  to  e,  sufficient  points 
of  support  existing  as  before,  so  that  the  cavities  d  were  produced.  A 
third  movement  taking  place,  after  these  second  cavities  were  filled, 
similar  results  would  follow,  and  a  third  set  of  cavities,  /,  would  be 
filled.  These  successive  settlements  or  movements  of  the  masses  of 
rock,  divided  by  fissures,  are  seen  in  some  localities  to  have  been  very 
frequently  repeated. 

When  the  fissures  are  more  complicated,  so  that  not  only  the  different 
cavities  have  been  subsequently  filled  by  the  introduction  of  mineral 
matter  into  those  formed  by  the  mere  sliding  at  intervals,  of  the  rocks 
on  one  side,  but  fractures  also  traverse  the  substances  variously  accu- 
mulated in  them,  and  are  not  confined  to  them,  extending  to  the  adja- 
cent rocks  on  either  side,  even  breaking  the  walls  into  fragments,  and  the 
whole  is  again  cemented  by  mineral  matter  newly  introduced,  the  study 
of  the  contents  of  such  fissures  requires  no  little  caution.  In  such 
cases  a  careful  search  for  the  substances  traversed  will  usually  lead  to 
the  information  sought,  particularly  when  combined  with  any  evidence 
that  can  be  obtained  from  fractures  in  the  adjoining  rocks.  If  in  the 
following  section  (fig.  296)  r  r  represent  the  rocks  on  either  side  of  a 
vein  ;  a,  an  arrangement  of  quartz  or  other  crystals,  showing  the  filling 
of  a  separate  cavity  now  occupied  by  them ;  5,  another  and  similar 
mode  of  occurrence  of  any  crystallized  mineral ;  c9  copper  pyrites,  or 
any  other  substance  separated  from  another,  e,  by  a  surface  of  polish 


662    FRACTUKES    THROUGH    THE    CONTENTS    OP    FISSURES. 

and  striation  (slicJcensides),  d,  and  the  whole  be  traversed  by  a  string 
of  some  other  body,  /,  g,  such  as  sulphuret  of  zinc,  then,  independently 
of  the  evidence  of  separate  movements,  as  shown  by  the  two  sets  of 


crystallized  substances,  a  and  5,  and  the  polished  and  striated  surface, 
c?,  between  the  substances  c  and  e,  another  movement  would  be  shown 
by  the  string  of  mineral  matter, /gr,  more  especially  if,  as  in  the  figure, 
a  kind  of  small  shift  of  the  various  substances,  including  the  walls  of 
the  rock  originally  divided,  has  been  effected.  In  this  manner  many 
decompositions  of, the  substances  first  introduced  into  fissures  seem  often 
to  have  taken  place,  while  mineral  matter,  new  to  its  contents,  has  been 
introduced. 

We  have  hitherto  supposed  the  successive  movements  to  have  been 
effected  in  planes,  either  corresponding  with  those  of  the  original  frac- 
tures, or  not  far  removed  from  them.  As  has  been  shown,  veins  tra- 
verse each  other  at  considerable  and  even  right  angles,  one  series  being 
formed  subsequently  to  another,  as  proved  by  the  contents  of  one  vein 
forming  parts  of  the  walls  of  the  other  (p.  618).  In  such  cases  the 
study  of  any  changes  which  have  taken  place  in  the  veins  cut  through 
is  one  of  much  interest  in  itself,  and  is  still  more  so  when  combined 
with  any  modifications  found  in  the  contents  of  the  traversing  vein.  It 
sometimes  occurs  that  the  mineral  matter  in  the  traversed  vein  is  much 
modified,  so  that,  independently  of  any  removal  of  its  parts  into  the 
new  cavity,  it  might  appear  as  beneath  (fig.  297),  where  the  vein  a  b 

Fig.  297. 


being  cut  at  a  considerable  angle  by  another,  cd,  a  movement  of  certain 
substances  from  b  to  e,  and  a  removal  of  similar  substances  from  /  to 


MODIFICATIONS    AT    THE    CROSSING    OF    VEINS.          663 

a,  is  supposed  to  have  occurred,  so  that  if  the  vein  c  d  were  again 
removed,  the  parts  broken  through  would  not  correspond  to  the  same 
extent  that  they  did  prior  to  the  second  fracture.  When  the  mineral 
matter  is  apparently  moved  on  the  one  side,  and  on  the  other  ore  is 
sought  by  the  miner,  this  becomes  at  once  known ;  but  it  will  reward 
the  attention  of  an  observer,  not  only  to  study  the  veins  with  reference 
to  ore,  but  also  to  all  the  substances  so  traversed.  It  is  also  important 
to  direct  his  attention  to  the  deposits  of  any  substances  or  larger  bodies 
of  them  where  the  walls  may  be  formed  of  the  contents  of  a  first-formed 
fissure,  since  these  then  occupy  the  position  of  any  dissimilar  rocks  (p. 
641),  and  may  be  found  favourable  or  unfavourable  to  the  deposit  of 
some  given  substances,  whether  ores  of  the  useful  metals  or  otherwise. 
In  some  mining  countries  certain  mineral  substances  are  found  more 
abundantly  where  one  vein  crosses  another,  or  within  moderate  dis- 
tances from  the  intersection,  than  elsewhere  in  such  veins. 

When  engaged  in  this  investigation  it  becomes  needful  well  to  con- 
sider the  fact  so  commonly  observed  in  mining  districts  of  various  parts 
of  the  world,  that  where  two  or  more  veins  come  together  at  a  moderate 
angle,  the  ores  of  the  useful  metals  sought  in  them  usually  occur  more 
abundantly  than  elsewhere.  This  may  be  far  from  constant,  neverthe- 
less the  percentage  of  instances  in  which  this  happens  is  so  considerable 
as  commonly  to  have  arrested  the  attention  of  the  miners  in  numerous 
districts.  The  circumstance  has  been  remarked  as  well  when  the  fissures 
cut  each  other  somewhat  vertically,  as  beneath  (fig.  298),  representing 

Fig.  298. 

/  g 


d          e 

a  (North),  b  (South)  surface  of  the  country ;  /,  e,  North  lode ;  g,  d,  Iron  shaft  lode ;  c, 
their  intersection,  where  the  riches  of  the  mine  were  improved ;  s  s,  slate  traversed  by 
the  lodes. 

a  vertical  section  of  the  lodes  at  East  Wheal  Crinnis  Mine,  Cornwall, 
as  where  they  traverse  each  other  somewhat  horizontally,  when  a  plan 
resembling  this  section  would  ajso  suffice  for  numerous  examples.  Even 
a  large  horse*  has  been  observed  to  afford  more  ore  at  the  sharp  ends 

*  This  term  is  applied  in  many  of  our  mining  districts  to  large  fragments  in  mineral 
veins,  portions  of  the  adjoining  rocks,  which,  from  a  complication  of  the  fracture  form- 
ing the  main  fissure,  become  isolated  and  jammed  in  between  its  sides. 


664  DENUDATION. 

of  the  fragment  than  in  other  adjacent  portions.  The  miners  often  give 
the  significant  name  of  leaders  to  the  contents  of  small  fissures  ranging 
out  from  a  main  fissure,  it  frequently,  though  by  no  means  constantly, 
occurring  that  a  bunch  of  ore  is  found  where  they  unite. 

When  the  observer  regards  the  infiltration  of  solutions  into  cavities 
of  various  kinds,  whether  such  solutions  be  merely  derived  from  the 
rocks  adjacent  to  or  surrounding  them,  or  come  from  other  sources,  the 
deposits  of  different  mineral  substances  in  such  cavities,  whether  fissures 
or  otherwise,  under  the  conditions  above  mentioned,  the  selection,  as  it 
were,  of  certain  rocks  by  them  being  one  of  those  conditions,  and  the 
various  modifications  and  changes  which  the  arrangement  of  the  diffe- 
rent kinds  of  mineral  matter  found  in  such  situations  have  sustained,  he 
will  probably  be  led  to  consider  the  general  subject  as  one  of  no  slight 
scientific  interest,  while  at  the  same  time  the  investigations  into  which 
he  will  have  to  enter  also  possess  no  little  importance  from  their  direct 
bearing  on  the  discovery  and  extraction  of  many  substances  so  important 
to  the  progress  of  mankind. 

Partial  removal  or  denudation  of  Rocks. — Although  mention  has 
often  been  previously  made  of  the  partial  removal  of  the  mineral  accumu- 
lations of  various  geological  times,  and  this  has  been  referred  to  the 
action  of  breakers  on  coasts,  to  the  decomposition  of  different  rocks  by 
atmospheric  influences,  and  to  their  erosion  and  subsequent  transport 
by  running  waters,  a  few  words  on  geological  denudation,  regarded  by 
itself,  may  be  usefully  added.  Viewed  with  reference  to  the  causes  of 
the  partial  removal  of  rock  accumulations,  there  are  few  subjects  con- 
nected not  only  with  the  present,  but  also  with  many  prior  conditions 
of  the  earth's  surface  in  different  regions,  which  more  impress  the  geolo- 
gist with  the  great  lapse  of  time  required  in  explanation  of  the  facts 
observed.  Making  all  due  allowance  for  the  abrasion  and  transport  of 
an  immense  mass  of  mineral  matter  by  means  of  atmospheric  influences, 
the  kind  of  smoothing  or  levelling  of  great  areas  so  often  found,  and 
the  isolation  of  portions  of  various  dimensions,  outstanding  like  islands 
from  a  kind  of  main  coast  composed  of  like  deposits,  of  which  they  only 
constitute  detached  parts,  so  forcibly  remind  an  observer  of  the  action 
of  breakers  on  land,  that  there  seems  much  difficulty  in  avoiding  the 
inference  that  to  this  source  of  abrasion  geological  denudation  is 
chiefly  due. 

As  an  intermixture  of  land  and  water  is  needed  in  explanation  of  the 
production  and  distribution  of  detrital  matter  at  all  geological  times, 
and  as  tides,  or  the  absence  of  them,  would  be  produced  by  the  action 
of  the  same  causes  as  at  present  during  the  same  lapse  of  time,  so  far 
the  causes  for  the  abrasion  of  land  at  the  margin  of  waters  would  have 
been  always  the  same  as  now.  Winds,  however,  being,  with  the  excep- 
tion of  such  movements  as  those  of  earthquakes,  the  cause  of  the  waves 


GEEAT  DENUDATION  FROM  BREAKER  ACTION.    665 

which  break  on  coasts,  to  them  the  geologist  has  to  look  for  the  conti- 
nued disturbance  of  water,  where  its  level  cuts  the  land,  sufficient  to 
produce  the  abrasion  required.  As  the  winds  of  the  present  day  are 
arranged  generally  in  their  courses  by  the  action  of  the  sun  on  the  earth, 
and  the  movement  of  the  latter  around  its  axis,  the  observer  has  to  con- 
sider whether  the  former  has  ever  been  less  or  more  intense  than  it  now 
is  (assuming  the  rate  of  the  latter,  for  better  illustration,  to  have 
remained  the  same),  or  whether  counteracting  or  modifying  influences, 
such  as  a  temperature  sufficiently  high  of  the  whole  surface  of  our 
planet  to  prevent  the  present  differences  of  heat  arising  from  the  sun, 
have  had  an  appreciable  effect  in  that  direction.  He  has  thus  to  see  if 
there  be  evidence  of  breaker  action  at  different  and  especially  at  early 
geological  times.  The  facts  noticed  as  to  beaches  adjoining  land  in  the 
midst  of  the  accumulations  of  so  early  a  date  as  that  of  the  Silurian 
series  (p.  459),  may  satisfy  him  that  breakers  were  in  action  at  that 
time  as  now  on  sea-coasts.  Evidence  of  the  like  kind  being  seen  of 
similar  effects  at  various  geological  periods,  the  observer  may  feel 
assured  that  from  the  earliest  times  when  the  remains  of  marine  life 
were  entombed  amid  detrital  deposits,  to  the  present  day,  breaker  action 
was  in  force. 

Being  satisfied  that  this  action  has  been  an  important  geological  agent 
for  so  long  a  lapse  of  time,  the  observer  may  be  induced  to  inquire, 
from  such  evidence  as  may  present  itself,  if  any  particular  exposures  to 
great  oceans  can  be  traced.  Assuming  winds  to  produce  the  ordinary 
waves  breaking  on  shore,  and  that  the  present  causes  of  the  general 
arrangement  or  modification  of  land  and  sea  have  continued  far  back 
into  geological  time,  the  greater  the  ocean  exposure  of  given  coasts  to 
prevalent  and  strong  winds,  the  greater,  all  other  conditions  being  equal, 
would  be  the  abrasion  experienced.  Hence  the  study  of  denudation  in 
connexion  with  evidence  as  to  the  distribution  of  land  and  sea  at  different 
geological  times,  and  especially  as  to  the  direction  in  which  great  por- 
tions of  the  ocean  of  any  of  those  times  may  have  been  situated,  becomes 
important.  We  have  been  often  struck,  while  examining  the  geological 
structure  of  different  portions  of  the  British  Islands,  with  the  length  of 
time  during  which  the  various  modifications  of  coasts  attending  the  ele- 
vation or  depression  of  the  area  at  different  periods,  above  and  beneath 
the  level  of  the  sea,  may  have  been  exposed  to  or  sheltered  from  such 
an  ocean  as  the  Atlantic  on  the  westward.  The  position  of  the  conglo- 
merates of  the  new  red  sandstone  time,  arranged  against  and  around  -the 
older  rocks  of  the  Mendip  Hills,  and  portions  of  the  adjacent  country 
(fig.  167,  p.  462),  remind  the  observer,  while  on  the  spot,  very  forcibly 
of  an  exposure  to  a  considerable  range  of  water  on  the  westward.  Of 
the  surfaces  of  land  left  by  various  denudations  at  more  recent  times, 
the  impression  as  to  a  great  exposure  to  western  waters  is  still  greater, 


666  CAUTION    REQUIRED    RESPECTING    AMOUNT    OP 

inland  cliffs  presenting  themselves  precisely  where  they  would  be 
expected,  and  even  the  shelter  derived  from  protruding  land  being 
found.  In  illustration  of  this  circumstance,  an  observer,  regarding  the 
present  escarpments  of  the  oolitic  series,  including  the  lias,  from  their 
comparative  shelter  on  the  eastward  of  the  high  land  of  .Wales,  to  the 
English  Channel,  cannot  fail  to  be  struck,  making  all  due  allowance  for 
subsequent  changes  arising  from  atmospheric  influences,  with  the  mode 
of  occurrence  of  the  old  cliffs,  and  of  their  character  according  to  expo- 
sure or  shelter,  where  the  Mendip  Hills  and  other  elevations  of  the  same 
character,  would  modify  the  force  of  the  great  Atlantic  waves  breaking 
on  such  a  range  of  coast. 

The  removal  of  portions  of  "the  accumulations  of  various  periods,  ex- 
tending back  in  time  to  those  of  the  Cambrian  series  in  our  islands,  is 
something  very  considerable,  and  to  be  measured  by  thousands  of  cubic 
miles  of  mineral  matter.  In  Ireland,  the  abrasion  of  the  Silurian  rocks, 
anterior  to  the  conglomerates  of  the  old  red  sandstone,  is  well  marked. 
Large  surfaces  were  evidently  there  shorn  down  by  denudation  previous 
to,  or  at  that  time,  the  granitic  protrusions  then  existing  in  parts  of 
that  land  being  also  cut  partially  away,  and  having  from  that  period  to 
this  been  exposed  to  abrasion  and  loss  of  volume  whenever  brought 
within  the  range  of  the  breakers,  or  raised  up  within  the  influences  of 
the  atmosphere.  In  regarding,  therefore,  such  masses  of  mineral  matter, 
the  observer  has  before  him  the  results  of  many  partial  removals  of  rock 
accumulations,  and  sees  the  remains  only  of  many  modifications  of  sur- 
faces wrought  by  denudations  during  a  long  lapse  of  time. 

In  estimating  any  amount  of  matter  which  may  have  been  removed, 
either  from  igneous  rocks  or  from  deposits  formed  by  the  aid  of  water, 
much  care  is  sometimes  needed,  so  that  a  correct  estimate  may  be  formed 
of  the  probable  prior  arrangement  of  the  parts  of  it.  This  is  especially 
necessary  when  a  series,  or  parts  of  a  series,  of  deposits  may  extend 
over  or  conceal  another,  or  portions  of  itself,  otherwise  by  supposing  an 
extension  of  accumulations  in  directions  where  they  never  existed,  far 
more  mineral  matter  might  be  inferred  to  have  been  removed  than  has 
been  the  case.  For  example,  the  old  red  sandstone  of  Herefordshire, 
South  Wales,  and  parts  of  Southern  Ireland,  so  occurs,  that,  viewed  as 
a  whole,  the  higher  portion  gradually  overlapped  or  passed  over  a 
variety  of  older  and  subjacent  beds  in  a  southerly  and  westerly  direc- 
tion, a  relative  depression  of  land  and  sea-bottom  in  that  direction 
having  probably  been  the  cause  of  this  overlap.*  In  such  a  case  the 
probable  range  and  limit  of  the  conditions  for  the  deposit  of  this  higher 
portion  of  the  old  red  sandstone  have  to  be  carefully  estimated,  so  that 

*  Part  of  tliis  overlap  will  be  seen  by  reference  to  Sheets  38,  40,  of  the  Geological 
Survey  of  Great  Britain,  and  also  to  the  small  General  Map  of  South  Wales,  inserted  in 
the  Memoirs  of  the  Geological  Survey,  vol.  i. 


DENUDATION    OF    OVERLAPPING    ROCKS. 


667 


the  removal  of  matter,  never  deposited,  may  not  be  inferred.  It  fortu- 
nately happens  that,  in  Southern  Pembrokeshire,  the  extension  of  the 
old  red  sandstone,  at  the  time  of  the  deposit  of  the  carboniferous  lime- 
stone of  the  same  district,  can  be  clearly  seen  at  Slebech,  the  latter 
there  overlapping  the  sandstone,  as,  in  like  manner,  in  the  same  county, 
the  extent  of  the  carboniferous  limestone,  at  the  time  of  the  accumula- 
tion of  the  lower  part  of  the  coal  measures,  can  also  be  well  observed  at 
the  overlap  of  the  latter  over  the  former,  near  Haverfordwest.  The 
following  section  (fig.  299)  may  serve  to  illustrate  the  need  of  caution 
on  this  subject.  If  a  b  be  a  series  of  consecutive  detrital  deposits, 
formed  under  conditions  which  allowed  them  completely  to  cover  each 
other,  so  far  as  the  area  represented  in  the  section  is  concerned,  and 

Fig.  299. 


c,  d,  e,  be  other  accumulations,  formed  after  a  movement,  in  the  direc- 
tion of  6,  had  lowered  that  end  of  the  deposits  a  6,  so  that  c,  d,  e  were 
successively  formed  in  planes  parallel  to  each  other,  but  at  an  angle 
with  that  of  a  5,  the  successive  extensions  of  c,  d,  and  e,  in  the  direc- 
tion a,  being  governed  by  causes  such  as  a  line  of  coast,  and  its  gradual 
depression  beneath  a  sea  level  in  that  direction,  after  the  first  movement 
tilting  the  inferior  rocks  a  b  towards  5,  the  rocks  <?,  d,  and  e,  would  gra- 
dually spread  beyond,  or  overlap  each  other  towards  a.  If  now,  from 
subsequent  breaker  action,  atmospheric  influences,  and  final  elevation  of 
the  mass  as  now  found,  a  surface  should  be  exposed  corresponding  with 
the  line/#,  a  section  of  the  following  kind  (fig.-  300)  would  be  obtained, 

Fig.  300. 


one  very  deceptive,  without  care  and  attention  to  the  general  geological 
structure  of  the  country,  as  to  the  prior  extension  of  the  beds  c,  d,  e, 
towards  a,  inasmuch  as  a  vast  extent  of  country  composed  of  them 
might  be  assumed  as  shorn  down  in  that  direction,  and  a  mass  of  mineral 
removed,  which  never  existed.  ^ 

It  thus  becomes  essential,  when  endeavouring  to  estimate  any  mineral 

*  Those  who  have  examined  the  escarpments  of  the  coal  measures,  carboniferous 
limestone  and  old  red  sandstone  on  the  northern  boundary  of  the  great  coal  districts  of 
Monmouthshire  and  South  Wales,  "will  at  once  see  the  application  of  these  sections. 


668  ISLAND    MASSES    LEFT    BY    DENUDATION. 

matter  removed  by  denudation,  carefully  to  weigh  the  probability  of  the 
conditions  under  which  the  accumulations,  supposed  to  be  removed,  may 
have  extended.  We  may  here  again  refer  with  advantage  to  the  small 
area  represented  in  the  map  of  the  Mendip  Hills  and  adjoining  country 
(fig.  167,  p.  462),  for  illustration  on  this  head.  Upon  the  portion  of 
country  where  the  new  red  marl  and' sandstone  (5)  occupies  the  surface, 
several  isolated  patches  of  lias  (6)  may  be  seen  distributed.  These 
patches  are  only  the  remains  of  beds  which  once  continuously  covered 
the  former  deposits,  and  joined  the  main  mass  of  the  lias  seen  on  the 
southern  portion  of  the  map.  The  mode  of  accumulation  of  this  lias, 
and  its  modification  where  adjoining  the  dry  land  of  the  time,  have 
been  previously  mentioned  (p.  464).  It  is  sufficient  here  to  remark,  that 
while  this  rock  was  thus  modified  near  the  Mendip  Hills,  it  stretched 
away  with  common  characters  in  other  directions,  patches  of  it  being 
found  in  various  other  localities  scattered  over  the  prior  and  subjacent 
rocks,  such  being  the  remains  of  a  wide  area  once  occupied  by  this 
deposit.  As  with  the  lias,  so  also  with  the  accumulations  which  imme- 
diately succeeded  it — those  of  the  inferior  oolite  (7,  fig.  167),  detached 
patches  of  which  are  also  seen  isolated  upon  prior-formed  rocks,  such 
patches  once  portions  of  a  continuous  deposit  in  a  sea.  One  small  islet 
of  inferior  oolite  will  be  observed  towards  the  left  corner  of  the  map 
(fig.  167).  Other  patches  will,  however,  be  seen  at  Dundry  and  Brent 
Knoll,  by  reference  to  more  extended  geological  maps.  By  careful 
examination  it  is  found  that  the  mode  of  occurrence  of  their  component 
beds  is  such  as  to  point  towards  their  termination,  as  a  deposit  of  the 
time,  at  no  great  distance  westward,  so  that  .when  considering  the  mass 
of  mineral  matter  removed  by  denudation  in  that  direction,  with  refe- 
rence to  the  general  structure  of  the  district,  due  allowance  has  to  be 
made  for  this  probable  termination  of  these  rocks  westward.  As  illus- 
trative of  denudation  towards  the  termination  of  accumulations,  the  fol- 
lowing section  (fig.  301)  may  be  useful.  It  is  one  of  the  country  near 


Fig.  301. 

Main  Down,  Wiveliscombe.  Castle  Hill. 

I     a. 


Wiveliscombe,  Somersetshire,  d  d  being  rocks  of  the  Devonian  series, 
disturbed  and  denuded  anterior  to  the  accumulation  of  the  sandstones, 
5,  of  the  new  red  sandstone  series  of  that  district,  and  of  a  conglome- 
rate, a  a,  composed  of  rounded  portions  of  the  adjacent  disturbed  rocks, 
d  d,  cemented  by  calcareo-magnesian  matter.  In  this  case  the  former 
continuous  portion  of  the  conglomerate  a  a,  and  of  part  of  the  sand- 
stones beneath  it,  5,  have  been  removed  by  denudation,  not  only  from 
the  minor  valley,  v,  but  also  from  the  larger  surface  hollowed  out  be- 


CONTORTIONS     WORN    DOWN    BY    DENUDATION. 


669 


tween  Main  and  Castle  Hills.  The  conglomerates,  a  a,  have  thus  been 
cut  off,  as  it  were,  from  the  source  of  their  pebbles,  the  country  towards 
Main  Down,  the  portion  left  being  only  the  remains  of  a  once  continuous 
accumulation  of  them,  probably  along  a  line  of  coast  existing  at  that 
time  at  a  short  distance  westward. 

Notwithstanding  these  modifications  required  in  our  estimate  of  the 
amount  of  accumulations  removed  in  some  districts,  there  often  remains 
so  great  a  gap  in  the  connexion  which  evidently  once  existed  between 
portions  of  deposits  in  others,  that  collectively  the  removed  portions 
can  only  b«  satisfactorily  measured  by  a  considerable  amount  of  cubic 
miles  of  missing  mineral  matter.  The  smoothing  off  of  the  surfaces  of 
even  the  most  disturbed  deposits,  portions  of  these  deposits  now 
variously  consolidated,  and  apparently  possessing  that  character  when 
so  worn  down,  is  often  to  be  found.  The  coasts  of  Northern  Devon- 
shire, where  the  variously  consolidated  beds  of  the  lower  coal  measures 
are  so  much  bent  and  plicated,  will  afford  the  geologist  excellent  oppor- 
tunities for  observation.  It  is  of  the  order  represented  beneath  (fig. 
302),  where  #,  5,  being  the  sea  line,  cliffs,  <?,  are  exposed,  showing 

Fig.  302. 


numerous  flexures,  the  continuations  of  which  can  be  readily  supplied 
by  the  dotted  lines  above  the  present  surface  of  the  land,  d,  and  be- 
neath the  level  of  the  sea,  a,  b.  The  importance  of  cliffs,  either  inland 
or  on  the  sea-coast,  in  properly  appreciating  the  matter  removed  from 
a  district  presenting  no  very  great  differences  of  surface  elevation  and 
depression  (mere  common  undulations  of  country),  is  very  considerable. 

Tig.  303. 


Without  them  the  observer  might  often  be  uninstructed  as  to  the  real 
amount  of  flexure  and  plication  planed  down  and  concealed  beneath  the 


670       BREAKERS    CUTTING    OFF    NEW    SLICES    OF    LAND. 

ordinary  smooth  surfaces  exposed.  Of  this  the  preceding  section  (fig.  303) 
is  an  example.  It  is  a  sketch  from  Trenance  Point,  of  High  Cove,  on 
the  north  coast  of  Cornwall,  exhibiting  a  section  of  hard  sandstones  of 
the  older  rocks  of  that  country,  worn  down,  probably,  by  the  same  kind 
of  heavy  Atlantic  breakers  which  are  now  cutting  off  a  further  slice  of 
these  ancient  accumulations  down  to  a  new  level.* 

By  consulting  the  geological  maps  of  various  lands,  when  such  maps 
have  been  carefully  prepared,  abundant  evidence  will  frequently  appear 
of  the  surface  denudation  to  which  very  extended  areas  have  been  ex- 
posed. Taken  alone,  without  carefully  constructed  sections,  and  a  due 
regard  to  the  circumstances  above  noticed,  no  very  accurate  estimate 
can  usually  be  framed.  We  may,  indeed,  infer,  when  we  find,  as  at 
Orleigh  Court,  near  Bideford,  Devon,  a  part  of  the  lower  portion  of 
the  cretaceous  series,  possessing  all  the  essential  characters  of  the  same 
portion  when  last  seen  in  mass  to  the  eastward,  at  the  Black  Down 
Hills,  forty-two  miles  distant,  that  the  whole  intermediate  country  was 
once  covered  with  the  sands  and  chert,  of  which  this  portion  of  the  cre- 
taceous series  in  that  part  of  England  is  composed,  so  that  by  taking  a 
given  area  and  the  thickness  of  the  accumulation,  the  number  of  cubic 
miles  of  the  deposit  removed  by  denudation  may  be  approximately  esti- 
mated. When,  however,  the  observer  has  to  deal  with  a  bent  or  con- 
torted set  of  beds  in  a  considerable  area,  it  is  only  by  very  carefully 
following  these  flexures  and  contortions  that  any  fair  approximation  to 

*  With  regard  to  the  present  action  of  breakers  thus,  as  it  were,  removing  new  slices 
of  deposits,  whether  contorted,  or  in  their  original  planes  of  accumulation,  it  not  only 
effects  this,  but  also,  when  the  conditions  for  the  elevation  and  depression  of  masses  of 
land  have  been  favourable,  will  cut  away  the  accumulations  of  former  times  so  as  to 
restore  old  worn  surfaces.  Of  this,  examples  may  be  seen  on  the  shores  of  the  Bristol 
Channel  in  several  places  (Aust  Passage,  Bendrick  Rocks,  &c.)  The  following  section 
(fig.  304),  near  Portishead,  exhibits  beds  of  coal  measures,  a,  a,  upturned  prior  to  the 

Fig.  804. 


accumulation  of  dolomitic  conglomerate,  and  new  red  sandstone,  b,  the  part  towards  e 
being  now  swept  by  breaker  action,  which  has  cut  away  the  beds,  b,  to  the  cliff,  d ;  a 
portion  being,  for  the  present,  left  at  c,  and  thus  a  part  of  an  old  surface  becomes 
again  exposed  at  the  level  of  the  sea,  s  s,  after  a  long  lapse  of  time. 

As  to  denudation  generally,  which  has  removed  large  portions  of  the  deposits  now 
exposed  on  the  surface  of  land,  the  observer  will  find  numerous  illustrations  in  pre- 
ceding figures,  viz.,  figs.  7,  10,  11,  15,  47,  57,  79,  80,  95,  109,  136,  156,  158,  105,  1G(3, 
169,  171,  174,  177,  181,  209,  212,  213,  217,  218. 


DENUDATION    IN    HEREFORDSHIRE. 


671 


the  matter  removed  from  the  general  mass  can  be  made.  The  various 
bends  and  contortions  must  not  only  be  properly  ascertained,  due 
allowance  being  made  for  fractures  at  the  extreme  parts  of  flexures 


X 


672  DENUDATION    IN    SOMERSETSHIRE    AND    WALES. 

(p.  607),  but  also  the  amount  of  faults  that  have  occurred,  and  which 
may  interfere  with  these  flexures  and  plications,  be  carefully  consi- 
dered. 

Availing  himself  of  the  observations  made  on  the  Geological  Survey, 
Professor  Ramsay  has  endeavoured  to  point  out  that  a  vast  mass  of 
matter  has  been  removed  by  denudation  from  South  Wales  and  the  ad- 
jacent English  counties,  the  amount  of  which  may  to  a  certain  extent 
be  estimated.*  Taking  the  evidence  obtained  respecting  the  thick- 
nesses of  the  various  beds  of  Silurian  rocks  and  their  curvature,  in  the 
Woolhope  district  (fig.  305),  he  infers  that,  if  the  amount  of  mineral 
matter  now  removed  were  restored,  so  as  to  complete  the  section  of  the 
manner  in  which  the  rocks  probably  occurred  at  the  time  they  were 
bent,  it  would  give  them  the  great  additional  height  of  about  3500  feet. 
Employing  the  same  kind  of  evidence  for  the  old  red  sandstone,  carbo- 
niferous limestone,  and  coal  measures  of  the  Mendip  Hills  district,  the 
Professor  considers  that  an  additional  mass  of  accumulations,  4000  feet 
in  thickness,  would  be  required  above  the  Mendip  Hills  to  supply  the 
place  of  beds  removed  by  denudation,  and  another  of  5000  feet,  for  the 
denudation  of  the  same  rocks  on  the  north  of  Bristol,  f  The  missing 
matter  above  the  vale  of  the  Towey,  near  Langadoc,  Caermarthenshire, 
he  estimates  at  from  10,000  to  11,000  feet  in  thickness.  The  preceding 
section  (fig.  306)  is  one  of  those  given  in  illustration  of  this  subject, 
and  will  serve  to  exhibit  the  disturbed  beds  of  carboniferous  limestone, 
old  red  sandstone,  and  Silurian  rocks,  shorn  down  by  denudation  in  the 
slightly  elevated  districts  of  Southern  Pembrokeshire.  These  and  other 
calculations  induce  Professor  Ramsay  to  infer,  with  reference  to  the 
Silurian  rocks,  old  red  sandstone,  and  coal  measures  of  South  Wales, 
that  by  "  simply  estimating  their  cubic  contents  in  the  area  they  now 
occupy,  and  adding  to  this  the  amount  removed  by  denudation,  and 
that  existing  beneath  the  level  of  the  sea,  it  is  evident  that  the 
quantity  of  matter  employed  to  form  these  strata  was  many  times 
greater  than  the  entire  amount  of  solid  land  they  now  represent  above 
the  waves.  "J  f 

Viewing  such  considerable  denudations,  quite  as  readily  seen  in  many 
other  and  distant  regions,  as  in  the  minor  districts  noticed,  and  com- 
bining them  with  the  elevations  and  depressions  of  land  that  have  taken 
place  at  all  geological  times,  sometimes  slowly  moving  great  surfaces 
above  and  beneath  the  level  of  the  sea,  at  others  squeezing  and  folding 

*  "Memoirs  of  the  Geological  Survey  of  Great  Britain,"  vol.  i.  p.  297. 

f  Referring  to  the  reduction  of  the  Horizontal  Section  of  the  Geological  Survey, 
sheet  17,  extending  from  Glastonbury  Tor,  across  the  Mendip  Hills,  by  Clifton,  Bristol, 
to  the  flat  land  at  the  Severn,  and  to  the  sketch  for  filling  up  denudation,  pi.  4,  fig.  4, 
in  the  "Memoirs  of  the  Geological  Survey,"  vol.  i. 

J  "Memoirs  of  the  Geological  Survey,"  vol.  i.  p.  334. 


NEEDFUL  ATTENTION  TO  THE  GREATER  PROBLEMS.  673 

various  mineral  accumulations  into  great  ranges  of  mountains,  the  ob- 
server will  be  at  no  loss  for  evidence,  not  only  that  the  surface  of  the 
earth  has  so  long  continued  in  an  unquiet  state,  but  also  that  the  same 
amount  of  mineral  matter  may  have  been  repeatedly  employed  in  part, 
or  as  a  whole,  in  the  production  of  deposits  spread  over  various  areas 
for  the  time  being,  these  deposits  either  fossiliferous  or  without  organic 
exuviae,  as  the  conditions  for  the  preservation  of  the  remains  of  the 
animal  and  vegetable  life  of  different  times,  may  or  may  not  have  pre- 
vailed. As  considerations  of  this  kind  constitute  a  part  of  those  which 
lead  to  the  most  extended  views,  by  the  aid  of  which  we  endeavour  to 
trace  back  the  past  conditions  of  our  planet,  they,  and  the  class  to 
which  they  belong,  tending,  as  they  do,  to  keep  attention  alive  to  the 
greater  problems,  while  the  detail  necessary  for  their  solution  is  col- 
lected, cannot  be  too  frequently  present  to  the  mind  of  the  geological 
observer. 


APPENDIX. 


G-eological  Maps  and  Sections. — Though  an  observer  may  be  sup- 
posed usually  to  have  access  to  the  best  maps  of  any  country  he  may 
examine  geologically,  and,  in  general,  to  find  such  maps  containing  the 
information  which  is  desirable,  as  well  respecting  the  natural  physical 
features  of  the  country,  as  the  artificial  modifications  of,  or  arrange- 
ments on,  its  surface,  so  that  he  can  always  ascertain  his  exact  position, 
and  possess  the  power  of  recording  any  circumstances  considered  suffi- 
ciently important,  in  their  true  relative  places  on  such  maps  ;  it,  never- 
theless, sometimes  happens  that  the  maps  of  a  district  are  inaccurate, 
or  do  not  contain  those  things  which  are  needed.  A  geologist  will  not 
long  have  endeavoured  to  record  his  observations  upon  maps,  before  he 
will  ascertain  that  many  a  beautiful  engraving  may  be  worthless,  while 
some  coarse,  unpromising  plan  may  be  most  valuable.  In  case  of  need, 
therefore,  it  becomes  important  for  an  observer  to  be  so  far  skilled  in 
the  construction  of  maps,  as  not  only  to  be  able  to  correct  one  which 
may  be  imperfect  in  an  efficient  manner,  but  also  to  make  such  a  sketch 
of  ground  as  may  suffice  for  his  purpose.  A  knowledge  of  the  kind  of 
surveying,  commonly  termed  military  drawing,  will  be  found  most 
advantageous  for  his  progress.  He  will  scarcely  accomplish  much  on 
this  head  by  the  aid  of  books  alone,  and  therefore  should  study  it  in 
the  field.  If  possessing  a  good  eye  for  form,  he  will  by  no  means  find 
the  acquisition  of  this  knowledge  difficult,  while  he  will  soon  perceive 
that  it  affords  him  great  additional  power  in  satisfactorily  recording  his 
observations. 

Even  in  many  a  map  where  the  lines  representing  rivers,  coasts,  and 
other  natural  features,  are  exceedingly  accurate,  as  also  those  showing 
the  roads,  canals,  villages,  and  other  artificial  arrangements,  are  equally 
so,  it  too  often  happens  that  the  relief  of  the  ground,  the  true  forms  of 
the  inequalities  of  surface  of  the  hills  and  mountains,  is  either  not 
given,  or  so  inaccurately  that  it  would  have  been  better  if  no  attempts 
had  been  made  to  represent  it.*  Now,  the  true  relief  of  the  surface  of 

*  The  method,  too  often  adopted,  of  representing  the  lines  of  water-shed  as  those  of 
the  highest  ground  in  many  regions,  cannot  be  too  much  deprecated,  leading  as  it  often 
does,  to  the  most  imperfect  views  as  to  the  real  inequalities  of  surface  in  them,  and  as 
to  the  action  of  those  geological  causes  which  have  produced  such  inequalities. 


GEOLOGICAL    MAPS    AND    SECTIONS.  675 

a  district  is  often  of  the  greatest  value  to  the  observer.  It  is  only 
necessary  for  him  to  attempt  a  record  of  his  observations  upon  maps 
with  and  without  a  correct  representation  of  this  relief,  fully  to  appre- 
ciate the  difference.  A  power,  therefore,  accurately  to  sketch  in  the 
forms  required  becomes  of  no  slight  advantage.*  Much  may  be  accom- 
plished by  the  improved  prismatic  compass  (care  being  taken  in  districts 
where  rocks  containing  much  protoxide  of  iron  are  present,  such  as 
many  of  those  of  igneous  origin  in  which  hornblende  and  augite  pre- 
vail, which  will  divert  the  magnetic  needle),  and  by  some  effective 
arrangement  of  a  spirit  level,  by  which  close  approximations  to  slopes 
may  be  obtained.  For  approximations  to  heights  within  a  certain  range, 
the  aneroid  barometer  will  be  found  useful,  especially  in  regions  where 
the  mercurial  barometer  and  sympesometer  may  not  be  easily  carried, 
and  where  atmospheric  changes,  affecting  such  instruments,  are  not 
considerable.  Possessing  these  simple  instruments,  and  a  fair  know- 
ledge of  military  drawing,  the  observer  may  make  many  a  sketch  of  a 
country,  the  geological  structure  of  which  would  otherwise  have  been 
imperfectly  represented. 

Supposing  the  possession  of  a  proper  map,  either  previously  made,  or 
constructed  during  the  progress  of  his  work,  it  is  needful  that  a  geologist 
should  follow  up  the  rocks  he  may  be  investigating,  quitting  them  as 
little  as  opportunities  permit,  so  that  all  connected  with  their  modes  of 
occurrence  may  be  carefully  ascertained,  and  all  the  points  of  importance 
be  as  carefully  entered  upon  his  map.  Without  caution  of  this  kind, 
very  grave  errors  may  readily  be  committed,  inaccurate  inferences  being 
drawn  respecting  the  mode  of  occurrence  of  accumulations,  seen  only  at 
different  and  frequently  distant  points,  which  more  detailed  examination 
would  have  prevented,  and  this  more  especially  in  districts  of  highly- 
disturbed  and  Broken  rocks.  As  to  the  boundaries  of  the  different  mineral 
masses  which  it  may  be  thought  desirable  to  insert  on  geological  maps, 
these  necessarily  depend  upon  the  scale  of  the  map  on  the  one  hand,  and  the 
view  taken  of  their  relative  value  on  the  other.  Whatever  the  scale,  it  is 
desirable  that  the  great  distinctions  considered  imporfant  should  be  clearly 
apparent,  and  that  the  detail  should  be  so  represented  as  not  to  impede 
a  correct  view  of  them.  It  is  better  to  select  such  portions  of  a  map 
for  enlargement  as  may  be  required  for  the  illustration  of  any  particular 

*  With  reference  to  the  sketching  of  ground,  the  method  of  representing  a  hilly  or 
mountainous  country  by  lines,  approximating  to  those  of  equal  altitudes,  as  is  shown 
by  fig.  180,  p.  476,  will  be  found  very  serviceable  for  geological  investigations,  especially 
those  where  relative  altitudes  are  important,  or  where  the  small  inclinations  of  beds  can 
only  be  measured  by  the  heights  they  occupy  and  at  distances  too  considerable  to  be 
ascertained  by  instruments  constructed  to  measure  the  dip  of  rocks  (clinometers). 
The  contour  lines,  or  those  of  equal  levels,  upon  some  of  the  Ordnance  Maps  in 
England  and  Ireland,  and  so  valuable  for  many  purposes,  form  an  accurate  representa- 
tion of  this  method. 


676  GEOLOGICAL    MAPS    AND    SECTIONS. 

detail,  than  to  sacrifice  broad  comprehensive  views  for  the  sake  of  its 
introduction  when  only  really  needed  in  particular  localities. 

As  with  the  objects  to  be  represented  on  geological  maps,  so  with  the 
colouring  employed  upon  them.  Comprehensive  clear  views  should  not 
be  sacrificed  to  attempts  to  introduce  detail  only  important  locally,  and 
which  can  be  best  shown  by  the  enlargement  of  such  portions  of  a  map. 
The  employment  of  given  colours  to  represent  certain  divisions  of  the 
geological  series  has  been  considered  very  desirable,  so  that  the  eye 
becoming  accustomed  to  them  may,  as  it  were,  currently  read  off  maps 
thus  coloured.  This  is  certainly  important,  and  might  be  accomplished, 
to  a  considerable  extent,  in  the  general  maps,  national  maps  for  exam- 
ple, of  different  countries. 

Much  may  be  and  has  been  effected  as  to  the  information  to  be 
afforded  by  geological  maps,  by  a  mixture  of  signs  and  colours ;  the 
latter  representing  some  accumulation,  or  series  of  accumulations ;  and 
the  former,  certain  modifications  of  it  considered  important.  In  this 
manner,  for  example,  igneous  rocks  may  be  represented  by  some  given 
tint  or  colour  ;  and  the  variations  in  their  mineral  structure,  so  far  as 
regards  the  surface  of  the  land,  by  various  signs.  The  like  with  those 
divisions  in  the  sedimentary  deposits  of  different  geological  dates  to 
which  names  have  been  given,  various  signs  also  readily  show  their 
mineral  structure  in  different  parts  of  their  surface  exposure.  Among 
the  signs  employed  amid  the  stratified  rocks,  it  is  very  needful  to  have 
a  sufficient  number  representing  their  modes  of  occurrence  as  to  the 
position  of  their  beds,  showing  when  these  are  horizontal,  inclined  at 
any  particular  angle,  or  contorted ;  when  the  latter,  the  kind  of  contor- 
tion, and  the  like.  The  following  signs  (fig.  307)  have  been  found 
useful  for  this  purpose.  The  point  of  the  arrow,  a,  shows  the  dip  or 
inclination  of  the  beds  as  respects  the  horizon ;  and  it  is  desirable  to 
place  on  one  side  of  this  sign  the  amount  of  the  dip,  such  as  5°,  15°, 
23°,  as  it  may  happen  to  be.  The  sign  b  is  intended  to  point  out  that, 
while  the  general  inclination  or  dip  of  the  beds  may  be  in  the  direction 


corresponding  with  that  of  the  arrow,  they  undulate  on  the  minor  scale ; 
e,  shows  that  the  strata  are  vertical,  their  range,  or  strike,  as  it  is  often 
termed,  being  in  the  direction  of  the  longest  line.  Beds  much  plicated 


GEOLOGICAL    MAPS    AND    SECTIONS.  677 

on  the  minor  scale,  while  they  have  a  general  range,  are  shown  by  d, 
the  straight  line  pointing  out  the  general  range.  An  anticlinal  ridge 
is  represented  by  the  sign  /;  the  two  arrow-heads  showing  the  direction 
of  the  dip  on  either  side,  and  the  cross  line  that  of  the  range  of  this 
form  of  beds  ;  e  is  intended  to  indicate  the  occurrence  of  beds  so  con- 
torted and  folded  in  various  planes,  that  no  definite  dip  or  range  of 
them  can  be  inferred  in  the  locality  where  this  sign  may  be  entered 
upon  the  map.  The  cross  g  represents  a  horizontal  arrangement  of  the 
beds.  By  attention  to  such,  or  any  other  system  of  signs  considered 
effective,  the  arrangement  of  the  component  beds  of  stratified  rocks  is 
so  exhibited  as  to  present  the  observer  with  evidence  enabling  him  to 
take  a  comprehensive  view  of  this  part  of  his  subject.  By  combining 
any  system  of  this  kind  with  another  for  the  distribution  of  organic  re- 
mains, in  the  fossiliferous  rocks,  he  still  further  advances  his  general 
views  ;  so  that  with  colours,  and  with  signs  for  mineral  structure,  dis- 
tribution of  organic  remains,  and  any  movements  which  the  beds  may 
have  sustained  since  their  deposit,  his  map  not  only  becomes  a  record 
of  his  observations,  but  also  presents  him  with  a  classified  collection  of 
'facts  from  which  he  may  deduce  important  general  conclusions  that 
otherwise  might  not  so  readily  be  attained. 

Geological  maps  conveying  information  only  as  to  the  surface 
arrangement  of  rocks,  vertical  sections  of  the  country,  either  directly 
obtained  from  natural  or  artificial  exposures  of  the  various  accumula- 
tions, or  inferrred  from  abundant  and  satisfactory  information,  col- 
lected at  various  points  on  the  line  of  section  or  within  safe  distances 
from  it,  become  essential  for  a  right  view  of  the  manner  in  which  the 
various  rocks  of  a  district  may  occur.  Too  much  stress  cannot  be  laid 
on  the  importance  of  rendering  all  such  sections  strictly  proportional, 
so  that  they  should,  as  much  as  possible,  be  miniature  representations 
of  nature.  The  distortions  and  erroneous  conclusions  which  arise  from 
a  want  of  attention  to  this  point  are  endless.  In  the  first  place,  the 
outlines  of  countries  are  usually  so  exaggerated,  as  to  elevations  and 
depressions,  that  the  real  forms  of  the  surface  are  falsified,  and  that 
true  appreciation  of  them,  which  would  lead  to  just  views  of  their  rela- 
tive importance,  and  of  the  conditions  which  may  have  produced  them, 
superseded  by  most  imperfect  ideas  as  to  the  real  relief  of  a  district, 
even  of  such  as  may  be  mountainous.  True  surface  sections  of  the  latter 
are  often  especially  needed  to  afford  the  geologist  a  correct  view  of  the 
different  heights  and  depressions,  so  that  he  may  insert  his  observations 
on  that  which  will  not  deceive  him  in  his  endeavours  to  trace  the  amount 
and  direction  of  any  general  disturbance,  to  ascertain  the  value  of  any 
curves  or  plication  of  beds,  and  to  restore  the  various  component  parts 
to  their  inferred  original  positions  in  such  regions. 

Though  with  known  altitudes  at  sufficiently  numerous  points  on  any 


678  GEOLOGICAL    .MAPS    AND    SECTIONS. 

given  line  of  proposed  section,  the  various  distances  from  these  points 
being  known,  much  may  be  accomplished  by  a  practised  and  steady  eye 
by  sketching  in  the  intermediate  ground ;  and  this  may  be  the  only 
means  at  command  in  somewhat  rapid  excursions  :*  the  line  given  by 
instrumental  work,  when  time  suffices,  is  the  only  real  method  of  obtain- 
ing the  object  sought.  All  lines  of  section  are  thus  run  on  the  Geolo- 
gical Survey  of  Great  Britain,  and  the  results  thence  obtained  have 
been  so  satisfactory  that  few,  once  experiencing  the  advantages  so  de- 
rived, would  probably  be  disposed  to  abandon  this  method  of  observa- 
tion. In  certain  districts,  such  as  those  where  that  important  product 
coal  is  obtained,  exact  sections  of  surface  are  as  indispensable  as  the 
exact  relative  positions  of  the  beds  themselves  with  reference  to  them, 
so  that  the  true  positions  of  the  coal  beds  may  appear.  With  his  level 
or  his  theodolite  an  observer  feels  that  confidence  in  his  labours  which  he 
might  not  otherwise  possess.  Having  the  surface  right,  he  can  enter  the 
dips  and  other  modes  of  occurrence  of  the  rocks  found  in  their  real  rela- 
tive situations  on  his  section,  and  have  a  collective  miniature  represen- 
tation of  the  needful  circumstances,  such  as  no  other  less  correct 
method  will  insure,  be  his  powers  of  generalization  what  they  may. 

As  in  many  lines  of  section,  all  the  various  accumulations  cannot  be 
so  traversed,  as  to  have  all  deposits  cut  at  right  angles  by  them,  care  is 
required  to  represent  only  the  relative  thickness  of  such  deposits  where 
the  section  passes  ;  that  is,  the  lines  of  separation  of  beds,  or  collections 
of  them,  as  given  in  the  section,  should  correspond  exactly  with  those 
which  would  appear  if  the  rocks  supposed  to  be  vertically  cut  through, 
were  really  so  ;  and  the  beds  on  one  side  of  the  cut  being  removed,  the 
face  of  the  other  was  exposed,  as  if  on  a  cliff.  By  turning  to  fig.  257 
(p.  601),  it  will  be  found  that  a  line  of  section  parallel  to  the  cliff  repre- 
sented would  even  give  the  beds  there  shown  as  horizontal,  while  they 
really  dipped  considerably  at  right  angles  to  it,  as  seen  in  the  sketch, 
fig.  258.  It  is  easy  in  such  cases  to  notice  the  true  amount  and  direc- 
tion of  the  beds  on  the  section,  and  thus  make  the  real  value  of  the 
lines  on  such  section  clear.  By  giving  more  dip  than  such  lines  repre- 
sent, a  greater  thickness  is  shown  than  really  exists,  and  the  total 
amount  of  mineral  matter  which  the  surface  of  the  ground  and  the  line 
of  section  should  exhibit,  is  misrepresented. 

In  addition  to  these  vertical  and  proportional  sections,  it  sometimes 
becomes  necessary  to  enlarge  a  part,  so  far  as  regards  a  column  rising 
vertically  to  the  plane  of  accumulations.  In  like  manner,  also,  this 
should  be  proportional,  and  on  a  scale  sufficient  to  render  the  object 

*  For  example,  the  section  from  the  Jura  to  and  across  the  Mont  Blanc,  above  given 
(fig.  264,  p.  611),  was  obtained  from  known  heights  of  different  points  on  the  line  by 
barometric  measurements  of  intermediate  altitudes,  and  a  sketching  of  the  ground  on 
the  spot. 


GEOLOGICAL    MAPS    AND    SECTIONS. 


679 


sought  by  the  enlargement  clear.  The  scale  of  such  sections  adopted 
by  the  Geological  Survey  is  that  of  40  feet  to  the  inch  ;  and  it  has  been 
found  one  amply  sufficient  for  very  considerable  detail,  as  may  be  seen 
by  reference  to  the  vertical  sections  of  the  coal  measures,  those  which 
can  be  used  for  mining  purposes  (sections  Nos.  1  to  11). 

Vertical  sections,  deposits  represented  as  piled  one  above  the  other 
horizontally,  whatever  may  be  their  real  inclinations  in  different  locali- 
ties, may  also  be  usefully  employed  for  comparing  distant  accumulations 
with  each  other,  especially  as  regards  their  thickness.  As,  for  exam- 
ple, the  following  section  (fig.  308),  serves  to  show  the  different  thick- 
nesses and  modifications  of  the  cretaceous  and  oolitic  groups  as  developed 
in  southern  and  northern  England.  In  these  sections  (the  same  letters 
being  employed  to  represent  equivalent  deposits  in  both),  the  cretaceous 
series  in  Wilts  and  Somerset  is  divided  into  chalk,  a ;  upper  green  sand, 

Fig.  308. 

WILTS   AND    SOMERSET.  YORKSHIRE. 

v.  t  ~'F=r^^rv^':^c;rs<f::?:: 


Cretaceous  Group. 


Oolitic  Group. 


Cretaceous  Group. 


Oolitic  Group. 


b ;  gault,  a  clay  bed  so  named,  c ;  and  d,  lower  green  sand ;  while  in 
the  same  series  in  Yorkshire,  b  and  d  are  supposed  to  be  absent.  As 
regards  the  oolitic  group,  e  represents  the  Kimmeridge  clay ;  /,  coral 
rag  and  its  calcareous  grits ;  </,  Oxford  clay  and  the  Kelloway  rock  in 
its  lower  part ;  h,  Cornbrash  and  forest  marble ;  i,  Bradford  clay ;  7c, 
great  oolite ;  I,  Fuller's  earth ;  m,  inferior  oolite ;  n,  marlstone ;  0, 
lias.  The  superficial  gravels,  &c.,  above  the  chalk,  are  represented  by 
t.  As  respects  the  divisions  e,  /,  and  g,  the  two  sections  do  not  much 
vary,  while  a  considerable  difference  is  seen  in  the  beds  A,  z,  &,  and  I, 
as  found  developed  in  southern  and  northern  England.  There  has 


680  ADDITIONAL    NOTICES. 

apparently  been  a  modification  of  the  conditions  under  which  these 
equivalent  portions  of  the  oolitic  series  were  deposited  in  the  two  locali- 
ties, so  that  while  in  the  south  marine  remains  point  merely  to  deposits 
beneath  the  waters  of  a  sea,  shales  and  sandstones  on  the  north  contain 
the  remains  of  terrestrial  fossil  plants  (p.  496) ;  thus  not  only  the  close 
proximity  of  land  has  to  be  inferred,  but  also  the  existence  of  marshy 
land  itself,  supporting  a  growth  of  certain  plants  (Equisetum\  entombed 
as  they  stood.  The  different  character  of  the  lias  on  the  north  and 
on  the  south  will  also  appear,  this  deposit  being  not  only  thicker  on  the 
north,  but  also  there  exhibiting  a  certain  depth  of  upper  lias  marls,  not 
continued  to  Wiltshire,  though  it  can  be  seen  gradually  fining  off 
southerly  into  Gloucestershire.  In  this  manner,  it  will  be  obvious  that 
much  useful  evidence  may  be  embodied ;  so  that,  by  the  combined  aid 
of  the  maps  and  the  sections  of  various  kinds,  a  sound  and  comprehen- 
sive view  of  the  different  rock  accumulations  of  a  country  may  be 
obtained. 

Page  34.  The  composition  of  the  various  felspars  will  be  better  seen, 
by  reference  to  p.  352. 

Page  36.  With  respect  to  the  decomposition,  by  atmospheric  influences, 
of  the  igneous  rocks  chiefly  composed  of  felspar  and  hornblende,  when 
the  former  mineral  prevails,  the  surfaces  of  these  rocks  has  usually  a 
white  aspect,  the  soluble  silicates  of  soda  or  potash  being  removed,  and 
a  crust  principally  formed  of  silicate  of  alumina  remaining.  Where 
hornblende  much  prevails,  a  brownish  and  reddish  surface  is  common, 
the  protoxide  of  iron  of  that  mineral  having  been  converted  into  a 
peroxide. 

Page  39.  As  regards  the  weathering  of  calcareous  rocks,  it  can  be 
seen  to  great  advantage  on  the  Lake  of  Killarney,  where  the  carboniferous 
f  limestone  partly  forming  the  shores  of  the  lake  and  of  its  islands,  is 
found  hollowed  into  fantastic  forms,  near  the  level  of  the  water.  The 
well-known  and  strangely-shaped  rock,  named  O'Donaghue's  Horse,  has 
been  thus  formed.  Carbonic  acid  in  the  water,  near  its  level,  has  acted 
upon  the  limestone  very  conspicuously  in  this  locality. 

Page  45.  Further  remarks  respecting  the  composition  of  sea-waiter 
will  be  found  at  p.  129.  With  respect  to  its  specific  gravity,  Sir  James 
Ross  (Voyage  of  Discovery  and  Research  in  the  Southern  and  Antarctic 
Regions)  mentions  that  in  lat.  39°  16'  S.  and  long.  177°  2'  W.  (there 
being  no  bottom  at  3600  feet),  the  specific  gravity  at  the  surface  was 
1-0274  ;  at  900  feet,  1-0272 ;  and  at  2700  feet,  1-0268,  all  ascertained 
at  a  temperature  of  60°  Fahrenheit.  He  further  states  that  his  daily 
experience  gave  this  diminished  kind  of  specific  gravity  in  the  depths. 
As  evaporation  would  tend  to  render  the  surface  waters  more  saline,  it 
may  be  deserving  of  attention  how  far  this  cause  may  operate  down- 


ADDITIONAL    NOTICES.  681 

wards  in  the  sea.     See  on  this  subject,  the  experiments  of  Dr.  Davy, 
mentioned  at  p.  121. 

Page  54.  The  cut  (fig.  15)  representing  the  slipping  downwards  of 
the  superficial  decomposed  portions  of  rocks  on  hillsides  in  many 
counties,  represents,  in  somewhat  too  stiff  a  manner,  the  turning  over 
of  the  edges  of  the  beds.  This  more  frequently  occurs  as  shown 
beneath  (fig.  309). 

Fig.  309. 


Page  75.  As  to  the  force  of  breakers  on  the  coasts  of  the  British 
Islands,  Mr.  Stevenson  has  found  by  experiments  at  the  Bell  Rock  and 
Skerry vore  lighthouses  (Proceedings  of  the  British  Association  for  the 
Advancement  of  Science,  Edinburgh,  1850),  that  while  the  force  of  the 
breakers  on  the  side  of  the  German  Ocean  may  be  taken  at  about  a  ton 
and  a  half  per  square  foot,  the  Atlantic  breakers  were  discharged  with 
about  double  that  force,  or  about  three  tons  to  the  square  foot. 

Page  91.  M.  Morlot  infers  that  the  land  round  the  head  of  the  Adri- 
atic is  gradually  sinking,  but  that  the  deposits  of  the  rivers  are  still 
sufficient  to  effect  a  general  gain  upon  the  shores  of  that  sea. 

Page  94.  With  respect  to  the. volcanic  matter  which  overwhelmed 
Herculaneum,  it  is  considered  that  it  was  formed  of  ash  and  cinders, 
like  that  which  covered  Pompeii,  and  not  of  lava. 

Page  103.  According  to  Mr.  Dana  (Geology  of  the  United  States 
Exploring  Expedition,  1838-42,  p.  26),  the  tides  rise  only  2  or  3  feet 
through  the  eastern  part  of  Polynesia ;  at  Samoa  4  feet ;  at  the  Eeejee 
Islands  6  feet ;  and  at  New  Zealand  8  feet. 

Page  135.  It  is  considered  that  it  is  rather  humic  acid  than  tannin 
which  preserves  the  animal  substances  in  bogs. 

Page  159.  As  regards  the  pressure  at  different  depths  of  the  sea, 
Dr.  Buckland  mentions  (Bridgewater  Treatise,  vol.  i.  p.  345),  that 
"  Captain  Smyth,  R.N.,  found,  on  two  trials,  that  the  cylindrical  copper 
air- tube,  under  the  vane,  attached  to  Massey's  Patent  Log,  collapsed, 
and  was  crushed  quite  flat  under  the  pressure  of  about  300  fathoms 
(1800  feet).  A  claret  bottle,  filled  with  air,  and  well  corked,  was  burst 
before  it  descended  400  fathoms  (2400  feet).  He  also  found  that  a 
bottle  filled  with  fresh  water,  and  corked,  had  the  cork  forced  in  at 
about  180  fathoms  (1080  feet).  In  such  cases  the  fluid  sent  down  is 
replaced  by  salt  water,  and  the  cork  which  had  been  forced  in  is  some- 
times reversed."  Dr.  Buckland  adds,  that  Sir  Francis  Beaufort  had 
informed  him  that  he  has  frequently  sunk  corked  bottles  in  the  sea  more 


682  ADDITIONAL    NOTICES. 

than  600  feet  deep,  some  of  them  empty,  others  containing  some  fluid. 
"  The  empty  bottles  were  sometimes  crushed,  at  other  times  the  cork 
was  forced  in,  and  the  fluid  exchanged  for  sea-water.  The  cork  was 
always  returned  to  the  neck  of  the  bottle,  sometimes,  but  not  always, 
in  an  inverted  position." 

Dr.  Scoresby  (Arctic  Regions,  vol.  ii.  p.  193)  gives  an  account  of  a 
boat  pulled  down  to  a  considerable  depth  by  a  whale,  after  which  the 
wood  became  too  heavy  to  float,  the  air  having  been  forced  out  of  the 
pores,  and  replaced  by  water. 

Page  180.  Currents  of  comparatively  low  temperature  sweep  from 
the  colder  and  southern  regions  against  the  continents  of  Africa  and 
America. 

Page  217.  With  reference  to  the  snow-line  on  the  northern  flank 
of  the  Himalaya,  Dr.  Hooker  states  (letter  to  Sir  William  Hooker,  from 
Tungu,  N.B.  Sikkim,  altitude  13,500  feet,  July  25,  1849),  that  "  the 
snow-line  in  Sikkim  lies  on  the  Indian  side  of  the  Himalayan  range,  at 
below  15,000  feet ;  on  the  Thibetan  (northern)  slope,  at  about  16,000 
feet." 

Page  218.  Experiments  do  not  seem  to  give  the  temperature  at  which 
the  evaporation  of  snow  or  water  ceases,  so  that  though  a  limit  may  be 
inferred  for  this  evaporation  at  some  height  to  which  parts  of  a  moun- 
tain chain  might  be  elevated,  it  may  readily  happen  that  there  are  none 
such  on  the  solid  face  of  the  globe,  the  vapour  of  water  always  mixing 
with  the  gases  of  the  atmosphere  up  to  all  the  heights  in  it  to  which 
the  parts  of  the  earth's  surface  have  been  protruded. 

Pag;e  224.  The  debris  on  mountain  sides  often  completely  masks 
their  character  as  left  anterior  to  such  coverings.  There  are  few  moun- 
tainous regions  which  do  not  show  this  when  carefully  examined. 
Mining  operations  often  prove  it  on  the  sides  of  hills.  Ravines,  where 
ravines  may  not  be  uncommon,  are  usually  favourable  for  observations 
on  this  head;  as,  for  example,  many  instances  are  to  be  found  in 
Derbyshire,  where  the  faces  of  steep  ground  are  often  modified  in  this 
manner,  the  long-continued  action  of  atmospheric  influences  having 
smoothed  off  many  a  precipitous  hillside,  where  the  same  effects  are  in 
daily  progress.  As  to  this  action,  it  has  greatly  modified  the  face  of 
most  countries,  old  cliffs  being  obliterated  in  various  directions,  in  the 
manner  shown,  figs.  156,  157,  (p.  442,)  especially  when  the  weather- 
ing of  the  protruding  rocks,  and  the  abundant  fall  of  fragments  of 
them,  are  combined  with  landslips,  such  as  take  place  as  well  inland 
as  on  certain  sea-coasts,  fig.  14,  p.  53. 

Page  242.  Any  outward  motion  of  the  great  ice  barrier,  however 
slow,  by  bringing  portions  of  it  forward  which  were  based  on  land  or 
shallow  sea-bottoms,  into  the  depths  where  its  base  could  be  melted, 
would  tend  also  to  keep  those  parts  flattened  which  otherwise  might 


ADDITIONAL    NOTICES.  683 

have  a  large  amount  of  snow  and  ice  accumulated  upon  them,  supposing 
such  accumulation  to  be  beyond  the  loss  by  melting  and  evaporation. 

Page  243.  The  cut,  fig.  93,  gives  the  floating  ice  a  form  somewhat 
too  regular. 

Page  406.  With  respect  to  the  boracic  acid  lagunes  of  Tuscany,  we 
would  refer  for  a  general  view  of  their  mode  of  occurrence  to  the 
memoir  by  Sir  Roderick  Murchison,  "  On  the  Vents  of  Hot  Vapour  in 
Tuscany,  and  their  Relations  to  Ancient  Lines  of  Fracture  and  Erup- 
tion ;"  Journal  of  the  Geological  Society  of  London,  vol.  vi.  p.  367. 

A  boracite  is  inferred  to  constitute  part  of  a  rock-salt  formation  at 
Strassfurth,  occurring  as  a  compact  bed.  Its  composition  is :  boracic 
acid  69-49 ;  magnesia  29*48 ;  carbonate  of  iron  1-03 ;  with  traces  of 
carbonate  of  manganese  and  hydrous  peroxide  of  iron. 

Page  445.  With  reference  to  the  raised  masses  of  blown  sands  in 
Cornwall,  Mr.  Edmonds  has  found  (Proceedings  of  the  Geological 
Society  of  Cornwall,  1848),  the  abundant  remains  of  Helix  pulcJiella  in 
those  sand-hills,  a  mollusc,  however,  formerly  abundant,  now  becoming 
extinct.  In  Phillack  Towans  (sand-hills)  the  remains  of  land  molluscs 
have  been  discovered,  not  now  known  near  them,  viz.,  Helix  fulva, 
Pupa  marginata,  Vertigo  palustris,  V.  pygmcea,  and  Zonites  pyg- 
mceus. 

Page  574.  As  sea,  or  rather  estuary  waters,  are  inferred  partly  to 
percolate  into  the  chalk  beneath  London,  supplying  the  place  of  the 
waters  pumped  up  from  it,  some  caution  is  needed  as  to  the  source  of 
all  the  chloride  of  sodium  in  the  chalk  so  situated. 

Page  577.  As  respects  the  alteration  of  detrital  rocks  in  contact 
with  mineral  matter  which  has  been  in  a  molten  state,  it  is  needful  to 
bear  in  mind  that  this  may  also  be  effected  should  detrital  accumula- 
tions cover  a  mass  of  igneous  rock  beneath  water  before  it  is  completely 
cooled,  so  that  even  a  comparatively  cooled  surface  may  again  be,  to 
a  certain  extent,  re-heated,  and  act  on  the  superjacent  sediment,  through 
which  the  heat  passing  off  from  the  igneous  rock  has  now  to  pass. 

Page  582.  The  change  of  the  great  mass  of  coal  in  South  Wales  and 
Ireland,  by  which,  without  reference  to  contortions  and  foldings  of  the 
beds,  the  anthracitic  state  is  produced  on  the  large  scale,  forcibly  re- 
minds us  of  a  modification  produced  by  descent  beneath  the  surface  of 
the  earth  to  conditions  where  a  high  temperature  is  obtained. 

Page  603.  Directions  of  Mountain  Ranges.— In  a  note  "  Sur  la 
Correlation  des  Directions  des  differents  Systemes  de  Montagnes," 
(Comptes  Rendus,  9  Septembre,  1850),  M.  Elie  de  Beaumont  calls 
attention  to  the  present  known  directions  of  mountains,  and  their  ad- 
justment to  a  pentagonal  network  formed  by  the  intersection  of  fifteen 
great  circles  of  the  sphere.  For  the  mode  of  investigation  on  which 
this  view  is  founded,  our  limits  compel  us  to  refer  to  the  memoir  itself. 


684  ADDITIONAL    NOTICES. 

M.  Elie  de  Beaumont  concludes  his  note  by  remarking  that  "  the  fifteen 
circles  which  divide  the  surface  of  the  sphere  into  twelve  regular  pen- 
tagons, possess  the  property  of  the  minimum  contour  of  the  system  of 
lines  of  most  easy  crushing  (plus  facile  ecrasement).  If  the  ridgings  of 
the  earth's  crust  were  simultaneously  produced,  these  fifteen  circles 
would,  perhaps,  be  alone  traced ;  but  as  the  production  of  the  different 
systems  of  mountains  has  been  successive,  the  octahedral,  dodecahedral, 
and  others,  have  probably  been  the  forms  necessarily  intermediate  in 
passing  from  one  to  the  other  of  the  fundamental  circles." 

Page  639.  Mines  of  Cornwall  and  Devon. — The  observer  will  find  a 
considerable  mass  of  important  information  respecting  these  mine's,  in 
Mr.  Kenwood's  work  on  the  Metalliferous  Deposits  of  Cornwall  and 
Devon ;  with  Appendices  on  Subterranean  Temperature,  the  Electricity 
of  Rocks  and  Veins,  the  Quantities  of  Water  in  the  Cornish  Mines, 
and  Mining  Statistics,  forming  vol.  v.  of  the  "  Transactions  of  the 
Royal  Geological  Society  of  Cornwall,"  Penzance,  1843. 

Page  284.  By  casting  a  glance  at  a  map  representing  the  range  of 
isothermal  lines  on  the  surface  of  the  earth,  it  will  be  seen  that  the 
temperature  of  the  area  of  the  British  Islands  would  be  materially 
lowered  by  the  comparatively  slight  geological  depression  of  the 
Isthmus  of  Panama,  which  should  permit  the  passage  of  the  waters  of 
the  Gulf  of  Mexico  into  the  Pacific,  thus  destroying  the  Gulf  Stream. 


INDEX. 


Aar  Glacier,  view  and  description  of,  225. 

Action,  elevatory,  recent,  at  the  Santorin 
Group,  384. 

Abich,  Dr.,  on  the  composition  of  volcanic 
tuffs  near  Naples,  363. 

Achafalaya  River,  raft  in  the,  136. 

Adjustment  of  ancient  marine  life  to  depths  of 
water  and  kinds  of  sea-bottom,  519. 

JEgean,  conditions  of  its  bed,  if  converted  into 
land,  165. 

Agassiz,  M.,  on  glaciers,  218,  272,  273. 

Age  of  rocks,  relative,  insufficient  of  itself  for 
mineral  character,  566. 

Air  in  sea-water,  161. 

Albite,  composition  of,  356. 

Alps,  detritus  of,  59 ;  glaciers  of,  218,  268 ; 
erratic  blocks  of,  276  ;  part  of,  including 
Mont  Blanc,  proportional  section  of,  611. 

Alteration  of  rocks,  from  descent  beneath 
earth's  surface,  572. 

Altered  rocks,  sulphuret  of  iron  in  certain, 
562;  formation  of  crystals  in,  577;  produc- 
tion of  certain  minerals1  in,  580;  mineral 
matter  transmitted  into,  581. 

Amazon  River,  sediment  of  the,  89. 

America,  form  of  its  coasts,  150 ;  volcanoes  of, 
392. 

Ammonites,  multitudes  of,  lias,  Marston 
Magna,  Somersetshire,  515. 

Ancient  volcanic  products,  organic  remains  in, 
514. 

Andalusite,  production  of,  in  altered  rocks, 
580. 

Anglesea,  igneous  dykes  of,  539. 

Animal  and  vegetable  life,  marine,  effects  of 
sinking  of  sea-bottom  upon,  519. 

Antarctic  ice  barrier,  240. 

Anticlinal  and  synclinal  lines,  609. 

Appalachian  zone,  United  States,  bending  and 
plication  of  rocks  in,  609. 

Arago,  M.,  on  temperature  found  at  the  Ar- 
tesian well,  Grenelle,  450. 

Arctic  Ocean,  coasts  of,  156 ;  glaciers  and  ice- 
bergs in,  233. 

Area,  extension  of,  required,  in  reducing  beds. 
in  mountain  chains,  to  horizontality,  607. 

Areas,  large,  of  undisturbed  rocks,  raised  in 
mass,  606. 

Argillo-calcareous  nodules,  lamination  of 
some,  567. 

Argillaceous  limestone,  concretionary  nodules 
and  layers  of,  567. 

Ari  Atoll,  190. 


Arrangement,  diagonal,  of  the  minor  parts  of 
detrital  rocks,  510. 

Artesian  wells,  temperature  of  waters  in,  450. 

Artificial  minerals,  method  of  producing  cer- 
tain, 550. 

Ascension,  Island  of,  laminated  volcanic  rocks 
in,  361. 

Ashes,  volcanic,  composition  of,  362. 

Ash-beds,  ancient  volcanic,  deceptive  charac- 
ter of,  after  consolidation,  529. 

Asia,  great  central  depression  of,  126 ;  form 
of  its  coasts,  152. 

Asiatic  volcanoes,  393. 

Atlantic  and  Pacific  Oceans,  effects  of  gradu- 
ally joining,  on  marine  animal  life,  518. 

Atlantic,  ancient  exposure  of  coasts  to,  665. 

Atmospheric  influences,  effects  of,  on  upper 
parts  of  mineral  veins,  650. 

Augite,  composition  of,  356. 

Austen,  Mr.  R.  C.,  on  distribution  of  detritus 
in  English  Channel,  446. 

Axmouth,  destruction  of  cliffs  at,  53. 


Babbage,  Mr.,  on  elevation  and  depression  of 
coasts,  of  Bay  of  Naples,  426 ;  on  move- 
ments of  land  from  increase  and  decrease  of 
its  heat,  427. 

Baku,  mud  volcanoes  or  salses  of,  403. 

Baltic,  deposits  in  the,  97;  analysis  of  its 
water,  98;  effects  of  ice  in,  253. 

Barrier  Reef  of  Australia,  193,  205. 

Basalt,  mineral  composition  of,  396 ;  relative 
fusibility  of,  396  ;  chemical  composition  of, 
396;  relative  antiquity  of,  397;  globular 
structure  of,  397 ;  columnar  structure  of, 
398. 

Beaches,  changes  of  relative  level  of,  on  tidal 
coasts  depressed  or  elevated,  439 ;  ancient, 
among  fossiliferous  rocks,  importance  of, 
459 ;  of  the  time  of  the  Silurian  rocks,  459 ; 
of  old  red  sandstone  period,  Scotland,  459  ; 
of  Chair  of  Kildare,  Ireland,  460;  of  new 
red  sandstone  time,  460. 

Beaufort,  Admiral  Sir  Francis,  on  inflamma- 
ble gas  of  the  Yanar,  402. 

Beaumont,  M.  Elie  de,  on  declivities  of  gla- 
ciers, 269;  on  the  direction  of  the  fissures 
of  Etna,  375  ;  on  Etna,  378  ;  on  origin  of 
the  Val  del  Bove,  381  ;  his  views  respect- 
ing directions  of  mountain  chains,  603 ;  on 
metalliferous  and  volcanic  emanations,  634  ; 
on  initial  volatilization  of  metallic  substances 


686 


INDEX. 


in  veins,  G35 ;  on  correlation  of  directions  of 
mountain  chains,  684. 

Becquerel,  M.,  on  partial  conversion  of  steel 
plate  into  silver,  Mint,  Paris,  654 ;  on  sub- 
stances produced  by  slow  secondary  electri- 
cal action,  636. 

Beechey,  Captain,  on  coral  islands,  186. 

Beds,  formed  around  volcanic  islands,  charac- 
ter of,  383 ;  formed  by  unequal  drift,  511. 

Beds  of  rocks,  different  consolidations  of,  in 
same  group,  574. 

Belcher,  Sir  E.,  on  the  movement  of  a  current 
at  40  fathoms,  507. 

Belemnites,  multitudes  of,  lias,  Golden  Cope, 
near  Lyme  Regis,  515. 

Bending,  contortion,  and  fracture  of  rocks,  599. 

Bending  and  plication  of  rocks,  artificial  illus- 
tration of,  608. 

Bermudas,  coral  reefs  at,  210. 

Binney,  Mr.,  on  Stigmaria,  482. 

Birds,  preservation  of  their  remains,  140 ;  foot- 
prints of,  on  surfaces  of  rock,  Connecticut, 
502. 

Bischoff,  M.  Gustav,  experiments  illustrative 
of  deposit  of  mineral  matter  in  fissures,  631. 

Black  Sea,  deposits  in  the,  97. 

Boring    molluscs,    carboniferous    limestone 

Eierced  by,  at  time  of  inferior  oolite,  468 ; 
as  conglomerate  drilled  by,  469 ;  inferior 
oolite  pierced  by,  during  accumulation,  470. 

Breakers,  force  of,  74,  80;  action  of,  on  vol- 
canic products,  St.  Paul's  Island,  Indian 
Ocean,  391 ;  force  of,  in  Scotland,  on  side 
of  German  Ocean,  and  of  Atlantic,  682. 

Breaker  action,  great  denudation  from,  665. 

Brewer's  Hill,  County  Wicklow,  complication 
of  bedding,  cleavage,  and  jointing  near,  599. 

Bridgend,  Glamorganshire,  quartz  rock,  in 
trias  near,  575. 

Bristol  Channel,  deposits  in,  108,  111,  148; 
beaches  of  time  of  new  red  sandstone  near, 
461, 464 ;  mode  of  accumulation  of  dolomitic 
limestone  near,  479 ;  footprints  of  animals 
on  muddy  shores  of,  504. 

Bristol,  amount  of  denudation  near,  672. 

Britain,  climate  formerly  colder,  282 ;  tertiary 
mammalia  in,  294. 

British  Islands,  map  of  the  100  fathom  line 
round,  114;  map  of,  when  depressed  1000 
feet,  265 ;  effects  of  submergence  on,  266  ; 
older  igneous  products  of,  528;  effects  of 
squeezing  and  elevation  of,  into  great  range 
of  mountains,  605. 

British  Seas,  distribution  of  marine  life  in,  168 ; 
mammoth  remains  found  in,  294. 

Bogs,  how  formed,  133. 

Bombs,  volcanic,  330. 

Boracic  acid,  of  Tuscany,  406. 

Bath,  springs  of,  49. 

Boutigny,  M.,  experiments  on  incandescent 
bodies,  338. 

Bourbon,  Isle  of,  coral  reefs  near,  192. 

Bow  Island,  account  of,  187. 

Brighton,  raised  beach  near,  445. 

Brongniart,  M.  Alex.,  on  raised  coast  of  Ud- 
devalla,  430. 

Brown,  Mr.  Richard,  on  vertical  plants  in  coal 
measures,  Cape  Breton,  487. 

Buckland,  Dr.,  on  glaciers  in  Scotland,  273; 
on  the  fossil  elephant,  292;  on  Kirkdale 
Cave,  298;  on  osseous  breccia,  310;  on 
fossil  trees  and  ancient  soils  of  Isle  of  Port- 


land, 497;  on  mammal  remains,  oolitic  series, 
Stonesfield,  525. 

Buckland,  Dr.?  and  Mr.  VV.  D.  Conybeare,  on 
submarine  forest,  Bridgewater  Levels,  435. 

Buddie,  Mr.,  on  erosion  of  coal  beds,  Forest 
of  Dean,  492. 

Bunsen,  Professor,  on  the  composition  of  pa- 
lagonite  tuff  of  Iceland,  364 ;  on  action  of 
water  and  acids  on  palagonite  tuff,  366  ;  on 
the  mode  of  action  of  the  Geysers,  Iceland, 
367 ;  on  gypsum  deposits  of  Iceland,  372 ; 
on  volcanic  sublimations  of  muriate  of  am- 
monia, 372. 

Bwlchhela,  near  Penrhyn  Quarries,  North 
Wales,  cleavage  through  contorted  sand- 
stones at,  587. 

Caiman  of  West  Indies,  139. 

Caldera,  the,  Island  of  Palma,  Canaries,  378. 

Cambrian  rocks,  conglomerates  of,  Bangor, 
North  Wales,  459. 

Carbonic  acid,  action  of,  on  certain  silicates, 
576. 

Carburetted  hydrogen,  exhalations  of,  402. 

Cardigan  Bay,  map  of,  106  ;  tides  in,  107. 

Carglaze  Tin  Mine,  Cornwall,  stanniferous 
veins  amid  joints  in  granite  of,  647. 

Carne,  Mr.,  on  character  of  rocks  in  Corn- 
wall, affecting  contents  of  mineral  veins, 
641. 

Carnon  tin-stream  works,  human  skulls  found 
in,  436. 

Caspian  Sea,  nature  of  its  waters,  98,  127; 
deposits  in,  124. 

Caves  and  minor  cavities,  metalliferous,  of 
Derbyshire,  592. 

Cavities,  circular,  produced  during  earth- 
quakes, 416 ;  amid  rocks,  action,  and  reac- 
tion of  substances  in,  637. 

Cawsand,  Plymouth  Sound,  porphyry  of,  543. 

Central  Asia,  volcanoes  of,  393. 

Central  France,  extinct  volcanoes  of,  394. 

Cetaceans,  remains  of,  149. 

Chair  of  Kildare,  hills  of,  range  of  cleavage, 
diagonally  through  beds  of,  587. 

Chalk,  composition  of  water  of,  beneath  Lon- 
don, 573;  altered  by  basalt,  Isle  of  Raghlin, 
578. 

Channels,  eroded  in  coal  measures,  Forest  of 
Dean,  492;  of  erosion  in  coal  measure  de- 
trital  deposits,  Pembrokeshire,  493. 

Character  of  surfaces  of  rocks,  505. 

Charlestown  and  Crinnis  Mines,  Cornwall, 
range  of  mineral  veins  at,  620. 

Chesil  Bank,  Dorsetshire,  84. 

Chiastolite,  formation  of,  in  altered  rocks, 
580. 

Chili,  elevation  of  coast  of,  during  earth- 
quakes, 423 ;  extent  of  great  earthquake  at, 
408. 

Chloride  of  sodium,  dissemination  of,  amid 
rocks,  574. 

Clarke,  Rev.  W.  B.,  on  Lafu  Island,  207. 

Cleavage,  influence  of,  on  the  decomposition 
of  rocks,  40. 

Cleavage,  583;  in  mixed  beds  of  sandstone 
and  argillaceous  matter,  584  ;  in  limestone 
and  shale,  585 ;  modification  of,  in  passing 
through  thin  beds  of  limestone  amid  shale, 
585  ;  minor  interruption  of,  passing  junction 
of  beds,  585;  on  the  large  scale,  586; 
through  contorted  beds,  587 ;  ranging  dia- 


INDEX. 


68T 


gonally  through  bedding,  587;  double,  588 ; 
relative  dates  of,  588  ;  distortion  of  organic 
remains  by,  590;  different  directions  of,  in 
same  or  juxtaposed  districts,  591;  gathering 
of  mineral  matter  in  planes  of,  592. 

Cleaved  and  jointed  rocks,  subsequent  move- 
ment of,  597. 

Cliffs,  effects  of  the  sea  on,  76. 

Clyde,  newer  pliocene  deposits  of  the,  283. 

Coal  beds,  extent  of,  491;  partial  removal  of, 
during  coal  measure  deposit,  492 ;  effects  of 
squeezing  upon,  Pembrokeshire,  613. 

Coal  measures,  evidence  afforded  by,  482; 
stigmaria  beds  of,  482 ;  vertical  stems  of 
plants  in,  483 ;  mode  of  filling  up  hollow 
vertical  stems  of,  484 ;  growth  of  terrestrial 
plants  in  successive  planes  in,  486;  thick- 
ness of,  482 ;  false  bedding  in  sandstones  of, 
489 ;  surfaces  of  sandstones  of,  489  ;  drifts 
of  matted  plants  in,  490 ;  extent  of  coal  beds 
in,  491 ;  partial  removal  of  coal  beds  of, 
during  general  deposit,  492;  lapse  of  time 
during  accumulation  of,  493 ;  pebbles  of  coal 
in,  494 ;  marine  remains  in  parts  of,  495 ; 
mode  of  deposit  of,  496  ;  flexures  and  plica- 
tions of,  in  South  Wales,  612. 

Coal,  pebbles  of,  in  coal-measure  accumula- 
tions, 494. 

Coasts,  action  of  sea  on,  74;  influence  on  or- 
ganic life  and  preservation  of  remains,  150, 
175  ;  distribution  of  animals  on,  170;  effects 
of  ice  on,  251. 

Coasts,  rivers,  and  lakes,  effects  on,  during 
continued  elevation  of  land  above  sea,  472. 

Cold,  effects  of  its  general  increase,  257,  268. 

Colenso,  Mr.,  on  beds  composing  Pentuan 
tin-stream  works,  Cornwall,  437. 

Colours  and  signs,  advantage  of  mixture  of,  in 
geological  maps,  677. 

Compact  felspar,  character  and  composition 
of,  545. 

Complication  of  surface,  produced  by  smooth- 
ing down  single  dislocation,  under  certain 
conditions,  619. 

Component  parts  of  rocks,  consolidation  and 
adjustment  of,  565. 

Component  parts  of  beds,  flexures,  and  plica- 
tions of,  612. 

Composition  of  the  volcanic  tuffs  near  Naples, 
363. 

Conglomerates  and  volcanic  tuffs,  mixed  beds 
of,  with  lava,  in  Pacific  islands,  383. 

Conglomerates,  joints  in,  596. 

Cooling  globe,  effects  of,  on  rocks  on  surface, 
602. 

Corals,  in  British  seas,  169;  general  distribu- 
tion of,  179;  migrations  of,  when  young, 
181 ;  chemical  composition  of,  181 ;  condi- 
tions of  growth,  204. 

Coral  reefs,  formation  of,  182;  conditions 
under  which  they  occur,  199;  influence  of 
volcanoes  on,  202,  215 ;  elevation  of,  above 
the  sea,  207.  ' 

Cordier,  M.,  on  mode  of  obtaining  tempera- 
ture of  the  earth,  450. 

Cornwall,  action  of  the  sea  on  coasts  of,  83; 
sand-hills  on  coasts  of,  88 ;  joints  among 
granite  in,  593  ;  fragmentary  lodes  in,  656. 

Cornwall  and  Devon,  granites  of,  537;  influ- 
ence of  dissimilar  rocks  on  mineral  veins 
in,  641. 

Correa  de  Serra,  Mr.,  on  submarine  forests, 
Lincolnshire,  435. 


Cotopaxi,  structure  of  its  cone,  330,  331;  de- 
scent of  water  from,  347. 

Covering,  slight,  above  granites,  in  Wicklow, 
Wexford,  and  Cornwall,  552. 

Cracked  surfaces  of  deposits,  501. 

Crag  deposits,  315. 

Crantock  Church,  Cornwall,  built  of  consoli- 
dated shell-sand,  443. 

Craters  of  elevation,  318;  eruption,  319. 

Crater  lagoons,  volcanic  islands,  390. 

Cretaceous  rocks,  overlap  of,  in  England,  500. 

Crust  of  the  earth,  proportion  of  100  miles 
deep  of,  to  volume  of  world,  600. 

Crystalline  modification  of  rocks,  518. 

Currents  in  the  Mediterranean,  96  ;  the  ocean, 
116  ;  influence  of,  in  distributing  sediment, 
121. 

Cwm  :Llech,  Glamorganshire,  vertical  stems 
of  plants  in  coal  measures  of,  482. 

Cwm-ddu,  Llangammarch,  concretionary  ar- 
rangement of  beds  of  Silurian  series  near, 
570. 

Cwm  Idwal,  Caernarvonshire,  distortion  of 
organic  remains,  by  cleavage  at,  589. 

Cyanite,  formation  of,  in  altered  rocks,  581. 

Dana,  Mr.  J.,  on  corals,  181;  on  volcanoes  ot 
Hawaii,  332  ;  on  volcanic  islands  in  the  Pa- 
cific, 383  ;  on  volcanic  fissures  of  the  Ha- 
waiian Islands,  375. 

Dardanelles,  effect  of  closing  the  Straits  of 
Gibraltar  upon,  474. 

Darwin,  Mr.  C.,  on  coral  islands,  182 ;  on  ele- 
vation of  coral  reefs,  212 ;  on  glaciers  in 
Wales,  274 ;  on  elevation  of  erratic  blocks, 
275 ;  on  the  lamination  of  volcanic  rocks, 
360 ;  on  volcanic  tuff  of  Chatham  Island, 
364. 

Daubeny,  Dr.,  on  globules  and  lamination  of 
Lipari  obsidian,  361  ;  on  the  gas  evolved 
from  the  Solfatara,  Puzzuoli,  367;  on  nitro- 
gen of  volcanoes,  371 ;  on  Santprin  group, 
385,  386;  on  mud  volcanoes  of  Maculaba, 
404. 

Dean,  Forest  of,  removal  of  coal  beds  at,  time 
of  coal-measure  deposit  in,  492. 

Decomposition  of  rocks,  33. 

Dear,  footprints  of,  around  trees  of  sunk 
forests,  South  Wales,  438. 

Deltas  in  pools  of  water,  55  ;  in  lakes,  72  ;  in 
tideless  seas,  89;  in  tidal  seas,  108;  preser- 
vation of  organic  remains  in,  137,  145,  146. 

Delta  lands,  effects  of  gradual  subsidence  of, 
on  vegetation,  496. 

Denudation,  effects  of,  on  surface,  after  dislo- 
cation of  various  rocks  and  mineral  veins, 
619 ;  or  partial  removal  of  rocks,  664 ; 
island  masses  of  rock  left  by,  668 ;  contorted 
rocks  worn  down  by,  669  ;  exposure  of  old 
rock-surfaces  by,  670 ;  amount  of  matter  re- 
moved by,  672  ;  in  South  Wales,  and  adja- 
cent English  counties,  amount  of,  672. 

Densities,  relative  mean,  of  surface  and  mass 
of  earth,  635. 

Derbyshire,  igneous  rocks  associated  with 
carboniferous  limestone  of,  533 ;  mineral 
veins  amid  limestones  and  igneous  rocks  of, 
642 ;  various  modes  of  occurrence  of  mineral 
veins  in,  644;  debris  on  hillsides  of,  683. 

Detrital  deposits,  variable  consolidation  of, 
574. 

De  Verneuil,  M.,  on  mud  volcanoes  of  Taman 
and  Eastern  Crimea,  404. 


688 


INDEX. 


Devonshire,  action  of  the  sea  on  its  coasts, 
82. 

Devon  and  Cornwall,  ancient  igneous  pro- 
ducts in,  532. 

Devonian  rocks,  contemporaneous  igneous 
products  in,  532. 

Diagonal  arrangement  of  the  minor  parts  of 
beds  among  detrital  rocks,  510. 

Diallage  rock  of  Cornwall,  554. 

Diatomaceae,  distribution  of,  245. 

Different  rocks,  influence  of,  on  mineral  veins, 
641. 

Dip  of  beds,  fallacious  appearances  respecting, 
602. 

Distribution  of  animal  and  vegetable  life  at 
different  geological  times,  517. 

Dukhun,  great  area  of  basalt  in,  397. 

Dismal  Swamp,  135. 

Deposits,  siliceous,  from  the  Geysers,  Iceland, 
369. 

Detrital  and  fossiliferous  rocks,  mode  of  accu- 
mulation of,  455 ;  chiefly  old  sea-bottoms, 
456 ;  diagonal  arrangement  of  minor  parts 
of,  510. 

Detritus,  of  the  Alps,  60;  with  remains  of 
molluscs,  282  ;  transport  of,  by  rivers,  59  ; 
by  tides,  102,  113  ;  by  currents,  121 ;  by 
icebergs,  238,  244 ;  by  river-ice,  249;  drift 
of,  from  shallow  to  deep  sea-bottoms,  510. 

Dolerite,  composition  of,  349. 

Dolomitic  limestone,  mode  of  deposit  of,  near 
Bristol,  479. 

Dome-shaped  igneous  matter,  raising  and 
splitting  of,  378.  • 

Dorsetshire,  action  of  the  sea  on  coasts  of,  84. 

Dranse,  temporary  lake  and  floods  of,  70. 

Drawing,  military,  advantage  of,  C75. 

Drifted  organic  remains,  513. 

Drifts  of  matted  plants  in  coal  measures,  490. 

Dry  land,  in  great  part  bottoms  of  ancient 
seas  and  lakes,  456 ;  present,  variable  effects 
of  submergence  of,  480. 

Dubois  de  Montpereux,  M.,  on  mud  volcanoes 
of  Taman,403. 

Dufrenoy,  M.,  on  composition  of  volcanic 
ashes,  362 ;  on  the  composition  of  volcanic 
tuffs,  363  ;  on  fossiliferous  volcanic  tuff  of 
Monte  Somma,  382 ;  on  structure  of  vol- 
canic tuff,  near  Naples,  382 ;  on  origin  of 
Monte  Somma,  383. 

Duncan,  Dr.,  on  footprints  of  animals  on  sur- 
faces of  rocks,  Corn  Cockle  Muir,  Dum- 
friesshire, 501. 

Dunraven  Castle,  South  Wales,  mode  of  oc- 
currence of  lias  at,  466. 

Dykes  of  lava,  Val  del  Bove,  Etna,  373. 

Dykes  amid  conglomerates  of  ancient  igneous 
rocks,  530. 

Dykes,  igneous,  uncertain  date  of  many,  538. 

Earthquakes,  406;  connexion  of,  with  vol- 
canoes, 407 ;  areas  disturbed  by,  408 ;  trans- 
mission of  vibrations  of,  408;  earth-waves 
of,  410;  sea-waves  of,  410;  unequal  trans- 
mission of,  413;  local  interruptions  of,  413; 
locally  extended  range  of,  414 ;  effects  of,  on 
lakes  and  rivers,  419;  sounds  accompany- 
ing, 420;  fissures  produced  during,  416; 
settlement  of  unconsolidated  beds  during, 
416 ;  circular  cavities  produced  during,  416 ; 
elevation  and  depression  of  land  during,  421; 
action  of,  on  sea-bottoms,  508. 

Earth's  surface,  unstable  state  of,  431. 


Earth,  temperature  of,  548. 

Earth- wave,  of  earthquakes,  410. 

Ebelmen,  M.,  method  of  producing  artificial 
minerals  by,  550. 

Effects  of  earthquakes  on  sea-bottoms,  508. 

Effects  of  gradual  subsidence  of  delta  lands 
on  vegetation,  495. 

Effects  of  sea-bottom  being  raised  round  Bri- 
tish Islands,  499. 

Egerton,  Sir  P.,  on  the  ossiferous  caves  of  the 
Hartz,  304. 

Ehrenberg,  Prof.,  on  coral  reefs,  198  ;  on  infu- 
sorial remains  in  rocks,  524. 

Elephant,  fossil,  notice  of,  286,  292,  295,  313. 

Elevation  and  depression  of  bottom  in  the 
ocean, 504. 

Elevation  of  land,  present,  gradual  in  Norway 
and  Sweden,  428. 

Elevations  of  mountain  chains,  602. 

Elvans  of  Cornwall  and  Devon,  mode  of  de- 
composition of,  36 ;  range  of,  540 ;  composi- 
tion of,  540 ;  dates  of,  542 ;  of  Wicklow  and 
Wexford,  543;  character  of  mineral  veins 
traversing,  in  Cornwall,  639. 

Elvan  dyke,  fallacious  appearance  of,  travers- 
ing mineral  veins,  621. 

Emanations,  metalliferous  and  volcanic,  634. 

England,  former  connexion  of,  with  the  Conti- 
nent, 291,  294. 

English  Channel,  tides  in  the,  104;  analysis 
of  water  of,  130;  distribution  of  detritus  in, 
446. 

Erie,  Lake,  draining  of,  68. 

Erratic  blocks,  origin  of  260 ;  transportal  of,  by 
glaciers,  272;  ot  the  Alps,  276 ;  of  northern 
Europe,  278;  of  America,  279. 

Erroob  Island,  coral  reefs  with  lava,  215. 

Eschscholtz  Bay,  elephant  remains  at,  292. 

Etna,  eruptions  from,  341,347;  direction  of 
fissures  at,  376;  form  and  structure  of,  381. 

Europe,  form  of  its  coasts,  156;  effects  of  sub- 
mergence on,  268. 270 ;  changes  of  land  and 
sea  in,  289 ;  mammoth  remains  in,  297. 

Extent  of  coal  beds,  491. 

Extinct  volcanoes,  394. 

Exeter,  igneous  rocks  near,  542. 

False  bedding  in  coal  measure  sandstones, 
489. 

Faraday,  Dr.,  on  the  liquidity  of  gases  under 
pressure,  377. 

Faults,  temperature  of  water  rising  through, 
451;  well  seen  usually  in  mining  districts, 
614;  of  different  dates,  616;  of  Somerset- 
shire, in  coal  measures,  and  inferior  rocks, 
smoothed  off  before  deposit  of  new  red 
sandstone,  616 ;  caution  respecting  the  shift- 
ing of  one  by  another,  618;  considerable, 
shifting  rocks  and  mineral  veins,  near  Red- 
ruth,  Cornwall,  618  ;  fallacious  appearances 
arising  from,  620 ;  different  traversing,  621 ; 
range  of,  in  Cornwall  and  Devon,  (523  ;  in- 
laying mass  of  coal  measures,  Norton  and 
Newgale,  Pembrokeshire,  622;  in  Somer- 
set and  Dorsetshire,  624;  near  Swansea, 
625 ;  inclination  of,  626 ;  parts  of  deposits 
preserved  by,  627 ;  complicated,  627. 

Fawnog,  Flintshire,  remarkable  "  flat"  of 
lead  ore  at,  645. 

Felspars,  chemical  compositions  of  various, 
table  of,  352. 

Felspar  crystals,  amid  altered  stratified  rocks, 
577. 


INDEX. 


689 


Fingal's  Cave,  basalt  of,  400. 

Fish  ejected  from  volcanoes,  346;  fossil,  oc- 
curring as  if  suddenly  destroyed,  514. 

Fissures,  in  volcanoes,  filled  by  molten  lava, 
373;  earthquake,  flame,  and  vapours  from, 
420 ;  through  rocks,  production  and  direc- 
tions of,  614 ;  in  rocks,  split  at  their  ends, 
621;  effects,  amid  mixed  rocks,  of  lines  of 
least  resistance  to,  621;  filling  of,  with 
mineral  matter,  628 ;  filling  of  minor,  630 ; 
deposits  from  solutions  in,  633  ;  opened  be- 
neath seas,  634 ;  character  of  substances 
filling,  635;  action  and  reaction  of  sub- 
stances in,  636 ;  coating  of  walls  of,  by 
mineral  matter,  655;  coated  by  dissimilar 
substances,  657;  several  successive  move- 
ments in  the  same,  657;  sliding  of  sides  of, 
on  mineral  matter  accumulated  at  intervals, 
658  ;  fractures  through  contents  of,  661. 

Fitton,  Dr.,  on  earthy  (ancient  soil)  bed,  Vale 
of  Wardour  and  Boulonnais,  497;  on  fossil 
shells  in  the  position  in  which  their  animals 
lived,  513. 

Fitzroy,  Capt.,  R.N.,  on  effects  of  earthquake 
on  coasts  of  Chili,  423. 

Flames  from  volcanoes,  323. 

Floods,  geological  effects  of,  57. 

Footprints  of  air-breathing  animals  on  the 
surfaces  of  rocks,  502 ;  on  mud  and  sand, 
146. 

Forbes,  Prof.  E.,  on  the  distribution  of  marine 
animals  in  the  JEgean  sea,  162 ;  on  zones  of 
depth  in,  162;  in  British  seas,  168;  on  the 
origin  of  the  British  flora,  284;  on  Santorin 
Group,  388  ;  on  movements  of  coast,  Bay  of 
Macri,  430 ;  on  shells  in  raised  beaches  of 
the  Clyde,  445 ;  on  fossils  of  Longmynd  dis- 
trict, 459  ;  on  conditions  of  Portland  and 
Purbeck  deposits,  497. 

Forbes,  Prof.  James,  on  glaciers,  219,  223  ; 
measurements  of  the  motion  of  glaciers,  228 ; 
on  glaciers  in  Skye,  273. 

Forchhammer,  Prof.,  on  the  salts  in  sea- 
water,  129;  on  the  effects  of  ice  in  the  Bal- 
tic, 253 ;  on  solubility  of  part  of  matter  of 
felspars,  632. 

Forest  marble,  diagonal  arrangement  of  or- 
ganic remains  of,  513. 

Fossil  trees  and  ancient  soils,  Island  of  Port- 
land, 497. 

Fractures,  considerable,  of  beds,  amid  plicated 
rocks  of  mountain  chains,  608. 

Fresh- water  deposits,  evidence  of  land  from, 
471. 

Friction-marks  on  rock  surfaces,  506. 

Frome,  Somersetshire,  mode  of  occurrence  of 
inferior  oolite,  near,  469 ;  forest-marble  of, 
513. 

Fontainebleau,  crystallized  sandstone  of,  583. 

Fournet,  M.,  on  character  of  rocks  affecting 
mineral  veins,  641. 

Fox,  Mr.  Robert  Were,  on  electro-magnetic 
properties  of  mineral  veins,  637 ;  experi- 
ments illustrative  of  cleavage,  590. 

Fundy,  Bay  of,  footprints  of  animals  on 
muddy  shores  of,  503. 

Fusibility  of  rocks,  to  be  viewed  with  refer- 
ence to  complete  mixture  of  their  component 
parts,  561. 

Gambier's  Island,  189. 

Ganges,  bore-wave  in  the,  103 ;  Delta  of  the, 
109. 


Garnets,  in  altered  sandstone,  581;  production 
of,  in  altered  rocks,  581;  composition  of,  581. 

Gases,  certain,  liquid  under  different  pres- 
sures, 377. 

Geneva,  Lake  of,  soundings  in,  71;  deposits 
^in,  73. 

Geological  maps  and  sections,  675. 

Geysers  of  Iceland,  46 ;  situation  of,  368 ; 
mode  of  action,  368  ;  mineral  contents,  369. 

Giant's  Causeway,  jointed  columnar  structure 
of  basalt  at,  400. 

Glaciers,  in  the  Alps,  218 ;  motion  of,  222,  227; 
transport  of  boulders  by,  228 ;  rocks  grooved 
by,  229;  advance  and  retreat  of,  222,  231; 
supposed  extension  of,  269 ;  table  of  their 
declivities,  269  ;  in  Himalaya,  233  ;  in  the 
Arctic  regions,  233 ;  in  the  Antarctic  regions, 
239  ;  in  South  Georgia,  246  ;  in  the  British 
Islands,  273. 

Glamorganshire,  thickness  of  coal  measures 
of,  488. 

Glydyr  Vawr,  false  and  irregular  beds  in,  511. 

Gneiss,  production  of  certain  kinds  of,  582. 

Godolphin  Bridge,  Cornwall,  lode  of,  659. 

Graham  Island,  formation  of,  95. 

Granite,  mode  of  decomposition,  34,  37;  rela- 
tive date  of,  in  Wicklow  and  Wexford,  an- 
terior to  old  red  sandstone,  537;  in  Cornwall 
and  Devon,  posterior  to  the  coal  measures, 
537 ;  mode  of  occurrence  of,  in  Southwest 
England  and  Southeast  Ireland,  546 ;  veins 
of,  548 ;  schorlacequs,  of  Cornwall  and  De- 
von, 550  ;  porphyritic,  552  ;  minerals,  addi- 
tional to  those  in  ordinary,  563  ;  general 
resemblance  of,  in  different  regions,  558; 
chemical  difference  of,  from  hornblendic 
rocks,  558;  prevalence  of  silica  and  alumina 
in,  559 ;  of  comparatively  recent  date  in 
Catalonia,  560 ;  columnar  appearance  of, 
from  joints,  594  ;  masses  of,  exposed  by  de- 
nudation amid  disturbed  rocks,  611. 

Granitic  rocks,  chemical  composition  of,  549; 
alterations  of  rocks  near,  579. 

Graves,  Captain,  R.  N.,  survey  of  Santorin 
Groups  386. 

Great  circles  of  comparison,  for  directions  of 
mountain  chains,  604. 

Great  Crinnis  Lode,  Cornwall,  change  of 
character  of,  in  range  of,  649. 

Greenland,  glaciers  in,  234,  235;  gradual  de- 
pression of  land  at,  430. 

Greenstone, composition  and  character  of,  557. 

Crenelle,  near  Paris,  temperature  found  at 
Artesian  well  of,  450. 

Ground,  gradual  submergence  of,  during  de- 
posit of  coal  measures,  485. 

Ground-ice,  formation  of,  249. 

Gypsum,  deposits  of,  Iceland,  371. 

Gwennap,  Cornwall,  range  of  elvans,  lodes 
and  cross  courses  in,  540. 

Habits,  probable,  of  animals,  regarded  with 

reference  to  distribution  of  organic  remains,  • 

523. 
Hausman,  M.,  on  change  of  sulphuret  into 

carbonate  of  lead,  in  mineral  veins,  652. 
Hawaii,  volcanoes  of,  332. 
Heat,  alteration  of  rocks  on  minor  scale  by,  577. 
Hecla,  eruptions  of,  342. 
Henry,  Mr.,  on  deposits  of  silica,  from  silicate 

of  soda,  576. 
Henwood,  Mr.,  on  mines  of  Cornwall  and 

Devon,  685. 


690 


INDEX. 


Hillsborough,  Ilfracombe,  North  Devon, 
cleavage  near,  585. 

Hitchcock,  Prof.,  on  footprints  of  birds  in  red 
sandstone  series,  Connecticut,  502. 

Hohnbaum,  Dr.,  on  footprints  of  animals  on 
surfaces  of  rocks,  501. 

Holyhead  Mountain,  Anglesea,  cleavage 
through  quartz  rock  at,  587. 

Homogeneity,  effects  of  want  of,  among  rock 
accumulations,  upon  production  of  fissures, 
616. 

Hooker,  Dr.,  on  height  of  snow-line,  north 
and  south  sides  of  Himalaya,  683. 

Hopkins,  Mr.  William,  on  production  and 
direction  of  fissures,  614. 

Horizontal  deposits,  upon  contorted  rocks, 
caution  respecting,  601. 

Hornblende,  chemical  composition  of,  35. 

Hornblendic  rocks,  chief  chemical  differences 
of,  from  granite,  559;  slate,  produced  by 
alteration  of  hornblendic  ash  beds,  580. 

Homer,  Mr.,  on  submarine  forest  of  Bridge- 
water  Levels,  435. 

Humboldt,  Alex.,  von,  on  the  snow-line,  218 ; 
on  mud  volcanoes,  403 :  on  local  interrup- 
tions of  earthquakes,  403 ;  on  earthquakes 
traversing  mountain  chains,  415 ;  on  sounds 
accompanying  earthquakes,  420. 

Hunt,  Mr.  Robert,  experiments  illustrative  of 
cleavage,  591. 

Hyena  bones  in  caves,  299. 

Hypersthene  rock,  Cocks  Tor,  Dartmoor,  580. 


Icebergs,  range  towards  the  equator,  236, 238, 
244;  formation  of,  237;  geological  effects 
of,  238,  243,  253. 

Ice,  influence  of,  in  transporting  mineral  mat- 
ter, 216,  248,  250,  254  ;  effects  on  sea  coasts, 
252 ;  of  glaciers,  structure  of,  220. 

Iceland,  submarine  eruptions  near,  123;  erup- 
tions of  volcanoes,  341 ;  composition  of  pa- 
lagonite  tuff  of,  364  ;  geysers  of,  368. 

Igneous  matter,  flow  of,  Irom  submarine  vents, 

(UMM 

37/.  » 

Igneous  products,  more  ancient  than  modern 
volcanic,  526 ;  simple  substances  composing, 
527;  fossils  amid  older,  in  British  Islands, 
529. 

Igneous  rocks,  ancient,  range  of,  in  counties 
Waterford,  Wexford,  and  Wicklow,  531 ; 
of  Derbyshire,  mode  of  occurrence  of,  533; 
structure  of,  535;  range  of,  from  Scilly 
Islands  towards  Tiverton  and  Exeter,  542  ; 
chemical  composition  of  ancient,  544  ;  gene- 
ral resemblance  of,  in  various  parts  of  the 
world,  557;  matter  added  to,  by  melting  of 
parts  of  other  rocks,  564  ;  general  remarks 
respecting,  565;  readjustment  of  parts  of 
altered,  580 ;  modifications  of,  from  percola- 
tions of  solutions,  562. 

Icthyosaurus,  preservation  of  skeletons  of,  516. 

Ilfracombe,  North  of  Devon,  cleavage  through 
contorted  beds  near,  587. 

Imbaburu,  fish  ejected  from,  346. 

Indian  Ocean,  form  of  its  coasts,  155. 

Inferior  oolite,  boring  molluscs  of  time  of,  468 ; 
overlap  of,  Mendip  Hills,  468. 

Infusorial  animals,  remains  of,  in  rocks,  524. 

Insects,  recent,  drifted  from  land  by  winds, 
524. 

Insects,  remains  of,  in  rocks,  140. 

Inversion  of  coal  measures,  mountain  lime- 


stone   and    old    red   sandstone,    Langum 

Ferry,  Pembrokeshire,  612. 
Ireland,  granite  of  Southeastern,  alterations 

of  rocks  near,  579. 

Iron  oxides,  influence  on  colour  of  rocks,  41. 
Iron  pyrites,  crystals  of,  in  clays  and  shales, 

571. 

Island  masses,  left  by  denudation,  668. 
Island  of  Cape  Breton,  successive  growths  of 

terrestrial  plants  at,  in  coal  measures,  487. 
Island  of  Jura,  Hebrides,  raised  beaches  of, 

448. 

Islands,  volcanic,  of  Pacific,  383. 
Isomorphous  substances,  350. 

Jamaica,  great  earthquake  at,  416. 

James,  Capt.,  R.  E.,  on  mode  of  occurrence 
of  old  red  sandstone,  Ross,  Herefordshire, 
512. 

Java,  volcanoes  in,  345,  346. 

Joints,  592;  approximation  of,  to  cleavage, 
592;  among  granitic  rocks,  593  ;  amid  sedi- 
mentary rocks,  595  ;  among  coarse  conglo- 
merates, 596  ;  in  compact  limestones,  596  ; 
in  lias  shales,  597 ;  metalliferous  deposits  in, 
646. 

Jorullo,  sudden  production  of,  344. 

Jukes,  Mr.  Beete,  on  Great  Barrier  Reef,  194. 

Jupiter  Serapis,  temple  of,  Puzzuoli,  rise  and 
depression  of,  425. 

Junctions  of  granite  and  schistose  rocks,  Corn- 
wall, character  of  mineral  veins  traversing, 
639. 

Kaimeni,  New,  Santorin  Group,  elevation  of, 
385. 

Kaup,  Prof.,  on  footprints  of  animals  on  sur- 
faces of  rocks,  501. 

Keeling  Atoll,  account  of,  182. 

Kent's  Hole,  Devon,  303,  308. 

Kettle  and  Pans,  Scilly  Islands,  37. 

Killarney,  Lake  of,  decomposition  of  lime- 
stone at  margin  of,  681. 

Kilauea,  description  of  its  crater,  332,  337. 

Killingworth  colliery,  Newcastle,  vertical 
stems  at,  483. 

Kirkdale  bone  cave,  298. 

Labradorite,  composition  of,  356. 

Lafu  Island,  207. 

Lakes,  formation  and  removal  of,  by  rivers, 
67;  deposits  in,  71-74;  temperature  of, 
119;  organic  remains  in,  139;  of  North 
America,  extent  of,  157. 

Lakes  and  rivers,  effects  of  earthquakes  on, 
419. 

Lakes,  great,  of  North  America,  effects  of 
submergence  of,  481. 

Land,  ancient,  of  Silurian  period,  459;  effects 
of  rise  of,  over  a  wide  area,  475 ;  effects  of 
unequal  elevation,  475;  elevation  and  de- 
pression of,  during  earthquakes,  421 ;  eleva- 
tion and  depression  of  masses  of,  from 
variations  in  their  heat,  427 ;  quiet  rise  and 
subsidence  of,  424?  varied  effects  of  sub- 
mergence of,  beneath  sea,  478;  depression 
of,  beneath  sea,  effects  on  distribution  of 
marine  life,  520. 

Landes,  sand-hills  in  the,  87. 

Lapilli,  volcanic,  among  igneous  products, 
amid  Silurian  rocks,  529. 

Lapse  of  time  during  deposit  of  coal-measures, 
493. 


INDEX. 


691 


Lateral  pressure,  evidence  of,  in  chains  of 
mountains,  607. 

Lava,  molten  action  of  juxtaposed,  on  subja- 
cent rocks,  577. 

Lava,  streams,  325,  337 ;  forms  of,  328  ;  effects 
of,  on  trees,  338 ;  composition  of,  353  ;  lami- 
nation of,  360 ;  currents,  slow  cooling  of, 
361 ;  dyke  of,  crater  of  Vesuvius,  374 ; 
ejected  through  fissures,  375. 

Lavas,  comparison  of  those  of  Monte  Somma 
and  Vesuvius,  383. 

Lavas  and  tuffs,  softening  and  raising  of,  378. 

Laverwock  Point,  Glamorganshire,  compli- 
cated fault  near,  627. 

Lead,  sulphuret  of,  converted  into  carbonate, 
in  mineral  veins,  653. 

Lenz,  M.,  on  saltness  of  the  ocean,  45. 

Leucite,  chemical  composition  of,  355. 

Lias,  beaches  at  the  time  of,  464  ;  resting  on 
disturbed  carboniferous  limestone,  466 ;  of 
South  Wales,  466;  varied  mode  of  occur- 
rence of,  467 ;  land  of  time  of,  470. 

Life,  effects  on  distribution  of,  from  elevation 
and  depression  of  land,  519. 

Life,  animal  and  vegetable,  conditions  for 
distribution  of,  at  all  times,  517 ;  modifica- 
tions of,  from  altered  positions  of  land  and 
sea,  518. 

Light,  influence  of,  on  marine  life,  160,  164. 

Lime,  bicarbonate  of,  in  solution,  42;  in  seas, 
127;  how  deposited,  131. 

Limestone  districts,  temperature  of  waters  in, 
454. 

Limestone,  fossiliferous,  fragments  of  ejected, 
from  Vesuvius,  359. 

Limestone  and  shale,  irregular  alternating 
deposits  of,  566. 

Limestones,  how  decomposed,  38;  joints  in, 
596. 

Lime  and  magnesia  added  to  lava  by  melting 
of  limestone  and  dolomite,  359. 

Lipari  Islands,  eruptions  in,  345. 

Lipari  obsidian,  globules  in,  and  lamination  of, 
361. 

Lisbon,  great  earthquake  of,  408. 

Little  Sole  Bank,  off  southern  British  shores, 
rugged  character  of  bottom  near,  446. 

Littoral  sea-bottom,  raised  near  New  Quay, 
Cornwall,  444;  at  Porth-dinlleyn,  Caernar- 
vonshire, 445. 

Logan,  Mr.,  on  vertical  stems  of  coal  mea- 
sures, 482. 

Lb'ven,  Prof.,  on  the  molluscs  of  Norway,  166. 

Lyell,  Sir  Charles,  on  glaciers  in  Forfarshire, 
273;  on  the  habits  of  fossil  elephant,  287; 
on  origin  of  the  Val  del  Bove,  Etna,  381 ; 
on  great  Lisbon  earthquake,  408 ;  on  earth- 
quakes of  the  Mississippi  valley,  419;  on 
earthquake  in  the  Runn  of  Cutch,  423  ;  on. 
rise  and  depression  of  coasts  of  Puzzuoli, 
425  ;  on  gradual  rise  of  land  in  Norway  and 
Sweden,  428 ;  on  vertical  fossil  forests  in 
coal  measures,  Bay  of  Fundy,  486  ;  on  foot- 
prints of  birds,  shores  of  Bay  of  Fundy,  503. 

Lyme  Regis,  landslips  at,  53  ;  fracture  in  rocks 
near,  321 ;  joints  in  shales  of  lias  at,  597. 

Maculaba,  mud  volcanoes  of,  404. 

Maldiva  Islands,  190,  213. 

Mallet,  Mr.,  on  earthquakes,  409. 

Mammals,  remains  of,  in  sunk  forests,  West- 
ern England,  436 ;  remains  of,  in  oolitic 
rocks,  525. 


Mammoth  remains,  286,  294,  295,  313,  316. 

Mantell,  Dr.,  on  raised  beach  near  Brighton, 
445  ;  on  Wealden  deposits,  499. 

Maps,  sketch  construction  of,  676. 

Marcet,  Dr.,  on  salt  in  sea-water,  45. 

Marine  remains  in  parts  of  the  coal  measures, 
495. 

Marmora,  M.  de  la,  on  elevation  of  coast  in 
Sardinia,  431. 

Maui,  Hawaiian  Islands,  great  volcanic  fissure 
at,  375. 

Mauna  Kea,  volcano,  331. 

Mauna  Loa,  volcano,  331,  334. 

Mauritius,  coral  reefs  of,  192. 

Mastodon,  remains  of,  292,  294,  315. 

Mediterranean  Sea,  salt  in  water  of,  45 ;  vol- 
canic accumulations  in,  94 ;  deposits  in,  96; 
currents  in,  97  ;  distribution  of  animals  in, 
162;  effects  of  closing  the  Straits  of  Gibral- 
tar on,  474. 

Mendip  Hills,  beaches  of  time  of  new  red 
sandstone  at,  460;  geological  map  of,  462  ; 
lias  of,  467 ;  inferior  oolite  of,  468 ;  overlap 
of  inferior  oolite  at,  469;  faults  in,  616; 
character  of  ancient  coasts  of,  665  ;  denuda- 
tion of  rocks  in  vicinity  of,  668 ;  amount  of 
denudation  at,  672. 

Merope  Rocks,  Cornwall,  79. 

Metals,  certain,  in  mineral  veins,  occurrence 
of  sulphur  and  arsenic  with,  635  ;  analogous 
properties  of  certain  ores  of,  634. 

Methone,  ancient  volcano  at,  343. 

Mexico,  Gulf  of,  99;  currents  in,  117. 

Miallet,  ossiferous  cave  of,  305. 

Mica,  introduction  of  matter  of,  into  altered 
rocks,  582. 

Mica  slate,  production  of  certain  kinds  of,  582. 

Millstone  grit,  granite  character  of,  if  meta- 
morphosed, 582. 

Mine  waters,  character  of,  637. 

Mineral  matter  gathered  together  in  planes  of 
cleavage,  592;  filling  of  fissures  and  other 
cavities  of  rocks  by,  628;  solubility  and  de- 
posit of,  in  fissures,  630 ;  replacement  of  one 
kind  by  another,  in  veins,  654. 

Mineral  springs  and  veins,  similar  substances 
in.  635. 

Mineral  substances,  certain,  more  abundant 
at  crossing  of  veins,  663 ;  infiltration  of,  into 
cracks  of  ironstone  nodules,  568. 

Mineral  veins,  or  lodes,  character  of,  amid 
dissimilar  rocks,  638,  641 ;  through  junc- 
tions of  granite  and  schistose  rocks,  Corn- 
wall, 639;  character  of  traversing  elvans, 
Cornwall,  639;  of  Derbyshire,  642;  direc- 
tions of,  in  Cornwall,  648  ;  modifications  of, 
in  depth  and  range,  649 ;  character  of,  on 
"  backs,"  or  upper  parts  of,  649;  effects  of 
atmospheric  influences  on  upper  parts  of, 
651;  modification  of  contents  of,  653  ;  frag- 
mentary condition  of  contents  of  many,  656. 

Mineral  veins  and  common  faults,  range  of,  in 
Cornwall  and  Devon,  623. 

Minerals,  different  fusibility  of,  in  volcanic 
rocks,  357 ;  sinking  of  unfused,  in  molten 
rocks,  according  to  specific  gravity,  358. 

Mimisan,  destroyed  by  sand-hills,  88. 

Mississippi,  floods  in,  57;  delta  of,  100;  rafts 
of  wood  in,  136  ;  extension  of  earthquakes 
up  the  valley  of,  414. 

Mode  of  occurrence  of  organic  remains,  512. 

Mode  of  illustrating  movements  from  faults, 
620. 


692 


INDEX. 


Modifications  in  the  distribution  of  life  from 
changes  in  the  relative  positions  of  land  and 
sea,  518. 

Molluscs,  entombment  of,  in  detritus  while 
living,  516;  sudden  destruction  of  multi- 
tudes of,  515  ;  remains  of,  range  of  certain 
genera  through  different  deposits,  525;  ma- 
rine, littoral  species  of,  covered  up  by  de- 
pression of  coasts,  520. 

Mollusc  shells,  in  rocks,  replacement  of,  by 
various  mineral  substances,  629. 

Mont  Blanc,  view  of  the  glaciers  of,  221  ; 
proportional  section  from  the  Jura  over,  611. 

Monte  Nuovo,  sudden  formation  of,  344. 

Monte  Somma,  Vesuvius,  origin  of,  381. 

Moraines,  glacier,  formation  of,  224. 

Morris,  Mr.  J.,  on  mammalian  remains  at 
Brentford,  313. 

Mountains,  production  of  lakes  on  outskirts 
of,  476 ;  ranges  of,  relative  proportion  of,  to 
volume  and  radius  of  earth,  600;  produc- 
tion of,  at  different  geological  times,  601. 

Movements,  several  successive  in  the  same 
fissures,  657. 

Muriate  of  ammonia  of  volcanoes,  372. 

Murchison,  Sir  R.,  on  the  effects  of  ice  in 
northern  rivers,  250,  264  ;  on  the  lowering 
of  lakes,  259  ;  on  the  elevation  of  Britain, 
282 ;  on  the  fossil  elephant  of  Siberia,  287, 
290,  297;  on  mud  volcanoes  of  Taman  and 
Kertch,  405;  on  gradual  rise  of  land  in  Swe- 
den and  Norway,  429 ;  on  Silurian  rocks, 
458 ;  on  Caspian  region,  475  ;  on  vertical 
stems  of  plants,  oolitic  series,  Yorkshire, 
496;  on  date  of  rocks  containing  nummu- 
lites,  560 ;  on  great  area  of  undisturbed  rocks 
in  Russia,  606. 

Naphtha,  springs  of,  405. 

Nelson,  Capf.,  on  Bermudas,  210. 

Newfoundland,  Bank  of,  208 ;  map  of,  209. 

New  red  sandstone,  beaches  of  time  of,  in 
England  and  Wales,  460;  distribution  of 
land  and  sea  at  time  of,  in  western  Europe, 
470;  of  Devon,  igneous  rocks  amid  lower, 
541. 

Niagara,  Falls  of,  68. 

Nicol,  Mr.  J.,  on  the  composition  of  felspars, 
356. 

Nile,  sediment  an4  delta  of  the,  90 ;  map  of 
its  delta,  91. 

Nitrogen,  in  connexion  with  volcanic  products, 
371  ;  evolved  from  mud  volcanoes,  Taman, 
405. 

Nodules  of  impure  carbonate  of  iron  or  lime, 
cracking  of  centres  of,  568. 

North  America,  lakes  of,  effects  of  submer- 
gence of,  481. 

North  Devon,  denudation  of  contorted  rocks 
in,  669. 

North  Wales,  cleavage  of  rocks  in,  586. 

Norton  and  Newgale,  Pembrokeshire,  inlay- 
ing of  mass  of  coal  measures  by  faults  at,  622. 

Norway,  distribution  of  molluscs  on  coasts  of, 
167. 

Nullipora,  nature  of,  183. 

Nunney,  Somersetshire,  boring  molluscs  in 
carboniferous  limestone,  near,  at  time  of  in- 
ferior oolite,  468. 

Obsidian,  chemical  composition  of,  355 ;  lami- 
nae of  spherules  in,  361 ;  merely  vitreous 
state  of  rock,  361. 


Ocean,  influence  of  its  temperature  on  life, 
159;  influence  of  depth  of,  on  life,  159; 
floor  of,  effects  of  elevation  and  depression 
of,  504. 

Old  red  sandstone,  beaches  of  time  of,  in 
Scotland  and  Ireland,  459  ;  mode  of  occur- 
rence of,  Ross,  Herefordshire,  512. 

Olivine,  composition  of,  355. 

Oolitic  series,  ancient  cliffs  of,  Southwest 
England,  666. 

Ordinary  springs,  temperature  of,  453. 

Organic  remains,  mode  of  preservation  of, 
132;  on  dry  land,  137;  in  the  ocea^  171 ; 
on  coasts,  172,  177 ;  in  volcanic  tuff,  Santo- 
rin  Group,  380;  mixture  of  beds  with  and 
without,  457  ;  variable  mode  of  occurrence 
of,  amid  fossiliferous  rocks,  458 ;  mixture 
of,  of  different  periods,  478  ;  mode  of  occur- 
rence of,  512  ;  in  the  positions  where  their 
animals  lived  and  died,  513 ;  drift  of,  by 
currents,  513;  diagonal  arrangement  of, 
514;  among  ancient  volcanic  tuffs,  515; 
viewed  with  reference  to  land  and  sea  at  all 
times,  516  ;  effects  of  rise  and  fall  of  land, 
on  distribution  of,  521 ;  particular  kinds  of, 
reference  to  conditions  respecting,  522 ; 
forming  beds  of  rocks,  523;  sometimes  seen 
only  by  weathering  of  rocks,  523 ;  chemical 
composition  of,  524 ;  caution  respecting 
supposed  characteristic  of  deposits,  525  ; 
distortion  of,  by  cleavage  action,  589. 

Orleigh  Court,  Bideford,  widely  separated 
patch  of  greensand  at,  670. 

Ossiferous  caves,  138,  317;  general  state  of, 
299,  306;  remains  found  in,  301;  human 
remains  in,  302,  304  ;  dens  of  extinct  carni- 
vora,  304  ;  pebbks  found  in,  308. 

Overlap  of  cretaceous  beds  in  England,  500. 

Owen,  Professor,  on  the  fossil  elephant,  288, 
291 ;  on  the  tertiary  mammals  of  Great 
Britain,  294. 

Oxen,  footprints  of,  among  trees  of  sunk 
forests,  South  Wales,  438. 

Oxidation  of  crust  of  earth,  effects  of,  602. 

Pacific  Ocean,  currents  in,  118  ;  coral  islands 
in,  186. 

Papandayang  volcano,  falling  in  of,  345. 

Partial  removal  of  coal  beds  during  the  depo- 
sit of  the  coal  measures,  492. 

Paviland  Cave,  human  remains  in,  302,  315. 

Pebbles  of  coal  in  coal-measure  accumula- 
tions, 494. 

Palagonite  tuff,  composition  of,  364 ;  action 
of  pure  water  on,  365 ;  of  sulphuretted  hy- 
drogen, hydrochloric,  and  sulphuric  acid  on, 
366. 

Pele's  Hair,  337,  354. 

Pembre,  Caermarthenshire,  footprints  of  deer 
and  oxen  in  sunk  forest  of,  438. 

Pentuan,  character  of  elvan  of,  541. 

Pentuan  tin-stream  work,  Cornwall,  beds 
composing,  437. 

Pemland  Frith,  tides  in,  105. 

Pepys,  Mr.,  on  production  of  iron  pyrites 
around  bodies  of  mice,  571. 

Perran  Bay,  Cornwall,  raised  sand-dunes  at, 
444. 

Phillips,  Professor  John,  on  Malvern  Hills, 
459 ;  on  igneous  rock  (loadstone)  of  Derby- 
shire, 533. 

Pierre  k  Bot,  erratic  block,  277. 

Pilla,  Professor,  on  flames  in  volcanoes,  323. 


INDEX. 


693 


Pingel,  Dr.,  on  gradual  depression  of  land  in 
Greenland,  430. 

Plants,  fossil,  distribution  of,  in  beds  of  coal 
measures,  487;  drifts  of,  in  coal  measures, 
490. 

Playfair,  Professor,  on  the  transporting  power 
of  glaciers,  272;  on  the  habits  of  extinct 
elephants,  287. 

Plesiosaurus,  preservation  of  skeletons  of,  516. 

Plymouth  Sound,  coast  of,  cleavage  through 
Devonian  rocks  and  porphyry  veins  at,  589. 

Polventon  Cove,  Cornwall,  79. 

Porphyritic  structure  in  certain  altered  sedi- 
mentary deposits,  577. 

Porthdinlleyn,  Caernarvonshire,  raised  littoral 
sea-bottom  at,  445. 

Portishead,  near  Bristol,  re-exposure  of  old 
rock  surfaces  by  breaker  action  at,  670. 

Portland, "Island  of,  fossil  trees  and  ancient 
soils  of,  497. 

Port  Famine,  climate  of,  247. 

Port  Royal,  Jamaica,  sinking  of  part  of,  dur- 
ing an  earthquake,  417. 

Port  Talbot,  Glamorganshire,  footprints  of 
deer  and  oxen  in  sunk  forest  of,  438. 

Po,  rise  of  its  bed,  61;  delta  of  the,  91. 

Pratt,  Mr.,  on  comparatively  recent  granite  in 
Catalonia,  560. 

Preservation  of  entire  skeletons  of  Saurians, 
516. 

Prestwich,  Mr.  J.,  on  fossil  shells  in  the  posi- 
tions in  which  their  animals  lived,  513. 

Products,  ancient,  igneous,  contemporaneous 
among  Silurian  rocks,  528 ;  among  Devo- 
nian rocks,  532 ;  in  lower  part  of  new  red 
sandstone,  541. 

Proportion  of  height  to  distance,  importance 
of,  in  geological  sections,  679. 

Pumice,  composition  of,  354. 

Puzzuoli.  Naples,  rise  and  depression  of 
coasts'  of,  425. 

Quartz  rock,  structure  of,  574. 

Raine's  Island,  195. 

Rain,  marks  of,  on  surfaces  of  rocks,  503. 

Ranges  of  mountains,  obliteration  of,  during 
lapse  of  geological  time,  605  ;  usual  marked 
squeezing  and  contortion  of  rocks  in,  606. 

Ramsay,  Professor,  on  land  of  Silurian  period, 
459 ;  on  denudation,  672. 

Raised  beaches,  of  Plymouth,  441;  of  Fal- 
mouth,  442  ;  of  New  Quay,  Cornwall,  443 ; 
with  reference  to  heights  of  tide,  439;  con- 
cealed by  detritus,  441. 

Raised  coast-lines, care  required  in  tracing,447. 

Ravines,  how  formed,  65,  66. 

Red  Sea,  coral  reefs  in,  198. 

Remains,  marine  organic,  in  parts  of  coal 
measures,  495. 

Rhine,  bending  and  plication  of  Devonian 
rocks  of,  610. 

Rhinoceros,  extinct,  287,  288,  294,  315. 

Rhone,  debacle  in  valley  of  the,  70;  delta  of 
the,  91. 

Ripple  or  friction-marks  on  surfaces  of  rocks, 
506. 

Rise  and  subsidence  of  land,  quiet,  424. 

Riobamba,  great  earthquake  at,  409. 

River-ice,  effects  of,  249. 

Rivers,  transporting  powers  of,  57 ;  action  of, 
on  their  beds,  63  ;  deposits  in  estuaries  of, 
109,  145  ;  organic  remains  in  estuaries  of, 


145  ;  subterranean,  deposits  in  their  chan- 
nels, 308;  effects  of  continued  elevation  of 
land  above  sea  on,  472. 

Rocks,  specific  gravity  of,  56,  350 ;  chemical 
composition  of  volcanic,  350;  fusion  of  por- 
tions, broken  off  in  volcanic  vents,  359 ; 
mixed  volcanic  molten  and  conglomerates, 
383  ;  filters,  allowing  water  to  pass  through 
in  given  quantity  and  time,  451;  modification 
in  the  structure  of,  after  accumulation,  572  ; 
alteration  of,  near  granitic  masses,  579; 
bending,  contortion,  and  fracture  of,  599. 

Rocks,  calcareous,  sometimes  wholly  formed 
of  organic  remains,  523. 

Rogers,  the  Professors,  on  the  bending  and 
plication  of  rocks,  609. 

Rossberg,  slide  of  the,  52. 

Ross,  Herefordshire,  mode  of  occurrence  of 
old  red  sandstone  at,  512. 

Ross,  Sir  James,  observations  on  the  tempe- 
rature of  the  ocean,  119  ;  on  -the  Antarctic 
seas,  241. 

Runn  of  Cutch,  effects  of  earthquake  at,  423. 

Sabrina  Island,  formation  of,  123. 

Sahara,  Great,  effects  of  submergence  of,  480. 

Salses,  or  mud  volcanoes,  401. 

Salt  in  ocean,  45,  129. 

Saltash,  examples  of  ancient  igneous  products 
at,  532. 

Sandberger  and  Damour,  MM.,  analysis  of 
Great  Geyser  water,  368. 

Sand  dunes,  raised,  at  St.  Ives  and  Perran 
Bays,  Cornwall,  444. 

San  Filippo,  baths  of,  43. 

Sand-hills,  formation  of,  85  ;  of  the  Landes, 
87;  of  Cornwall,  88  ;  of  Ireland,  88. 

Sandstones,  forms  of,  when  decomposed,  39  ; 
coal-measure,  false  bedding  of,  489. 

Santorin  Group,  384 ;  submarine  character  of, 
387;  view  of,  388 ;  quiet  deposits  inside  of, 
389. 

Sardinia,  elevation  of  coast  at,  431. 

Saurians,  preservation  of  skeletons  of,  in 
rocks,  516. 

Saussure,  M.  de,  on  glaciers,  218. 

Scandinavia,  upraised  marine  shells  in,  285 ; 
raised  coasts  of,  429 ;  raised  coast -lines  of, 
448. 

Schmerling,  Dr.,  on  the  ossiferous  caves  of 
Liege,  305. 

Schorl,  composition  of,  581;  in  altered  rocks, 
Cornwall,  581. 

Sciacca  Island,  formation  of,  95,  202. 

Shingle.beaches,  81,  82. 

Sea-bottom,  effect  of  raising,  around  British 
Islands,  499  ;  rugged  and  mountainous,  off 
British  shores,  446  ;  elevation  of,  around 
British  Islands,  effects  of,  on  littoral  marine 
life,  521. 

Sea-bottoms,  ancient,  marks  of  wave  and  cur- 
rent friction  upon,  508 ;  effects  of  earth- 
quakes upon,  509  ;  different  kinds  of,  distri- 
bution of  organic  remains  with  reference  to, 
522. 

Sea-waves  produced  during  earthquakes,  410; 
breaking  of,  on  coasts,  418. 

Sea-water,  analysis  of,  45,  98,  129  ;  specific 
gravity  of,  45;  temperature  of,  119,  120, 
159,  241;  amount  of  air  in,  161. 

Seas,  fissures,  highly  heated  in  depth,  opened 
beneath,  633. 

Sections,  of  denuded  igneous  rocks,  535 ;  ot 


694 


INDEX. 


mountain  ranges  required  to  be  proportion- 
al, 607. 

Sections,  geological  construction  of,  678. 

Sedgwick,  Professor,  on  cleavage  of  rocks, 
583,  586  ;  on  joints,  593. 

Serpentine  of  Cornwall,  553 ;  of  Caernarvon- 
shire and  Anglesea,  554 ;  chemical  compo- 
sition of,  556 ;  composition  of,  and  of  olivine 
compared,  556. 

Serpentines,  various  dates  of,  560. 

Severn,  tides  in  the,  103,  108. 

Shells,  specific  gravity  of  land,  141  :  marine, 
176. 

Shell-sand,  use  of,  178  ;  consolidated,  of  New 
Quay,  Cornwall,  443. 

Shepton  Mallet,  Somersetshire,  mode  of  oc- 
currence of  lias  near,  464. 

Siau,  M.,  on  coral  reefs  at  the  Isle  of  Bour 
bon,  192. 

Siberia,  fossil  elephant  of,  286 ;  frozen- soil  of, 
292, 293  ;  temperature  of,  at  different  depths, 
449. 

Silicate  of  lime,  effect  of,  in  igneous  rocks, 
544. 

Silica,  in  water,  46 ;  different  fusibility  of 
when  free  or  combined,  357;  relative  amount 
of,  in  crust  of  earth,  527. 

Silica  and  silicates,  imp.ortance  of,  in  consoli- 
dation of  detrital  deposits,  576. 

Silliman,  Professor  B.,  on  composition  of 
corals,  181;  of  lava,  355. 

Silurian  rocks,  contemporaneous  igneous  pro- 
ducts amid,  528  ;  spheroidal  concretions  in, 
570. 

Skerries,  County  Dublin,  good  examples  of 
joints  through  conglomerates  near,  596. 

Skulls,  human,  found  in  tin-stream  works, 
Cornwall,  436. 

Slices  of  land,  new,  now  cutting  off  by  breaker 
action,  670. 

Smith,  Mr.  James,  of  Jordan  Hill,  on  Arctic 
shells  in  British  deposits,  283. 

Snow-line,  height  of  the,  256. 

Snows,  sudden  melting  of,  on  volcanoes,  373. 

Soda  felspar  (albite)  in  granite,  559. 

Soils,  ancient,  of  Isle  of  Portland,  497;  condi- 
tions for  production  of,  497. 

Solfatara,  near  Puzzuoli,  367  . 

Solutions,  deposits  from,  in  fissures,  632. 

Sounds  accompanying  earthquakes,  420. 

South  Georgia,  glaciers  of,  246. 

South  Pembrokeshire,  denudation  of,  671. 

South  Wales,  beaches  of  time  of  new  red 
sandstone,  460 ;  altered  condition  of  coal  in, 
684. 

Southeastern  Ireland,  relative  dates  of  cleav- 
age of  rocks  in,  588. 

Southwestern  England,  faults  in,  623. 

Southwest  England  and  Southeast  Ireland, 
mode  of  occurrence  of  granite  in,  546. 

Species,  littoral,  of  molluscs,  destruction  of, 
by  depression  of  land,  520. 

Species  of  fossils,  relative  abundance  of  indi- 
viduals in  different  localities, '525. 

Spitzbergen,  glaciers  in,  234,  236. 

Spratt,  Capt.,  R.  N.,  on  movements  of  coast, 
Bay  of  Macri,  430;  on  Santorin  Group, 
388. 

Springs,  mode  of  origin,  42;  substances  in 
solution  in,  48 ;  thermal,  49. 

Steam  and  vapours  of  mineral  substances, 
effects  of,  in  fissures,  632. 

Stems  of  plants,  vertical,  in  coal  measures, 


482 ;  filling  up  of  hollow,  484 ;   in  oolitic 

series,  Yorkshire,  496. 
Stevenson,  on  force  of  breakers.  Atlantic  and 

German  Ocean,  682. 
Stigmaria,  roots  of  sigillaria,  distribution  of, 

in  beds  beneath  coal,  482. 
St.  Agnes,  Cornwall,  minor  contemporaneous 

cracks  tat,    with  fallacious    appearance  of 

two  movements,  618. 
St.  Lawrence  River,  tides  in,  107;  effects  of 

ice  in,  249. 
St.  Michael's  Mount,  Cornwall,  granite  veins 

at,  548;  metalliferous  joints  amid  granite  of, 

646 
St.  Paul,  Island  of,  Indian  Ocean,  structure 

ot,  390. 
Staurolite,  production  of,   in  altered  rocks, 

580. 

Straits  of  Gibraltar,  effects  of  closing,  474. 
Strickland,  Mr.,  on  fresh-water  shells  with 

bones  of  extinct  mammals,  297. 
Stromboli,  in  constant  activity,  342. 
Structure,  globular,  of  basalt,  397;  columnar, 

of  basalt,  399. 

Sublimations  from  volcanoes,  324. 
Submarine  volcanic  deposits,  modifications  of, 

384. 

Successive  disturbances  of  rocks,  601. 
Substances  forming  solid  surface  of  earth, 

chiefly  oxides,  635 ;  character  of,  filling  fis- 
sures, 635. 
Sudden  destruction  of  multitudes  of  molluscs, 

515. 
Sulphate  of  lime,  mode  of  occurrence  of,  in 

trias  marls,  571. 

Sulphate  of  baryta,  solubility  of,  632. 
Sulphurel  of  iron,  common  in  many  hornblen- 

dic  and  felspathid  rocks,  562. 
Sulphurets  of  lead,  copper,  and  iron  replacing 

the  matter  of  shells,  629. 
Sulphuretted  hydrogen,  evolved  from  the  Sol- 
fatara, Puzzuoli,  367. 
Sulphurous  waters  of  Iceland,  370. 
Sunk,  or  submarine  forests,  432 ;  of  Western 

Europe,  433;  beneath  sea  in   roadsteads, 

434  ;  mode  of  occurrence  of,  435 ;  localities 

of,  435. 
Surface  of  earth,  rending  and  squeezing  of, 

forming  mountains,  599. 
Surfaces  of  coal-measure  sandstones,  489. 
Surfaces  of  rocks,  cracked,  501;  footprints  of 

air-breathing  animals  on,  501;  character  of, 

505;    friction-marks  on,  506;  ridging  and 

furrowing  of,  507  ;  various  modifications  of, 

508. 

Surfaces,  old,  of  rocks,  again  exposed  by  denu- 
dation, 670. 

Swansea,  range  of  faults  near,  625. 
Syenite,  composition  of,  558. 

Tahiti,  volcanic  rocks  of,  383. 

Taman  and  Kertch,  mud  volcanoes  of,  403. 

Temperature,  changes  of,  effect  of,  upon  the 
structure  of  rocks,  572. 

Temperature  of  lakes,  119;  of  the  sea,  119, 
120,  159,  216  ;  of  space,  216;  of  the  atmo- 
sphere, 216;  constant  in  the  caves,  Paris 
Observatory,  450;  variable  from  unequal 
percolation  of  water  through  rocks,  451;  rate 
of  increase  of,  in  rocks,  in  depth,  455. 

Tenby,  flexures  and  plications  of  coal  mea- 
sures and  mountain  limestone  near,  612. 

Teneriffe,  Peak  of,  384. 


INDEX. 


695 


Thickness  of  coal  measures,  South  Wales,  488. 
Therria,  M.,  on  the  Grotto  de  Fouvent,  310. 
Thnrlstone  Rock,  Devon,  79. 
Tides,  influence  of  the,  on  the  distribution  of 

sediment,   102,  113;    rise    of,  in   different 

places,  103. 

Tierra  del  Fuego,  glaciers  in,  247. 
Tin-stream  works,  Cornwall,  beds  composing, 

436  ;  sunk  forests  of,  436. 
Toadstone  of  Derbyshire,  533;    character  of 

mineral  veins  traversing,  642. 
Tomboro,  volcanic  eruption  at,  142. 
Tongariro,  New  Zealand,  mud  ejected  from, 

323. 

Towey  River,  deposits  from,  111. 
Town   Hill,  Swansea,  coal  pebbles  in  coal 

measures  of,  494. 
Trafalgar    Square,  London,   composition    of 

waters  in  Artesian  well  of,  573. 
Tramore,  Waterford,  sand-hills  at,  88. 
Trachyte,  nature  of,  349  ;  composition,  353. 
Trappean  rocks,  taken  as  a  class,  558. 
Travertine,  43. 

Trees,  fossil,  of  Island  of  Portland,  497;  con- 
ditions of  growth  of,  497. 
Trimmer,  Mr.,  on  shells  on  Moel  Trefan,  282 ; 

on  the  Norfolk  craig,  315. 
TufF,  fossiliferous,  volcanic,  363  ;  modification 

of,  by  gases  and  vapours,  365  ;    volcanic, 

raised,  of  Santorin  Group,  389. 

Underclays,  soils  in  which  plants  grew  at  time 
of  coal  measures,  488;  quartzose,  near 
Mumbles,  Swansea,  575. 

Val  de  Bagnes,  debacle  in,  70. 

Val  del  Bove,  Etna,  description  of,  378  ;  origin 
of,  381. 

Vale  of  Towey,  Caermarthenshire,  amount  of 
denudation  in,  672. 

Vapours  and  gases  in  molten  lava,  327. 

Variable  composition  and  hardness  of  rocks, 
to  be  regarded  in  their  disturbance,  605. 

Veins,  granite,  547. 

Veins,  mineral,  effects  of  crossing  of,  at  small 
angles,  585. 

Vesuvius,  eruptions  from,  143,  339,  347. 

Vesuvius  and  Etna,  sections  of,  380. 

Vetch,  Captain,  R.  E.,  on  raised  beaches, 
Island  of  Jura,  Hebrides,  448. 

Victoria  Land,  sea-bottom  near,  245  ;  volca- 
noes in,  348. 

Virtuous  Lady  Mine,  Tavistock,  successive 
modifications  of  contents  of  vein  at,  653. 

Volatilization  of  substances  found  in  veins,  635. 

Volcanic  eruptions,  submarine,  94,  122,  322 ; 
of  Tomboro,  142;  of  Vesuvius,  143,  339;  of 
Skaptar-jokull,  144,  341;  of  Etna,  340:  of 
Icelandic  volcanoes,  341;  matter,  distribu- 
tion of,  in  tideless  seas,  94 ;  in  tidal  seas,  1 21 ; 
rocks,  nature  of,  347;  cones,  formation  of, 
330  ;  vapours  and  gases,  323. 

Volcanic  products  amid  the  older  rocks,  527. 

Volcanic  tuff,  ancient,  amid  Silurian  series  of 
Wales  and  Ireland,  530. 

Volcanic  ashes  and  cinders,  effects  of  acids 
and  vapours  on,  362;  products,  fusibility  of, 
372  ;  fissures,  direction  of,  376 ;  gases,  ef- 


fects of  sea  upon,  376;  action,  variable  ac- 
cording to  proximity  of  water,  394;  tuff, 
fossiliferous,  of  Monte  Somma,  Vesuvius, 
382. 

Volcanoes  and  their  products,  317;  elevation 
above  the  sea,  318 ;  water  ejected  from,  346 ; 
sudden  changes  of  temperature,  on  surfaces 
of,  372 ;  distribution  of,  in  the  ocean,  392 ; 
on  continents  and  amid  inland  seas,  393 ; 
proximity  of,  to  water,  393. 

Von  Buch,  Leopold,  on  present  gradual  rise 
of  land  in  Norway  and  Sweden,  428;  on 
the  Caldera,  Island  of  Palma,  378. 

Vorticose  movements  of  earthquakes,  409. 

Walferdin,  M. ,  on  temperatures  found  at  Arte- 
sian well,  Grenelle,  450. 

Warington  Smyth,  Mr.,  on  "  flat"  of  lead  ore, 
Fawnog,  Flintshire,  645;  on  character  of 
Spital  Vein,  Schemnitz,  650. 

Watchet,  Somerset,  faults  near,  626 ;  occur- 
rence of  sulphate  of  lime,  in  trias  near,  572. 

Water,  soluble  substances  in,  44 ;  compressi- 
bility of,  172 ;  ejected  from  volcanoes,  346 ; 
sea,  analysis  of,  45,  98, 129  ;  specific  gravity, 
45,  121;  maximum  density,  120;  action  of 
heated,  on  palagonite  tuff,  365  ;  sulphurous, 
of  Iceland,  370 ;  variable  proximity  of,  to 
volcanoes,  394;  arrangement  of,  in  rocks, 
according  to  its  densities,  452 ;  permeation 
of,  through  joints  and  fissures  of  rocks,  455  ; 
circulation  of,  in  mines,  449 ;  movement  of, 
in  chalk  beneath  London,  574. 

Waterford,  joints  through  old  red  conglome- 
rate at,  595 ;  coast  of,  fine  sections  of  igneous 
rocks  on,  530. 

Waterford  Harbour,  flexure  and  plication  of 
component  parts  of  beds  at,  613. 

Watt,  Mr.  Gregory,  on  fusion  of  rocks,  325. 

Waves,  earthquake,  transmission  of,  compli- 
cated, 411. 

Wealden  deposits,  Southeastern  England,  499. 

Weibye,  M.,  on  the  effects  of  ice  on  coasts, 
251. 

Werner,  on  coating  of  veins  by  dissimilar  sub- 
stances, 657. 

Western  Europe,  distribution  of  land  and  sea 
in,  at  new  red  sandstone  time,  470. 

Wheal  Fortune  Mine,  Cornwall,  range  of  lodes 
at,  621. 

Wheal  Julia,  Cornwall,  successive  movements 
of  lode  of,  658. 

Wicca  Pool,  Cornwall,  granite  veins  at,  548. 

Wicklow  granite,  outline  of  range  of,  547. 

Wicklpw  and  Wexford,  granites  of,  536. 

Wiveliscornbe,  Somersetshire,  denudation 
near,  668. 

Woolhope,  denudation  of  rocks  near,  671. 

Yellow  sandstone,  of  Clonea,  county  of 
Waterford,  false  bedding  of,  510. 

Zermatt,  glacier,  226. 

Zinc,  sulphuret  of,  converted  into  carbonate, 

in  mineral  veins,  653. 
Zones,  in  depth,  of  marine  life,  in  JEgean  Sea, 

162 ;  on  coast  of  Norway,  167 ;  in  British 

Seas,  168. 


CATALOGUE 


OF 


BLANCHAKD  AND  LEA'S  PUBLICATIONS. 

JULY,  1851. 


SPENCE'S  EQUITY  JURISDICTION— (Now  Complete.) 
VOLUME  II.  JUST  ISSUED. 

TH~E 

EQUITABLE  JURISDICTION  OF  THE  COURT  OF  CHANCERY, 

BY  GEORGE  SPENCE,  ESQ.,  QUEEN'S  COUNSEL. 

VOLUME    I. 

COMPRISING  ITS  RISE,  PROGRESS,  AND  FINAL  ESTABLISHMENT. 
To  which  is  prefixed,  with  a  view  to  the  elucidation  of  the  main  subject,  a  concise  account  of  the 
Leading  Doctrines  of  the  Common  Law,  and  of  the  Course  of  Procedure  in  the  Courts  of 
Common  Law,  with  regard  to  Civil  Rights ;  with   an  attempt  to   trace  them  to 
their  sources;  and  in  which  the  various  Alterations  made  by  the  Legis- 
lature down  to  the  present  day  are  noticed. 

VOLUME    II. 

COMPRISING    EQUITABLE    ESTATES    AND    INTERESTS;    THEIR   NATURES, 

QUALITIES  AND  INCIDENTS. 

In  which  is  incorporated,  so  far  as  relates  to  these  subjects,  the  substance  of"  Maddock's  Treatise 
on  the  Principles  and  Practice  of  the  High  Court  of  Chancery." 

The  whole  forming  two  very  large  octavo  volumes,  of  over  Sixteen  Hundred  large  pages,  strongly 

bound  in  the  best  law  sheep. 

In  the  first  volume,  the  History  of  the  Court  of  Chancery  has  been  brought  down  to  the  time 
when  its  modern  jurisdiction  was  established,  and  the  various  heads  under  which  its  jurisdiction 
may  be  classed,  were  there  stated.  The  object  of  the  second  volume  is  to  illustrate  the  principles 
upon  which  the  jurisdiction  of  the  Courts  of  Chancery  is  now  exercised,  in  regard  to  what  are,  for 
the  purposes  of  this  work,  designated  as  "  Equitable  Estates  and  Interests." 

Some  three  years  ago,  we  had  occasion  to  notice  the  first  volume  of  this  work.  (4  West.  Law.  Jour.  96.) 
We  then  said,  uThe  second  volume  will  treat  the  subject  of  Chancery  jurisdiction  practically  as  it  is  now 
exercised;  and,  judging  from  what  we  have  now  seen,  we  should  think  the  whole  work  would  prove  to  be 
by  far  the  most  learned  and  elaborate  work  yet  written  upon  the  subject."  This  prediction  has  bten  fully 
realized  by  the  appearance  of  the  second  volume  It  seems  to  exhaust  the  learning  connected  with  all  the 
subjects  of  which  it  treats.  These  sufficiently  appear  from  the  title-page.  The  leading  cases  are  so  fully 
analyzed,  as  almost  to  supersede  the  necessity  of  consulting  the  reports.—  Western  Law  Journal,  April  1850. 

Thus  he  has  given  us  the  most  perfect  and  faithful  hisiory  of  the  English  Law,  especially  in  remote  ages, 
which  has  ever  been  offered  to  the  legal  profession.  Reeves  is  undoubtedly  more  fin!  and  particular  in  minute 
details,  but  the  present  is  the  only  work  to  which  we  can  have  recourse  for  a  satisfactory  and  philosophical 
acquaintance  with  the  growth  of  English  jurisprudence.  To  the  professional  lawyer,  no  recommendation  is 
necessary  to  gain  favor  for  a  production  which  will  elucidate  much  that  is  dark  in  tiie  history  and  practice 
o<"  the  law,  and  furnish  him  with  the  history  and  growth  of  the  courts  in  which  he  practices,  and  the  princi- 
ples which  it  is  his  duty  to  expound.  We  will  now  leave  this  inestimable  work,  wish  a  general  commenda- 
tion and  a  hearty  concurrence  wnh  the  eulogy  pronounced  by  the  London  Jurists  trusting,  less  on  account 
of  its  own  merits,  than  for  the  credit  of  the  profession  in  Virginia,  that  lawyers  at  least  will  not  neglect  to 
study  its  pages  most  diligently.—  Richmond  Whig. 

From  Prof.  Simon  Greenleaf. 

It  is  one  of  the  most  valuable  works  on  English  Law  issued  from  the  American  press,  and  I  earnestly  hope 
that  your  enterprise  will  be  liberally  rewarded  by  the  patronage  of  the  profession. 


ADDISON    ON_CONTRACTS. 

A  TREATISE  ON  THE  LAW  OF  CONTRACTS  AND  RIGHTS  AND  LIABILITIES  EX  CON- 
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In  this  treatise  upon  the  most  constantly  and  frequently  administered  branch  of  law.  the  author  has  collected, 
arranged,  and  developed  in  an  intelligible  and  popular  form,  the  rules  and  principles  of  the  Law  of  Contracts, 
and  has  supported,  illustrated,  or  exemplified  them  by  references  to  nearly  four  thousand  adjudged  cases. 
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HILL    ON  JTRUSTEES. 

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leges, and  liabilities.     By  JAMES  HILL,  Esq.,  of  the  Inner  Temple.  Barrister  at  Law.    Edited  by  FRANCIS  J. 
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A   NEW  LAW  DICTIONARY, 

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WHEATON'S    INTERNATIONAL    LAW. 

ELEMENTS  OF  INTERNATIONAL  LAW.      By  HENRY  WHEATON,  LL.  D.,  Minister  of  the 
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of  our  author  it  is  a  delightful  one.— North  American. 

A     NEW    WORK    ON     COURTS     MARTIAL. 

A  TREATISE  ON  AMERICAN  MILITARY  LAW,  AND  THE  PRACTICE  OF  COURTS- 
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This  work  stands  relatively  to  American  Military  Law  in  the  same  position  that  Blackstone's  Commenta- 
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CAMPBELL'S    LORD    CHANCELLORS. 

LIVES  OF  THE  LORD  CHANCELLORS  AND  KEEPERS  OF  THE  GRKAT  SEAL  OF  ENGLAND, 
from  the  earliest  tunes  to  the  Reign  of  King  George  IV.  BY  Jon  .\LoRD  CAMPBELL,  A.  M..  F.  R.  S.  E.  Com- 
plete in  seven  very  neat  volumes,  crown  octavo,  extra  cloth. 

CAMPBELL'S  CHIEF  JUSTICES— (Now  Ready.) 

LIVES  OF  THE  CHir.K  JtJSTICES  OF  KNtJI.A  \  D,  from  the  Norman  Conquest  to  the  DeatH  of  Lord 
Mansfield.  In  two  handsome  crown  octavo  volumes,  extra  cloth.  (To  match  the  "  Chancellors.") 


BLANCHARD  &  LEA'S  NEW  PUBLICATIONS.-fgfrtory  and  Biography.}     3 
CAMPBELL' S  CHIEF  JUSTICES— (Xow  Ready.) 
ZiIVES~Or    THE 

CHIEF  JUSTICES  OF  ENGLAND, 

From  the  Norman  Conquest  to  the  Death  of  Lord  Mansfield. 
BY  LORD  CHIEF  JUSTICE  CAMPBELL. 

In  two  very  neat  vols.,  crown  8vo.,  extra  cloth, 
To  match  the  "Lives  of  the  Chancellors,"  of  the  same  author. 

In  this  work  the  author  has  displayed  the  same  patient  investigation  of  historical  facts,  depth  of 
research,  and  quick  appreciation  of  character  which  have  rendered  his  previous  volumes  so  de- 
servedly popular.  Though  the  "  Lives  of  the  Chancellors"  embrace  a  long  line  of  illustrious  per- 
sonages intimately  connected  with  the  history  of  England,  they  leave  something  still  to  be  filled  up 
to  complete  the  picture,  and  it  is  this  that  the  author  has  attempted  in  the  present  work.  Although 
it  naturally  presents  greater  interest  to  lawyers  than  to  the  rest  of^he  public,  still  the  vast  amount 
of  curious  personal  details  concerning  the  eminent  men  whose  biographies  it  contains,  the  lively 
sketches  of  interesting  periods  of  history,  and  the  graphic  and  vivid  style  of  the  author,  render  it 
a  work  of  great  attraction  for  the  student  of  history  and  general  reader. 

The  following  eminent  men  are  the  subjects  of  this  work  : — 

Odo  first  Chief  Justiciar. —  William  Fitz-Osborne. —  William  de  Warrene.— Richard  de  Benefacta. — 
William  tie  Canlefo. — Flambard.—  Roger,  Bishop  of  Salisbury.— Ralph  Basset. — Prince  Henry. — Richard  de 
Luci.—  Robert.  Earl  of  Leicester. — Ranulphus  de  Glanville. — Hugh  Pusar. — William  Longchamp.—  Walter 
Hubert— Geoffrey  Fitz  Peter.— Peter  de  Rupibus.— Hubert  de  Burgh  — Stephen  de  Segrave  —  Huph  le  Des- 
peneer. — Philip  I3asset. — Henry  de  Bracton.— Ralph  de  Hengharn — De  Wayland  — De  Thornton. — Roger 
le  Brabancon. — Henry  le  Scrope. — Henry  de  Staunton  —  Sir  Robert  Parnyni?. — Sir  William  de  Thorpe. — 
Sir  William  Shareshall.— Sir  Henry  Green.— Sir  John  Knyvet.— Sir  John  de  Cavendish.— Sir  Robert  Tre- 
sillian.-  Sir  Robert  Belknappe.—  Sir  William  Thirnyng— Sir  William  Gascoigne.—  Sir  William  Hankford. 
— Sir  John  Foriescue. — Sir  John  Markham.— Sir  Thomas  Billing.— Sir  John  Hussey.—  Sir  John  Fineux. — 
Sir  John  Fitzjames.—  Sir  Edward  Montague.— Sir  James  Dyer.— Sir  Robert  Catlyn. — Sir  Christopher  Wray. 
— Sir  John  Popham. — Sir  Thomas  Fleming. — Sir  Edward  Coke  —  Sir  Henry  Montagu.—  Sir  James  Ley. — Sir 
Randolph  Crewe. — Sir  Nicholas  Hyde.— Sir  Thomas  Richardson.— Sir  John  Brampston.— Sir  Robert  Heath. 
— Rolle.—  Glynn.— Newdegate.-Oliver  St.  John .—  Bradshawe.— Sir  Robert  Foster.— Sir  Robert  Hyde.— Sir 
John  Kelynge.— Sir  Matthew  Hale. — Sir  Richard  Ruynsford — Scroggs. — Sir  Francis  Pemberton. — Sir  Ed- 
mund Saunders.— Jeffreys.— Sir  Edward  Herbert. — Sir  Robert  Wright.— Sir  John  Holt— Sir  Thomas  Parker. 
—Sir  John  Pratt.— Lord  Raymond.— Lord  Hardwicke.— Sir  William  Lee.— Sir  Dudley  Ryder.— Sir  John 
Willes.— Wilmot—  Lord  Mansfield. 

Although  the  period  of  history  embraced  by  these  volumes  had  been  previously  traversed  by  the  recent 
work  of  the  noble  and  learned  author,  and  a  great  portion  of  its  rno?t  exciting  incidents,  especially  those  of 
a  constitutional  nature,  there  narrated,  yet  in  -'The  Lives  of  the  Chief  Justices''  there  is  a  fund  both  of  inter- 
esting information  and  valuable  matter,  which  renders  the  book  well  worthy  of  perusal  by  every  one  who 
desires  to  obtain  an  acquaintance  with  the  constitutional  history  of  his  country,  or  aspires  to  the  rank  or 
either  a  statesman  or  a  lawyer.  Few  lawyers  of  Lord  Campbell's  eminence  could  have  produced  such  a 
work  as  he  has  put  forth.  None  but  lawyers  of  his  experience  and  acquirements  could  have  compiled  a 
work  combining  the  same  interest  as  a  narration,  to  the  public  generally,  wuh  the  same  amount  ofpracticai 
information,  for  professional  aspirants  more  particularly.— Britannia. 


CAMPBELL'S    LORD    CHANCELLORS. 

LIVES  OF  THE  LORD  CHANCELLORS 

AND 

KEEPERS  OF  THE  GREAT  SEAL  OF  ENGLAND, 

FROM 

THE  EARLIEST  TIMES  TO  THE  REIGN  OF  RING  GEORGE  lY^*,*  A 
BY  JOHN  LORD  CAMPBELL,  A.  M.,  F.  R.  S.  E. 

Complete  in  seven  handsome  crown  octavo  volumes,  extra  cloth. 
Volumes  Four  and  Five,  and  Six  and  Seven  may  still  be  had  separate  to  complete  sets. 

Of  the  solid  merit  of  the  work  our  judgment  may  be  gathered  from  what  has  already  been  said.  We  will 
add.  that  from  its  infinite  fund  of  anecdote,  and  happy  variety  of  style,  the  book  addresses  itself  with  equal 
claims  to  the  mere  general  reader,  as  to  the  legal  or  historical  inquirer;  and  while  we  avoid  the  stereotyped 
commonplace  of  affirming  that  no  library  can  be  complete  without  it,  we  feel  constrained  to  afford  it  a  higher 
tribute  by  pronouncing  it  entitled  to  a  distinguished  place  on  the  shelves  of  every  scholar  who  is  fortunate 
enough  to  possess  it. —  Frazer's  Magazine. 

A  work  which  will  take  its  place  in  our  libraries  as  one  of  the  most  brilliant  and  valuable  contributions  to 
the  literature  of  the  present  day.—  Athenaum. 

A  work  which  we  shall  regard  as  both  an  ornament  and  an  honor  to  our  library.  A  history  of  the  Lord 
Chancellors  of  England  from  the  institution  of  the  office,  is  necessarily  a  history  of  the  Constitution,  the 
Court,  and  the  Jurisprudence  of  the  Kingdom,  and  these  volumes  teem  with  a  world  of  collateral  matter  of 
the  liveliest  character  for  the  general  reader,  as  well  as  with  much  of  the  deepest  interest  for  the  profes- 
sional or  philosophical  mind.—  Saturday  Courier. 

The  brilliant  success  of  this  work  in  England  is  by  no  means  greater  than  its  merits.  It  is  certainly  the 
most  brilliant  contribution  to  English  history  made  within  our  recollection;  it  has  the  charm  and  freedom  of 
Biography  combined  with  the  elaborate  and  careful  comprehensiveness  of  History.—  N.  Y.  Tribune. 

MEMOIRS  OF  THE  REIGN  OF  GEORGE  If,  from  his  Accession  to  the  death  of  Queen  Caroline.  By 
John  Lord  Hervey.  Edited,  from  the  original  MSS.,  by  the  Right  Hon.  John  Wilson  Croker.  In  two 
handsome  royal  12mo.  volumes,  exira  cloth. 

WALPOLE'S  MEMOIRS  OF  THE  REIUN  OF  GEORGE  HI,  now  Erst  published  from  the  original  MS,. 
In  two  handsome  octavo  volumes,  extra  cloth. 


4  BLANCHARD  &  LEA'S  PUBLICATIONS.—  (History and  "Biography.} 

IMPORTANT    NEW    WORK,    Nearly  Ready. 

HISTORY  OF  NORMANDY  AND  OF  ENGLAND. 

BY  SIR  FRANCIS  PALGRAVE, 

Author  of 4i  Rise  and  Progress  of  the  English  Commonwealth,"  &c. 

In  handsome  crown  octavo. 

Nearly  Ready,  Vol.  I.  The  General  Relations  of  Mediaeval  Europe;  the  Carlovingian  Empire, 
and  the  Danish  Expeditions  in  the  Gauls,  until  the  establishment  of  Rollo. 

Vols.  II.  and  III.  are  in  a  state  of  forward  preparation,  and  will  shortly  follow. 

A  NEW  LIFE  OF  WILLIAM  PEWW,    (Wow  Ready,) 

WILLIAM   PENN, 

AX  HISTORICAL  BIOGRAPHY,  FROM  NEW  SOURCES; 

With  an  extra  Chapter  on  the  "Macaulay  Charges." 

BY  W.  HEPWORTH  DIXOX, 

Author  of  "  John  Howard  and  the  Prison  World  of  Europe,"  &c. 

In  one  very  neat  volume,  royal  12mo.,  extra  cloth. 

The  volume  before  us  demands  especial  notice  for  two  reasons — in  the  first  place,  it  is  an  elaborate,  bio- 
graphy of  William  Penn,  exhibiting  great  research,  and  bringing  together  a  large  amount  of  curious  and 
original  information  J  in  the  .second,  it  makes  an  undeniable  exposure  of  blunders  committed  by  Mr.  Macau- 
lay  in  reference  10  its  hero,  which  will  go  far  to  compromise  his  character  as  a  historian.  This  latier  sub- 
jt-ct  i»  of  much  interest  and  importance,  as  Mr.  Oixon  discusses  Mr  Macaulay's  charges  against  IVnn,  and 
reinstates  the  character  of  the  latter  on  that  moral  elevation  from  which  it  had  been  most  unjustly  and  care- 
lessly overthrown.  The  task  is  by  no  means  a  pleasant  one ;  because,  whatever  the  charm  of  Mr.  Macau- 
lay's  narrative,  much  of  the  credit  due  to  his  statements  of  facts,  and  of  reliance  on  his  examination  of  au- 
thorities., are  destroyed  by  this  chapter  of  Mr.  Dixon's  work. 

AB  a  biography  the  work  has  claims  of  no  common  order.  Within  the  compass  of  a  single  volume  Mr. 
Dixon  has  compressed  a  great  variety  of  facts,  many  original,  and  all  skilfully  arranged  so  as  to  produce  an 
authentic  moral  portrait  of  his  hero.  The  literary  merits  of  the  volume  include  great  research,  and  a  narra- 
tive at  once  consecutive  and  vivid  The  author  has  had  access  to  a  variety  of  unpublished  material — to  the 
letters  ofPennand  his  immediate  family,  and  to  MSS.  of  rni-.moirs  of  several  persons,  yielding  lights  which  he 
wanted.  It  is  a  longtime  since  a  single  volume  has  been  published  wi:h  such  a  quantity  of  matter  interesting 
and  important  in  its  character.  Mr.  Dixon  compresses  his  materials  by  a  species  of  hydraulic  power. 
Mere  hook-making  might  have  padded  out  this  work  into  three  or  four  volumes.  It  is  another  merit  of  the 
book  that  its  subject  is  always  prom;nent,  the  writer  himself  being  kept  well  out  of  sight.  In  a  word,  we 
c;in  praise  the  work  at  once  for  its  earnest  spirit,  its  wealth  of  recovered  material,  and  the  art  with  which 
the  latier  has  been  disposed. — The  Atheneeum. 

On  account  of  the  very  wide  circulation  of  Mr.  Macaulay's  volumes,  containing  his  accusations 
against  William  Penn,  the  publishers  have  placed  this  work  at  a  low  price,  in  order  that  it  may 
reach  as  many  as  possible  of  those  who  may  have  been  biased  by  the  mistakes  and  misrepresenta- 
tions of  the  historian. 


CHEAPER   EDITION      LATELY    PUBLISHED. 

MEMOIRS  OF  THE  LIFE  OF  WILLIAM  WIRT. 

BY  JOHN  P.  KENNEDY. 

SECOND  EDITION,  REVISED.    I    rtf 
In  two  handsome  12mo.  volumes,  with  a  Portrait  and  fac-simile  of  a  letter  from  John  Adams. 

ALSO, 

A  liandsome  Library  Edition,  In  two  beautifully  printed  octavo  volumes* 

The  whole  of  Mr.  Wirt's  Papers,  Correspondence,  Diaries,  &c.,  having  been  placed  in  the  hands 
of  Mr.  Kennedy,  to  be  used  in  this  work,  it  will  be  found  to  contain  much  that  is  new  and  inter- 
esting relating  to  the  political  history  of  the  times,  as  well  as  to  the  private  life  of  Mr.  Wirt. 

In  its  present  neat  and  convenient  form,  the  work  is  eminently  fitted  to  assume  the  position 
which  it  merits  as  a  book  for  every  parlor-table  and  for  every  fire-side  where  there  is  an  appre- 
ciation of  the  kindliness  and  manliness,  the  intellect  and  the  affection,  the  wit  and  liveliness 
which  rendered  William  Wirt  at  once  so  eminent  in  the  world,  so  brilliant  in  society,  and  so 
loving  and  loved  in  the  retirement  of  his  domestic  circle.  Uniting  all  these  attractions,  it  cannot 
fail  to  find  a  place  in  every  private  and  public  library,  arid  in  all  collections  of  books  for  the  use  of 
schools  and  colleges,  for  the  young  can  have  before  them  no  brighter  example  of  what  can  be  ac- 
complished by  industry  and  resolution,  than  the  life  of  William  Wirt,  as  unconsciously  related  by 
himself  in  these  volumes. 


GRAHAME'S    UNITED   STATES. 

HISTORY  OF  TUT:  I  MIT-I)  STATES  FRO VI  TMK  PLANTATION  OF  THE  BRITISH  COLONIES 
TILL  TIir.lK  AS-IMITION  _  OF  INDEPENDENCE.  Second  American  edition,  enlarged  and 
amended,  with  a  Memoir  by  President  Qumcy,  and  a  Portrait  of  the  Author.  In  two  large  octavo  volumes, 
extra  cloth. 

HISTORICAL  SKETCH  OF  THE  SECOND  WAR  BET  WEEN  THE  UNITED  STATES  OF  AMERICA 
AND  GREAT  BRITAIN.  Hy  Charles  J.  Ingersoll,  Vol.  I.,  embracing  the  events  of  1812-13;  Vol.  II ,  the 
r\  rn<"  of  1-1-4.  Oc-iavo. 

HISTORY  01-  m\(;KE-S  UNDER  THE  ADMINISTRATION  OF  GENERAL  WASHINGTON. 
One  very  large  octavo  volume, 


BLANCHARD  &  LEA'S  PUBLICATIONS.— (History  and  Biography.]  5 

MRS.  MARSH'S  ROMANTIC  HISTORY  OF  THE  HUGUENOTS.— (Now  Ready.) 

HISTORY  OF  THE  PROTESTANT  REFORMATION  IN  FRANCE. 

BY  MRS.  MARSH, 

Author  of  "Two  Old  Men's  Tales,"  "Emilia  Wyndham,"  &c. 
In  two  handsome  volumes,  royal  12mo.,  extra  cloth. 

"The  object  of  this  unpretending  work  has  been  to  relate  a  domestic  story,  not  10  undertake  a  political  his- 
tory—to  display  the  virtues,  errors,  sufferings,  and  experiences  of  individual  men- rather  than  the.  affairs  of 
consistories  or  the  intrigues  of  cabinets — consequent  upon  the  great  struggle  to  diffuse  the  principles  of  the 
Reformed  Religion  in  France."— AUTHOR'S  PREFACB. 

These  two  delightful  volumes  belong  to  the  same  class  as  Miss  Pardoe's  popular  works  on  Francis 
I.  and  Louis  XIV.,  and  may  be  regarded  as  companions  to  them,  having  the  same  characteristics 
of  extensive  research,  lively  style,  and  entertaining  interest,  presenting  all  the  authority  and  utility 
of  History,  without  the  dryness  and  dulness  which  was  formerly  considered  necessary  to  its  dig- 
nity. Mrs.  Marsh's  subject  is  one  which  gives  full  scope  to  her  acknowledged  powers,  and  she 
has  treated  her  romantic  and  varying  story  with  all  the  skill  that  was  to  be  expected  of  the  author 
of  the  "  Two  Old  Men's  Tales." 


STRICKLAND'S    QUEENS    OF    ENGLAND. 

LIVES  OF  THK  QUEENS  OF  ENGLAND  FROM  THE  NORMAN  CONQUEST  TO  THE  ACCES- 
SION OF  TUB  HOUSE  OF  HANOVER.  With  Anecdotes  of  their  Courts,  now  first  published  from 
Official  Records,  Private  a.s  well  as  Public.  New  Edition,  with  Additions  and  Corrections.  By  Agnes 
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Copies  of  the  duodecimo  edition  in  twelve  volumes  may  still  be  had. 
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A  most  valuable  and  entertaining  work. —  Chronicle. 
This  interesting  and  well  written  work,  in  which  the  severe  truth  of  history  takes  almost  the  wildness  of 

romance,  will  constitute  a  valuable  addition  to  our  biographical  literature.—  Morning  Herald. 

THE  COURT  AND  REIGN  OF  FRANCIS  THE  FIRST.  KING  OF  FRANCE.  By  Miss  Pardoe,  author 
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MISS   KAVANAGH'S   WOMAN    IN   FRANCE. -(J  UST   PUBLISHED.) 
WOMAN  IN  FRANCE  IN  THE  EIGHTEENTH  CENTURY.    By  Julia  Kavanagh,  author  of  "  Natha- 
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PULSZKY'S    HUNGARIAN    LADY. -(JUST    PUBLISHED.) 

MEMOIRS  OF  AN  HUNGARIAN  LADY.     By  Theresa  Pulszky.     With  an  Historical  Introduction, by 
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! 


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work,  demanded  that  it  should  be  placed  in  a  form  for  more  general  circulation,  and  this  demand  is  met  in  the 
edition  we  have  before  u*.  Of  the  work  itself  nothing  need  be  said  in  its  praise,  the  judgment  of  the  public 
having  confirmed  its  excellence.  It  is  a  narrative  that  must  have  an  abiding  interest  for  all  lime,  and  that 
library  that  is  without  it  is  imperfect;  as  is  the  knowledge  imperfect  of  the  man  who,  however  otherwise 
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out saying  that,  apart  from  the  absorbing  interest  which  belongs  to  the  subject,  the  author  has  given  it  a  charm 
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when  h^  has  taken  up  the  volume,  to  lay  it  down  before  it  is  finished,  and  which  will  cause  him  to  return  to 
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LIBRARY  OF  ILLUSTRATED  SCIENTIFIC  WORKS. 

A  series  of  beautifully  printed  volumes  on  various  branches  of  science,  by  the  most  eminent 
men  in  their  respective  departments.  The  whole  printed  in  the  handsomest  style,  and  pro- 
fusely embellished  in  the  most  efficient  manner. 

fHr"No  expense  has  been  or  will  be  spared  to  render  this  series  worthy  of  the  supportof  the  scientific  pub- 
lic, while  at  the  same  time  it  is  one  of  the  handsomest  specimens  of  typographical  and  artislic  execution 
which  have  appeared  in  this  country. 

DE  1A  BECHE'S  GEOLOGY— (Just  Ready.) 

THE  GEOLOGICAL  OBSERVER. 

BY  SIR  HENRY  T.  DE  LA  BECHE,  C.  B.,  F.  R.  8., 

Director  General  of  the  (Geological  Survey  of  Great  Britain,  &c. 

In  one  very  large  and  handsome  octavo  volume, 
"WITH   OVER  THREE  HUNDRED  WOOD-CUTS. 

We  have  here,  presented  to  us,  by  one  admirably  qualified  for  the  task,  the  most  complete,  compendium  of 
the  science  of  Geoiopy  ever  produced,  in  which  the  different  facts  which  fall  under  the  cognizance  of  this 
branch  of  naiura!  science  are  arranged  under  the  different  causes  by  which  they  are  produced.  From  the 
ptyle  in  which  the  subject  is  treated,  ihe  work  is  calculated  not  only  for  the  use  of  the  professional  geologist, 
but  for  that  of  the  uninitiated  reader,  who  will  find  in  it  much  curious  and  interesting  information  on  the 
changes  which  ihe  surface  of  our  globe  has  undergone,  and  the  history  of  the  various  striking  appearances 
which  it  presents.  Voluminous  as  the  work  is,  it  is  not  rendered  unreadable  from  its  bulk,  owing  to  the  ju- 
dicious subdivision  of  its  contents,  and  the  copious  index  which  is  appended.— John  Bull. 

This  ample  volume  is  based  upon  a  former  work  of  the  author,  called  H  w  to  Observe  in  Geology  ;  which 
has  long  been  out  of  print,  but  in  its  day  gave  rise  to  several  other  directions  for  observing.  Tha  alteration, 
of  the  title  is  something  more  than  a  nominal  change;  it  extends  the  book  from  the  individual  to  the  general 
observer,  showing  what  has  been  scientifically  seen  in  the  globe,  instead  of  what  an  individual  might  see. 
It  is  a  survey  of  geological  facts  throughout  the  world,  classified  according  to  their  nature.—  Sprctator. 

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young  geologist,  or  to  aid  by  his  own  experience  the  studies  of  those  who  may  not  have  been  able  to  range 
so  extensively  over  the  earth's  surface.  We  strongly  recommend  Sir  Henry  De  la  Heche's  book  to  those 
who  desire  to  know  what  has  been  done,  and  to  learn  something  of  the  wide  examination  which  yet  lies 
wailing  for  the  industrious  observer. — The  AihencBum. 


CARPENTER'S  COMPARATIVE  PHYSIOLOGY— (Just  Ready.) 

PRINCIPLES   OF 

GENERAL  AND  COMPARATIVE  PHYSIOLOGY; 

INTENDED  AS  AN  INTRODUCTION  TO  THE  STUDY  OF 

HUMAN   PHYSIOLOGY, 

And  as  a  Guide  to  the  Philosophical  Pursuit  of  Natural  History, 
BY  WILLIAM  B.  CARPENTER,  M.D.,F.R.S., 

Author  of"  Human  Physiology,"  ''Vegetable  Physiology,"  £c.  &c. 

Third  Improved  and  Enlarged  Edition. 

In  one  very  large  and  handsome  octavo  volume,  with  several  hundred  beautiful  illustrations. 

This  valuable  work  will  supply  a  want  long  felt  by  the  scientific  public  of  this  country,  who 
have  had  no  accessible  treatise  to  refer  to,  presenting  in  an  intelligible  form  a  complete  and 
thorough  outline  of  this  interesting  branch  of  Natural  Science,  brought  up  to  the  most  advanced 
slate  of  modern  investigation.  The  high  reputation  of  the  author,  on  both  sides  of  the  Atlantic, 
is  a  sufficient  guarantee  for  the  completeness  and  accuracy  of  any  work  to  which  his  name  is  pre- 
fixed ;  but  this  volume  comes  with  the  additional  recommendation  that  it  is  the  one  on  which  the 
author  has  bestowed  the  greatest  care,  and  on  which  he  is  desirous  to  rest  his  reputation.  Though 
forming  a  very  large  octavo  volume,  beautifully  printed,  and  most  profusely  illustrated,  the  price 
will  be  very  moderate. 

MULLER'S    PHYSICS. 

PRINCIPLES   OF   PHYSICS  AND  METEOROLOGY.     By  PROFESSOR  J.  MULIER,  M.  D. 

Edited,  with  Additions,  by  R.  EGLESFELD  GRIFFITH,  M.  D.     In  one  large  and  handsome  octavo 

volume,  with  550  wood-cuts,  and  two  colored  plates. 

"The  style  in  which  the  volume  is  published  is  in  the  highest  degree  creditable  to  the  enterprise  of  the 
publishers  It  contains  nearly  four  hundred  engravings,  executed  in  a  style  of  extraordinary  elegance.  We 
commend  the  book  to  general  favor.  It  is  the  best  of  its  kind  we  have  ever  seen." — N.  Y.  Courier  and  En- 
quirer. 

KNAPP'S  CHEMICAL  TECHNOLOGY. 

TECHNOLOGY;  or,  CHEMISTRY  APPLIED  TO  THE  ARTS  AND  TO  MANUFACTURES.  By  DR.  F. 
KNAPP,  Professor  at  the  University  of  Giessen.  Edited,  with  numerous  Notes  and  Additions,  by 
DR.  EDMUND  RONALDS  and  Da.  THOMAS  RICHARDSON.  First  American  Edition,  with  Notes  and 
Additions  by  PROF.  WALTER  R.  JOHNSON.  In  two  handsome  octavo  volumes,  printed  and  illus- 
trated in  the  highest  style  of  art,  with  about  500  wood  engravings. 
The  style  of  excellence  in  which  the  first  volume  was  got  up  i.s  fully  preserved  in  this.  The  treatises 

themselves  are  admirable,  and  the  editing  both  by  the  English  and  American  editors,  judicious;  so  that  the 

work  maintains  itself  as  the  best  of  the  series  to  which  it  belongs,  and  worthy  the  attention  of  all  interested 

in  the  art  of  which  it.treats.—  Franklin  Institute  Journal. 


BLANCHARD  &  LEA'S  PUBLICATIONS.— (Science.) 


LIBRARY  OF  ILLUSTRATED  SCIENTIFIC  WORKS  (Continued). 

WEISBACH'S  MECHANICS. 

PRINCIPLES  OF  THE  MECHANICS  OF  MACHINERY  AND  ENGINEERING.  By  PRO- 
FESSOR  JULIUS  WEISBACH.  Translated  and  Edited  by  PROF.  GORDON,  of  Glasgow.  First  Ame- 
rican edition,  with  Additions  by  PROF.  WALTER  R.  JOHNSON.  In  two  octavo  volumes,  beautifully 
printed,  with  900  illustrations  on  wood 

The  most  valuable  contribution  lo  practical  science  that  has  yet  appeared  in  thi?  country  —  Athenrrvm. 
Unequalled  by  anything  of  the  kind  yet  produced  in  this  country— ihe  most  standard  book  on  mechanics, 

machinery  and  engineering-  now  extant — iV.  Y.  Commercial. 
In  every  way  worthy  of  being  recommended  to  our  readers.—  Franklin  Institute  Journal. 

'f  

MOHR,    REDWOOD,   AND  PROCTER'S  PHARMACY. 

PRACTICAL  PHARMACY:  Comprising  the  Arrangement?,  Apparatus,  and  Manipulations  of 
the  Pharmaceutical  Shop  and  Laboratory.  By  FRANCIS  MOHR,  Ph.  D.,  Assessor  Pharmacia  of 
the  Royal  Prussian  College  of  Medicine,  Coblentz;  and  THEOPHILUS  REDWOOD,  Professor  of 
Pharmacy  in  the  Pharmaceutical  Society  of  Great  Britain.  Edited,  with  extensive  Additions,  by 
PROF.  WILLIAM  PROCTER,  of  the  Philadelphia  College  of  Pharmacy.  In  one  handsomely  printed 
octavo  volume,  of  570  pages,  with  over  500  engravings  on  wood. 

GRAHAM'S   CHEMISTRY- NEW   EDITION— (In  Press  ) 

ELEMENTS  OF  CHEMISTRY;  including  the  Application  of  the  Science  to  the  Arts.  By 
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the  second  and  enlarged  London  edition.  In  two  parts,  large  8vo.,  with  several  hundred  wood- 
cuts. (Part  I  in  press.) 

In  preparation,  works  on  Metallurgy,  Food,  the  Steam  Engine,  Machines,  Rural 

Economy,  A'c.  &'c. 


INTRODUCTION  TO  PRACTICAL  CHEMISTRY,  including  Analysis.     By  JOHN  E.  BOWMAN,  M.  D. 

In  one  neat  royal  12mo.  volume,  extra  clo'h,  wiih  numerous  illustrations. 

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Of  enriching  their  libraries  with  ihis,  the  most  creditable  specimen  of  American  Ari  and  Science  as  yet  issued, 

•will  do  well  to  procure  copies  at  once. 

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BARON  HTJMBOLDT'S  LAST  WORK. 

ASPECTS  OF  NATURE  IN  DIFFERENT  LANDS  AND  D1FKERKNT  CLIMATES.  With  Scientific 
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CHEMISTRY  OF  THE  FOUR  SFASONS,  SPRING.  SUMMTR,  AUTUMN.  AND  A'INTEH.  By  THOMAS  GRIF- 
FITH. In  one  handsome  volume,  royal  12mo.,  extra  cloth,  with  numerous  illustrations. 

THE  MILLWRIGHT'S  GUIDE. 

THE  MILLWRIGHT'S  AND  MILLER'S  GUIDE.  By  OLIVER  EVANS.  Eleventh  Edition.  With  Addi- 
tions and  Corrections  by  ;he  Piofe??or  of  Mechanics  in  the  Franklin  Institute,  and  a  description  of  an  Im- 
proved Merchant  Flour  Mill.  By  C.  and  O.  EVANS.  In  one  octavo  volume,  with  numerous  engravings. 

HUMAN  HEALTH;  or.  the  Influence  of  Atmosphere  and  Locality,  Change  of  Air  and  Climate.  Seasons, 
Food,  Clothing,  Bathing.  Mineral  Springs.  Exercise.  Sleep,  Corporal  and  Mental  Pursuit*  &c.  Jtc.,  on 
Healthy  Man,  constituting  Elements  of  Hygiene.  By  ROULEY  DUNGLISON,  M.  D.  In  one  octavo  volume. 

THE  ANCIENT  WORLD.  OR  PICTURESQUE  SKETCHES  OF  CREATION.  By  D.  T.  ANSTSD,  au- 
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A  NEW  THEORY  OF  LIFE.  By  S.  T.  COLERIDGE.  Now  first  published  from  the  original  MS.  In  one 
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AN  INTRODUCTION  TO  ENTOMOLOGY:  or  Elements  of  the  Natural  History  of  Insects.  By  the  REV. 
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LECTURES  ON  THE  PHYSICAL  PHF.NOMF.NA  <  >F  LIVING  BEINGS.  By  CARLO  MATTKVCCI.  Edited 
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BLANCHARD  &  LEA'S  NEW  PUBLICATIONS.— (Science.)  9 

JOHNSTON'S    PHYSICAL    ATLAS. 

THE    PHYSICAL    ATLAS 

OF  NATURAL  PHENOMENA. 

FOR  THE  USE  OF  COLLEGES,  ACADEMIES,  AND  FAMILIES. 

BY  ALEXANDER  KEITH  JOHNSTON,  F.  R.  G.  S.,  F.  G.  S. 

In  one  large  volume,  imperial  quarto,  handsomely  and  strongly  bound, 

With  Twenty-six  Plates,  Engraved  and  Colored  in  the  best  style, 

Together  with  112  pages  of  Descriptive  Letterpress,  and  a  very  copious  Index. 

This  splendid  volume  will  fill  a  void  long  felt  in  this  country,  where  no  work  has 
been  attainable  presenting  the  results  of  the  important  science  of  Physical  Geography 
in  a  distinct  and  tangible  form.  The  list  of  plates  subjoined  will  show  both  the  design 
of  the  work  and  the  manner  in  which  its  carrying  out  has  been  attempted.  The  repu- 
tation of  the  author,  and  the  universal  approbation  with  which  his  Atlas  has  been 
received,  are  sufficient  guarantees  that  no  care  has  been  spared  to  render  the  book 
complete  and  trustworthy.  The  engraving,  printing,  and  coloring  will  all  be  found 
of  the  best  and  most  accurate  description. 

As  but  a  small  edition  has  been  prepared,  the  publishers  request  all  who  may  desire 
to  procure  copies  of  the  work  to  send  orders  through  their  booksellers  without  delay. 

LIST  OF  PLATES. 


GEOLOGY. 

1.  Geological  Structure  of  the  Globe. 

2.  Mountain  Chains  of  Europe  and  Asia. 
3    Mountain  Chains  of  America. 

4.  Illustration  of  the  Glacier  System  of  the  Alps, 

(Mont  Blanc.) 

5.  Phenomena  of  Volcanic  Action. 

Palaeontological    and    Geological   Map  of   the 
British  Islands.     (A  double  sheet.) 


HYDROGRAPHY.  used  as  Food' 


1.  Physical  Chart  of  the  Atlantic  Ocean. 

2.  Physical  Chart  of  the  Indian  Ocean. 

3.  Physical  Chart  of  the  Pacific  Ocean  or  Great  Sea. 

4.  Tidal  Chart  of  the  British  Seas. 

5.  The  River  Systems  of  Europe  and  Asia. 

6.  The  River  Systems  of  America. 

Tidal  Chart  of  the  World. 


METEOROLOGY. 

1.  Humboldt's  System  of  Isothermal  Lines. 

2.  Geographical  Distribution  of  the  Currents  of  Air. 

3.  Hyetographic  or  Rain  Map  of  the  World. 

4.  Hyetographic  or  Rain  Map  of  Europe. 

NATURAL  HISTORY. 

1.  Geographical  Distribution  of  Plants. 

2.  Geographical  Distribution  of  the  Cultivated  Plants 


3.  Geographical  Distribution  of  Quadrumana,  Eden- 

tata. Marsupialia,  and  Pacny  dermal  a. 

4.  Geographical  Distribution  of  Carnivora. 

5.  Geographical  Distribution  of  Rodentia  and  Runu- 


nantia. 


6.  Geographical  Distribution  of  Birds. 

7.  Geographical  Distribution  of  Reptiles. 

8.  Ethnographic  Map  of  the  World. 

9.  Ethnographic  Map  of  Great  Britain  and  Ireland. 


The  book  before  us  is,  in  short,  a  graphic  encyclopaedia  of  the  sciences — an  atlas  of  human  knowledge 
done  into  maps.  It  exemplifies  the  truth  which  it  expresses — that  he  who  runs  may  read.  The  Thermal 
Laws  of  Leslie  it  enunciates  by  a  bent  line  running  across  a  map  of  Europe;  the  abstract  researches  of 
Gauss  it  embodies  in  a  few  parallel  curves  winding  over  a  section  of  the  globe;  a  formula  of  Laplace  it 
melts  down  to  a  little  patch  of  mez/otint  shadow;  a  problem  of  the  transcendental  analysis,  which  covers 
pages  with  definite  integrals,  it  makes  plain  to  the  eye  by  a  little  stippling  and  hatching  on  a  given  degree  of 
longitude!  All  possible  relations  of  time  and  space,  heat  and  cold,  wet  and  dry,  frost  and  snow,  volcano 
and  s-torm.  current  and  tide,  plant  and  beast,  race  and  religion,  attraction  and  repulsion,  glacier  and  avalanche, 
fossil  and  mammoth,  river  and  mountain,  mine  and  forest,  air  and  cloud,  and  sea  and  sky — all  in  the  eanh 
and  under  the  earth,  and  on  the  earth,  and  above  the  earth,  that  the  heart  of  man  has  conceived  or  his  head 
understood— are  brought  together  by  a  marvellous  microcosm,  and  planted  on  these  little  sheets  of  paper, 
thus  making  themselves  clear  to  every  eye.  In  short,  we  have  a  summary  of  all  the  cross-questions  of  Na- 
ture for  twenty  centuries— and  all  the  answers  of  Nature  herself  set  down  and  .speaking  to  us  voluminous 

system  dans  un  mot Mr.  Johnston  is  well  known  as  a  geographer  of  great  accuracy  and  research  ; 

and  it  is  certain  that  this  work  will  add  to  his  reputation;  for  it  is  beautifully  engraved,  and  accompanied 
with  explanatory  and  tabular  letterpress  of  great  value. —  London  Athtnaum. 


SOMERVILLE'S    PHYSICAL   GEOGRAPHY. 

N7ew  Edition,  much  Improved— Just  Issued, 

PHYSICAL   G~E  0  G  R  A  P  H  Y. 

BY   MARY   SOMERVILLE. 

Second  American  front  the  Second  and  Revised  London  Edition. 

WITH  AMERICAN  NOTES,  GLOSSARY,  &c. 
In  one  neat  royal  12ino.  vol.,  extra  cloth,  of  over  550  pages. 

The  great  success  of  this  work,  and  its  introduction  into  many  of  our  higher  schools  and  academies,  have 
induced  the  publishers  to  prepare  a  new  and  much  improved  edition.  In  addition  to  the  corrections  and 
improvements  of  the  author  bestowed  on  the  work  in  its  passage  through  the  press  a  second  lime  in  London, 
notes  have  been  introduced  to  adapt  it  more  ful  ly  to  the  physical  geography  of  this  country :  and  a  comprehensive 
glossary  has  been  added,  rendering  the  volume  more  particularly  suited  to  educational  purposes.  The 
amount  of  these  additions  may  be  understood  from  the  fact  that  not  only  has  the  size  of  the  page  been  increased, 
but  the  volume  itself  enlarged  by  over  one  hundred  and  fifty  pages. 

Our  praise  comes  lagging  in  the  rear,  and  is  well-nigh  superfluous.  But  we  are  anxious  to  recommend  to 
our  youth  the  enlarged  method  of  studying  geography  which  her  present  work  demonstrates  to  be  as  capti- 
vating as  it  is  instructive.  We  hold  such  presents  as  Mrs  Somerville  has  bestowed  upon  the  public  10  be  of 
incalculable  value,  disseminating  more  sound  information  than  all  the  literary  and  scientific  institutions  will 
accomplish  in  a  whole  cycle  of  their  existence.— Blackwood's  Magazine. 


10    BLANCHARD   &   LEA'S   PUBLICATIONS.— (Work*  for  Colleges  and  Sclooh.) 

HANDBOOKS  OF  NATURAL  PHILOSOPHY. 

IJY    DYONYSIUS    LARDNER,    LL.D. 
first  Course— (Nearly  Ready.) 

COMPRISING  MECHANICS,  HYDROSTATICS,  HYDRAULICS,  PNEUMATICS,  SOUND,  AND  OPTICS. 

In  1  large  and  handsome  royal  J2mo.  vol  .  with  4'2ti  illustrations,  or  each  subject  done  up  and  sold  separately. 

Second  Courte— (Preparing.) 

COMPRISING  HEAT,  ELECTRICITY,  MAGNETISM,  AND  ASTRONOMY. 
In  one  volume,  same  size  and  style  as  the  First  Course,  with  about  400  wood  cuts.    Also,  each  subject  done 

up  separately. 

The  name  of  ?o  dHtinguished  an  author  as  Dr.  Lardner  is  a  sufficient  guarantee  of  the  value  of  this  work, 
and  of  its  perfect  adaptation  to  the  purposes  for  which  it  is  designed,  as  an  elementary  text-book  for  schools 
and  for  ihe  private  student ;  while  the  manner  in  which  il  is  printed  enables  the  purchaser  to  procure  either 
a  complete  manual  of  all  the  branches  of  Natural  Philosophy,  or  a  separate  treatise  on  any  subject,  com- 
plete in  itself.  Notwithstanding  the  handsome  manner  in  which  it  is  printed,  and  its  very  profuse  illustra- 
tions, the  price  wi.l  be  exceedingly  low,  placing  it  within  the  reach  of  all. 

ELEMENTARY    CH~EMISTRY; 

Theoretical  and  Practical.  By  George  Fownes,  Ph.D.,  F.  II.  S.,  &c.  Edited,  with 
Notes  and  Additions,  by  Robert  Bridges,  M.  D.  Third  American  from  a  late 
London  edition.  In  one  large  royal  12mo.  volume,  with  numerous  illustrations. 

We  know  of  no  treatise  so  well  calculated  to  aid  the  student  in  becoming  familiar  with  the  numerous  facts 
in  the  science  on  which  it  treats,  or  one  better  calculated  as  a  text  book  for  those  attending  Chemical  Lec- 
tures. *  *  *  *  The  best  text-book  on  Chemistry*  that  ha?  issued  from  our  press. —  American  Med.  Journal. 

We  know  of  none  within  the  same  limits,  which  has  higher  claim*  to  our  confidence  as  a  college  class- 
book,  both  for  accuracy  of  detail  and  scientific  arrangement.—  Augusta  Med.  Journal. 


OUTLINES    OF   ASTRONOMY. 

By  Sir  John  F.  W.  Herschel,  F.  R.  S.,  &c.  In  one  neat  volume,  crown  8vo.,  with 
six  plates  and  numerous  wood-cuts. 

We  now  take  leave  of  this  remarkable  work  ;  which  we  hold  to  be,  beyond  a  doubt,  the  greatest  and  most 
remarkable  of  the  work?  in  which  the  laws  of  astronomy  and  the  appearance  of  the  heavens  are  described 
to  those  who  are  not  mathematicians  nor  observers,  and  recalled  to  those  who  are.  It  is  the  reward  of  men 
who  can  descend  from  the  advancement  of  knowledge,  to  care  for  its  diffusion,  that  their  works  are  essen- 
tial to  all,  that  they  become  the  manuals  of  the  proficient  as  well  as  the  text- books  of  ihe  learner. — Athena-urn. 

Probably  no  hook  ever  written  upon  any  science. embraces  within  so  small  a  compass  an  entire  epitome  of 
of  everything  known  within  all  its  various  departments;  practical,  theoretical,  and  physical.—  Examiner. 

ELEMENTS   OF    NATURAL    PHILOSOPHY; 

Being  an  Experimental  Introduction  to  the  Physical  Sciences.  Illustrated  with  over 
three  hundred  wood-cuts.  By  Golding  Bird,  M.  D.,  Assistant  Physician  to  Guy's 
Hospital.  From  the  third  London  edition.  In  one  neat  volume,  royal  12mo. 

We  are  astonished  to  find  that  there  is  room  in  so  small  a  book  for  even  the  bare  recital  of  so  many  sub- 
ject*. Where  everything  is  treated  succinctly,  great  judgment  and  much  time  are  needed  in  making  a 
selection  iunl  winnowing  the  wheat  from  the  chaff".  Dr.  Bird  has  no  need  to  plead  the  peculiarity  of  his 
position  as  a  shield  against  criticism,  so  long  as  his  book  continues  to  be  the  best  epitome  in  the  English  lan- 
guage of  this  wide  range  of  physical  subjects.—  North  American  Review,  April,  1851. 

ELEMENTS  OF  PHYSICS  ;  or  Natnr»l  Philosophy,  General  and  Medical.  Written  for  universal  use,  in 
plain  or  non-technical  language.  By  NEILL  AKXOTT  M.  D.  A  new  edition,  by  ISAAC  HATS,  M.D.  Com- 
plete in  one  octavo  volume,  with  about  two  hundred  illustrations. 

r.LEMEX  I'S  OF  OI'TK'S.  by  SIR  DAVID  BKEWSTER.  With  Notes  and  Additions  by  A.  D.  BACHE,  LL.  D. 
In  one  12mo  volume,  luilf  bound,  with  numerous  wood-cuts 

A  TRK.vnsE  ON  ASTRONOMY.  By  SIR  JOHN  F.  W.  HERSCHEL.  Edited  by  S.  C.  WALKER, ESQ.  In  one 
l'2mo  volume,  with  numerous  plates  and  cuts 

AN  ATLAS  OF  ANCIENT  GEOGRAPHY.  By  SAMUEL  BCTLKR.  D.  D  ,  late  Lord  Bishop  of  Lincoln.  In 
one  octavo  volume,  half  bound,  containing  twenty-one  colored  Maps  and  an  accentuated  Index. 

(.r.OCKAI'IIIA  CLASSICA;  or.  the  Application  of  Ancient  Geography  to  the  Classics.  Hy  SAMUEL  BUT- 
LKR,  D.  D.,&c.  Fifth  American  from  the  lasi  London  Euition.  with  illustrations  by  John  Frost.  In  one 
royal  12mo.  volum*,  half  bound. 

I;:,I:MI,\  I'S  OF  UNIVERSAL  HISTORY,  on  anewplnn,  from  the  Creation  to  the  Congress  of  Vienna, 
with  a  Summary  of  the  Leading  Events  since  that  time.  By  H.  WHITE.  Edited,  with  a  "Series  of  Ques- 
tions, by  JOHN  S.  HAKT.  In  one  large  royal  r<2mo.  volume,  extra  cloth,  or  half  bound. 

BOLMAR'S    FRENCH    SERIES. 

New  editions  of  the  following  works,  by  A.  BOLMAR,  forming,  in  connection  with  ''Bolmar's  Levizac,"a 

complex  M-ne>-  for  the  acquisition  of  the  French  language.  :  — 

A  SELECTION  OF  ONE  HUNDRED  PERRIN'S  FABLES,  ACCOMPANIED  BY  A  KKY, containing  the  text, 
a  literal  and  free  translation,  arranged  in  such  a  manner  as  to  ponu  out  the  difference  between  the  French 
and  English  idiom,  Ac.,  in  one  vol  I'-.'mo 

A  COLLECTION  OF  roLLOi.jriAL  PHRASES.  ON  EVKRY  TOPIC  NKCESSAKY  TO  MAINTAIN  COVVFRSA- 
TION.  Arranged  under  tlitferent  h«*nd<*,  with  muntrons  remarks  on  the  peculiar  pronunciation  and  uses  of 
various  words;  the  whole  =o  disposed  as  considerably  to  facilitate  the  acquisition  of  a  correct  pronuncia- 
tion of  tlu-  French  In  one  vol.  ISmo. 

LT.S  AVENTl'RE^  I)E  TF.LEMAQUE,  PAR  FFAEI.oV,  in  one  vo!.  I2mo  ,  accompanied  by  a  Key  to 
the  fir*t  eight  books,  in  one  vol.  l^mo..  containing,  like  the  Fables,  the  text,  a  literal  anu  free  translation, 
intended  us  n  •.••ijiiel  10  the  Fsihles.  Either  volume  sold  separately. 

ALL  THE  FliEM'H   VERBS,  both  regular  and  irregular,  in  a  small  volume. 

OUTLINES  OF  ENGLISH  LITERATURE.    By  Thomas  B.  Shaw.    In  one  large  royal  18mo.  volume, 

extra  cloth. 
A  HANDBOOK  OF  EUROPEAN  LITERATURE.    By  Mrs.  Foster.    In  one  royal  12mo.  volume. 


BLANCHARD  &  LEA'S  PUBLIC  ATIONS-tlForJt* /or  Colleges  and  Schools.}     11 
A  NEW  L ATI3T  S>ICTIOI¥ARY  FOR  SCHOOLS— (ffoiT  Ready.) 

A  SCHOOL  DICTIONARY  OF"  THE  LATIN  LANGUAGE, 

BY  DR.  J.  H.  KALTSCHMIDT. 
IN  TWO  PARTS,  LATIN-ENGLISH  AND  ENGLISH-LATIN. 

Part  I,  Latin-English,  of  nearly  five  hundred  pages,  strongly  bound,  price  90  cents. 

Part  II,  English-Latin,  of  about  four  hundred  pag«s,  price  75  cents. 

Or  the  whole  complete  in  one  very  thick  royal  ISmo.  volume,  of  nearly  nine  hundred  closely 
printed  double  columned  pages,  strongly  bound  in  leather,  price  only  $1  25. 

While  several  valuable  arid  copious  Latin  Lexicons  have  within  a  few  years  been  published  in  this 
country,  a  want  has  long  been  felt  and  acknowledged  of  a  good  SCHOOL  DICTIONARY,  which  within  reasona- 
ble compass  and  at  a  moderate  price  should  present  to  the  student  all  the  information  requisite  for  his  pur- 
poses, as  elucidated  by  the  most  recent  investigations,  and  at  the  same  time  uniuoumbered  with  erudition 
useful  only  to  the  advanced  scholar,  and  increasing  the  size  and  cost  of  the  work  beyond  the  reach  of  a  iar^e 
portion  of  the  community.  It  is  wiih  this  view  especially  that  .he  present  work  has  been  prepared,  and  the 
names  of  its  distinguished  authors  are  a  sufficient  guarantee  that  this  intention  has  been  skillfully  and  accu- 
rately carried  out. 

The  present  volume  has  been  compiled  hy  Dr.  Kaltschmidt,  the  well  known  German  Lexicographer,  from 
the  best  Latin  Dictionaries  now  in  use  throughout  Europe,  and  has  been  carefully  revised  by  Dr  I.eonhard 
Schmitz.  Learned  discussions  nnd  disquisitions  could  not  be  introduced,  as  incompatible  with  the  objects 
for  which  the  Dictionary  i?  intended,  arid  because  they  would  have  swelled  considerably  the  bulk  ot  tiie 
volume  On  the  other  hand,  it  has  been  thought  advisable  to  give,  as  tar  HS  possible,  the  etymology  01  •  ;irti 
word,  not  only  tracing  it  to  its  Latin  or  Greek  root,  hut  to  roots  or  kindred  forms  of  words  occurring  in  the 
cognate  languages  of  the  great  Indo- Germanic  family.  This  feature,  which  distinguishes  the  prest-nt  Dic- 
tionary from  all  others,  cannot  fail  to  awaken  the  learner  to  the  interesting  fact  of  the  radical  identity  ot 
many  apparently  heterogeneous  languages,  and  prepare  him  at  anearly  stage  for  the  delightful  study  of  com- 
parative philology. 

The  aim  of  th«  publishers  has  been  to  carry  out  the  author's  views  as  far  as  possible  by  the  form  and  ar- 
rangement of  the  volume.  The  type,  though  clear  and  well  printed,  is  small,  and  the  size  of  the  page  such 
as  to  present  an  immense  amount  of  matter  in  the  compass  of  a  single  handsome  18mo.  volume,  furnished  at 
a  price  far  below  what  is  usual  with  such  works,  and  thus  placing  within  the  reach  of  the  poorest  student  a 
neat,  convenient,  and  complete  Lexicon,  embodying  the  investigations  of  the  most  distinguished  scholars  ot 
the  age. 

Although  the  first  part  of  this  work  has  been  issued  very  recently,  it  has  already  attracted  great  attention 

from  all  interested  in  education,  and  it  has  been  introduced  into  a  large  number  of  so  loots.    The  publishers 

subjoin  two  or  three  commendatory  letters  from  among  a  vast  number  with  which  they  have  been  favored. 

From  Prof.  J.  Forsyth,  Jr.,  of  Princeton,  University,  March  19,  1851. 

"With  the  School  Dictionary  I  am  greatly  pleased.  It  is  so  cheap,  so  convenient,  and  in  its  etymological 
features  so  peculiar,  and  withal  so  valuable,  that  on  many  a  student's  table  the  larger  and  more  costly  lexi- 
cons will  sustain  some  risk  of  being  superseded. 

From  Prof.  G.  Harrison,  University  of  Fa.,  March  17,  1851. 

I  am  very  much  pleased  with  it.  I  think  it  will  meet  an  existing  want  and  be  very  popular  with  the 
school  boys.  Jf  the  second  part  be  executed  as  well,  I  shall  take  great  pleasure  in  recommending  the  whole 
work  to  my  friends. 

From  Prof.  C.  D.  Cleveland,  Philadelphia.  March  12, 1851. 

You  have  done  a  very  great  service  to  the  cause  of  Classical  Education  in  publishing  the  ''School  Dic- 
tionary of  the  Latin  Language,"  by  Dr.  J.  H.  Kaltschmidt.  We  needed  something  of  the  kind  very  much. 
The  larger  dictionaries  of  Leverett  &  Andrews  are  excellent  for  advanced  scholars,  but  I  have  found,  in  my 
experience,  that  younger  students  were  confused  by  the  multiplicity  of  definitions  and  examples  in  them, 
and  I  have  therefore  long  wanted  to  see  a  work  better  adapted  to  their  wants  and  capacities.  This  deside- 
ratum you  have  very  happily  supplied. 

THIS  LATIN  DICTIONARY  FORMS  A  PORTION  OF 

SCHMITZ    &,    ZUMPT'S    CLASSICAL    SERIES. 

Under  which  title  BLANCHARI)  &  LEA  are  publishing  a  series  of  Latin  School  Books, 
edited  by  those  distinguished  scholars  and  critics,  Leonhard  Schmitz  and  C.  G.  Zumpt. 
The  object  of  the  series  is  to  present  a  course  of  accurate  texts,  revised  in  accordance  with  the 
latest  investigations  and  MSS.,  and  the  most  approved  principles  of  modern  criticism.  These 
are  accompanied  with  notes  and  illustrations  introduced  sparingly,  avoiding  on  the  one  hand  the 
error  of  overburdening  the  work  with  commentary,  and  on  the  other  that  of  leaving  the  student 
entirely  to  his  own  resources.  The  main  object  has  been  to  awaken  the  scholar's  mind  to  a 
sense  of  the  beauties  and  peculiarities  of  his  author,  to  assist  him  where  assistance  is  necessary, 
and  to  lead  him  to  think  and  to  investigate  for  himself.  For  this  purpose  maps  and  other  en- 
gravings are  given  wherever  useful,  and  each  author  is  accompanied  with  a  biographical  and 
critical  sketch.  The  form  in  which  the  volumes  are  printed  is  neat  and  convenient,  while  it 
admits  of  their  being  sold  at  prices  unprecedentedly  low,  thus  placing  them  within  the  reach  of 
many  to  whom  the  cost  of  classical  works  has  hitherto  proved  a  bar  to  this  department  of  study. 

OF    THIS    SERIES    THE    FOLLOWING    HAVE    APPEARED  : 

CJESARIS  DE  BELLO  GALLICO  LIBRI  IV.,  232  pages,  with  a  Map,  price  50  cents. 

P.  VIRGILII  MARONIS  CARMINA,  438  pages,  price  75  cents. 

C.  C.  SALLUSTII  CATILINA  ET  JUGURTHA,  168  pages,  with  a  Map,  price  50  cents. 

SCHMITZ'S  LATIN  GRAMMAR,  318  pages,  price  60  cents. 

Q.  CURTII  Run  DE  ALEXANDRI  MAGNI  QU^E  SUPERSUNT,  326  pages,  with  a  Map,  price  70  cents. 

M.  T.  CICERONIS  ORATIONES  SELECTS  XII.,  300  pages,  price  60  cents. 

T.  LIVII  PATAVINI  HISTORIARUM  LIBRI  I.,  II.,  XXL,  XXIL,  350  pages,  with  two  colored/ Maps, 

price  70  cents. 
KALTSCHMIDT'S  SCHOOL  LATIN  DICTIONARY,  in  two  parts,  Latin-English  and  English-Latin,  near 

900  pages,  double  columns,  price,  complete,  $1  25. 
In  preparation,  Schrnidtz's  Introduction  to  the  Latin  Grammar,  Horace,  Ovid,  First  and   Second 

Latin  Reading  and  Exercise  Books,  a  School^lassical  Dictionary,  &c. 

Teachers  desirous  of  examining  any  of  these  volumes  will  be  supplied  with  copies 

on  application  to  the  publishers. 


12  BLANCHARD  &  LEA'S  PUBLICATIONS.— (Fiction,  Poetry,  fa.) 

DICKENS'  WORKS,  Various  Styles  and  Prices, 

THE  ONLY   COMPLETE    AMERICAN    EDITIONS. 

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DON  QUIXOTE  DE  LA  MANCHA.  Translated  from  the  Spanish  of  Miguel 
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BLANCHARD   &   LEA'S   PUBLICATIONS .— (MweeZZ<me<w*.)  13 


THE    , 

NOTES  ON  SHOOTING;  OR  HINTS  TO  SPORTSMEN, 

COMPRISING 
THE  HABITS  OF  THE  GAME   BIRDS   AND   WILD  FOWL  OF  NORTH  AMERICA; 

The  Dog,  the  Gun,  the  Field,  and  the  Kitchen. 
BY   E.   J.    LEWIS,    M.  D., 

Editor  of  "  Youatt  on  the  Dog,1'  &c. 
In  one  handsome  volume,  royal  12mo.,  extra  cloth,  with  illustrations. 

Contents.— Technical  Terms  of  Ornithology ;  Sporting  Terms ;  Dogs;  Art  of  Shooting  on  the  Wing:  The 
Partridge;  Ruffed  Grouse;  Prairie  Hen;  woodcock;  English  Snipe;  Reed  Birds;  Rail;  Virginia  Rail; 
Red  Breasted  Rail;  Mud  Hen;  Short  Billed  Curlew;  Long  Billed  Curlew;  Black  Bellied  Piover;  Golden 
Plover;  Willet;  Red  Breasted  Snipe;  Wild  Fowl  Shooting;  Canvass  Back  Duck;  Present  and  Future 
Numbers  of  Ducks  on  Chesapeake  Bay  ;  Red  Headed  Duck,  American  Widgeon  ;  Mallard;  Black  Head; 
Blue  Winged  Teal ;  Green  Winged  Teal;  Buffet  Headed  Duck;  Black  Duck;  Pintail  Duck.  Summer  Duck; 
Canvass  Goose;  Snow  Goose;  Brant;  Sheldrake;  American  Swan;  Trumpeter  Swan;  American  Hare; 
Squirrel;  varieties  of  Squirrels;  Miscellaneous  Hints  :  Bursting  of  Guns  ;  Commodore  Stockton's  Experi- 
ments; Recoil;  Introduction  of  Gunpowder;  God  sends  meat,  who  sends  cooks?  Hints  ou  Taxidermy; 
General  Hygienic  Remarks. 

We  know  of  no  one  more  capable  of  writing  a  work  of  this  nature  than  Dr.  Lewis.  For  years  he  has  made 
Natural  History  his  study,  and  being  partial  to  the  sports  of  the  field,  the  book  may  be  looked  upon  as  spring- 
ing from  the  hands  of  a  practitioner,  whose  education  and  profession  are  peculiarly  adapted  to  aid  in  the  pro- 
duction of  such  a  work.  The  various  articles  from  the  pen  of  Dr.  Lewis,  which  have  from  time  to  time 
appeared  in  the  columns  of  this  paper,  will  no  doubt  be  remembered  by  the  majority  of  our  sporting  readers, 
and  will  be  a  sufficient  guarantee  for  the  value  of  the  work.  It  may  not  be  amiss  to  state,  that  Dr.  Lewis, 
some  time  back,  published  a  book  entitled  "  Youatt  on  the  Dog,"  which  met  with  a  very  rapid  sale,  and  is 
esteemed  the  best  work  of  the  kind  ever  issued,  and  we  think  it  likely  that  the  work  just  brought  out  will 
stand  in  the  same  enviable  position. — N.  Y.  Spirit  nf  the  Times. 

YOUATT  AND  LEWIS  ON   THE   DOG. 

THE  DOG.    By  William  Youatt.    Edited  by  E.  J.  Lewis,  M.  D.     With  numerous  and  beautiful  illustrations. 
In  one  very  handsome  volume,  crown  8vo.,  crirmon  cloth,  gilt. 


YOUATT  AND   SKINNER   ON  THE   HORSE. 

THE  HORSE.  By  William  Youatt.  A  new  edition,  with  numerous  illustrations;  together  with  a  general 
history  of  the  Horse;  a  Dissertation  on  the  American  Trotting  Morse;  how  trained  and  jockeyed;  an  Ac- 
count of  his  Remarkable  Performances;  and  an  Essay  on  the  Ass  and  the  Mule.  By  J.  S.  Skinner,  As- 
sistant Postmaster-General,  and  Editor  of  the  Turi  Register. 

This  edition  of  Youatt's  well-known  and  standard  work  on  the  Management.  Diseases,  and  Treatment  of 
the  Horse,  has  already  obtained  such  a  wide  circulation  throughout  the  country,  that  the  Publishers  need 
say  nothing  to  attract  to  it  the  attention  and  confidence  of  all  who  keep  Horses  or  are  interested  in  their  im- 
provement.   

THE  PIG  ;  a  Treatise  on  the  Breeds,  Management,  Feeding,  and  Medical  Treatment  of  Swine.  With 
directions  for  Salting  Pork,  and  Curing  Bacon  and  Hams.  By  William  Youatt,  V.  S.,  author  of  "The 
Horse,"  ''The  Dog,"  '•  Cattle,"  •'  Sheep,"  &c.  &c  Illustrated  with  engravings  drawn  from  life  by  William 
Harvey.  In  one  handsome  duodecimo  volume,  extra  cloth,  or  in  neat  paper  covers,  price  50  cents. 

EVERY  MAN  HIS  OWN  CATTLE  DOCTOR.  By  Francis  Clater  and  William  Youatt.  Revised  by 
J.  S.  Skinner.  1  vol.  12mo. 

EVERY  MAN  HIS  OWN  FARRIER.  By  Francis  and  John  Clater.  Revised  by  J.  S.  Skinner.  In  one 
vol.  12mo. 

HAWKER  ON  SHOOTING.  Instructions  to  Young  Sportsmen  in  all  that  relates  to  Guns  and  Shooting. 
With  extensive  additions  by  W.  T.  Porter.  In  one  beautiful  octavo  volume,  crimson  cloth,  with  plates. 

THE  DOG  AND  SPORTSMAN.    By  J.  S.  Skinner.    In  one  volume,  12mo.,  with  plates. 

THE   GARDENER'S  DICTIONARY. 
A  DICTIONARY  OF  MODERN  GARDENING.    By  G.  W.  Johnson,  Esq.    With  numerous  additions  by 

David  Landreth.    With  one  hundred  and  eighty  wood-cuts.    In  one  very  large  royal  12mo.  volume,  of 

about  650  double-columned  pages. 
This  work  is  now  offered  at  a  very  low  price. 

ACTON'S   COOKERY. 

MODERN  COOKERY  IN  ALL  ITS  BRANCHES,  r  -duced  to  a  System  of  Easy  Practice,  for  the  Use  of 
Private  Families;  in  a  Series  of  Practical  Receipts,  all  of  which  are  given  with  the  most  minute  exact- 
ness By  Eliza  Acton,  with  numerous  wood-cut  illustrations  ;  to  which  is  added  a  Table  of  Weights  and 
Measures.  The  whole  revised,  and  prepared  for  American  housekeepers,  by  Mrs.  Sarah  J.  Hale.  From 
the  Second  London  Edition.  In  one  large  IsJmo.  volume. 

MODERN  FRENCH  COOKERY.  By  Charles  E.  Francatelli.  In  one  large  octavo  volume,  extra  cloth, 
with  numerous  illustrations. 

SMALL  BOOKS  ON  GREAT  SUBJECTS.  By  a  few  well-wishers  to  Knowledge.  Comprising  a  Series 
of  Short  Treatises  on  Subjects  of  Universal  Interest.  In  twelve  parts,  paper,  price  15  cents  each  ;  or  in 
three  neat  royal  ISrno.  volumes,  extra  cloth. 

No  1.  "Philosophical  Theories  and  Philosoph'cal  Experience."— No  2.  "On  the  Connection  between 
Physiology  and  Intellectual  Science  "—No  3.  '-On  Man's  Power  over  Himself  to  Prevent  or  Com rol  Iii- 
1      '        to  Practical  Organic  Chemistry." — No.  5    •'  A  Brief  View  of  Greek  Phi- 
Brief  View  of  Greek  Philosophy  from  the  age  of  Socrates  >o 
id  Practice  in  the  Second  Century."— No.  8.  "  An  Ex- 

*  itrocluction  to 


J  nysioiogy  anu  tuieueuiucu  ouicn^c    — iiv  u.      ^n 
sanity."— No.  4.  "  An  Introduction  to  Practical  Organi 
losophy  up  to  the  as'e  of  Pericles."— No.  6.  "  A  Brief 
the  Coming  of  Christ.'1— No.  7    "  Christian  Doctrine  an 


posit  lot 


"sition  of  Vulgar  and  Common  Errors,  adapted  to  the  Year  of  Grace  1845." — No.  9  -'An  Int 
Vegetable  Physiology,  with  References  to  the  Works  of  De  Candolle.  Lindley,"  &c.— No.  10.  u  On  ihe  Prin- 
ciples of  Criminal  Law."— No.  11.  "Christian  Sects  in  the  Nineteenth  Century.'1— No.  12.  "Principles  of 
Grammar,"  &c. 


14  BLANCHARD  &  LEA'S  PUBLICATIONS.— (Miscellaneous.) 

CABINET  LIBRARY  FOR  DISTRICT  SCHOOLS  AND  FAMILIES, 

The  following  works,  which  are  handsomely  printed,  and  hound  in  a  uniform  royal  12mo.  style,  form  a 
very  valuable  Series  for  District  School  Libraries  and  fireeide  reading.  Comprehending  works  of  novel 
and  peculiar  interest  in  History,  Biography,  Voyages  and  Travels,  Popular  Science,  etc  ,  they  commend 
themselves,  by  the  variety  of  information  which  they  contain,  to  the  notice  of  all  who  are  engaged  in  the 
formation  of  collections,  for  their  own  or  for  public  use. 

MEMOIRS  OP  THE  LIFE  OF  WILLIAM  "WTRT.    By  John  P.  Kennedy.    2  vols. 

With  a  portrait. 
NARRATIVE   OF  THE   U.  S.  EXPEDITION   TO  THE   DEAD    SEA  AND 

RIVER  JORDAN.     By  W.  F.  Lynch.     Condensed  edition,  with  a  map.     One  volume. 

PHYSICAL  GEOGRAPHY.  By  Mrs.  Sornerville.  Second  edition,  with  American  Notes 
and  a  Glossary,  one  volume. 

ASPECTS  OF  NATURE.  By  Alex.  Von  Humboldt.  Translated  by  Mrs.  Sabine.  Se- 
cond edition,  one  volume. 

WOMAN  IN  FRANCE  IN  THE  EIGHTEENTH  CENTURY.  By  Julia  Kava- 
nagh.  One  volume. 

MEMOIRS  OF  AN  HUNGARIAN  LADY.     By  Theresa  Pulszky.     One  volume. 

TRAVELS  IN  SIBERIA.     By  Adolph  Erman.     Translated  by  Cooley.     Two  volumes. 

THE  WEST  INDIES  AND  NORTH  AMERICA.     By  Robert  Baird.     One  volume. 

TURKEY  AND  ITS  DESTINY.     By  Charles  Macfarlane.     Two  volumes. 

HUNGARY  AND  TRANSYLVANIA.     By  John  Paget.    Two  volumes. 

MIRABEAU,  a  Life  History.     One  volume. 

ZOOLOGICAL  RECREATIONS.     By  W.  J.  Broderip,  F.  R.  S.     One  volume. 

OUTLINES  OF  ENGLISH  LITERATURE.    By  Thomas  B.  Shaw.     One  volume. 

HANDBOOK  OF  EUROPEAN  LITERATURE.    By  Mrs.  Foster.      One  volume. 

NOTES    FROM    NINEVEH,    MESOPOTAMIA,    ASSYRIA   AND    SYRIA. 

By  the  Rev.  J.  P.  Fletcher.    One  volume. 

WILLIAM  PENN,  an  Historical  Biography.  With  a  Chapter  on  the"Macaulay  Charges." 
By  W.  H.  Dixon.  One  volume. 

The  above  works  are  handsomely  printed  on  good  paper,  in  a  large  royal  duodecimo  form,  and  are  pre- 
sented at  a  very  reasonable  price.  Order*  to  the  publishers  for  one  or  more  sets,  complete  in  twenty  volumes, 
will  be  furnished  in  a  neat  uniform  sheep  binding,  suitable  for  continued  use. 

THE   ENCYCLOPEDIA   AMERICANA, 

A  POPULAR  DICTIONARY  OF  ARTS,  SCIENCES,  LITERATURE,  HISTORY, 
POLITICS,  AND  BIOGRAPHY. 

ITT  FOURTEEN  LARGE  OCTAVO  VOLUMES  OF  OVER  SIX  HUNDRED  DOUBLE  COLUMNED  PAGES  EACH. 

For  sale  very  low,  in  various  styles  of  binding. 

Some  years  having  elapsed  since  the  original  thirteen  volumes  of  the  ENCYCLOPEDIA 
AMERICANA  were  published,  to  bring  it  up  to  the  present  day,  with  the  history  of  that  period, 
at  the  request  of  numerous  subscribers  the  publishers  have  issued  a 

SUPPLEMENTARY  VOLUME  (THE  FOURTEENTH), 
BRINGING  THE  WORK  THOROUGHLY  UP. 

Edited  by  HENRY  VETHAKE,  LL.D. 

In  one  large  octavo  volume  of  over  650  double  columned  pages,  which  may  be  had  separately, 

to  complete  sets. 


MURRAY'S    ENCYCLOPAEDIA    OF    GEOGRAPHY. 

THE  ENCYCLOPEDIA.  OF  GEOGRAPHY,  comprising  a  Complete  Description  of  the  Earth, 
Physical,  Statistical,  Civil  and  Political;  exhibiting  its  Relation  to  the  Heavenly  Bodies,  its 
Physical  Structure,  The  Natural  History  of  each  Country,  and  the  Industry,  Commerce,  Political 
Institutions,  and  Civil  and  Social  state  of  all  Nations.  By  HUGH  MURRAY,  F.  R.  S.  E.,  &c. 
Assisted  in  Botany,  by  Professor  Hooker — Zoology,  &c.,  by  W.  W.  Swainson — Astronomy,  &c., 
by  Professor  Wallace — Geology,  &c.,  by  Professor  Jameson.  Revised,  with  Additions,  by 
THOMAS  G.  BRADFORD.  The  whole  brought  up,  by  a  Supplement,  to  1843.  In  three  large  oc- 
tavo volumes,  various  styles  of  binding. 

This  great  work,  furnished  at  a  remarkably  cheap  rate,  contains  about  NINETEEN  HUNDRED  LARGE  IMPERIAL 
PAGES,  and  is  illustrated  by  En»HTT-TWX>  SMALL  MAPS,  and  a  colored  MAI-  OF  THK  UNITED  STATES,  alter  Tan- 
ner'*, together  with  about  ELEVEN  HUNDBKD  WOOD-CUTS  executed  in  the  best  style. 

TIIK  SUGAR  PLANTER'S  MANUAL.    By  W.  J.  Evans.    In  one  neat  octavo  volume  of  263  pages,  with 

cuts  and  plates. 
Till:  IIOMKSTIC'  MAXAGKMRNT  OP  THE  SICK  ROOM,  necessary,  in  aid  of  medical  treatment  for 

the  cure  of  diseases.    13y  A.  T.  Thomson,  M.  D.    Edited  by  R.  E.  Griffith,  M.  D.    In  one  volume  royal 

12mo.,  extra  cloth. 

BLANCH ARD  &  LEA  also  publish  numerous  valuable  Medical  works, 
Catalogues  of  which  may  be  had  on  application. 


TO  THE  MEDICAL  PROFESSION. 

The  Subscribers  subjoin  a  list  of  their  publications  in  medical  and  other  sciences,  to  which  they  would 
invite  the  attention  of  the  Profession,  with  the  full  confidence  that  they  will  be  found  to  correspond  in  everv 
respect  with  the  description.  They  are  to  he  had  of  all  the  principal  booksellers  throughout  the  Union,  from 
whom,  or  from  the  publishers  particulars  respecting  price,  &c.,  may  be  had  on  applif  siiion 

...      .  BLANCH  \RD  &  LE\, 

Philadelphia,  May,  1851.  (Late  LEA 

DICTIONARIES,  JOURNALS,  &c, 

American  Journal  of  the  Medical  Sciences,  quar- 
terly, at  $5  a  year. 

Cyclopaedia  of  Practical  Medicine,  by  Forbes, 
Tweedie,  &c.,  edited  by  Dunglison,in  4  super 
royal  volumes,  3154  double  columned  pages. 

Dunglison's  Medical  Dictionary,  7th  ed.,  1  vol. 
imp. Svo. ,912  large  pages,  double  columns. 

Hoblyn's  Dictionary  of  Medical  Terms,  by  Hays, 

1  vol.  large  12mo.,402  pages,  double  columns. 
Neill  and  Smith's  Compend  of  the  Medical  Sci- 
ences, 1  vol.,  large  12mo.,  900  pp.,  350  cuts. 

Transactions  of  the  American  Medical  Associa- 
tion, Vols.  I,  II,  and  III,  cloth  or  paper. 
Medical  News  and  Library,  monthly,  at  $  1  a  year. 

ANATOMY, 

Anatomical  Atlas,  by  Smith  and  Homer,  large 

imp.  8vo.,  650  figures.    New  and  cheaper  ed. 
Homer's  Special   Anatomy  and  Histology,  new 

edition,  2  vols.  8vo.,  many  cuts,  (nearly  ready.) 
Homer's   United  States  Dissector,  1  vol.  large 

royal  12mo.,  many  cuts,  444  pages. 
Maclise's  Surgical  Anatomy,  Parts  I.  II.  and  III., 

46  colored  plates,  imp.  4to.    Price  $2  00  each. 

(Part  IV  just  ready.) 
Sharpey  and  Quain's  Anatomy,  by  Leidy,  2  vols. 

8vo.,  1300  pages,  511  wood-cuts. 
Wilson's  Human  Anatomy,  by  Goddard,  4th  edi- 
tion, 1  vol.  8vo.,  252  wood-cuts,  580  pp. 
Wilson's  Dissector,  by  Goddard.     New  edition, 

with  cuts,  1  vol.  12mo.,  458  pages,  (now  ready.) 

PHYSIOLOGY, 

Carpenter's  Principles  of  Human  Physiology,  1 

vol.  8vo.,  752  pp.,  300  cuts  and  2  plates,  4th 

edition,  much  improved  and  enlarged.     1850. 
Carpenter's  Elements,  or  Manual  of  Physiology, 

new  and  improved  edition,  1  vol.  8vo.,  (nearly 

ready.) 

Carpenter's  General  and  Comparative  Physiolo- 
gy, 1  vol.  8vo.,  many  cuts,  (now  ready.) 
Dunglison's  Human  Physiology,  7th   edition,  2 

vols.  Svo.,  1428  pages,  and  472  wood-cuts. 
Harrison  on  the  Nerves,  1  vol.  8vo.,  292  pages. 
Kirkes  and  Paget's  Physiology,   1   vol.   12mo., 

many  cuts,  550  pages. 
Longet's  Physiology.    Translated  by  F.G.  Smith. 

2  vols.  8vo.,  many  cuts,  (preparing.) 
Matteucci  on  the  Physical  Phenomena  of  Living 

Beings,  1  vol.  12rno.,  388  pp.,  cuts. 
Solly  on  the  Brain,  1  vol.Svo.,  496  pp.,  118  cuts. 
Todd  and  Bowman's  Physiological  Anatomy  and 

Physiology  of  Man,  with  numerous  wood-cuts. 

Parts  I.,  II.  and  III.,  1  vol.  8vo.,  156  wood-cuts. 

PATHOLOGY, 

Abercrombie  on  the  Brain,  1  vol.  8vo.,  324  pp. 
Blakiston  on  Diseases  of  the  Chest,  1  vol.,  384  pp. 
Blood    and  Urine  Manuals,  by  Reese,  Griffith, 

Markwick,  Bird,  and  Frick,   2  vols.   12mo., 

many  cuts  and  plates. 
B«dd  on  the  Liver,  1  vol.  8vo.,  392  pages,  plates 

and  wood-cuts. 
Burrows  on   Cerebral  Circulation,  1  vol.  8vo., 

216  pages,  with  6  colored  plates. 
Billing's  Principles,  new  and  improved  edition, 

1  vol.  8vo.,  250  pages,  (just  issued.) 
Bird  on  Urinary  Deposits,  12mo.,  new  and  im- 
proved edition,  (just  ready.) 
Copland  on  Palsy  and  Apoplexy,  1  rol.  12mo., 

326  pp. 

Frick  on  Renal  Affections,  1  vol.  12mo.,  cuts. 
Hasse's  Pathological  Anatomy,  8vo.,  379  pages. 


Hope  on  the  Heart,  new  ed.,  pi's,  1  vol .  8vo.,  572  p. 
Hughes  on  the  Lungs,  &c.,  1  vol.  12mo.,  270  pp. 
Lallemand  on  Spermatorrhosa,  1  vol.Svo.,  320  pp. 
Mitchell  on  Fevers,  1  vol.  12mo.,  138  pages. 
Philip  on  Protracted  Indigestion,  8vo.,  240  pp. 
Philips  on  Scrofula,  1  vol.  Svo.,  350  pages. 
Ricord  on  Venereal,  new  ed.,  1  vol.  8vo.,  340  pp. 
Stanley  on  Diseases  of  the  Bones,  1  vol.  8vo., 

286  pages. 
Vb'gel's  Pathological   Anatomy   of  the  Human 

Body,   1   vol.  8vo.,  536  pages,  col.  plates. 
Wilson  on  the  Skin,  1  vol.  Svo.,  new  ed.,  440  pp. 

Same  work,  with  colored  plates. 
Whitehead  on  Sterility  and  Abortion,  1  vol.  8vo.. 

368  pages. 
Williams'  Principles  of  Medicine,  by  Clymer,  2d 

edition,  440  pages,  1  vol.  Svo. 
Williams  on  the  Respiratory  Organs,  by  Clymer, 

1  vol.  8vo.,  500  pages. 

PRACTICE  OF  MEDICINE, 

Ashwell  on  Females,  2d  ed.,  1  vol.  8vo.,  520  pp. 
Barlow's  Practice  of  Medicine,  (preparing.) 
Bennet  on  the  Uterus,  2d  and  enlarged  edition, 

1  vol.  8vo.,  356  pages. 
Bartlett  on  Fevers,  2d  edition,  550  pages. 
Benedict's  Compendium  of  Chapman's  Lectures, 

1  vol.  8vo.,  258  pages. 
Chapman  on  Fevers,  Gout,  Dropsy,  &c.  &c.,  1  vol. 

8vo.,  450  pages. 
Colombatde  L'Isere  on  Females, by  Meigs,  1  vol. 

8vo.,  720  pages,  cuts.     New  edition. 
Condie  on  the  Diseases  of  Children,  3d  edition, 

1  vol.  Svo. 

Churchill  on  the  Diseases  of  Infancy  and  Child- 
hood, 1  vol.  Svo. 

Churchill  on  the  Diseases  of  Females,  by  Huston, 
5th  edition,  revised  by  the  author,  1  vol.  8vo., 
632  pages. 

Churchill's  Monographs  of  the  Diseases  of  Fe- 
males, 1  vol.  Svo.,  now  ready,  450  pages. 

Clymer  and  others  on  Fevers,  a  complete  work 
in  1  vol.  Svo. ,600  pages. 

Day  on  Old  Age,  1  vol.  8vo.,  226  pages. 

Dewees  on  Children,  9th  ed.,  1  vol.  Svo.,  548  pp. 

DeweesonFemales,9thed.,  1  vol. Svo. ,532  p.  pis. 

Dunglison's   Practice  of  Medicine,  3d   edition, 

2  vols.  8vo.,  1500  pages. 

Esquirol  on  Insanity,  by  Hunt,  8vo.,  496  pagea. 
Meigs'  Letters  on  Diseases  of  Females,  1  vol. 

8vo.,  690  pp.,  2d  ed.,  improved,  (lately  i&sued.) 
Meigs  on  Certain  Diseases  of  Infancy,  1  vol.Svo., 

216  pp.,  (a  new  work.) 
Thomson  on  the  Sick  Room,  &c.,  1  vol.  large 

12mo.,  360  pages,  cuts. 
Watson's  Principles  and  Practice  of  Physic,  3d 

edition  by  Condie,  1  vol.  Svo. ,1060  large  pages. 
West's  Lectures  on  the  Diseases  of  Infancy  and 

Childhood.     1  vol.  8vo.,  452  pp. 
Walshe  on  the  Heart  and  Lungs.     A  new  work, 

just  ready,  1  vol.  royal  12mo.  ex.  cloth,  j  t'aoj 

SURGERY, 

Brodie  on  Urinary  Organs,  1  vol.  8vo.,  214  pages. 
Brodie  on  the  Joints,  1  vol.  8vo.,  216  pages. 
Brodie's  Lectures  on  Surgery,  1  vol.Svo.,  350  pp. 
Brodie's  Select  Surgical  Works,  780  pp.  1  vol  .Svo. 
Chelius'  System  of  Surgery,  by  South  and  Norris, 

in  3  large  Svo.  vols.,  near  2200  pages. 
Cooper  on  Dislocations  and  Fractures,  1  vol.  8vo., 

500  pages,  many  cuts. 

Cooper  on  Hernia,  1  vol.  imp.  8vo.,  many  plates. 
Cooper  on  the  Testis  and  Thymus  Gland,  1  vol. 

imperial  8vo.,  many  plates. 


16 


BLANCHARD  &  LEA'S  PUBLICATIONS.— (Medical 


Cooper  on  the  Anatomy  and  Diseases  ofthc  Breast. 

Surgical  Papers,  &c.&c.,  1  vol.  imp.Svo.,  pl'ts 
Druitt's  Principles  and  Practice  of  Modern  Sur- 
gery, 1  vol.  hvo.,  576  pages,  193  cuts,  4th  ed. 
Dufton  on  Deafness  and  Diseases  of  the  Ear,  1  vol. 

12mo.,  120  pages. 

Purlacheron  Corns,  Bunions, &c.,  12mo.,134  pp. 
Ear,  Diseases  of,  a  new  work,  (preparing.) 
Fergusson's  Practical   Surgery,   1   vol.  8vo.,  3d 

edition,  630  pages,  274  cuts. 
Guthrie  on  the  Bladder,  8vo.,  150  pages. 
Gross  on  Injuries  and  Diseases  of  Urinary  Organs, 

1  Irg.  vol.  8vo.,  726  pp.  many  cuts,  (now  ready.) 
Jones'  Ophthalmic   Medicine   and   Surgery,    by 

Hays,  1  vol.  12mo.,  529  pp.,  cuts  and  plates. 
Listorr's  Lectures  on  Surgery,  by  Miitter,  1  vol. 

8vo.,  566  pages,  many  cuts. 
Lawrence  on  the  Eye,  by  Hays,  new  ed.  much 

improved,  863  pp.,  many  cuts  and  plates. 
Lawrence  on  Ruptures,  1  vol.  8vo.,  480  pages. 
Miller's  Principles  of  Surgery,  2d  edition,  1  vol. 

8vo.,538pp.,  1848. 

Miller's  Practice  of  Surgery,  1  vol.Svo.,  496  pp. 
Malgaigne's  Operative  Surgery,  by  Brittan,  with 

cuts.     (Publishing  in  the  M«d.  News  and  Lib.) 
Maury's  Dental  Surgery,  1  vol.  8vo.,  286  pages, 

many  plates  and  cuts. 

Skey's  Operative  Surgery,  1  vol.  large  8vo.,  ma- 
ny cuts,  662  pages,  a  new  work,  (just  issued.) 
Sargent's  Minor  Surgery,  1  vol.  royal  I2mo.,  380 

pages,  128  cuts. 
Smith  on  Fractures,  1  vol.  8vo.,  200  cuts,  314  pp. 

MATERIA  MEDICA  AND  THERAPEUTICS, 

Bird's  (Golding)  Therapeutics,  (preparing.) 

Christison's  and  Griffith's  Dispensatory,  1  large 
vol.  8vo.,  216  cuts,  over  1000  pages. 

Carpenter  on  Alcoholic  Liquors  in  Health  and 
Disease,  1  vol.  12mo. 

Dunglison's  Materia  Medica  and  Therapeutics, 
now  ready,  4th  ed.,  much  improved,  182  cuts, 
2  vols.  Svo. ,1850. 

Dunglison  on  New  Remedies,  6th  ed.,  much  im- 
proved, 1  vol.8vo.,  750  pages. 

Do  Jongh  on  Cod-Liver  Oil,  I2mo. 

Ellis'  Medical  Formulary,  9th  ed.,  much  improv- 
ed, 1  vol.  8vo.,  268  pages. 

Griffith's  Universal  Formulary,  1  large  vol.  8vo., 
560  pages. 

Griffith's  Medical  Botany,  a  new  work,  1  large 
vol.  8vo.,  704  pp.,  with  over  350  illustrations. 

Mayne's  Dispensatory,  1  vol.  12rno.,  330  pages. 

Mohr,  Redwood,  and  Procter's  Pharmacy,  1  vol. 
8vo.,  550  pages,  506  cuts. 

Pereira's  Materia  Medica,  by  Carson,  3d  ed.,  2 
vols.  8vo.,  much  improved  and  enlarged,  with 
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Royle's  Materia  Medica  and  Therapeutics,  by 
Carson,  1  vol.  8vo.,  689  pages,  many  cuts. 

OBSTETRICS, 

Churchill's  Theory  and  Practice  of  Midwifery,  a 

new  and  improved  ed.,  by  Condie,  1  vol.  8vo., 

510  pp.,  many  cuts,  (now  ready.) 
Dewees'  Midwifery,  1 1th  ed.,  1  vol.  8vo.,660  pp., 

plates. 

Lee's  Clinical  Midwifery,  12mo.,238  pages. 
Meigs'  Obstetrics;  the  Science  and  the  Art;  1 

vol.  8vo.,  686  pages,  121  cuts. 
Ramsbotham  on  Parturition,  with  many  plates,  1 

large  vol.  imperial  Svo.,  520  pp.     oth  edition. 
Rigby's   Midwifery,  new  edition,   1   vol.   8vo., 

(just  issued,}  422  pages. 
Smith  (Tyler)  on  Parturition,!  vol.  12mo.,400  pp. 

"niKMlSTKY  AM)  HYGIENE, 

Bowman's    Practical   Chemistry,    1    vol.    12mo., 

97  cuts,  350  pages. 

Brigfiam  on  Excitement, &c.,  1  vol.!2mo.,  204  pp. 
Other  new  and  important 


Bowman's  Medical  Chemistry,  1  vol.  12mo., 
many  cuts,  just  ready,  288  pages. 

Dunglison  on  Human  Health, 2d  ed., Svo. ,  464  pp. 

Fowne's  Elementary  Chemistry,  3d  ed.,  1  vol. 
12mo.,  much  improved,  many  cuts,  now  ready. 

Graham's  Chemistry,  by  Bridges,  new  and  im- 
proved edition.  Part  1,  (in  press.) 

Gardner's  Medical  Chemistry,  1  vol.  12mo.  400pp. 

Griffith's  Chemistry  of  the  Four  Seasons,  1  vol. 
royal  12mo.,  451  pages,  many  cuts. 

Knapp's  Chemical  Technology,  by  Johnson,  2 
vols.  8vo.,  936  pp.,  460  large  cuts. 

Simon's  Chemistry  of  Man,  Svo.,  730  pp.,  plates. 

MEDICAL  JURISPRUDENCE,  EDUCATION,  &e, 

Bartlett's  Philosophy  of  Medicine,  1  vol.  8vo., 

312  pages. 
Bartlett  on  Certainty  in  Medicine,  1  vol.  small 

STO.,  84  pages. 

Dunglison's  Medical  Student, 2ded.l2mo., 312  pp. 
Taylor's  Medical  Jurisprudence,  by  Griffith,   1 

vol.  8vo.,  new  edition,  1850,  670  pp. 
Taylor  on  Poisons,  by  Griffith,  1  vol .  8vo.,  688  pp. 
Traill'sMedicalJurisprudence,!  vol.8vo.,234pp. 

NATURAL  SCIENCE,  to. 

Arnott's  Physics,  1  vol.  8vo.,  484  pp., many  cuts. 
Ansted's  Ancient  World,  Popular  Geology,  in  1 

12mo.  volume,  with  numerous  cuts,  382  pages. 
Bird's   Natural   Philosophy,  1  vol.  royal   12mo., 

402  pages  and  372  wood-cuts. 
Brewster'sOptics,  1  vol.  12mo.423  pp.  many  cuts. 
Broderip's  Zoological  Recreations,  1  vol.  12mo., 

376  pp. 

Coleridge's  Idea  of  Life,  12mo.,  94  pages. 
Carpenter's  General  and  Comparative  Physiology, 

1  large  Svo.  vol.,  many  wood-cuts,  (now  ready.) 
Dana  on  Zoophytes,  being  vol.  8  of  Ex.  Expedi- 
tion, royal  4to.,  extra  cloth. 

Atlas  to  "Dana  on  Zoophytes,"  im.  fol.,  col.  pi's. 
Gregory  on   Animal    Magnetism,   1   vol.,   royal 

12mo.,  '(now  ready.) 
De  la  Beche's  Geological  Observer,  1  large  Svo. 

vol.,  many  wood-cuts,  (just  ready.) 
Kale's  Ethnography  and  Philology  of  the  U.  S. 

Exploring  Expedition,  in  1  large  imp.  4to.  vol. 
Herschel's  Treatise  on  Astronomy,  1  vol.  12mo., 

417  pages,  numerous  plates  and  cuts. 
Herschel's  Outlines  of  Astronomy,  1   vol.  small 

8vo.,  plates  and  cuts.    (A  new  work.)    620  pp. 
Humboldt's  Aspects  ofNature,  1  vol.  12rno.,  new 

edition. 
Johnston's  Physical  Atlas,  1  vol.  imp.  4to.,  hal 

bound,  25  colored  maps. 
Kirby  and  Spence's  Entomology,  1  vol.  Svo.,  600 

large  pages;  plates  plain  or  colored. 
Knox  on  Races  of  Men,  1  vol.  12mo. 
Lardner's  Handbooks  of  Natural  Philosophy,  2 

vols.  royal  I2mo.,  with  800  cuts,  (in  press.) 
Muller's  Physics  and  Meteorology,  1  vol.  8vo., 

636  pp.,  with  540  wood-cuts  and  2  col'd  plates. 
Small  Books  on  Groat  Subjects,  12  parts,  done  up 

in  3  handsome  12mo.  volumes,  extra  cloth. 
Somervillc's  Physical  Geography,  1  vol.  12mo., 

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Weisbach's  Mechanics  applied  to  Machinery  and 

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Vol.  II.,  8vo.,  400  pp.,  340  cuts. 

VETERINARY  MEDICINE, 

Claterand  Skinner's  Farrier,  1vol.  12mo.,220  pp. 

Youatt's  Great  Work  on  the  Horse,  by  Skinner, 
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Youatt  and  Clater's  Cattle  Doctor,  1  vol.  12rno., 
282  pages,  cuts. 

Youatt  on  the  Dog,  by  Lewis,  1  vol.  demy  Svo., 
403  pages,  beautiful  plates. 

Youatt  on  the  Pig,  a  new  work,  with  beautiful  il- 
lustrations of  all  the  different  varieties,  12mo. 
works  are  in  preparation. 


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